ASTM C1784-20

Standard Test Method for Using a Heat Flow Meter Apparatus for Measuring Thermal Storage Properties of Phase Change Materials and Products

SIGNIFICANCE AND USE
5.1 Materials used in building envelopes to enhance energy efficiency, including PCM products used for thermal insulation, thermal control, and thermal storage, are subjected to transient thermal environments, including transient or cyclic boundary temperature conditions. This test method is intended to enable meaningful PCM product classification, as steady-state thermal conductivity alone is not sufficient to characterize PCMs.
Note 3: This test method defines a dynamic test protocol for complex products or composites containing PCMs. Due to the macroscopic structure of these products or composites, conventional measurements using a Differential Scanning Calorimeter (DSC) as specified in E793 and E967, which use very small specimens, are not necessarily representative of the relationship between temperature and enthalpy of full-scale PCM products due to the specimen size limitation.  
5.2 Dynamic measurements of the thermal performance of PCM products shall only be performed by qualified personnel with understanding of heat transfer and error propagation. Familiarity with the configuration of both the apparatus and the product is necessary.  
5.3 This test method focuses on testing PCM products used in engineering applications, including in building envelopes to enhance the thermal performance of insulation systems.  
5.3.1 Applications of PCM in building envelopes take multiple forms, including: dispersed in, or otherwise combined with, a thermal insulation material; a separate object implemented in the building envelope as boards or membranes containing concentrated PCM that operates in conjunction with a thermal insulation material. Both of these forms enhance the performance of the structure when exposed to dynamic, that is, fluctuating, boundary temperature conditions.  
5.3.2 PCMs can be studied in a variety of forms: as the original “pure” PCM; as a composite containing PCM and other embedded materials to enhance thermal performance; as a product cont...
SCOPE
1.1 This test method covers the measurement of non-steady-state heat flow into or out of a flat slab specimen to determine the stored energy (that is, enthalpy) change as a function of temperature using a heat flow meter apparatus (HFMA).  
1.2 In particular, this test method is intended to measure the sensible and latent heat storage capacity for products incorporating phase-change materials (PCM).  
1.2.1 The storage capacity of a PCM is well defined via four parameters: specific heats of both solid and liquid phases, phase change temperature(s) and phase change enthalpy (1).2  
1.3 To more accurately predict thermal performance, information about the PCM products’ performance under dynamic conditions is needed to supplement the properties (thermal conductivity) measured under steady-state conditions.
Note 1: This test method defines a dynamic test protocol for products or composites containing PCMs. Due to the macroscopic structure of these products or composites, small specimen sizes used in conventional Differential Scanning Calorimeter (DSC) measurements, as specified in E793 and E967, are not necessarily representative of the relationship between temperature and enthalpy of full-scale PCM products.  
1.4 This test method is based upon the HFMA technology used for Test Method C518 but includes modifications for specific heat and enthalpy change measurements for PCM products as outlined in this test method.  
1.5 Heat flow measurements are required at both the top and bottom HFMA plates for this test method. Therefore, this test method applies only to HFMAs that are equipped with at least one heat flux transducer on each of the two plates and that have the capability for computerized data acquisition and temperature control systems. Further, the amount of energy flowing through the transducers must be measureable at all points in time. Therefore, the transducer output shall never be saturated during a test.  ...

General Information

• Status: Published
• Publication Date: 31-Mar-2020
• ICS: 17.200.10 - Heat. Calorimetry
• Technical Committee: C16 - Thermal Insulation
• Drafting Committee: C16.30 - Thermal Measurement

Relations

• Replaces: ASTM C1784-14 - Standard Test Method for Using a Heat Flow Meter Apparatus for Measuring Thermal Storage Properties of Phase Change Materials and Products
• Effective Date: 01-Apr-2020
• Refers: ASTM C168-24 - Standard Terminology Relating to Thermal Insulation
• Effective Date: 15-Apr-2024
• Refers: ASTM C168-18 - Standard Terminology Relating to Thermal Insulation
• Effective Date: 15-Apr-2018
• Refers: ASTM C168-17 - Standard Terminology Relating to Thermal Insulation
• Effective Date: 01-Jun-2017
• Refers: ASTM C168-15a - Standard Terminology Relating to Thermal Insulation
• Effective Date: 15-Oct-2015
• Refers: ASTM C518-15 - Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus
• Effective Date: 01-Sep-2015
• Refers: ASTM C168-15 - Standard Terminology Relating to Thermal Insulation
• Effective Date: 01-Jun-2015
• Refers: ASTM C168-13 - Standard Terminology Relating to Thermal Insulation
• Effective Date: 01-Apr-2013
• Refers: ASTM E793-06(2012) - Standard Test Method for Enthalpies of Fusion and Crystallization by Differential Scanning Calorimetry
• Effective Date: 01-Sep-2012
• Refers: ASTM C518-10 - Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus
• Effective Date: 01-May-2010
• Refers: ASTM C168-10 - Standard Terminology Relating to Thermal Insulation
• Effective Date: 01-Jan-2010
• Refers: ASTM C168-08b - Standard Terminology Relating to Thermal Insulation
• Effective Date: 15-Dec-2008
• Refers: ASTM C168-08a - Standard Terminology Relating to Thermal Insulation
• Effective Date: 01-Sep-2008
• Refers: ASTM E967-08 - Standard Practice for Temperature Calibration of Differential Scanning Calorimeters and Differential Thermal Analyzers
• Effective Date: 01-Sep-2008
• Refers: ASTM C168-08 - Standard Terminology Relating to Thermal Insulation
• Effective Date: 01-Jun-2008

Overview

ASTM C1784-20 is the Standard Test Method for Using a Heat Flow Meter Apparatus (HFMA) for Measuring Thermal Storage Properties of Phase Change Materials (PCMs) and Products. Developed by ASTM, this standard is instrumental for evaluating the dynamic energy storage characteristics of materials used for thermal control in building envelopes and other engineering applications. The method is designed to address the limitations of steady-state thermal conductivity tests by incorporating transient temperature conditions that more closely simulate real-world environments.

A unique aspect of ASTM C1784-20 is its focus on the enthalpy (stored energy) changes in PCM products as a function of temperature, under non-steady-state conditions using an HFMA. This offers a dynamic measurement protocol well-suited for large or complex PCM products, where small-scale Differential Scanning Calorimetry (DSC) may not yield representative data.

Key Topics

• Measurement of Thermal Storage Properties: The standard defines procedures for quantifying both sensible and latent heat storage capacity in PCM products, including enthalpy changes during phase transitions (melting and freezing).
• Phase Change Material (PCM) Active Range: Establishes how to determine the temperature interval where phase transitions occur, capturing the real-world performance of PCMs.
• Specimen Types and Preparation: Guidance for preparing a variety of specimens, such as solid PCM composites, loose blends, or discrete PCM containment systems.
• Dynamic Test Protocols: Steps for conducting dynamic tests using HFMA to evaluate enthalpy-temperature relationships of PCM specimens under cyclic or transient thermal loads.
• Analysis of Challenges with PCMs: Addresses practical challenges such as imprecise phase transition temperature ranges, hysteresis, sub-cooling, and multiple phase transitions within tested products.
• Qualified Personnel: Emphasizes the importance of operator expertise in heat transfer analysis and error propagation when conducting these complex measurements.

Applications

The applications of ASTM C1784-20 span a range of areas where accurate assessment of PCM performance is crucial:

• Building Envelope Thermal Efficiency: Enables manufacturers, engineers, and architects to evaluate PCM-enhanced insulation products or systems for buildings under realistic, fluctuating temperature conditions.
• Material Development and Quality Control: Provides a standardized method for PCM classification and performance benchmarking, supporting material innovation and consistent quality.
• Energy Modeling and HVAC Design: Supplies critical thermophysical data - such as enthalpy curves and specific heat values - that are necessary for accurate building energy modeling, simulation, and efficient HVAC system design.
• Retrofit and New Construction: Assists in selecting or verifying PCM-based products used in retrofitting existing structures or in new sustainable building projects.
• Research and Product Comparison: Useful for comparative studies among different PCM technologies and for validating manufacturer claims.

By focusing on the dynamic thermal storage properties, ASTM C1784-20 helps bridge the gap between laboratory analysis and in-situ performance, providing valuable data for improved building energy performance and occupant comfort.

Related Standards

To support comprehensive PCM testing and terminology, ASTM C1784-20 references several other standards:

• ASTM C518: Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus.
• ASTM C168: Terminology Relating to Thermal Insulation.
• ASTM E793: Test Method for Enthalpies of Fusion and Crystallization by Differential Scanning Calorimetry.
• ASTM E967: Test Method for Temperature Calibration of Differential Scanning Calorimeters and Differential Thermal Analyzers.
• RAL-GZ 896: Phase Change Material, Quality Association PCM e.V.

These standards provide additional context for sample preparation, apparatus calibration, terminology, and supplementary testing protocols relevant to the evaluation of phase change and thermal insulation materials.

