ASTM E422-22

Standard Test Method for Measuring Net Heat Flux Using a Water-Cooled Calorimeter

SIGNIFICANCE AND USE
5.1 The purpose of this test method is to measure the net heat flux to a water-cooled surface for purposes of calibration of the thermal environment into which test specimens are placed for evaluation. The measured net heat flux is one of the important parameters for correlating the behavior of materials. If the calorimeter and holder size, shape, and surface finish are identical to that of the test specimen, the measured net heat flux to the calorimeter is presumed to be the same as that to the sample's heated surface. If the calorimeter configuration (holder size, shape, finish, etc.) is not identical to that of the test specimen, then the measurement results may need to be modified to account for those differences. See Appendix X1.  
5.2 The water-cooled calorimeter is one of several calorimeter concepts used to measure net heat flux. The prime drawback is its long response time, that is, the time required to achieve steady-state operation. To calculate energy added to the coolant water, accurate measurements of the rise in coolant temperature are needed, all energy losses should be minimized, and steady-state conditions must exist both in the thermal environment and fluid flow of the calorimeter.  
5.3 Regardless of the source of energy input to the water-cooled calorimeter surface (radiative, convective, or combinations thereof) the measurement is averaged over the surface-active area of the calorimeter. If the water-cooled calorimeter is used to measure only radiative flux or combined convective-radiative net heat flux rates, then the surface reflectivity of the calorimeter shall be measured over the wavelength region of interest (depending on the source of radiant energy). If nonuniformities exist in the gas stream, a large surface area water-cooled calorimeter would tend to smooth or average any variations. Consequently, it is advisable that the size of the calorimeter be limited to relatively small surface areas and applied to where the net heat flux is u...
SCOPE
1.1 This test method covers the measurement of a steady net heat flux to a given water-cooled surface by means of a system energy balance.  
1.2 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.3 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 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.

General Information

• Status: Published
• Publication Date: 31-Mar-2022
• ICS: 17.200.10 - Heat. Calorimetry
• Technical Committee: E21 - Space Simulation and Applications of Space Technology
• Drafting Committee: E21.08 - Thermal Protection

Relations

• Refers: ASTM E176-24 - Standard Terminology of Fire Standards
• Effective Date: 01-Jan-2024
• Refers: ASTM E230/E230M-23a - Standard Specification for Temperature-Electromotive Force (emf) Tables for Standardized Thermocouples
• Effective Date: 01-Nov-2023
• Refers: ASTM E230/E230M-23 - Standard Specification for Temperature-Electromotive Force (emf) Tables for Standardized Thermocouples
• Effective Date: 01-May-2023
• Refers: ASTM E456-13a(2022)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Apr-2022
• Refers: ASTM E3057-19 - Standard Test Method for Measuring Heat Flux Using Directional Flame Thermometers with Advanced Data Analysis Techniques
• Effective Date: 01-Jun-2019
• Refers: ASTM E176-18a - Standard Terminology of Fire Standards
• Effective Date: 15-Dec-2018
• Refers: ASTM E176-18 - Standard Terminology of Fire Standards
• Effective Date: 01-Mar-2018
• Refers: ASTM E456-13A(2017)e3 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Oct-2017
• Refers: ASTM E456-13A(2017)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Oct-2017
• Refers: ASTM E3057-16 - Standard Test Method for Measuring Heat Flux Using Directional Flame Thermometers with Advanced Data Analysis Techniques
• Effective Date: 01-Apr-2016
• Refers: ASTM E176-15ae1 - Standard Terminology of Fire Standards
• Effective Date: 01-Aug-2015
• Refers: ASTM E176-15a - Standard Terminology of Fire Standards
• Effective Date: 01-Aug-2015
• Refers: ASTM E176-15 - Standard Terminology of Fire Standards
• Effective Date: 01-Feb-2015
• Refers: ASTM E176-14c - Standard Terminology of Fire Standards
• Effective Date: 01-Oct-2014
• Refers: ASTM E176-14b - Standard Terminology of Fire Standards
• Effective Date: 15-Aug-2014

Overview

ASTM E422-22: Standard Test Method for Measuring Net Heat Flux Using a Water-Cooled Calorimeter is an international standard developed by ASTM International. This test method provides a precise and reliable approach for measuring the steady-state net heat flux to a water-cooled surface. By employing a water-cooled calorimeter, this standard supports the calibration and evaluation of thermal environments, especially where accurate assessment of heat transfer to test specimens is critical.

This test method is essential when correlating the behavior of materials subjected to controlled heat flux, making it valuable in research, development, and quality assurance settings in aerospace, fire safety, materials science, and related industries.

Key Topics

• Net Heat Flux Measurement: The standard details the process of determining net energy transfer to a water-cooled surface using an energy balance based on coolant water flow rate and temperature rise.
• Calorimeter Configuration: Emphasizes the importance of matching calorimeter size, shape, and surface finish to test specimens for accurate calibration.
• Instrumentation and Apparatus: Describes requirements for calorimeter materials (commonly OFHC copper), flow meters, temperature sensors (such as thermocouples), and data acquisition systems.
• Calibration and Uncertainty: Covers calibration of instrumentation, estimation of uncertainty, and verification of measurement accuracy, ensuring consistent and reliable results.
• Steady-State Operation: Outlines the need for establishing steady thermal and fluid flow conditions prior to data collection.
• Reporting and Data Recording: Provides guidance on recording key measurement parameters and calculating net heat flux values.

