ASTM D7896-19

Standard Test Method for Thermal Conductivity, Thermal Diffusivity, and Volumetric Heat Capacity of Engine Coolants and Related Fluids by Transient Hot Wire Liquid Thermal Conductivity Method

SIGNIFICANCE AND USE
5.1 This test method covers the measurement of thermal properties for engine coolants (aqueous or non-aqueous) and related fluids.  
5.2 With each single measurement, the thermal conductivity (λ) and thermal diffusivity (α) are measured directly, and volumetric heat capacity (VHC) is determined by the relationship:
5.3 The test method is transient and requires only a small amount of specimen and a short duration of time (0.8 s) to run a measurement. These attributes minimize heat convection in the liquid.  
5.4 The brief application of current to the sensor wire adds very little heat to the test specimen and ten repetitive tests may be applied at 30 s intervals without causing any significant convection or temperature drift.
SCOPE
1.1 This test method covers the use of a transient hot wire liquid thermal conductivity method and associated equipment (the System) for the determination of thermal conductivity, thermal diffusivity and volumetric heat capacity of aqueous engine coolants, non-aqueous engine coolants, and related fluids. The System is intended for use in a laboratory.  
1.2 The System directly measures thermal conductivity and thermal diffusivity without the requirement to input any additional properties. Volumetric heat capacity is calculated by dividing the thermal conductivity by the thermal diffusivity of the sample measured.  
1.3 This test method can be applied to any aqueous or non-aqueous engine coolants or related fluid with thermal conductivity in the range of 0.1 to 1.0 W/m∙K.  
1.4 This test method excludes fluids that react with platinum.  
1.5 The range of temperatures applicable to this test method is –20 to 100 °C.  
1.6 This test method requires a sample of approximately 40 mL.  
1.7 The System may be used without external pressurization for any fluid having a vapor pressure of 33.8 kPa (4.9 psia) or less at the test temperature.  
1.8 For a fluid having a vapor pressure greater than 33.8 kPa (4.9 psia) at the test temperature, external pressurization is required (see Annex A2).  
1.9 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard.  
1.10 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.  
1.11 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-May-2019
• ICS: 71.100.45 - Refrigerants and antifreezes
• Technical Committee: D15 - Engine Coolants and Related Fluids
• Drafting Committee: D15.22 - Non-Aqueous Coolants

Relations

• Replaces: ASTM D7896-14 - Standard Test Method for Thermal Conductivity, Thermal Diffusivity and Volumetric Heat Capacity of Engine Coolants and Related Fluids by Transient Hot Wire Liquid Thermal Conductivity Method
• Effective Date: 01-Jun-2019
• Refers: ASTM D5931-20 - Standard Test Method for Density and Relative Density of Engine Coolant Concentrates and Aqueous Engine Coolants by Digital Density Meter
• Effective Date: 15-May-2020
• Refers: ASTM D1176-14(2019) - Standard Practice for Sampling and Preparing Aqueous Solutions of Engine Coolants or Antirusts for Testing Purposes
• Effective Date: 01-Oct-2019
• Refers: ASTM D5931-13(2017) - Standard Test Method for Density and Relative Density of Engine Coolant Concentrates and Aqueous Engine Coolants by Digital Density Meter
• Effective Date: 01-Nov-2017
• Refers: ASTM D1176-14 - Standard Practice for Sampling and Preparing Aqueous Solutions of Engine Coolants or Antirusts for Testing Purposes
• Effective Date: 01-Apr-2014
• Refers: ASTM D5931-13 - Standard Test Method for Density and Relative Density of Engine Coolant Concentrates and Aqueous Engine Coolants by Digital Density Meter
• Effective Date: 01-May-2013
• Refers: ASTM E691-13 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-May-2013
• Refers: ASTM E691-11 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Nov-2011
• Refers: ASTM E691-08 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Oct-2008
• Refers: ASTM D1176-98(2008) - Standard Practice for Sampling and Preparing Aqueous Solutions of Engine Coolants or Antirusts for Testing Purposes
• Effective Date: 01-Apr-2008
• Refers: ASTM D5931-96(2007) - Standard Test Method for Density and Relative Density of Engine Coolant Concentrates and Aqueous Engine Coolants by Digital Density Meter
• Effective Date: 01-Oct-2007
• Refers: ASTM E691-05 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Nov-2005
• Refers: ASTM E691-99 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 10-May-1999
• Refers: ASTM D1176-98 - Standard Practice for Sampling and Preparing Aqueous Solutions of Engine Coolants or Antirusts for Testing Purposes
• Effective Date: 10-Apr-1998
• Refers: ASTM D1176-98(2002) - Standard Practice for Sampling and Preparing Aqueous Solutions of Engine Coolants or Antirusts for Testing Purposes
• Effective Date: 10-Apr-1998