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Keywords: ASTM C1784-20, heat flow meter apparatus, phase change material, PCM testing, dynamic thermal storage, building insulation performance, thermal enthalpy, engineering applications, energy-efficient building materials, thermal conductivity, enthalpy-temperature curve.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C1784 − 20
Standard Test Method for
Using a Heat Flow Meter Apparatus for Measuring Thermal
Storage Properties of Phase Change Materials and
Products
This standard is issued under the fixed designation C1784; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope through the transducers must be measureable at all points in
time. Therefore, the transducer output shall never be saturated
1.1 Thistestmethodcoversthemeasurementofnon-steady-
during a test.
state heat flow into or out of a flat slab specimen to determine
1.6 This test method makes a series of measurements to
the stored energy (that is, enthalpy) change as a function of
determine the thermal energy storage of a test specimen over a
temperature using a heat flow meter apparatus (HFMA).
temperature range. First, both HFMA plates are held at the
1.2 In particular, this test method is intended to measure the
same constant temperature until steady state is achieved.
sensible and latent heat storage capacity for products incorpo-
Steadystateisdefinedbythereductionintheamountofenergy
rating phase-change materials (PCM).
entering the specimen from both plates to a very small and
1.2.1 ThestoragecapacityofaPCMiswelldefinedviafour
nearly constant value. Next, both plate temperatures are
parameters: specific heats of both solid and liquid phases,
changed by identical amounts and held at the new temperature
phase change temperature(s) and phase change enthalpy (1).
until steady state is again achieved. The energy absorbed or
released by the specimen from the time of the temperature
1.3 To more accurately predict thermal performance, infor-
change until steady state is again achieved will be recorded.
mation about the PCM products’ performance under dynamic
Using a series of temperature step changes, the cumulative
conditions is needed to supplement the properties (thermal
enthalpy stored or released over a certain temperature range is
conductivity) measured under steady-state conditions.
determined.
NOTE 1—This test method defines a dynamic test protocol for products
1.6.1 The specific heats of the solid and liquid phases are
orcompositescontainingPCMs.Duetothemacroscopicstructureofthese
products or composites, small specimen sizes used in conventional determined from the slope of the temperature-dependant en-
Differential Scanning Calorimeter (DSC) measurements, as specified in
thalpy function during sensible heating/cooling, before and
E793 and E967, are not necessarily representative of the relationship
after the phase change process.
between temperature and enthalpy of full-scale PCM products.
1.7 Calibration of the HFMA to determine the ‘correction
1.4 This test method is based upon the HFMA technology
factors’ for the energy stored within the plate heat flux
used for Test Method C518 but includes modifications for
transducers and any material placed between the test specimen
specific heat and enthalpy change measurements for PCM
and the HFMAplates must be performed following AnnexA1.
products as outlined in this test method.
These correction factors are functions of the beginning and
1.5 Heatflowmeasurementsarerequiredatboththetopand ending temperatures for each step, as described in Annex A1.
bottom HFMA plates for this test method. Therefore, this test
1.8 This test method applies to PCMs and composites,
method applies only to HFMAs that are equipped with at least
products and systems incorporating PCMs, including those
oneheatfluxtransduceroneachofthetwoplatesandthathave
with PCM dispersed in or combined with a thermal insulation
the capability for computerized data acquisition and tempera-
material, boards or membranes containing concentrated or
ture control systems. Further, the amount of energy flowing
dispersed PCM, etc. Specific examples include solid PCM
composites and products, loose blended materials incorporat-
ing PCMs, and discretely contained PCM.
ThistestmethodisunderthejurisdictionofASTMCommitteeC16onThermal
1.9 This test method may be used to characterize material
Insulation and is the direct responsibility of Subcommittee C16.30 on Thermal
properties, which may or may not be representative of actual
Measurement.
conditions of use.
Current edition approved April 1, 2020. Published May 2020. Originally
approved in 2013. Last previous edition approved in 2014 as C1784 – 14. DOI:
1.10 The values stated in SI units are to be regarded as
10.1520/C1784-20.
standard. No other units of measurement are included in this
The boldface numbers in parentheses refer to the list of references at the end of
this standard. standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1784 − 20
1.11 This standard does not purport to address all of the 3.3.4 c (T)—specific heat as a function of temperature,
p
safety concerns, if any, associated with its use. It is the J/kg-°C.
responsibility of the user of this standard to establish appro-
3.3.5 c —specific heat of a melted PCM product, defined
pM
priate safety, health, and environmental practices and deter- atatemperaturegreaterthantheupperlimitofthePCMActive
mine the applicability of regulatory limitations prior to use.
Range, J/kg-°C.
1.12 This international standard was developed in accor-
3.3.6 c —areal specific heat of a melted PCM product,
pM,A
dance with internationally recognized principles on standard-
defined at a temperature greater than the upper limit of the
ization established in the Decision on Principles for the
PCM Active Range, J/m -°C.
Development of International Standards, Guides and Recom-
3.3.7 c —volumetric specific heat of a melted PCM
pM,V
mendations issued by the World Trade Organization Technical
product,definedatatemperaturegreaterthantheupperlimitof
Barriers to Trade (TBT) Committee.
the PCM Active Range, J/m -°C.
3.3.8 c —specific heat of a frozen PCM product, defined at
pF
2. Referenced Documents
a temperature less than the lower limit of the PCM Active
2.1 ASTM Standards: Range, J/kg-°C.
C518 Test Method for Steady-State Thermal Transmission 3.3.9 c —areal specific heat of a frozen PCM product,
pF,A
Properties by Means of the Heat Flow Meter Apparatus
defined at a temperature less than the lower limit of the PCM
C168 Terminology Relating to Thermal Insulation Active Range, J/m -°C.
E793 Test Method for Enthalpies of Fusion and Crystalliza-
3.3.10 c —volumetric specific heat of a frozen PCM
pF,V
tion by Differential Scanning Calorimetry
product, defined at a temperature less than the lower limit of
E967 Test Method for Temperature Calibration of Differen-
the PCM Active Range, J/m -°C.
tial Scanning Calorimeters and Differential Thermal Ana-
3.3.11 E—heat flux transducer output, µV.
lyzers
3.3.12 f—fraction of total PCM mass in the sample that has
2.2 Other Standard: undergone phase change, dimensionless.
RAL-GZ 896 Phase Change Material, Quality Association 3.3.13 h—enthalpy, J/kg.
PCM e.V.
3.3.14 h —areal enthalpy, J/m .
A
3.3.15 h —latent heat per unit mass, J/kg.
fs
3. Terminology
3.3.16 h —latent heat per unit area, J/m .
fs,A
3.1 Definitions—Terminology C168 applies to terms used in 3.3.17 h —latent heat per unit area, J/m .
V
this specification.
3.3.18 k—thermal conductivity, W/m-K.
3.3.19 L—thickness of the test specimen, usually equal to
3.2 Definitions of Terms Specific to This Standard:
theseparationbetweenthehotandcoldplateassembliesduring
3.2.1 phase change material (PCM), n—a material that
testing, m.
changes it physical state (solid to liquid or vice-versa) over a
3.3.20 N—number of heat flux readings at a specific tem-
certain temperature range, used in engineering applications
perature step.
specifically to take advantage of its latent heat storage proper-
3.3.21 q—heat flux (heat flow rate, Q, through area A),
ties.
W/m .
3.2.2 PCM Active Range, n—a broad temperature range in
3.3.22 q —average heat flux at the end of a specific
equilibrium
which a PCM changes phase from solid to liquid (melting) or
temperature step, W/m .
liquid to solid (freezing), with associated enthalpy changes.
3.3.23 Q—heat flow rate in the metered area, W.
3.2.3 PCM composite, n—material embedded with PCM to
3.3.24 R—thermal resistance, (m ·K)/W.
enhance its thermal performance.
3.3.25 S—calibration factor of the heat flux transducer,
3.2.4 PCM product, n—material amended to include energy 2
(W/m )/V.
storage capabilities via inclusion of PCM or PCM composites.
3.3.26 T—temperature, °C.
3.2.5 PCM system, n—array or assembly of PCM products.
3.3.27 T —beginning temperature for each temperature
begin
step, °C.
3.3 Symbols and Units—The symbols used in this test
3.3.28 T —ending temperature for each temperature step,
method have the following significance:
end
°C.
3.3.1 A—HFMA metering area, m .
3.3.2 C (T ,T )—correction factor for heat storage in 3.3.29 T —lower temperature limit of the PCM Active
hft begin end L
the heat flux transducers, J/(m -°C). Range, °C.
3.3.3 C (T ,T )—correction factor for heat storage 3.3.30 T —upper temperature limit of the PCM Active
other begin end
U
in other materials used to surround the test specimen, J/(m -
Range, °C.
°C).
3.3.31 ∆T—temperature difference during a temperature
step (T –T ), °C.
end begin
3.3.32 α—thermal diffusivity, m /s.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
3.3.33 ρ—(bulk) density of the material tested, kg/m .
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
3.3.34 λ—thermal conductivity, W/(m·K).
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. 3.3.35 τ—time interval, s.
C1784 − 20
3.3.36 ∆τ—time interval corresponding to each individual 5.3 This test method focuses on testing PCM products used
flux reading (data value), s. in engineering applications, including in building envelopes to
enhance the thermal performance of insulation systems.
3.4 Subscripts and Superscripts:
5.3.1 Applications of PCM in building envelopes take
3.4.1 A—areal, per m .
multiple forms, including: dispersed in, or otherwise combined
3.4.2 F—frozen, solid.
with, a thermal insulation material; a separate object imple-
3.4.3 fs—latent, associated with the transition from solid to
mented in the building envelope as boards or membranes
liquid or liquid to solid.
containingconcentratedPCMthatoperatesinconjunctionwith
th th
3.4.4 i,k—index denoting i ,k member of a series.
a thermal insulation material. Both of these forms enhance the
3.4.5 L—lower.
performance of the structure when exposed to dynamic, that is,
3.4.6 M—melted, liquid.
fluctuating, boundary temperature conditions.
3.4.7 U—upper.
5.3.2 PCMs can be studied in a variety of forms: as the
3.4.8 V—volumetric, per m .
original “pure” PCM;asa composite containing PCM and
other embedded materials to enhance thermal performance; as
4. Summary of Test Method a product containing PCM or composite (such as micro- or
macro-encapsulated PCM); or as a system, comprising arrays
4.1 Thistestmethoddescribesamethodofusingaheatflow
or assemblies of PCM products.
meter apparatus (HFMA) to perform heat flux measurements
5.4 Thistestmethoddescribesamethodofusingaheatflow
on samples exposed to dynamic, that is non-steady-state,
temperature conditions. The HFMA plates are allowed to meter apparatus to determine key properties of PCM products,
which are listed below. Engineers, architects, modelers, and
stabilize at a certain identical temperature, above or below the
PCMActive Range, and then their temperatures are incremen- others require these properties to accurately predict the in-situ
performance of the products (2).
tally decreased or increased.The plates are allowed to stabilize
after each temperature step and the enthalpy change of the test
5.5 The objective is generally to conduct a test under
specimen is determined for each step change in temperature,
temperature conditions that will induce a phase transition (for
hence the dynamic nature of the test.
example, melting or freezing) in the PCM product during the
course of the test.
NOTE 2—Since the ‘dynamic’ portion of the test method does not
involve measurements made under steady-state conditions, nor lead to
5.6 Determination of thermal storage properties is the ob-