Applications

ASTM E422-22 plays a critical role in various practical scenarios where precise heat flux measurement is required:

• Thermal Protection Systems: Used in aerospace testing to characterize heat flux on protective materials during simulated re-entry or aerodynamic heating.
• Fire Testing and Safety Research: Supports calibration of fire testing environments to ensure accurate heat flux exposure to material samples, crucial for regulatory compliance and performance evaluation.
• Industrial Process Monitoring: Applicable in industries such as metallurgy and manufacturing, where understanding heat transfer to surfaces is important for process control and product quality.
• Material Evaluation: Vital in research and development, helping engineers correlate material performance with exposure to known thermal loads.
• Environmental Simulation: Used to replicate and evaluate material response to specific thermal conditions, ensuring safety and reliability in demanding environments.

Related Standards

• ASTM E176: Terminology of Fire Standards - Key definitions relevant to fire testing and thermal analysis.
• ASTM E459: Test Method for Measuring Heat Transfer Rate Using a Thin-Skin Calorimeter - Alternative approach for heat flux measurement with thin-skin devices.
• ASTM E3057: Test Method for Measuring Heat Flux Using Directional Flame Thermometers with Advanced Data Analysis Techniques - Focuses on advanced heat flux measurement under flame exposure.
• ASTM E230/E230M & ASTM E235: Specifications for thermocouples-relevant for accurate temperature sensing in calorimeter applications.
• ASTM E456: Terminology Relating to Quality and Statistics-useful for understanding precision, bias, and measurement uncertainty.

Practical Value

Adopting ASTM E422-22 ensures accurate and reproducible measurement of net heat flux, which is fundamental for:

• Calibrating test environments.
• Ensuring data comparability across different research facilities.
• Supporting compliance with international fire and materials testing standards.
• Improving the safety and performance of products exposed to high thermal loads.

By integrating this standard into laboratory or industrial procedures, practitioners benefit from a globally recognized methodology for heat flux measurement, enhancing confidence in material evaluation and thermal protection assessments.

Keywords: ASTM E422-22, water-cooled calorimeter, net heat flux measurement, heat transfer, thermal calibration, fire testing, material testing, thermocouple, data acquisition, uncertainty analysis