Overview

ASTM D7896-19 is the Standard Test Method developed by ASTM International for determining the thermal conductivity, thermal diffusivity, and volumetric heat capacity of engine coolants and related fluids. This method utilizes the transient hot wire liquid thermal conductivity method, providing direct and precise measurement of these thermal properties in both aqueous and non-aqueous fluids. The procedure is widely referenced in laboratory environments for quality control, research, and development purposes related to automotive and industrial heat transfer fluids.

Key benefits of this test method include fast measurement time, small required sample volume, and high accuracy. The method minimizes heat convection and temperature drift, supporting reliable thermal property analysis essential for coolant formulation and selection.

Key Topics

• Thermal Conductivity: Measurement of a fluid’s ability to conduct heat, crucial for evaluating how well engine coolants transfer thermal energy.
• Thermal Diffusivity: Directly measured, this parameter shows how quickly a fluid responds to changes in temperature, impacting coolant system performance.
• Volumetric Heat Capacity: Calculated from the measured thermal conductivity and diffusivity, this value indicates the amount of heat needed to raise the temperature of a unit volume of fluid.
• Sample and Equipment Requirements:
  • Approximately 40 mL of fluid is needed for each test.
  • The method is applicable to fluids with thermal conductivities in the range of 0.1 to 1.0 W/m·K and temperatures from –20 to 100 °C.
  • The system can operate without pressurization for fluids with vapor pressures ≤33.8 kPa (4.9 psia) at the test temperature; higher vapor pressures require external pressurization.
• Exclusions: Not suitable for fluids that react with platinum.
• Quick, Repeatable Testing: Each measurement takes just 0.8 seconds, and ten repetitive measurements can be performed at 30-second intervals with minimal risk of convection effects.

Applications

The ASTM D7896-19 test method is particularly valuable in automotive, industrial, and laboratory settings for:

• Engine Coolant Evaluation: Essential for manufacturers and formulators to assess the thermal performance of both traditional (aqueous) and advanced (non-aqueous or waterless) engine cooling fluids.
• Quality Control: Used by manufacturers for batch-to-batch verification of coolant properties to ensure product consistency.
• R&D and Comparative Analysis: Supports research into new coolant formulations, additives, or related heat transfer fluids.
• Compliance and Technical Specification: Enables industry stakeholders to meet technical standards and regulatory requirements regarding heat transfer fluid performance.

Related Standards

Several ASTM standards are commonly referenced alongside ASTM D7896-19 to provide a comprehensive analysis of engine coolants and related fluids:

• ASTM D1176: Practice for Sampling and Preparing Aqueous Solutions of Engine Coolants or Antirusts for Testing Purposes.
• ASTM D5931: Test Method for Density and Relative Density of Engine Coolant Concentrates and Aqueous Engine Coolants by Digital Density Meter.
• ASTM E691: Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method.

These complementary standards address sampling, density measurement, and interlaboratory test precision, supporting the accurate and reliable application of the ASTM D7896-19 method in diverse testing scenarios.