determination of steady-state thermal transmission properties, the Test
jective of this test method, and key properties of interest
Method C518 cannot be used.
include the following:
4.1.1 The test method is specifically designed to address
5.6.1 PCM Active Range, that is the temperature interval
materials and products that undergo physical changes with
over which the phase transitions occur, for both melting and
latentheatabsorptionorreleaseduringthecourseofthetest.In
freezing of the PCM product or composites containing PCMs.
particular, a phase transition will occur within PCM products,
5.6.2 Specific heat of the fully melted and fully frozen
when the test temperatures span the PCM Active Range.
product, defined outside the PCM Active Range.
4.2 The object of the test, especially for a PCM product, is 5.6.3 Enthalpy as a function of temperature, h(T).
generally to determine the temperature dependence of the 5.6.4 Enthalpy plot—a histogram or table that indicates the
enthalpy of the specimen. change in enthalpy associated with incremental temperature
changes that span the tested temperature range.
5.6.5 Enthalpy changes associated with phase transitions
5. Significance and Use
during the PCM melting and freezing processes in materials
5.1 Materials used in building envelopes to enhance energy
and composites containing PCMs.
efficiency,includingPCMproductsusedforthermalinsulation,
5.7 PCM products often possess characteristics that compli-
thermal control, and thermal storage, are subjected to transient
cate measurement and analysis of phase transitions during a
thermal environments, including transient or cyclic boundary
test. Following are some of the known issues with PCMs:
temperature conditions. This test method is intended to enable
5.7.1 Imprecise PCM Active Range—PCMs in general do
meaningfulPCMproductclassification,assteady-statethermal
not have precise melting or freezing temperatures, and the
conductivity alone is not sufficient to characterize PCMs.
entire active temperature range, from the beginning to the end
NOTE 3—This test method defines a dynamic test protocol for complex
products or composites containing PCMs. Due to the macroscopic
of phase transitions, must be determined.
structure of these products or composites, conventional measurements
NOTE 4—The onset of freezing will not necessarily coincide with the
using a Differential Scanning Calorimeter (DSC) as specified in E793 and
end of melting. Therefore, the freeze and melt enthalpy curves must be
E967, which use very small specimens, are not necessarily representative
independently defined to determine the PCM Active Range.
of the relationship between temperature and enthalpy of full-scale PCM
products due to the specimen size limitation.
5.7.2 Multiple Phase Transitions—Many PCMs exhibit a
5.2 Dynamic measurements of the thermal performance of solid-solid transition with significant latent heat effects at
PCM products shall only be performed by qualified personnel temperatures near the melting transition.
with understanding of heat transfer and error propagation. 5.7.3 Sub-cooling—Occurs when the specimen cools below
Familiaritywiththeconfigurationofboththeapparatusandthe its nominal freezing temperature before it actually begins to
product is necessary. freeze, thus exhibiting an unusual enthalpy-temperature curve.
C1784 − 20
Solid-liquid and solid-solid phase changes are often dependent effect on the thermal measurement. This shall be verified by
on heating and cooling rate. separate measurement on solid specimens made with and
5.7.4 Hysteresis—Occurs when a specimen heated from one without the sample frame.
temperature to another, and then returned to the original
7.4 For arrays of PCM pouches or PCM containers (8).
temperature, absorbs more (or less) heat at any particular
7.4.1 Ensure the portion of the product within the metered
temperature during the heating stage than it releases during
area is representative of the array pattern.
cooling.
7.4.2 A sketch or photograph of the test specimen is
5.8 Thepropertiesmeasuredaredeterminedbyfundamental required for this type of product, due to the spatial non-
thermophysical properties of the constituent materials of the uniformities and discontinuities that are common with this
product, and are thus inherent to the PCM product.The desired product type.
thermal performance enhancement, however, will depend
7.5 Ensure good contact between the HFMA plates and the
strongly on the particular environment, climate, and mode of
product. If necessary, use an elastomeric or soft foam rubber
the actual engineering application of the PCM.
sheet between one or both sides of the product and the
corresponding apparatus plate. This sheet will improve contact
6. Apparatus
between the controlled temperature plates and prevent air
6.1 Follow theApparatus section ofTest Method C518 with
circulation between the panel and the plates. The energy
these additional requirements:
storage correction for the sheet(s) must be independently
6.1.1 Aminimumoftwoheatfluxtransducers,onemounted
measured,inthesamemannerasfortheHFMAtransducers,as
on each plate of the apparatus, are required.
described in Annex A1. The measured heat flow into the
6.1.2 The ability to scan temperature and heat flux data at
assembly must then be corrected for this material as described
specified intervals and store results in a form that is immedi-
in 10.3.
ately accessible in real time to the user or other programs
7.6 For PCM products with high lateral thermal
running concurrently is required; for example, a text file to
conductivity, use an insulating frame to avoid significant edge
which data are written after each scan. The ability to record a
losses. Ensure the frame is far away from the metered area to
time stamp of each scan is required.
maximize the one-dimensional heat flow in the metered area.
6.1.3 The ability to accept a user-defined temperature pro-
gram for control of both plate temperatures. This test method
8. Calibration
includes a series of temperature steps, with specified intervals
8.1 Prior to using this test method, calibrate the HFMA to
determined by time or equilibrium criteria.
determine the temperature-dependent calibration coefficients
NOTE 5—Independent time or equilibrium criteria control for each
for both heat flux transducers using the procedure for the
setpoint will facilitate the test.
multiple temperature and thickness points in the Calibration
6.1.4 The amount of energy flowing through the transducers
section of Test Method C518.
must be measureable at all times. To avoid saturating the
8.2 The heat flux levels obtained during an HFMA test run
transducers, either their voltage gain must be variable, or in
are, in general, determined by heat flowing into or out of the
apparatus without variable transducer gain, the alternative
specimen. The heat flux readings are also impacted by the heat
approaches described in Appendix X2 must be followed.
that enters or leaves the transducers themselves, as a result of
the change of the transducer temperature that corresponds to
7. Specimen Preparation
the change in plate temperature. Such heat flow is incidental to
7.1 Instructions are given here separately for solid samples,
the values used in characterizing the PCM product. Therefore,
loose blended materials, and discretely contained PCM.
separately calibrate the heat flux transducers within the HFMA
7.2 For solid samples such as gypsum wallboard containing
tomeasurethecorrectionfactorforheatstorageintheheatflux
PCM (3-5).
transducers. This additional apparatus calibration is described
7.2.1 Cut the specimen to the same size as the HFMAplate
in Annex A1.
area.
9. Procedure
NOTE 6—If the specimen has a conductive facing, for example, foil,
place a sheet of craft paper between the facing and the corresponding
9.1 Personnel Qualifications—This test method shall only
apparatus plate. If the heat capacity of this sheet is expected to be
be performed by qualified personnel with experience in heat
significant relative to the energy storage of the specimen, independently
transferanalysisandexperimentalerrorpropagation.Toensure
measure the heat capacity in the same manner as for the HFMA
accurate measurement, the operator shall be fully proficient in
transducers, described in AnnexA1. Then correct the measured heat flow
the operation of the equipment and must have detailed famil-
into the assembly for this material as described in Section 10.
iarity with the configuration of the apparatus, the apparatus
7.3 For loose material blended with PCM (6, 7).
control and data reporting software, and the specimen itself.
7.3.1 Construct the sides of a frame using thin low mass
material between 2.5 to 5 cm in height and sized so the frame 9.2 Procedure Overview—In order to characterize the PCM
will be located at the periphery of the test chamber.Affix a net product, test parameter definitions are required, as are multiple
material to form the frame bottom. series of measurements at discrete temperature steps. Instruc-
7.3.2 Since the frame is located far from the metering area, tions are given here to first define the general process used
it is unlikely that the frame presence will have a significant during a series of measurements (9.3); describe how to
C1784 − 20
determine the test parameters (9.4); and finally, to apply this 9.4.4 Repeat this procedure starting at the fully melted
process to characterize the PCM product (9.5). Additional temperature condition and decreasing the plate temperatures in
instructions are included to describe an optional investigation 1.5 6 0.5°C steps until the amount of energy stored in a
of the hysteresis within partially melted or frozen specimens temperature step returns to a small value, that is, when the test
(9.6, Appendix X3).
specimen is fully frozen. See 10.2.
9.4.5 Examine the data as described in Section 10. Deter-
9.3 Define general series of temperature steps for both
mine the estimated PCM Active Range, the desired tempera-
plates, for example, 11°C and 11°C, 13°C and 13°C, 15°C and
ture step size, and the amount of time required for each step.
15°C, and so on.
9.3.1 To measure the enthalpy stored in the test specimen in 9.4.6 An example of such a test series is shown in Annex
A2.
each temperature range, make a series of measurements.
9.3.2 First, both plates shall be held at the same constant
9.5 Characterize the PCM product:
temperature until steady state is achieved.
9.5.1 Make a series of measurements, as described in 9.3,
NOTE 7—Please see Annex A1 for a description of experimental work
starting at a temperature at least 10°C below estimated PCM
that has been done with an apparatus with plates at different temperatures
Active Range, and heating the plates with temperature differ-
to achieve the same goals.
ence steps of 1.5 6 0.5°C. End at a temperature at least 10°C
9.3.2.1 Steady state is defined by the reduction in the
above the estimated PCM Active Range. The amount of time
amount of energy entering the specimen from both plates to a
required at each temperature step shall be as determined in
very small and nearly constant value. See 10.2.
10.2.
9.3.3 After steady state is achieved, both plate temperatures
NOTE 10—The minimum and maximum temperature difference step
will be changed to the same new temperature and held at that
size will be limited by the combined uncertainty of the temperature
value until steady state is again achieved.
measurement and heat flux measurement within the HFMA.
9.3.4 The cumulative amount of energy that enters the
NOTE 11—To enable testing over a sufficient temperature range while
specimen from the time of the temperature change until steady
considering any HFMAlimits on number of allowable temperature steps,
variable temperature differences can be utilized. For example, Biswas et
state is again achieved will be recorded.
al. (10) used temperature differences of 1°C close to and within the PCM
9.3.5 Heat flux readings shall include the proper sign to
Active Range and 2°C away from the PCM Active Range.
indicate direction of heat flow; for example, a positive reading
9.5.2 Make a series of measurements, as described in 9.3,
may indicate heat entering the test specimen, and negative
values indicating heat leaving the specimen. starting at a temperature at least 10°C above the estimated
PCM Active Range, and cooling the plates with temperature