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: E422 − 22
Standard Test Method for
Measuring Net Heat Flux Using a Water-Cooled Calorimeter
This standard is issued under the fixed designation E422; 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 3. Terminology
1.1 This test method covers the measurement of a steady net 3.1 Definitions—Refer to Terminologies E176 and E456 for
heat flux to a given water-cooled surface by means of a system
definitions of terms used in this test method.
energy balance.
3.2 Definitions of Terms Specific to This Standard:
1.2 Units—The values stated in SI units are to be regarded
3.2.1 absorbed heat flux, n—incident radiative heat flux less
as standard. No other units of measurement are included in this
the reflected radiative flux, W/m .
standard.
3.2.2 convective heat flux, n—the addition or loss of energy
1.3 This standard does not purport to address all of the
per unit area into the sensing surface due to convection, =
safety concerns, if any, associated with its use. It is the
h*(T -T ), W/m .
fs s
responsibility of the user of this standard to establish appro-
3.2.3 control volume, n—user defined volume over which an
priate safety, health, and environmental practices and deter-
energy balance is determined.
mine the applicability of regulatory limitations prior to use.
3.2.4 emitted heat flux, n—energy per unit area emitted from
1.4 This international standard was developed in accor-
4 2
a hot surface – ε*σ*T , W/m .
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
3.2.5 incident radiative heat flux (irradiance; q ),
inc,r
Development of International Standards, Guides and Recom-
n—radiative heat flux (energy per unit area) impinging on the
mendations issued by the World Trade Organization Technical
surface of the calorimeter from an external environment,
Barriers to Trade (TBT) Committee.
W/m .
3.2.6 heat flux or energy flux, n—energy per unit area,
2. Referenced Documents
W/m .
2.1 ASTM Standards:
3.2.7 net heat flux or net energy flux, n—net energy divided
E176 Terminology of Fire Standards
by the sensing surface area transferred to the calorimeter face;
E230/E230M Specification for Temperature-Electromotive
it is equal to the [absorbed radiative heat flux + convective heat
Force (emf) Tables for Standardized Thermocouples
flux] – [re-radiation from the exposed surface].
E235 Specification for Type K and Type N Mineral-
3.2.8 reflected heat flux, n— that part of the incident
Insulated, Metal-Sheathed Thermocouples for Nuclear or
radiative flux that is not absorbed by or transmitted into the
for Other High-Reliability Applications
surface of the calorimeter, W/m .
E456 Terminology Relating to Quality and Statistics
E459 Test Method for Measuring Heat Transfer Rate Using
3.2.9 verified, n—the process of checking that a data acqui-
a Thin-Skin Calorimeter
sition channel correctly measures an input value, to a pre-set,
E3057 Test Method for Measuring Heat Flux Using Direc-
acceptable level condition defined by the user.
tional Flame Thermometers with Advanced Data Analysis
3.3 Symbols:
Techniques
A—sensing surface area of calorimeter, m
Cp—water specific heat, J/(kg-K)
h—convective heat transfer coefficient, W/m -K
This test method is under the jurisdiction of ASTM Committee E21 on Space
Simulation and Applications of Space Technology and is the direct responsibility of m—mass flow rate of coolant water, kg/sec
Subcommittee E21.08 on Thermal Protection.
q—heat flux, W/m
Current edition approved April 1, 2022. Published May 2022. Originally
T—temperature, K
approved in 1971. Last previous edition approved in 2016 as E422 – 05(2016). DOI:
10.1520/E0422-22.
T —calorimeter water inlet bulk temperature during
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
operation, K
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
T —calorimeter water exhaust bulk temperature during
Standards volume information, refer to the standard’s Document Summary page on 02
the ASTM website. operation, K
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E422 − 22
T —calorimeter water inlet bulk temperature before Interpretation of the data obtained is not within the scope of
operation, K this discussion; consequently, such effects as recombination
T —calorimeter water exhaust bulk temperature before efficiency of the surface and thermochemical state of the
operation, K boundary layer are outside the scope of this test method. It
ΔT = T – T —calorimeter water bulk temperature rise should be noted that recombination effects at low pressures can
0 02 01
during operation, K cause serious discrepancies in net heat flux measurements
ΔT = T -T —calorimeter water apparent bulk temperature (such as discussed in Ref (1)) depending upon the surface
1 2 1
rise before operation, K material on the calorimeter.
ε—emissivity of sensing surface
4.3 For the particular control volume cited, the energy
2 4
σ—Stefan-Boltzmann constant, 5.67E-08 W/m -K
balance can be written as follows:
3.4 Abbreviations:
E 5 @mC ~ΔT 2 ΔT !#/A (1)
CAL p 0 1
3.4.1 TC—thermocouple
where:
3.4.2 PPE—personal protective equipment
E = energy flux (or net heat flux) transferred to calorim-
CAL
3.4.3 U —total uncertainty to 95 % confidence
−2,
eter face, W·m
−1
3.4.4 t —“Students t”
m = mass flow rate of coolant water, kg·s ,
−1 −1
C = water specific heat, J·kg ·K ,
3.4.5 B —total bias uncertainty p
T
ΔT = T – T calorimeter water bulk temperature rise
0 0 0
2 1
3.4.6 S —total systematic or precision uncertainty
T
during operation, K,
3.4.7 DOF—degrees of freedom
ΔT = T – T , calorimeter water apparent bulk temperature
1 2 1
rise before operation, K,
4. Summary of Test Method
T = calorimeter water exhaust bulk temperature during
4.1 A measure of the net heat flux to a given water-cooled
operation, K,
surface is based upon the following measurements: (1) the T = calorimeter water inlet bulk temperature during
water mass flow rate and (2) the temperature rise of coolant operation, K,
T = calorimeter water exhaust bulk temperature before
water. The net heat flux is determined numerically by multi-
operation, K,
plying the water coolant flow rate by the specific heat and rise
T = calorimeter water inlet bulk temperature before
in temperature of the water and dividing this value by the 1
operation, K, and
surface area across which heat has been transferred.
A = sensing surface area of calorimeter, m .
4.2 The apparatus for measuring net heat flux by the
4.4 An examination of Eq 1 shows that to obtain a value of
energy-balance technique is illustrated schematically in Fig. 1.
the energy transferred to the calorimeter, measurements must
It is a typical constant-flow water calorimeter used to measure
be made of the water coolant flow rate, the temperature rise of
stagnation region net heat flux to a flat-faced specimen. Other
the coolant, and the surface area across which heat is trans-
calorimeter shapes can also be easily used. The net heat flux is
ferred. With regard to the latter quantity, it is assumed that the
measured using the central circular sensing area, shown in Fig.
surface area to which heat is transferred is well defined. As is
1. The water-cooled annular guard ring serves the purpose of
indicated in Fig. 1, the design of the calorimeter is such that the
preventing heat transfer to the sides of the calorimeter and
heat transfer area is confined by design to the front or directly
establishes flat-plate flow. An energy balance on the control
heated surface. To minimize side heating or side heat losses, a
volume that surrounds the sensing surface (the centrally
located calorimeter in Fig. 1) requires that the energy crossing
the sensing surface (A, in Fig. 1) of the calorimeter be equated 3
The boldface numbers in parentheses refer to the list of references at the end of
to the energy absorbed by the calorimeter cooling water. this test method.
FIG. 1 Steady-State Water-Cooled Calorimeter.
E422 − 22
water-cooled guard ring or shroud is utilized and is separated this, a more detailed net heat flux measurement can be applied
physically from the calorimeter by means of an air gap and low to the specimen test and more information can be deduced from
the test.
conductivity bushing such as nylon. The air gap is recom-
mended to be no more than 0.5 mm on the radius. Thus, if
6. Apparatus
severe pressure variations exist across the face of the
calorimeter, side heating caused by flow into and out of the air 6.1 General—The apparatus shall consist of a water-cooled
gap will be minimized. Also, since the water-cooled calorim- calorimeter and the necessary instrumentation to measure the
heat transferred to the calorimeter. Although the recommended
eter and guard ring operate at low surface temperatures
instrumentation accuracies are state-of-the-art values, more
(usually lower than 100 °C) heat losses across the gap by
rugged and higher accuracy instrumentation may be required
radiant interchange are negligible and consequently no special
for high pressure and high net heat applications. A number of
calorimeter surface gap finishes are necessary. Depending upon
materials can be used to fabricate the calorimeter, but oxygen
the size of the calorimeter surface, large variations in net heat
free high conductivity (OFHC) copper is often preferred
flux may exist across the face of the calorimeter. Consequently,
because of its superior thermal properties. The user should
the measured net heat flux represents an average net heat flux
decide before fabrication and use of the water-cooled calorim-
over the surface area of the water-cooled calorimeter. The
eter what the total acceptable uncertainty is for the application
water-cooled calorimeter can be used to measure net heat flux
2 2
of interest. Some applications can accommodate larger uncer-
levels over a range from 10 kW/m to 60 MW/m .
tainties than others, and typically the smaller the required
uncertainty, the higher the cost. For the water-cooled
5. Significance and Use
calorimeter, there are four parameters that can be uncertain: the
5.1 The purpose of this test method is to measure the net
water flow rate, the temperature difference, the water specific
heat flux to a water-cooled surface for purposes of calibration
heat, and the sensing surface area. The acceptable total
of the thermal environment into which test specimens are uncertainty should be expressed as xx % of reading or maxi-
placed for evaluation. The measured net heat flux is one of the
mum value good to a certain confidence level. An example (but
important parameters for correlating the behavior of materials. not a recommended value) would be a 65 % uncertainty to
If the calorimeter and holder size, shape, and surface finish are 95 % confidence level.
identical to that of the test specimen, the measured net heat flux
6.2 Coolant Flow Measurement—The water flow rate to
to the calorimeter is presumed to be the same as that to the
each component of the calorimeter shall be chosen to cool the
sample’s heated surface. If the calorimeter configuration
apparatus adequately and to ensure accurately measurable rise
(holder size, shape, finish, etc.) is not identical to that of the test
in water temperature. The error in water flow rate measurement
specimen, then the measurement results may need to be
should be not more than 62 %, assuming this value has been
modified to account for those differences. See Appendix X1.
apportioned with the total acceptable uncertainty preferred.
Suitable equipment that can be used is listed in Refs (2, 3) and
5.2 The water-cooled calorimeter is one of several calorim-
includes turbine flowmeters, variable area flowmeters, etc.
eter concepts used to measure net heat flux. The prime
Care must be exercised in the use of all these devices. In
drawback is its long response time, that is, the time required to
particular, it is recommended that appropriate filters be placed
achieve steady-state operation. To calculate energy added to
in all water inlet lines to prevent particles or unnecessary
the coolant water, accurate measurements of the rise in coolant
deposits from being carried to the water-cooling passages,
temperature are needed, all energy losses should be minimized,
pipe, and meter walls. Water flow rates and pressure shall be
and steady-state conditions must exist both in the thermal
adjusted to ensure that no bubbles are formed (no boiling). If
environment and fluid flow of the calorimeter.
practical, the water flowmeters shall be placed upstream of the
calorimeter in straight portions of the piping. The flowmeter
5.3 Regardless of the source of energy input to the water-
device shall be checked and calibrated periodically. Pressure
cooled calorimeter surface (radiative, convective, or combina-
gages, if required, shall be used in accordance with the
tions thereof) the measurement is averaged over the surface-
manufacturer’s instructions and calibration charts.
active area of the calorimeter. If the water-cooled calorimeter is
used to measure only radiative flux or combined convective-
6.3 Coolant Temperature Measurement—The method of
radiative net heat flux rates, then the surface reflectivity of the
temperature measurement must be sufficiently sensitive and
calorimeter shall be measured over the wavelength region of
reliable to ensure accurate measurement of the coolant water
interest (depending on the source of radiant energy). If non-
temperature rise. There are two calorimeter water temperature
uniformities exist in the gas stream, a large surface area
sensors in the calorimeter, one to measure inlet water tempera-
water-cooled calorimeter would tend to smooth or average any
ture and the other to measure outlet water temperature.
variations. Consequently, it is advisable that the size of the
Procedures similar to those given in Specification E235, Type