9.3.6 The initial temperature selection, the temperature
difference steps of 1.5 6 0.5°C. End at a temperature at least
difference between setpoints, and the number of temperature
10°C below the estimated PCM Active Range.
steps, will vary according to the purpose of each particular test
series.
9.5.3 Examine the data as described in Section 10 to
determine:
NOTE 8—The temperature range available depends on the construction
9.5.3.1 Whether either of the data series shall be repeated
of the HFMA equipment, the heat rejection bath temperature, and the
calibration of the equipment.
using longer equilibrium times at any particular temperature.
9.4 Determine the test parameters: 9.5.3.2 Whether the temperature range needs to be ex-
panded to capture the full PCM Active Range.
9.4.1 An initial test shall be used to estimate the PCM
Active Range and determine the time required for each
9.5.4 A minimum of three heating series, as described in
temperature step. This step is not required if the specimen
9.5.1, and a minimum of three cooling series, as described in
phase change characteristics are already well known, for
9.5.2, are required.
example from differential thermal analysis (DTA) tests or
9.5.4.1 In order to define the enthalpy curve of energy
differential scanning calorimetry (DSC) tests (using the step
storage vs. temperature with adequate precision, select begin-
method or appropriately slow heating and cooling rates, as
ningtemperaturesforthesubsequentheatingandcoolingseries
described by Castellon et al. (9)).
that differ from those used for the initial heating and cooling
9.4.2 Make series of measurements, as described in 9.3,
series.
starting at a temperature at least 10°C below the expected
NOTE 12—For example: If the initial heating series spanned 10 to 30°C
melting temperature, or at the lowest temperature available on
in 2°C steps, retain the 2°C step size, but start the second heating series at
the HFMA, whichever is higher. Use temperature difference
10.6°C and the third heating series at 11.3°C. If the initial cooling series
steps of 1.5 6 0.5°C.Allow a minimum of two hours for each
spanned 30 to 10°C in 2°C steps, retain the 2°C step size, but start the
setpoint during the initial specimen characterization.
second heating series at 29.4°C and the third heating series at 28.7°C.
9.4.3 End the series when the amount of energy stored in a
9.5.4.2 Examine the data as described in 10.2 to determine
temperature step returns to a small value, that is, when the test
whether either of the data series shall be repeated using longer
specimen is fully melted. See 10.2.
equilibrium times at any particular temperature.
NOTE 9—As described in 10.2, the amount of time required at each
9.6 Hysteresis effects when starting from partially frozen or
temperature step will vary depending on the size of the temperature step,
partially melted material may be explored using the method
the thermal diffusivity of the specimen, and the amount of energy storage
that occurs over that temperature step. described in Appendix X3.
C1784 − 20
10. Calculations τ 5
min, est
Estimated enthalpy storage for a particular temperature step
10.1 Calculations Overview—The calculations require sev-
Maximum conductance rate through specimen
eral separate stages. First it is necessary to examine the data to
or,
evaluatewhetheranadequateamountoftimewasspentateach
c ~T!ρL∆T c ~T!ρL
and every temperature step (10.2). Once this has been p p
τ 5 5
min, est
k∆T 2k
established, it is possible to calculate the net energy storage
S D
L⁄2
~ !
within the test specimen corresponding to each temperature
(1)
step (10.3). That data form can then be used to express the
NOTE 13—If data are available to permit the calculation shown in Eq 1,
enthalpy of the product as a function of temperature (10.4); to
reasonable rules of thumb for the adequate total time for that temperature
define the specific heat of the fully melted and fully frozen
stepwouldbe:(1)forheatingawayfromtheexpectedlatentrange,use1.5
product(10.5,10.6);andtodefinethelatentheatoftheproduct
times the estimated minimum; (2) for heating within the latent range, use
(10.7).
2.5 times the estimated minimum; (3) for cooling away from the expected
latent range, use 2.5 times the estimated minimum; (4) for cooling within
10.2 Evaluate adequacy of time intervals at each tempera-
the latent range, use 5 times the estimated minimum.
ture step.
10.2.2 Plottheheatfluxsignalvs.timeforeachtemperature
10.2.1 Theamountoftimerequiredateachtemperaturestep
step for each plate as shown in Fig. 1. This plot is also useful
will vary depending on the size of the temperature step, the
in determining how much time is required at each temperature
thermal diffusivity of the specimen, the material thickness, and
step. For example, the time spent at temperatures labeled 20.5
the amount of energy storage that occurs over that temperature
and 19.5 is longer than necessary and the time spent at
step. The time interval required to reach steady state during
temperature 18.5 is barely sufficient.
phase change phenomena are much greater than time intervals
required when the material is subjected to sensible energy
NOTE 14—The raw data are evaluated in this step. The raw data,
storage phenomena.
typically in microvolts, will be transformed into the integrated heat flux in
10.2.1.1 The maximum heat rate into or out of the specimen a subsequent step as described in 10.3.
NOTE 15—It is useful to examine the equilibrium portions of the curves
is limited by apparatus capability and the specimen thermal
by either limiting the range of the plot on the y-axis, or plotting the
diffusivity. It is possible to estimate the minimum amount of
absolute values of the electrical signal on a log axis.
time (τ ) needed for each step by neglecting the apparatus
min,est
10.2.3 As shown in 10.2.2 and Fig. 1, at steady state
limits and the impact of thermal storage on the thermal
conditions at the end of each temperature step, a small
transmittance through the specimen, as shown in Eq 1. This
non-zero HFMA signal remains, largely due to edge heat
approach is only possible when there is some basis for
losses. For each series of temperature steps, determine whether
estimating the energy storage needed for that particular tem-
each temperature step was held for an adequate length of time
perature step and when an estimate is available for the thermal
by examining this residual, or equilibrium, HFMA signal.
conductivity of the material. Possible sources for the energy
10.2.3.1 Calculate the residual heat flux transducer output
storage estimate include prior heating or cooling series or data
from a DSC run. (E), which is average output over the last 60 minutes of each
FIG. 1 Example of Transducer Output (E) Data Taken During a Series of Cooling Temperature Steps of the Lower Plate of an HFMA
C1784 − 20
temperature step. Plot this residual value vs. the plate tempera- 10.3 Calculate the net energy storage for each temperature
ture for that step. All the steps that have reached steady-state step.
will show very similar values, or values that vary slightly with
10.3.1 After determining that the time spent at each and
plate temperature.
every temperature step within the series was adequate to reach
steadystateasdescribedin10.2,calculatetheheatgain/lossfor
NOTE 16—In Fig. 2, the test was initially run with 6 h for each
each plate for each temperature step as shown in Eq 2 (9).
temperature step. For all of the data points except the four highlighted
witharrows,thisappearstohavebeenanadequatelengthoftime.Thetest
10.3.2 The equilibrium, or residual, heat flux described in
was then repeated with those four steps increased to 9.25 h. It appears that
10.2 shall be subtracted in the summation, independently for
the cooling step at 18.5°C (temperature step from 19 to 18°C) requires
each plate.
even more than 9 h. Note the entire cooling sequence would need to be
repeated, starting at the highest temperature, to get the data for this
NOTE 18—It is possible that this correction is pre-programmed in the
temperature step interval.
HFMA control software. Determine whether this is so in order to avoid
10.2.3.2 Another way to examine the residual heat flux data erroneous heat gain/loss calculations.
is to look at the difference between the output from the
10.3.3 The energy that is stored within the transducers
transducers in the upper and lower plates, as shown in Fig. 3.
themselves (see AnnexA1) must also be subtracted, as well as
The PCMActive Range for this example, based on the sample
the heat stored in any material placed between the test
data, is about 17–21°C. For a few data points, far away from
specimen and the HFMA plates. These correction factors for
the PCMActive Range, there is no difference between the data
the transducer energy storage and for any other material
at 3 h and 6 h.Within the PCMActive Range, some of the data
included with the test specimen are functions of the beginning
points in the cooling series still show significant changes
and ending temperatures for each step, as described in Annex
between the 6 and 9 h values. This is also shown in the lower
A1.
linearregressioncoefficientforthe9hcoolingdataseries.This
would also indicate that the time intervals between 18 and NOTE 19—It is possible that this correction is pre-programmed in the
HFMA control software. Determine whether this is so in order to avoid
20°C during the cooling series need to be longer.
erroneous heat gain/loss calculations.
10.2.4 Use the data from 10.2.3 to determine whether the
time spent at each temperature step within the series was
10.3.4 Eq 2 shows the calculation of the energy storage in
adequate. If not, adjust the time interval settings and repeat the
the specimen for a given temperature interval (T , T ).
begin end
entire series of temperature steps.
The recorded heat flux for both plates, corrected for the
10.2.5 Time interval estimates based on results from a
residual equilibrium heat flux, is multiplied by the length of
heating series are not a reliable predictor for the same
time (∆τ) for each data point (q), and summed over the total
i
temperature steps during a cooling series.
number of data points (N) for the given temperature interval
(∆T). After subtracting the transducer heat storage correction
NOTE 17—Experience has shown that for some materials the time
factors, as well as the correction for any other material
intervals required for some freezing phenomena are much greater than for
the melting phenomena. included within the HFMA, from the sum of the heat flow into
FIG. 2 Residual Transducer Output (E) Over the Last 60 Minutes During Heating and Cooling for Upper and Lower Plates at Two Differ-
ent Time Periods for Each Temperature Step
C1784 − 20
FIG. 3 Transducer Output Difference (∆E=E –E ) for Different Temperature Step Time Periods During Heating and
upper plate lower plate
Cooling Series
the specimen, the total amount of enthalpy stored in the 10.4.3 That plot of areal enthalpy (h , J/m ) can also be
A
specimen during that temperature interval is calculated as
manipulated to show the specific enthalpy (h, J/kg) and
shown in Eq 2.
volumetricenthalpy(h ,J/m )asafunctionoftemperature.See
V
N Annex A2 for an example of merging the data from multiple
h 5 q 2 q ∆τ 2 C T , T ∆T
FS ~ ! D ~ !
A i quilibrium hft begin end series onto a single plot of h vs. T.
(
V
i51
N
h~T! 5 h ~T!⁄~ρ L! (3)
A
2 C T , T ∆T 1 q 2 q ∆τ
~ ! G FS ~ ! D
other begin end ( i quilibrium
i51 h T 5 h T ⁄L (4)
upper ~ ! ~ !
V A
10.4.4 The data from heating series and cooling series shall
2 C ~T , T !∆T 2 C ~T , T !∆T (2)
G
hft begin end other begin end
lower
be kept separate except that the final enthalpy from the heating
10.4 Combine the temperature step data to define the energy
series shall be taken as the starting enthalpy for the cooling
storage as a function of temperature.
series. See Annex A2.
10.4.1 Define the zero amount of cumulative heat as corre-
10.5 Definethespecificheatofthefullyfrozenproduct,c ,
sponding to the bottom of the step(s) starting from the lowest
pF
and define T , the lower temperature limit of the PCM Active
temperature used in 9.5.
L
10.4.2 Plot the corrected cumulative heat into or out of the Range, when the melting initiates or freezing ends. Fig. 4
shows a sample PCM behavior during melting and freezing. In
specimen vs. the ending temperature for each step.An example
is shown in Annex A2. this example, the freezing ends at a lower temperature than the
FIG. 4 Sample PCM Behavior During Melting and Freezing
C1784 − 20
melting initiation, and T needs to be defined based on the experience, the enthalpy function of the PCM exhibits a sharp
L
freezing series. See A2.6 for an example calculation. transition at the freezing onset. Therefore, T is defined solely
U
by the temperature below which the correlation coefficient
NOTE 20—The accuracy of T will be limited by the temperature step
L
drops below 0.995.
size.
10.6.3 Use the calculated slope of the line connecting the
10.5.1 Examine the data for h vs. T from 10.4.3. Start with
first to the last data point set with a regression coefficient
the values at the lowest temperatures measured for the com-
greater than 0.995 as the specific heat of the fully melted
bined heating and cooling series. Perform a linear regression
product, c .
pM
forthefirst2datapointsandcalculateboththeslopeoftheline
2 2
10.7 Calculate the latent heat.
(in units of J/m ·°C) and the regression coefficient (R ). Since
10.7.1 The total enthalpy change between T and T in-
L U
only 2 data points were used, the regression coefficient is 1.0.
cludes both sensible and latent heat effects. Use the specific
10.5.2 Perform the linear regression again using the first 3,
heat of the fully frozen product below the mean temperature of
4, 5, 6, etc. data points until the regression coefficient is less
the PCM Active Range, and the specific heat of the fully
than 0.995. Prior experience has shown that, during melting,
melted state above the mean temperature of the PCM Active
thereisnosharptransitionatthebeginningofmeltingofPCMs
Range to define the sensible heat storage over the temperature
(also evident in the melting curve of Fig. 4). Therefore, using
range. The difference between the total and sensible heat
a threshold correlation coefficient of 0.995 to define melting
storage is the latent heat (h ).
fs
onset is not appropriate.
T T
U U
10.5.3 The melting onset, for the purpose of this test, is
h 5 ~∆ h! 2 c ~T 2 T ! 2 c ~T 2 T !5 ~∆ h!
fs ( pF Mean L pM U Mean (
definedbya20%deviationfromthebaselinelinearcumulative
T T
L L
enthalpy of the frozen PCM. To obtain this baseline, fit a
~c 1 c !~T 2 T !
pF pM U L
2 (7)
straight line through the data points with regression coefficient
greater than or equal to 0.995. Identify the lower temperature
10.7.2 The areal form of the latent heat is shown in Eq 8.
limit of the PCM Active Range, T , as that temperature above
L
which the percentage deviation of the measured cumulative h 5 h 3ρ 3L (8)
fs,A fs
enthalpy deviates by more than 20% from the calculated
baseline linear cumulative enthalpy. See A2.6 for the example 11. Report
calculation.
11.1 For each test, report the following information:
10.5.4 Use the calculated slope (in units of J/m ·°C) of the
11.1.1 Identify the report with a unique numbering system
line connecting the first to the last data point with the percent
toallowtraceabilitybacktotheindividualmeasurementstaken
deviation in measured cumulative enthalpy from the calculated
during the test performed.
baseline less than 20% as the areal specific heat of the fully
11.1.2 Identify the material and give a physical description.
frozen product, c . The areal specific heat can be manipu-
pF,A
11.1.2.1 Provide a specimen diagram or photograph if any
lated to show the specific heat and volumetric specific heat as
materials other than the PCM product were placed in the
a function of temperature.
HFMA, or if the area of the specimen is different from the area
c ~T! 5 c ~T!⁄~ρ L! (5)
of the HFMA plates.
pF pFA
11.1.2.2 Provide a specimen diagram if the test specimen
c T 5 c T ⁄L (6)
~ ! ~ !
pFV pFA
consisted of arrays of PCM pouches or PCM containers.
10.6 Define the specific heat of the fully melted product,
11.1.3 Provide a brief conditioning history of the specimen,
c , and define T , the upper temperature limit of the PCM
pM U
if known.
Active Range, when melting ends or freezing initiates. In the
11.1.4 Thickness of the specimen as received and as tested,
example shown in Fig. 4, the melting ends at a higher
m.
temperature and will define T . See A2.6 for an example
U
11.1.5 Mass of the specimen, kg.
calculation.
11.1.6 Volume of the specimen, m .
NOTE 21—The accuracy of T will be limited by the temperature step 11.1.7 Density of the specimen, kg/m .
U
size.
11.1.8 Area of the specimen exposed to each HFMA plate,
m .
10.6.1 Examine the data for h vs. T from 10.4.3. Start with
the values at the highest temperatures measured for the 11.1.9 Method and environment used for conditioning, if
used.
combined heating and cooling series. Perform a linear regres-
sion for the first 2 data points and calculate both the slope of 11.1.10 Dates the tests started and ended.
the line (in units of J/kg·°C) and the regression coefficient (R ). 11.1.11 The temperature step size(s) used in the melting and
Since only 2 data points were used, the regression coefficient is
freezing tests.
1.0.
11.1.12 Table of corrected cumulative enthalpy into or out
10.6.2 Perform the linear regression again using the first 3, of the specimen vs. the end temperature for each step,
4, 5, 6, etc. data points until the regression coefficient is less combining the data from the multiple heating and cooling
than 0.995. Identify the upper temperature limit of the PCM series as described in Annex A2. Present the data as shown in
Active Range, T , as that temperature at which the regression Table1.Anacceptablealternativeistopresentseparateheating
U
coefficient first dropped below 0.995. Based on prior and cooling test data following RAL-GZ 896 (Appendix X4).
C1784 − 20
TABLE 1 Required Enthalpy Change Data Report Table TABLE 3 Heat Storage Correction Factor Calibration Test Report
Format
Enthalpy change Enthalpy change
Mean temperature, °C
3 3
during heating, J/m during cooling, J/m
Date: ____________
Correction Factor,
Calibration Material(s): Temperature, °C
First entry at least 3°C
J/m ·°C
__________________
below T
L
Lowest temperature
Maximum step size
used, °C
between entries is 1°C
Maximum step size
Last entry at least 3°C
between entries is 10°C
above T
U
Maximum temperature
used, °C
11.1.13 Plot of corrected cumulative heat into or out of the
11.4 The name of the operator performing the tests and the
specimen vs. the end temperature for each step, as shown by
data analyst preparing the test report.
the combined data curve in Fig. A2.1 (Annex A2)orthe
histograms in Figs. X4.1 and X4.2 (Appendix X4).
11.5 Describe impact of any machine/calibration tempera-
11.1.14 Measured parameters, as listed in Table 2.
ture range limitations upon the test procedure. List the HFMA
type and model, and the name and version identification of the
11.2 Description of calibration test r
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: C1784 − 14 C1784 − 20
Standard Test Method for
Using a Heat Flow Meter Apparatus for Measuring Thermal
Storage Properties of Phase Change Materials and
Products
This standard is issued under the fixed designation C1784; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers the measurement of non-steady-state heat flow into or out of a flat slab specimen to determine the
stored energy (that is, enthalpy) change as a function of temperature using a heat flow meter apparatus (HFMA).
1.2 In particular, this test method is intended to measure the sensible and latent heat storage capacity for products incorporating
phase-change materials (PCM).
1.2.1 The storage capacity of a PCM is well defined via four parameters: specific heats of both solid and liquid phases, phase
change temperature(s) and phase change enthalpy (1).
1.3 To more accurately predict thermal performance, information about the PCM products’ performance under dynamic
conditions is needed to supplement the properties (thermal conductivity) measured under steady-state conditions.
NOTE 1—This test method defines a dynamic test protocol for products or composites containing PCMs. Due to the macroscopic structure of these
products or composites, small specimen sizes used in conventional Differential Scanning Calorimeter (DSC) measurements, as specified in E793 and
E967, are not necessarily representative of the relationship between temperature and enthalpy of full-scale PCM products.
1.4 This test method is based upon the HFMA technology used for Test Method C518 but includes modifications for specific
heat and enthalpy change measurements for PCM products as outlined in this test method.
1.5 Heat flow measurements are required at both the top and bottom HFMA plates for this test method. Therefore, this test
method applies only to HFMAs that are equipped with at least one heat flux transducer on each of the two plates and that have
the capability for computerized data acquisition and temperature control systems. Further, the amount of energy flowing through
the transducers must be measureable at all points in time. Therefore, the transducer output shall never be saturated during a test.
1.6 This test method makes a series of measurements to determine the thermal energy storage of a test specimen over a
temperature range. First, both HFMA plates are held at the same constant temperature until steady state is achieved. Steady state
is defined by the reduction in the amount of energy entering the specimen from both plates to a very small and nearly constant
value. Next, both plate temperatures are changed by identical amounts and held at the new temperature until steady state is again
achieved. The energy absorbed or released by the specimen from the time of the temperature change until steady state is again
achieved will be recorded. Using a series of temperature step changes, the cumulative enthalpy stored or released over a certain
temperature range is determined.
1.6.1 The specific heats of the solid and liquid phases are determined from the slope of the temperature-dependant enthalpy
function during sensible heating/cooling, before and after the phase change process.
1.7 Calibration of the HFMA to determine the ‘correction factors’ for the energy stored within the plate heat flux transducers
and any material placed between the test specimen and the HFMA plates must be performed following Annex A1. These correction
factors are functions of the beginning and ending temperatures for each step, as described in Annex A1.
1.8 This test method applies to PCMs and composites, products and systems incorporating PCMs, including those with PCM
dispersed in or combined with a thermal insulation material, boards or membranes containing concentrated or dispersed PCM, etc.
Specific examples include solid PCM composites and products, loose blended materials incorporating PCMs, and discretely
contained PCM.
This test method is under the jurisdiction of ASTM Committee C16 on Thermal Insulation and is the direct responsibility of Subcommittee C16.30 on Thermal
Measurement.
Current edition approved Oct. 1, 2014April 1, 2020. Published December 2014May 2020. Originally approved in 2013. Last previous edition approved in 20132014 as
C1784C1784 – 14.-13. DOI: 10.1520/C1784-14.10.1520/C1784-20.
The boldface numbers in parentheses refer to the list of references at the end of this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1784 − 20
1.9 This test method may be used to characterize material properties, which may or may not be representative of actual
conditions of use.
1.10 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.11 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.12 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
C518 Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus
C168 Terminology Relating to Thermal Insulation
E793 Test Method for Enthalpies of Fusion and Crystallization by Differential Scanning Calorimetry
E967 Test Method for Temperature Calibration of Differential Scanning Calorimeters and Differential Thermal Analyzers
2.2 Other Standard:
RAL-GZ 896 Phase Change Material, Quality Association PCM e.V.
3. Terminology
3.1 Definitions—Terminology C168 applies to terms used in this specification.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 phase change material (PCM), n—a material that changes it physical state (solid to liquid or vice-versa) over a certain
temperature range, used in engineering applications specifically to take advantage of its latent heat storage properties.