calorimeter be limited to relatively small surface areas and
K (chromel/alumel, range 0 °C to 1260 °C, accuracy 62.2 °C
applied to where the net heat flux is uniform. Where large
or 0.75 % of reading in °C, whichever is greater, for standard
samples are tested, it is recommended that a number of smaller
tolerances), and Ref (4) should be followed in the calibration
diameter water-cooled calorimeters be used (rather than one and preparation of temperature sensors. Specification E230/
large unit). These shall be located across the heated surface
E230M provides information on thermocouples (TCs) with a
such that a net heat flux distribution can be described. With smaller temperature range and higher accuracy than Type K
E422 − 22
TCs (for example, Type T, copper/constantan, range is 0 °C to that the differential temperature (ΔT) be made of the desired
+370 °C, 61.0 °C or 60.75 % of reading in °C, whichever is parameters rather than absolute measurements.
greater, for standard tolerances) that might be more appropriate 6.4.2 In all cases, parameters of interest, such as water flow
if the water coolant temperature does not rise too high. There rates and cooling water temperature rises should be automati-
are also special tolerances (that is, more accurate) available for cally recorded throughout the measurement period. Recording
both Type T and Type K TC wire. The bulk or average speed or sampling frequency will depend on the variations of
temperature of the coolant shall be measured at the inlet and the parameters being recorded. Digital data acquisition systems
outlet lines of each cooled unit, as accurately as possible given (DASs) are widely available and cost effective. It is important
the required total uncertainty, the sensors available, and the to sample the data fast enough to ensure one can establish
data acquisition system used. The error in measurement of steady state, but slow enough such that the sample rate is not
temperature difference between inlet and outlet shall be deter- faster than the calorimeter response time. Test Method E459
mined when the total aceptable uncertainty is established, and recommends that the sample rate for a digital data acquisition
when uncertainty (or accuracy) limits are portioned for the four system be no more than 40 % of the calorimeter response time.
uncertain parameters (temperature, water flow rate, specific When a strip chart recorder is used, the response time of the
heat of water, and sensing surface area). A reasonable value for recorder shall be 1 s or less for full-scale deflection. Timing
total temperature uncertainty is about 61-2 % of the reading in marks should be an integral part of the recorder with a
K (Ref (5)). The user must realize that the temperature minimum requirement of 1/s.
measurement uncertainty includes the sensor accuracy and the
7. Hazards
uncertainty from the data acquisition system, not just the
sensor alone. At temperatures of interest in this standard, the
7.1 This standard does not purport to address all of the
uncertainty contribution from the data acquisition system can
safety concerns, if any, associated with its use. It is the
be 61 °C (Ref (5)), which is comparable to the sensor
responsibility of the user of this standard to establish appro-
uncertainty. See 13.5. The water temperature indicating devices
priate safety, health, and environmental practices and deter-
shall be placed as close as practical to the calorimeter’s heated
mine the applicability of regulatory limitations prior to use.
surface in the inlet and outlet lines. However, care must be
8. Calibration and Standardization
exercised so as not to place the temperature sensors where
there is energy exchange between the incoming (cold) water
8.1 It is desirable, but most often not possible, to obtain
and the outgoing (heated) water. This occurs most readily at
estimates of the precision and bias of all sensors and instru-
flow dividers and at the calorimeter sensing surface. No
ments. For example, it is not possible to obtain bias errors for
additional apparatus shall be placed in the line between the
thermocouples mounted on surfaces or inside a water flow
temperature sensor and the heat source. The temperature
system because the bias errors depend on specifics of the setup,
measurements shall be recorded continuously to verify that
which varies for each different test. As a result, most often
steady-state operation has been achieved. Refs (2, 3) list a
manufacturers provide information for the sensor only. For
variety of commercially available temperature sensors. Tem-
example, ASTM’s specifications for thermocouple accuracy
perature sensors which are applicable include liquid-in-glass
are provided in Specification E230/E230M as “tolerances.” An
thermometers, thermopiles, thermocouples, and thermistors.
example for Type K thermocouples is a standard tolerance of
During operation of the heat source, care should be taken to
“the greater of 62.2 °C or 60.75 % of the reading in °C”.
minimize deposits on the temperature sensors and to eliminate
There is no mention of a precision or bias in that tolerance; it
any possibility of sensor heating because of specimen radiation
would be very difficult to obtain such numbers. Also, most
to the sensor. In addition, all water lines should be shielded
manufacturers do not provide an estimate of the confidence
from direct-flow impingement or radiation from the test
level associated with the accuracy specification. For example,
environment.
one does not often see a specification like this: the accuracy is
6.3.1 If at all practical, a TC shall be placed on the 65 % with a confidence level of 95 %. The manufacturer only
provides this: the accuracy is 65 %. Fortunately, many speci-
water-cooled side of the heated calorimeter surface. Although
this surface temperature (water side) measurement is not used fications imply the accuracy specification assumes the largest
confidence, that is, about 99 %.
directly in the calculation of net heat flux it is necessary for the
calculation of the surface temperature (front face) used in the
8.2 Thermocouple Calibration—The user should purchase
correction of the measured net heat flux to walls of different
thermocouples or thermocouple wire from a reputable source
temperatures.
and confirm that the sensors at least meet ASTM tolerances
shown in Specification E230/E230M. Individual thermo-
6.4 Recording Means:
couples can be calibrated in a certified laboratory if more
6.4.1 Since measurement of the energy transfer requires that
accurate values are needed. But those calibrations only apply to
the calorimeter operate as a steady state device, all calculations
a bare wire or shielded thermocouple not attached to a surface
will use only measurements taken after it has been established
or in a water flow stream. If more information is desired
...