3.2.2 PCM Active Range, n—a broad temperature range in which a PCM changes phase from solid to liquid (melting) or liquid
to solid (freezing), with associated enthalpy changes.
3.2.3 PCM composite, n—material embedded with PCM to enhance its thermal performance.
3.2.4 PCM product, n—material amended to include energy storage capabilities via inclusion of PCM or PCM composites.
3.2.5 PCM system, n—array or assembly of PCM products.
3.3 Symbols and Units—The symbols used in this test method have the following significance:
3.3.1 A—HFMA metering area, m .
3.3.2 C (T ,T )—correction factor for heat storage in the heat flux transducers, J/(m -°C).
hft begin end
3.3.3 C (T ,T )—correction factor for heat storage in other materials used to surround the test specimen, J/(m -°C).
other begin end
3.3.4 c (T)—specific heat as a function of temperature, J/kg-°C.
p
3.3.5 c —specific heat of a melted PCM product, defined at a temperature greater than the upper limit of the PCM Active
pM
Range, J/kg-°C.
3.3.6 c —areal specific heat of a melted PCM product, defined at a temperature greater than the upper limit of the PCM
pM,A
Active Range, J/m -°C.
3.3.7 c —volumetric specific heat of a melted PCM product, defined at a temperature greater than the upper limit of the PCM
pM,V
Active Range, J/m -°C.
3.3.8 c —specific heat of a frozen PCM product, defined at a temperature less than the lower limit of the PCM Active Range,
pF
J/kg-°C.
3.3.9 c —areal specific heat of a frozen PCM product, defined at a temperature less than the lower limit of the PCM Active
pF,A
Range, J/m -°C.
3.3.10 c —volumetric specific heat of a frozen PCM product, defined at a temperature less than the lower limit of the PCM
pF,V
Active Range, J/m -°C.
3.3.11 E—heat flux transducer output, μV.
3.3.12 f—fraction of total PCM mass in the sample that has undergone phase change, dimensionless.
3.3.13 h—enthalpy, J/kg.
3.3.14 h —areal enthalpy, J/m .
A
3.3.15 h —latent heat per unit mass, J/kg.
fs
3.3.16 h —latent heat per unit area, J/m .
fs,A
3.3.17 h —latent heat per unit area, J/m .
V
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
C1784 − 20
3.3.18 k—thermal conductivity, W/m-K.
3.3.19 L—thickness of the test specimen, usually equal to the separation between the hot and cold plate assemblies during
testing, m.
3.3.20 N—number of heat flux readings at a specific temperature step.
3.3.21 q—heat flux (heat flow rate, Q, through area A), W/m .
3.3.22 q —average heat flux at the end of a specific temperature step, W/m .
equilibrium
3.3.23 Q—heat flow rate in the metered area, W.
3.3.24 R—thermal resistance, (m ·K)/W.
3.3.25 S—calibration factor of the heat flux transducer, (W/m )/V.
3.3.26 T—temperature, °C.
3.3.27 T —beginning temperature for each temperature step, °C.
begin
3.3.28 T —ending temperature for each temperature step, °C.
end
3.3.29 T —lower temperature limit of the PCM Active Range, °C.
L
3.3.30 T —upper temperature limit of the PCM Active Range, °C.
U
3.3.31 ΔT—temperature difference during a temperature step (T – T ), °C.
end begin
3.3.32 α—thermal diffusivity, m /s.
3.3.33 ρ—(bulk) density of the material tested, kg/m .
3.3.34 λ—thermal conductivity, W/(m·K).
3.3.35 τ—time interval, s.
3.3.36 Δτ—time interval corresponding to each individual flux reading (data value), s.
3.4 Subscripts and Superscripts:
3.4.1 A—areal, per m .
3.4.2 F—frozen, solid.
3.4.3 fs—latent, associated with the transition from solid to liquid or liquid to solid.
th th
3.4.4 i,k—index denoting i , k member of a series.
3.4.5 L—lower.
3.4.6 M—melted, liquid.
3.4.7 U—upper.
3.4.8 V—volumetric, per m .
4. Summary of Test Method
4.1 This test method describes a method of using a heat flow meter apparatus (HFMA) to perform heat flux measurements on
samples exposed to dynamic, that is non-steady-state, temperature conditions. The HFMA plates are allowed to stabilize at a certain
identical temperature, above or below the PCM Active Range, and then their temperatures are incrementally decreased or
increased. The plates are allowed to stabilize after each temperature step and the enthalpy change of the test specimen is determined
for each step change in temperature, hence the dynamic nature of the test.
NOTE 2—Since the ‘dynamic’ portion of the test method does not involve measurements made under steady-state conditions, nor lead to determination
of steady-state thermal transmission properties, the Test Method C518 cannot be used.
4.1.1 The test method is specifically designed to address materials and products that undergo physical changes with latent heat
absorption or release during the course of the test. In particular, a phase transition will occur within PCM products, when the test
temperatures span the PCM Active Range.
4.2 The object of the test, especially for a PCM product, is generally to determine the temperature dependence of the enthalpy
of the specimen.
5. Significance and Use
5.1 Materials used in building envelopes to enhance energy efficiency, including PCM products used for thermal insulation,
thermal control, and thermal storage, are subjected to transient thermal environments, including transient or cyclic boundary
temperature conditions. This test method is intended to enable meaningful PCM product classification, as steady-state thermal
conductivity alone is not sufficient to characterize PCMs.
NOTE 3—This test method defines a dynamic test protocol for complex products or composites containing PCMs. Due to the macroscopic structure
of these products or composites, conventional measurements using a Differential Scanning Calorimeter (DSC) as specified in E793 and E967, which use
very small specimens, are not necessarily representative of the relationship between temperature and enthalpy of full-scale PCM products due to the
specimen size limitation.
5.2 Dynamic measurements of the thermal performance of PCM products shall only be performed by qualified personnel with
understanding of heat transfer and error propagation. Familiarity with the configuration of both the apparatus and the product is
necessary.
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5.3 This test method focuses on testing PCM products used in engineering applications, including in building envelopes to
enhance the thermal performance of insulation systems.
5.3.1 Applications of PCM in building envelopes take multiple forms, including: dispersed in, or otherwise combined with, a
thermal insulation material; a separate object implemented in the building envelope as boards or membranes containing
concentrated PCM that operates in conjunction with a thermal insulation material. Both of these forms enhance the performance
of the structure when exposed to dynamic, that is, fluctuating, boundary temperature conditions.
5.3.2 PCMs can be studied in a variety of forms: as the original “pure” PCM; as a composite containing PCM and other
embedded materials to enhance thermal performance; as a product containing PCM or composite (such as micro- or
macro-encapsulated PCM); or as a system, comprising arrays or assemblies of PCM products.
5.4 This test method describes a method of using a heat flow meter apparatus to determine key properties of PCM products,
which are listed below. Engineers, architects, modelers, and others require these properties to accurately predict the in-situ
performance of the products (2).
5.5 The objective is generally to conduct a test under temperature conditions that will induce a phase transition (for example,
melting or freezing) in the PCM product during the course of the test.
5.6 Determination of thermal storage properties is the objective of this test method, and key properties of interest include the
following:
5.6.1 PCM Active Range, that is the temperature interval over which the phase transitions occur, for both melting and freezing
of the PCM product or composites containing PCMs.
5.6.2 Specific heat of the fully melted and fully frozen product, defined outside the PCM Active Range.
5.6.3 Enthalpy as a function of temperature, h(T).
5.6.4 Enthalpy plot—a histogram or table that indicates the change in enthalpy associated with incremental temperature changes
that span the tested temperature range.
5.6.5 Enthalpy changes associated with phase transitions during the PCM melting and freezing processes in materials and
composites containing PCMs.
5.7 PCM products often possess characteristics that complicate measurement and analysis of phase transitions during a test.
Following are some of the known issues with PCMs:
5.7.1 Imprecise PCM Active Range—PCMs in general do not have precise melting or freezing temperatures, and the entire
active temperature range, from the beginning to the end of phase transitions, must be determined.
NOTE 4—The onset of freezing will not necessarily coincide with the end of melting. Therefore, the freeze and melt enthalpy curves must be
independently defined to determine the PCM Active Range.
5.7.2 Multiple Phase Transitions—Many PCMs exhibit a solid-solid transition with significant latent heat effects at temperatures
near the melting transition.
5.7.3 Sub-cooling—Occurs when the specimen cools below its nominal freezing temperature before it actually begins to freeze,
thus exhibiting an unusual enthalpy-temperature curve. Solid-liquid and solid-solid phase changes are often dependent on heating
and cooling rate.
5.7.4 Hysteresis—Occurs when a specimen heated from one temperature to another, and then returned to the original
temperature, absorbs more (or less) heat at any particular temperature during the heating stage than it releases during cooling.
5.8 The properties measured are determined by fundamental thermophysical properties of the constituent materials of the
product, and are thus inherent to the PCM product. The desired thermal performance enhancement, however, will depend strongly
on the particular environment, climate, and mode of the actual engineering application of the PCM.
6. Apparatus
6.1 Follow the Apparatus section of Test Method C518 with these additional requirements:
6.1.1 A minimum of two heat flux transducers, one mounted on each plate of the apparatus, are required.
6.1.2 The ability to scan temperature and heat flux data at specified intervals and store results in a form that is immediately
accessible in real time to the user or other programs running concurrently is required; for example, a text file to which data are
written after each scan. The ability to record a time stamp of each scan is required.
6.1.3 The ability to accept a user-defined temperature program for control of both plate temperatures. This test method includes
a series of temperature steps, with specified intervals determined by time or equilibrium criteria.
NOTE 5—Independent time or equilibrium criteria control for each setpoint will facilitate the test.
6.1.4 The amount of energy flowing through the transducers must be measureable at all times. To avoid saturating the
transducers, either their voltage gain must be variable, or in apparatus without variable transducer gain, the alternative approaches
described in Appendix X2 must be followed.
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7. Specimen Preparation
7.1 Instructions are given here separately for solid samples, loose blended materials, and discretely contained PCM.
7.2 For solid samples such as gypsum wallboard containing PCM (3-5).
7.2.1 Cut the specimen to the same size as the HFMA plate area.
NOTE 6—If the specimen has a conductive facing, for example, foil, place a sheet of craft paper between the facing and the corresponding apparatus
plate. If the heat capacity of this sheet is expected to be significant relative to the energy storage of the specimen, independently measure the heat capacity
in the same manner as for the HFMA transducers, described in Annex A1. Then correct the measured heat flow into the assembly for this material as
described in Section 10.
7.3 For loose material blended with PCM (6, 7).
7.3.1 Construct the sides of a frame using thin low mass material between 2.5 to 5 cm in height and sized so the frame will be
located at the periphery of the test chamber. Affix a net material to form the frame bottom.
7.3.2 Since the frame is located far from the metering area, it is unlikely that the frame presence will have a significant effect
on the thermal measurement. This shall be verified by separate measurement on solid specimens made with and without the sample
frame.