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: E422 − 05 (Reapproved 2016) E422 − 22
Standard Test Method for
Measuring Net Heat Flux Using a Water-Cooled Calorimeter
This standard is issued under the fixed designation E422; 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 a steady net heat flux to a given water-cooled surface by means of a system energy
balance.
1.2 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this
standard.
1.3 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.
1.4 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:
E176 Terminology of Fire Standards
E230/E230M Specification for Temperature-Electromotive Force (emf) Tables for Standardized Thermocouples
E235 Specification for Type K and Type N Mineral-Insulated, Metal-Sheathed Thermocouples for Nuclear or for Other
High-Reliability Applications
E456 Terminology Relating to Quality and Statistics
E459 Test Method for Measuring Heat Transfer Rate Using a Thin-Skin Calorimeter
E3057 Test Method for Measuring Heat Flux Using Directional Flame Thermometers with Advanced Data Analysis Techniques
3. Terminology
3.1 Definitions—Refer to Terminologies E176 and E456 for definitions of terms used in this test method.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 absorbed heat flux, n—incident radiative heat flux less the reflected radiative flux, W/m .
This test method is under the jurisdiction of ASTM Committee E21 on Space Simulation and Applications of Space Technology and is the direct responsibility of
Subcommittee E21.08 on Thermal Protection.
Current edition approved April 1, 2016April 1, 2022. Published April 2016May 2022. Originally approved in 1971. Last previous edition approved in 20112016 as
E422 – 05 (2011).(2016). DOI: 10.1520/E0422-05R16.10.1520/E0422-22.
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volume information, refer to the standard’s Document Summary page on the ASTM website.
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3.2.2 convective heat flux, n—the addition or loss of energy per unit area into the sensing surface due to convection, = h*(T -T ),
fs s
W/m .
3.2.3 control volume, n—user defined volume over which an energy balance is determined.
4 2
3.2.4 emitted heat flux, n—energy per unit area emitted from a hot surface – ε*σ*T , W/m .
3.2.5 incident radiative heat flux (irradiance; q ), n—radiative heat flux (energy per unit area) impinging on the surface of the
inc,r
calorimeter from an external environment, W/m .
3.2.6 heat flux or energy flux, n—energy per unit area, W/m .
3.2.7 net heat flux or net energy flux, n—net energy divided by the sensing surface area transferred to the calorimeter face; it is
equal to the [absorbed radiative heat flux + convective heat flux] – [re-radiation from the exposed surface].
3.2.8 reflected heat flux, n— that part of the incident radiative flux that is not absorbed by or transmitted into the surface of the
calorimeter, W/m .
3.2.9 verified, n—the process of checking that a data acquisition channel correctly measures an input value, to a pre-set, acceptable
level condition defined by the user.
3.3 Symbols:
A—sensing surface area of calorimeter, m
Cp—water specific heat, J/(kg-K)
h—convective heat transfer coefficient, W/m -K
m—mass flow rate of coolant water, kg/sec
q—heat flux, W/m
T—temperature, K
T —calorimeter water inlet bulk temperature during operation, K
T —calorimeter water exhaust bulk temperature during operation, K
T —calorimeter water inlet bulk temperature before operation, K
T —calorimeter water exhaust bulk temperature before operation, K
ΔT = T – T —calorimeter water bulk temperature rise during operation, K
0 02 01
ΔT = T -T —calorimeter water apparent bulk temperature rise before operation, K
1 2 1
ε—emissivity of sensing surface
2 4
σ—Stefan-Boltzmann constant, 5.67E-08 W/m -K
3.4 Abbreviations:
3.4.1 TC—thermocouple
3.4.2 PPE—personal protective equipment
3.4.3 U —total uncertainty to 95 % confidence
3.4.4 t —“Students t”
3.4.5 B —total bias uncertainty
T
3.4.6 S —total systematic or precision uncertainty
T
3.4.7 DOF—degrees of freedom
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4. Summary of Test Method
4.1 A measure of the net heat flux to a given water-cooled surface is based upon the following measurements: (1) the water mass
flow rate and (2) the temperature rise of coolant water. The net heat flux is determined numerically by multiplying the water coolant
flow rate by the specific heat and rise in temperature of the water and dividing this value by the surface area across which heat
has been transferred.
4.2 The apparatus for measuring net heat flux by the energy-balance technique is illustrated schematically in Fig. 1. It is a typical
constant-flow water calorimeter used to measure stagnation region net heat flux to a flat-faced specimen. Other calorimeter shapes
can also be easily used. The net heat flux is measured using the central circular sensing area, shown in Fig. 1. The water-cooled
annular guard ring serves the purpose of preventing heat transfer to the sides of the calorimeter and establishes flat-plate flow. An
energy balance on the system control volume that surrounds the sensing surface (the centrally located calorimeter in Fig. 1)
requires that the energy crossing the sensing surface (A, in Fig. 1) of the calorimeter be equated to the energy absorbed by the
calorimeter cooling water. Interpretation of the data obtained is not within the scope of this discussion; consequently, such effects
as recombination efficiency of the surface and thermochemical state of the boundary layer are outside the scope of this test method.
It should be noted that recombination effects at low pressures can cause serious discrepancies in net heat flux measurements (such
as discussed in Ref (1)) depending upon the surface material on the calorimeter.
4.3 For the particular control volume cited, the energy balance can be written as follows:
E 5 mC ΔT 2 ΔT /A (1)
@ ~ !#
CAL p 0 1
where:
−2
E = energy flux transferred to calorimeter face, W·m
CAL
−2,
E = energy flux (or net heat flux) transferred to calorimeter face, W·m
CAL
−1
m = mass flow rate of coolant water, kg·s ,
−1 −1
C = water specific heat, J·kg ·K ,
p
ΔT = T — T calorimeter water bulk temperature rise during operation, K,
0 0 0
2 1
ΔT = T – T calorimeter water bulk temperature rise during operation, K,
0 0 0
2 1
ΔT = T — T = calorimeter water apparent bulk temperature rise before operation, K,
1 2 1
ΔT = T – T , calorimeter water apparent bulk temperature rise before operation, K,
1 2 1
T = calorimeter water exhaust bulk temperature during operation, K,
T = calorimeter water inlet bulk temperature during operation, K,
T = calorimeter water exhaust bulk temperature before operation, K,
T = calorimeter water inlet bulk temperature before operation, K, and
A = sensing surface area of calorimeter, m .
4.4 An examination of Eq 1 shows that to obtain a value of the energy transferred to the calorimeter, measurements must be made
of the water coolant flow rate, the temperature rise of the coolant, and the surface area across which heat is transferred. With regard
FIG. 1 Steady-State Water-Cooled Calorimeter.
The boldface numbers in parentheses refer to the list of references at the end of this test method.
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to the latter quantity, it is assumed that the surface area to which heat is transferred is well defined. As is indicated in Fig. 1, the
design of the calorimeter is such that the heat transfer area is confined by design to the front or directly heated surface. To minimize
side heating or side heat losses, a water-cooled guard ring or shroud is utilized and is separated physically from the calorimeter
by means of an air gap and low conductivity bushing such as nylon. The air gap is recommended to be no more than 0.5 mm on
the radius. Thus, if severe pressure variations exist across the face of the calorimeter, side heating caused by flow into and out of
the air gap will be minimized. Also, since the water-cooled calorimeter and guard ring operate at low surface temperatures (usually
lower than 100°C)100 °C) heat losses across the gap by radiant interchange are negligible and consequently no special calorimeter
surface gap finishes are necessary. Depending upon the size of the calorimeter surface, large variations in net heat flux may exist
across the face of the calorimeter. Consequently, the measured net heat flux represents an average net heat flux over the surface
area of the water-cooled calorimeter. The water-cooled calorimeter can be used to measure heat-flux net heat flux levels over a
2 2
range from 10 kW/m to 60 MW/m .
5. Significance and Use
5.1 The purpose of this test method is to measure the net heat flux to a water-cooled surface for purposes of calibration of the
thermal environment into which test specimens are placed for evaluation. The measured net heat flux is one of the important
parameters for correlating the behavior of materials. If the calorimeter and holder size, shape, and surface finish are identical to
that of the test specimen, the measured net heat flux to the calorimeter is presumed to be the same as that to the sample’s heated
surface. The measured heat flux is one of the important parameters for correlating the behaviorIf the calorimeter configuration
(holder size, shape, finish, etc.) is not identical to that of the test specimen, then the measurement results may need to be modified
to account for those differences. See Appendix X1of materials.
5.2 The water-cooled calorimeter is one of several calorimeter concepts used to measure net heat flux. The prime drawback is its
long response time, that is, the time required to achieve steady-state operation. To calculate energy added to the coolant water,
accurate measurements of the rise in coolant temperature are needed, all energy losses should be minimized, and steady-state
conditions must exist both in the thermal environment and fluid flow of the calorimeter.
5.3 Regardless of the source of energy input to the water-cooled calorimeter surface (radiative, convective, or combinations
thereof) the measurement is averaged over the surface active surface-active area of the calorimeter. If the water-cooled calorimeter
is used to measure only radiative flux or combined convective-radiative heat-flux net heat flux rates, then the surface reflectivity
of the calorimeter shall be measured over the wavelength region of interest (depending on the source of radiant energy). If
nonuniformities exist in the gas stream, a large surface area water-cooled calorimeter would tend to smooth or average any
variations. Consequently, it is advisable that the size of the calorimeter be limited to relatively small surface areas and applied to
where the heat-flux net heat flux is uniform. Where large samples are tested, it is recommended that a number of smaller diameter
water-cooled calorimeters be used (rather than one large unit). These shall be located across the heated surface such that a heat-flux
net heat flux distribution can be described. With this, a more detailed heat-flux net heat flux measurement can be applied to the
specimen test and more information can be deduced from the test.
6. Apparatus
6.1 General—The apparatus shall consist of a water-cooled calorimeter and the necessary instrumentation to measure the heat
transferred to the calorimeter. Although the recommended instrumentation accuracies are state-of-the-art values, more rugged and
higher accuracy instrumentation may be required for high pressure and high heat-flux net heat applications. A number of materials
can be used to fabricate the calorimeter, but OFHC (oxygen oxygen free high conductivity) conductivity (OFHC) copper is often
preferred because of its superior thermal properties. The user should decide before fabrication and use of the water-cooled
calorimeter what the total acceptable uncertainty is for the application of interest. Some applications can accommodate larger
uncertainties than others, and typically the smaller the required uncertainty, the higher the cost. For the water-cooled calorimeter,
there are four parameters that can be uncertain: the water flow rate, the temperature difference, the water specific heat, and the
sensing surface area. The acceptable total uncertainty should be expressed as xx % of reading or maximum value good to a certain
confidence level. An example (but not a recommended value) would be a 65 % uncertainty to 95 % confidence level.
6.2 Coolant Flow Measurement—The water flow rate to each component of the calorimeter shall be chosen to cool the apparatus
adequately and to ensure accurately measurable rise in water temperature. The error in water flow rate measurement shallshould
be not more than 62 %. 62 %, assuming this value has been apportioned with the total acceptable uncertainty preferred. Suitable
equipment that can be used is listed in RefRefs (2, 3) and includes turbine flowmeters, variable area flowmeters, etc. Care must
be exercised in the use of all these devices. In particular, it is recommended that appropriate filters be placed in all water inlet lines
to prevent particles or unnecessary deposits from being carried to the water-cooling passages, pipe, and meter walls. Water flow
rates and pressure shall be adjusted to ensure that no bubbles are formed (no boiling). If practical, the water flowmeters shall be
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placed upstream of the calorimeter in straight portions of the piping. The flowmeter device shall be checked and calibrated
periodically. Pressure gages, if required, shall be used in accordance with the manufacturer’s instructions and calibration charts.
6.3 Coolant Temperature Measurement—The method of temperature measurement must be sufficiently sensitive and reliable to
ensure accurate measurement of the coolant water temperature rise. There are two calorimeter water temperature sensors in the