7.4 For arrays of PCM pouches or PCM containers (8).
7.4.1 Ensure the portion of the product within the metered area is representative of the array pattern.
7.4.2 A sketch or photograph of the test specimen is required for this type of product, due to the spatial non-uniformities and
discontinuities that are common with this product type.
7.5 Ensure good contact between the HFMA plates and the product. If necessary, use an elastomeric or soft foam rubber sheet
between one or both sides of the product and the corresponding apparatus plate. This sheet will improve contact between the
controlled temperature plates and prevent air circulation between the panel and the plates. The energy storage correction for the
sheet(s) must be independently measured, in the same manner as for the HFMA transducers, as described in Annex A1. The
measured heat flow into the assembly must then be corrected for this material as described in 10.3.
7.6 For PCM products with high lateral thermal conductivity, use an insulating frame to avoid significant edge losses. Ensure
the frame is far away from the metered area to maximize the one-dimensional heat flow in the metered area.
8. Calibration
8.1 Prior to using this test method, calibrate the HFMA to determine the temperature-dependent calibration coefficients for both
heat flux transducers using the procedure for the multiple temperature and thickness points in the Calibration section of Test
Method C518.
8.2 The heat flux levels obtained during an HFMA test run are, in general, determined by heat flowing into or out of the
specimen. The heat flux readings are also impacted by the heat that enters or leaves the transducers themselves, as a result of the
change of the transducer temperature that corresponds to the change in plate temperature. Such heat flow is incidental to the values
used in characterizing the PCM product. Therefore, separately calibrate the heat flux transducers within the HFMA to measure the
correction factor for heat storage in the heat flux transducers. This additional apparatus calibration is described in Annex A1.
9. Procedure
9.1 Personnel Qualifications—This test method shall only be performed by qualified personnel with experience in heat transfer
analysis and experimental error propagation. To ensure accurate measurement, the operator shall be fully proficient in the operation
of the equipment and must have detailed familiarity with the configuration of the apparatus, the apparatus control and data
reporting software, and the specimen itself.
9.2 Procedure Overview—In order to characterize the PCM product, test parameter definitions are required, as are multiple
series of measurements at discrete temperature steps. Instructions are given here to first define the general process used during a
series of measurements (9.3); describe how to determine the test parameters (9.4); and finally, to apply this process to characterize
the PCM product (9.5). Additional instructions are included to describe an optional investigation of the hysteresis within partially
melted or frozen specimens (9.6, Appendix X3).
9.3 Define general series of temperature steps for both plates, for example, 11°C and 11°C, 13°C and 13°C, 15°C and 15°C,
and so on.
9.3.1 To measure the enthalpy stored in the test specimen in each temperature range, make a series of measurements.
9.3.2 First, both plates shall be held at the same constant temperature until steady state is achieved.
NOTE 7—Please see Annex A1 for a description of experimental work that has been done with an apparatus with plates at different temperatures to
achieve the same goals.
9.3.2.1 Steady state is defined by the reduction in the amount of energy entering the specimen from both plates to a very small
and nearly constant value. See 10.2.
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9.3.3 After steady state is achieved, both plate temperatures will be changed to the same new temperature and held at that value
until steady state is again achieved.
9.3.4 The cumulative amount of energy that enters the specimen from the time of the temperature change until steady state is
again achieved will be recorded.
9.3.5 Heat flux readings shall include the proper sign to indicate direction of heat flow; for example, a positive reading may
indicate heat entering the test specimen, and negative values indicating heat leaving the specimen.
9.3.6 The initial temperature selection, the temperature difference between setpoints, and the number of temperature steps, will
vary according to the purpose of each particular test series.
NOTE 8—The temperature range available depends on the construction of the HFMA equipment, the heat rejection bath temperature, and the calibration
of the equipment.
9.4 Determine the test parameters:
9.4.1 An initial test shall be used to estimate the PCM Active Range and determine the time required for each temperature step.
This step is not required if the specimen phase change characteristics are already well known, for example from differential thermal
analysis (DTA) tests or differential scanning calorimetry (DSC) tests (using the step method or appropriately slow heating and
cooling rates, as described by Castellon et al. (9)).
9.4.2 Make series of measurements, as described in 9.3, starting at a temperature at least 10°C below the expected melting
temperature, or at the lowest temperature available on the HFMA, whichever is higher. Use temperature difference steps of 1.5 6
0.5°C. Allow a minimum of two hours for each setpoint during the initial specimen characterization.
9.4.3 End the series when the amount of energy stored in a temperature step returns to a small value, that is, when the test
specimen is fully melted. See 10.2.
NOTE 9—As described in 10.2, the amount of time required at each temperature step will vary depending on the size of the temperature step, the thermal
diffusivity of the specimen, and the amount of energy storage that occurs over that temperature step.
9.4.4 Repeat this procedure starting at the fully melted temperature condition and decreasing the plate temperatures in 1.5 6
0.5°C steps until the amount of energy stored in a temperature step returns to a small value, that is, when the test specimen is fully
frozen. See 10.2.
9.4.5 Examine the data as described in Section 10. Determine the estimated PCM Active Range, the desired temperature step
size, and the amount of time required for each step.
9.4.6 An example of such a test series is shown in Annex A2.
9.5 Characterize the PCM product.Characterize the PCM product:
9.5.1 Make a series of measurements, as described in 9.3, starting at a temperature at least 10°C below estimated PCM Active
Range, and heating the plates with temperature difference steps of 1.5 6 0.5°C. End at a temperature at least 10°C above the
estimated PCM Active Range. The amount of time required at each temperature step shall be as determined in 10.2.
NOTE 10—The minimum and maximum temperature difference step size will be limited by the combined uncertainty of the temperature measurement
and heat flux measurement within the HFMA.
NOTE 11—To enable testing over a sufficient temperature range while considering any HFMA limits on number of allowable temperature steps, variable
temperature differences can be utilized. For example, Biswas et al. (10) used temperature differences of 1°C close to and within the PCM Active Range
and 2°C away from the PCM Active Range.
9.5.2 Make a series of measurements, as described in 9.3, starting at a temperature at least 10°C above the estimated PCM
Active Range, and cooling the plates with temperature difference steps of 1.5 6 0.5°C. End at a temperature at least 10°C below
the estimated PCM Active Range.
9.5.3 Examine the data as described in Section 10 to determine:
9.5.3.1 Whether either of the data series shall be repeated using longer equilibrium times at any particular temperature.
9.5.3.2 Whether the temperature range needs to be expanded to capture the full PCM Active Range.
9.5.4 A minimum of three heating series, as described in 9.5.1, and a minimum of three cooling series, as described in 9.5.2,
are required.
9.5.4.1 In order to define the enthalpy curve of energy storage vs. temperature with adequate precision, select beginning
temperatures for the subsequent heating and cooling series that differ from those used for the initial heating and cooling series.
NOTE 12—For example: If the initial heating series spanned 10 to 30°C in 2°C steps, retain the 2°C step size, but start the second heating series at
10.6°C and the third heating series at 11.3°C. If the initial cooling series spanned 30 to 10°C in 2°C steps, retain the 2°C step size, but start the second
heating series at 29.4°C and the third heating series at 28.7°C.
9.5.4.2 Examine the data as described in 10.2 to determine whether either of the data series shall be repeated using longer
equilibrium times at any particular temperature.
9.6 Hysteresis effects when starting from partially frozen or partially melted material may be explored using the method
described in Appendix X3.
C1784 − 20
10. Calculations
10.1 Calculations Overview—The calculations require several separate stages. First it is necessary to examine the data to
evaluate whether an adequate amount of time was spent at each and every temperature step (10.2). Once this has been established,
it is possible to calculate the net energy storage within the test specimen corresponding to each temperature step (10.3). That data
form can then be used to express the enthalpy of the product as a function of temperature (10.4); to define the specific heat of the
fully melted and fully frozen product (10.5, 10.6); and to define the latent heat of the product (10.7).
10.2 Evaluate adequacy of time intervals at each temperature step.
10.2.1 The amount of time required at each temperature step will vary depending on the size of the temperature step, the thermal
diffusivity of the specimen, the material thickness, and the amount of energy storage that occurs over that temperature step. The
time interval required to reach steady state during phase change phenomena are much greater than time intervals required when
the material is subjected to sensible energy storage phenomena.
10.2.1.1 The maximum heat rate into or out of the specimen is limited by apparatus capability and the specimen thermal
diffusivity. It is possible to estimate the minimum amount of time (τ ) needed for each step by neglecting the apparatus limits
min,est
and the impact of thermal storage on the thermal transmittance through the specimen, as shown in Eq 1. This approach is only
possible when there is some basis for estimating the energy storage needed for that particular temperature step and when an
estimate is available for the thermal conductivity of the material. Possible sources for the energy storage estimate include prior
heating or cooling series or data from a DSC run.
τ 5
min, est
Estimated enthalpy storage for a particular temperature step
Maximum conductance rate through specimen
or,
(1)
c T ρLΔT c T ρL
~ ! ~ !
p p
τ 5 5
min, est
kΔT 2k
S D
~L ⁄ 2!
NOTE 13—If data are available to permit the calculation shown in Eq 1, reasonable rules of thumb for the adequate total time for that temperature step
would be: (1) for heating away from the expected latent range, use 1.5 times the estimated minimum; (2) for heating within the latent range, use 2.5 times
the estimated minimum; (3) for cooling away from the expected latent range, use 2.5 times the estimated minimum; (4) for cooling within the latent range,
use 5 times the estimated minimum.
10.2.2 Plot the heat flux signal vs. time for each temperature step for each plate as shown in Fig. 1. This plot is also useful in
determining how much time is required at each temperature step. For example, the time spent at temperatures labeled 20.5 and 19.5
is longer than necessary and the time spent at temperature 18.5 is barely sufficient.
NOTE 14—The raw data are evaluated in this step. The raw data, typically in microvolts, will be transformed into the integrated heat flux in a subsequent
step as described in 10.3.
NOTE 15—It is useful to examine the equilibrium portions of the curves by either limiting the range of the plot on the y-axis, or plotting the absolute
values of the electrical signal on a log axis.
10.2.3 As shown in 10.2.2 and Fig. 1, at steady state conditions at the end of each temperature step, a small non-zero HFMA