calorimeter, one to measure inlet water temperature and the other to measure outlet water temperature. Procedures similar to those
given in Specification E235, Type K, and Ref K (chromel/alumel, range 0 °C to 1260 °C, accuracy 62.2 °C or 0.75 % of reading
in °C, whichever is greater, for standard tolerances), and Ref ((34)) should be followed in the calibration and preparation of
temperature sensors. Specification E230/E230M provides information on thermocouples (TCs) with a smaller temperature range
and higher accuracy than Type K TCs (for example, Type T, copper/constantan, range is 0 °C to +370 °C, 61.0 °C or 60.75 %
of reading in °C, whichever is greater, for standard tolerances) that might be more appropriate if the water coolant temperature does
not rise too high. There are also special tolerances (that is, more accurate) available for both Type T and Type K TC wire. The bulk
or average temperature of the coolant shall be measured at the inlet and outlet lines of each cooled unit. unit, as accurately as
possible given the required total uncertainty, the sensors available, and the data acquisition system used. The error in measurement
of temperature difference between inlet and outlet shall be determined when the total aceptable uncertainty is established, and when
uncertainty (or accuracy) limits are portioned for the four uncertain parameters (temperature, water flow rate, specific heat of water,
and sensing surface area). A reasonable value for total temperature uncertainty is about 61-2 % of the reading in K (Ref (5not more
than 61 %. )). The user must realize that the temperature measurement uncertainty includes the sensor accuracy and the
uncertainty from the data acquisition system, not just the sensor alone. At temperatures of interest in this standard, the uncertainty
contribution from the data acquisition system can be 61 °C (Ref (5)), which is comparable to the sensor uncertainty. See 13.5.
The water temperature indicating devices shall be placed as close as practical to the calorimeter’s heated surface in the inlet and
outlet lines. However, care must be exercised so as not to place the temperature sensors where there is energy exchange between
the incoming (cold) water and the outgoing (heated) water. This occurs most readily at flow dividers and at the calorimeter sensing
surface. No additional apparatus shall be placed in the line between the temperature sensor and the heat source. The temperature
measurements shall be recorded continuously to verify that steady-state operation has been achieved. Reference Refs ((2), 3 lists)
list a variety of commercially available temperature sensors. Temperature sensors which are applicable include liquid-in-glass
thermometers, thermopiles, thermocouples, and thermistors. During operation of the heat source, care should be taken to minimize
deposits on the temperature sensors and to eliminate any possibility of sensor heating because of specimen radiation to the sensor.
In addition, all water lines should be shielded from direct-flow impingement or radiation from the test environment.
6.3.1 If at all practical, a thermocoupleTC shall be placed on the water-cooled side of the heated calorimeter surface. Although
this surface temperature (water side) measurement is not used directly in the calculation of net heat flux it is necessary for the
calculation of the surface temperature (front face) used in the correction of the measured net heat flux to walls of different
temperatures.
6.4 Recording Means:
6.4.1 Since measurement of the energy transfer requires that the calorimeter operate as a steady state device, all calculations will
use only measurements taken after it has been established that the device has achieved steady operating levels. To assure steady
flow or operating conditions, the above mentioned above-mentioned parameters shall be continuously recorded such that
instantaneous measurements are available to establish a measure of steady-state operation. Wherever possible, it is highly desirable
that the differential temperature (ΔT) be made of the desired parameters rather than absolute measurements.
6.4.2 In all cases, parameters of interest, such as water flow rates and cooling water temperature rises should be automatically
recorded throughout the measurement period. Recording speed or sampling frequency will depend on the variations of the
parameters being recorded. Digital data acquisition systems (DASs) are widely available and cost effective. It is important to
sample the data fast enough to ensure one can establish steady state, but slow enough such that the sample rate is not faster than
the calorimeter response time. Test Method E459 recommends that the sample rate for a digital data acquisition system be no more
than 40 % of the calorimeter response time. When a strip chart recorder is used, the response time of the recorder shall be 1 s 1 s
or less for full-scale deflection. Timing marks should be an integral part of the recorder with a minimum requirement of 1/s.
7. Hazards
7.1 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, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
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8. Calibration and Standardization
8.1 It is desirable, but most often not possible, to obtain estimates of the precision and bias of all sensors and instruments. For
example, it is not possible to obtain bias errors for thermocouples mounted on surfaces or inside a water flow system because the
bias errors depend on specifics of the setup, which varies for each different test. As a result, most often manufacturers provide
information for the sensor only. For example, ASTM’s specifications for thermocouple accuracy are provided in Specification
E230/E230M as “tolerances.” An example for Type K thermocouples is a standard tolerance of “the greater of 62.2 °C or 60.75 %
of the reading in °C”. There is no mention of a precision or bias in that tolerance; it would be very difficult to obtain such numbers.
Also, most manufacturers do not provide an estimate of the confidence level associated with the accuracy specification. For
example, one does not often see a specification like this: the accuracy is 65 % with a confidence level of 95 %. The manufacturer
only provides this: the accuracy is 65 %. Fortunately, many specifications imply the accuracy specification assumes the largest
confidence, that is, about 99 %.
8.2 Thermocouple Calibration—The user should purchase thermocouples or thermocouple wire from a reputable source and
confirm that the sensors at least meet ASTM tolerances shown in Specification E230/E230M. Individual thermocouples can be
calibrated in a certified laboratory if more accurate values are needed. But those calibrations only apply to a bare wire or shielded
thermocouple not attached to a surface or in a water flow stream. If more inform
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