signal remains, largely due to edge heat losses. For each series of temperature steps, determine whether each temperature step was
held for an adequate length of time by examining this residual, or equilibrium, HFMA signal.
FIG. 1 Example of Transducer Output (E) Data Taken During a Series of Cooling Temperature Steps of the Lower Plate of an HFMA
C1784 − 20
10.2.3.1 Calculate the residual heat flux transducer output (E), which is average output over the last 60 minutes of each
temperature step. Plot this residual value vs. the plate temperature for that step. All the steps that have reached steady-state will
show very similar values, or values that vary slightly with plate temperature.
NOTE 16—In Fig. 2, the test was initially run with 6 h for each temperature step. For all of the data points except the four highlighted with arrows,
this appears to have been an adequate length of time. The test was then repeated with those four steps increased to 9.25 h. It appears that the cooling
step at 18.5°C (temperature step from 19 to 18°C) requires even more than 9 h. Note the entire cooling sequence would need to be repeated, starting at
the highest temperature, to get the data for this temperature step interval.
10.2.3.2 Another way to examine the residual heat flux data is to look at the difference between the output from the transducers
in the upper and lower plates, as shown in Fig. 3. The PCM Active Range for this example, based on the sample data, is about
17–21°C. For a few data points, far away from the PCM Active Range, there is no difference between the data at 3 h and 6 h. Within
the PCM Active Range, some of the data points in the cooling series still show significant changes between the 6 and 9 h values.
This is also shown in the lower linear regression coefficient for the 9 h cooling data series. This would also indicate that the time
intervals between 18 and 20°C during the cooling series need to be longer.
10.2.4 Use the data from 10.2.3 to determine whether the time spent at each temperature step within the series was adequate.
If not, adjust the time interval settings and repeat the entire series of temperature steps.
10.2.5 Time interval estimates based on results from a heating series are not a reliable predictor for the same temperature steps
during a cooling series.
NOTE 17—Experience has shown that for some materials the time intervals required for some freezing phenomena are much greater than for the melting
phenomena.
10.3 Calculate the net energy storage for each temperature step.
10.3.1 After determining that the time spent at each and every temperature step within the series was adequate to reach steady
state as described in 10.2, calculate the heat gain/loss for each plate for each temperature step as shown in Eq 2 (9).
10.3.2 The equilibrium, or residual, heat flux described in 10.2 shall be subtracted in the summation, independently for each
plate.
NOTE 18—It is possible that this correction is pre-programmed in the HFMA control software. Determine whether this is so in order to avoid erroneous
heat gain/loss calculations.
10.3.3 The energy that is stored within the transducers themselves (see Annex A1) must also be subtracted, as well as the heat
stored in any material placed between the test specimen and the HFMA plates. These correction factors for the transducer energy
storage and for any other material included with the test specimen are functions of the beginning and ending temperatures for each
step, as described in Annex A1.
NOTE 19—It is possible that this correction is pre-programmed in the HFMA control software. Determine whether this is so in order to avoid erroneous
heat gain/loss calculations.
10.3.4 Eq 2 shows the calculation of the energy storage in the specimen for a given temperature interval (T ,T ). The
begin end
recorded heat flux for both plates, corrected for the residual equilibrium heat flux, is multiplied by the length of time (Δτ) for each
data point (q ), and summed over the total number of data points (N) for the given temperature interval (ΔT). After subtracting the
i
FIG. 2 Residual Transducer Output (E) Over the Last 60 Minutes During Heating and Cooling for Upper and Lower Plates at Two Differ-
ent Time Periods for Each Temperature Step
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FIG. 3 Transducer Output Difference (ΔE = E – E ) for Different Temperature Step Time Periods During Heating and
upper plate lower plate
Cooling Series
transducer heat storage correction factors, as well as the correction for any other material included within the HFMA, from the sum
of the heat flow into the specimen, the total amount of enthalpy stored in the specimen during that temperature interval is calculated
as shown in Eq 2.
N N
h 5 q 2 q Δτ 2 C T , T ΔT 2 C T , T ΔT 1 q 2 q Δτ 2 C T , T ΔT
F ~ ! ~ ! ~ ! G F ~ ! ~ !
S D S D
A ( i quilibrium hft begin end other begin end ( i quilibrium hft begin end
i51 i51
upper
2 C ~T , T !ΔT (2)
G
other begin end
lower
10.4 Combine the temperature step data to define the energy storage as a function of temperature.
10.4.1 Define the zero amount of cumulative heat as corresponding to the bottom of the step(s) starting from the lowest
temperature used in 9.5.
10.4.2 Plot the corrected cumulative heat into or out of the specimen vs. the ending temperature for each step. An example is
shown in Annex A2.
10.4.3 That plot of areal enthalpy (h , J/m ) can also be manipulated to show the specific enthalpy (h, J/kg) and volumetric
A
enthalpy (h , J/m )as a function of temperature. See Annex A2 for an example of merging the data from multiple series onto a
V
single plot of h vs. T.
V
h T 5 h T ⁄ ρ L (3)
~ ! ~ ! ~ !
A
h T 5 h T ⁄L (4)
~ ! ~ !
V A
10.4.4 The data from heating series and cooling series shall be kept separate except that the final enthalpy from the heating
series shall be taken as the starting enthalpy for the cooling series. See Annex A2.
10.5 Define the specific heat of the fully frozen product, c , and define T , the lower temperature limit of the PCM Active
pF L
Range, when the melting initiates or freezing ends. Fig. 4 shows a sample PCM behavior during melting and freezing. In this
example, the freezing ends at a lower temperature than the melting initiation, and T needs to be defined based on the freezing
L
series. See A2.6 for an example calculation.
NOTE 20—The accuracy of T will be limited by the temperature step size.
L
10.5.1 Examine the data for h vs. T from 10.4.3. Start with the values at the lowest temperatures measured for the combined
heating and cooling series. Perform a linear regression for the first 2 data points and calculate both the slope of the line (in units
2 2
of J/m ·°C) and the regression coefficient (R ). Since only 2 data points were used, the regression coefficient is 1.0.
10.5.2 Perform the linear regression again using the first 3, 4, 5, 6, etc. data points until the regression coefficient is less than
0.995. Prior experience has shown that, during melting, there is no sharp transition at the beginning of melting of PCMs (also
evident in the melting curve of Fig. 4). Therefore, using a threshold correlation coefficient of 0.995 to define melting onset is not
appropriate.
10.5.3 The melting onset, for the purpose of this test, is defined by a 20% deviation from the baseline linear cumulative enthalpy
of the frozen PCM. To obtain this baseline, fit a straight line through the data points with regression coefficient greater than or equal
C1784 − 20
FIG. 4 Sample PCM Behavior During Melting and Freezing
to 0.995. Identify the lower temperature limit of the PCM Active Range, T , as that temperature above which the percentage
L
deviation of the measured cumulative enthalpy deviates by more than 20% from the calculated baseline linear cumulative enthalpy.
See A2.6 for the example calculation.
10.5.4 Use the calculated slope (in units of J/m ·°C) of the line connecting the first to the last data point with the percent
deviation in measured cumulative enthalpy from the calculated baseline less than 20% as the areal specific heat of the fully frozen
product, c . The areal specific heat can be manipulated to show the specific heat and volumetric specific heat as a function of
pF,A
temperature.
c T 5 c T ⁄ ρ L (5)
~ ! ~ ! ~ !
pF pFA
c T 5 c T ⁄L (6)
~ ! ~ !
pFV pFA
10.6 Define the specific heat of the fully melted product, c , and define T , the upper temperature limit of the PCM Active
pM U
Range, when melting ends or freezing initiates. In the example shown in Fig. 4, the melting ends at a higher temperature and will
define T . See A2.6 for an example calculation.
U
NOTE 21—The accuracy of T will be limited by the temperature step size.
U
10.6.1 Examine the data for h vs. T from 10.4.3. Start with the values at the highest temperatures measured for the combined
heating and cooling series. Perform a linear regression for the first 2 data points and calculate both the slope of the line (in units
of J/kg·°C) and the regression coefficient (R ). Since only 2 data points were used, the regression coefficient is 1.0.
10.6.2 Perform the linear regression again using the first 3, 4, 5, 6, etc. data points until the regression coefficient is less than
0.995. Identify the upper temperature limit of the PCM Active Range, T , as that temperature at which the regression coefficient
U
first dropped below 0.995. Based on prior experience, the enthalpy function of the PCM exhibits a sharp transition at the freezing
onset. Therefore, T is defined solely by the temperature below which the correlation coefficient drops below 0.995.
U
10.6.3 Use the calculated slope of the line connecting the first to the last data point set with a regression coefficient greater than
0.995 as the specific heat of the fully melted product, c .
pM
10.7 Calculate the latent heat.
10.7.1 The total enthalpy change between T and T includes both sensible and latent heat effects. Use the specific heat of the
L U
fully frozen product below the mean temperature of the PCM Active Range, and the specific heat of the fully melted state above
the mean temperature of the PCM Active Range to define the sensible heat storage over the temperature range. The difference
between the total and sensible heat storage is the latent heat (h ).
fs
T T
U U
c 1 c T 2 T
~ !~ !
pF pM U L
h 5 ~Δ h! 2 c ~T 2 T ! 2 c ~T 2 T !5 ~Δ h! 2 (7)
fs ( pF Mean L pM U Mean (
T T
L L
10.7.2 The areal form of the latent heat is shown in Eq 8.
h 5 h 3ρ 3L (8)
fs,A fs
11. Report
11.1 For each test, report the following information:
11.1.1 Identify the report with a unique numbering system to allow traceability back to the individual measurements taken
during the test performed.
11.1.2 Identify the material and give a physical description.
C1784 − 20
11.1.2.1 Provide a specimen diagram or photograph if any materials other than the PCM product were placed in the HFMA,
or if the area of the specimen is different from the area of the HFMA plates.
11.1.2.2 Provide a specimen diagram if the test specimen consisted of arrays of PCM pouches or PCM containers.
11.1.3 Provide a brief conditioning history of the specimen, if known.
11.1.4 Thickness of the specimen as received and as tested, m.
11.1.5 Mass of the specimen, kg.
11.1.6 Volume of the specimen, m .
11.1.7 Density of the specimen, kg/m .
11.1.8 Area of the specimen exposed to each HFMA plate, m .
11.1.9 Method and environment used for conditioning, if used.
11.1.10 Dates the tests started and ended.
11.1.11 The temperature step size(s) used in the melting and freezing tests.
11.1.12 Table of corrected cumulative enthalpy into or out of the specimen vs. the end temperature for each step, combining
the data from the multiple heating and cooling series as described in Annex A2. Present the data as shown in Table 1. An acceptable
alternative is to present separate heating and cooling test data following RAL-GZ 896 (Appendix X4).
11.1.13 Plot of corrected cumulative heat into or out of the specimen vs. the end temperature for each step, as shown by the
combined data curve in Fig. A2.1 (Annex A2) or the histograms in Figs. X4.1 and X4.2 (Appendix X4).
11.1.14 Measured parameters, as listed in Table 2.
11.2 Description of calibration test results from Annex A1, including the date of the last heat flux transducer calibration, and
the type or types of calibration materials used, as shown in Table 3.
11.3 Estima
...