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Keywords: ASTM D7896, thermal conductivity, thermal diffusivity, volumetric heat capacity, engine coolant, heat transfer fluid, transient hot wire, laboratory testing, quality control, automotive standards, aqueous coolant, non-aqueous coolant, thermal property measurement

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: D7896 − 19
Standard Test Method for
Thermal Conductivity, Thermal Diffusivity, and Volumetric
Heat Capacity of Engine Coolants and Related Fluids by
Transient Hot Wire Liquid Thermal Conductivity Method
This standard is issued under the fixed designation D7896; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
1.1 This test method covers the use of a transient hot wire
mine the applicability of regulatory limitations prior to use.
liquid thermal conductivity method and associated equipment
1.11 This international standard was developed in accor-
(the System) for the determination of thermal conductivity,
dance with internationally recognized principles on standard-
thermal diffusivity and volumetric heat capacity of aqueous
ization established in the Decision on Principles for the
engine coolants, non-aqueous engine coolants, and related
Development of International Standards, Guides and Recom-
fluids. The System is intended for use in a laboratory.
mendations issued by the World Trade Organization Technical
1.2 The System directly measures thermal conductivity and
Barriers to Trade (TBT) Committee.
thermal diffusivity without the requirement to input any
2. Referenced Documents
additional properties.Volumetric heat capacity is calculated by
dividing the thermal conductivity by the thermal diffusivity of
2.1 ASTM Standards:
the sample measured.
D1176Practice for Sampling and Preparing Aqueous Solu-
tionsofEngineCoolantsorAntirustsforTestingPurposes
1.3 This test method can be applied to any aqueous or
D5931Test Method for Density and Relative Density of
non-aqueous engine coolants or related fluid with thermal
Engine Coolant Concentrates and Aqueous Engine Cool-
conductivity in the range of 0.1 to 1.0 W/m·K.
ants by Digital Density Meter
1.4 This test method excludes fluids that react with plati-
E691Practice for Conducting an Interlaboratory Study to
num.
Determine the Precision of a Test Method
1.5 Therangeoftemperaturesapplicabletothistestmethod
3. Terminology
is –20 to 100°C.
3.1 Definitions of Thermal Related Units:
1.6 This test method requires a sample of approximately 40
3.1.1 density (ρ),n—the mass per unit volume of a sub-
mL.
stance under specific conditions of pressure and temperature.
1.7 TheSystemmaybeusedwithoutexternalpressurization
Unit: kg/m .
for any fluid having a vapor pressure of 33.8 kPa (4.9 psia) or
3.1.2 specific heat capacity (Cp),n—the amount of heat
less at the test temperature.
required to raise the temperature of a unit mass of material by
1.8 Forafluidhavingavaporpressuregreaterthan33.8kPa
1°C. See Annex A1. Unit: J/(kg·K).
(4.9 psia) at the test temperature, external pressurization is
3.1.3 thermal conductivity (λ),n—rate of heat flow under
required (see Annex A2).
steady conditions through unit area, per unit temperature
1.9 The values stated in SI units are to be regarded as
gradient in the direction perpendicular to the area. Unit:
standard. The values given in parentheses after SI units are
W/m·K.
provided for information only and are not considered standard.
3.1.4 thermal diffusivity(α),n—ameasureoftheabilityofa
1.10 This standard does not purport to address all of the 2
substance to transmit a difference in temperature. Unit: m /s.
safety concerns, if any, associated with its use. It is the
3.1.5 volumetric heat capacity (VHC),n—the amount of
heat required to raise the temperature of a unit volume of
This test method is under the jurisdiction ofASTM Committee D15 on Engine
Coolants and Related Fluids, and is the direct responsibility of Subcommittee
D15.22 on Non-Aqueous Coolants. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved June 1, 2019. Published June 2019. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 2014. Last previous edition approved in 2014 as D7896–14. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D7896–19. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7896 − 19
material by 1°C. Volumetric heat capacity is the thermal specimen are determined. Volumetric heat capacity is deter-
conductivity of a material divided by its thermal diffusivity. mined by dividing the measured thermal conductivity by the
Unit: J/m ·K. measured thermal diffusivity of the specimen.
3.2 Definitions of Terms Specific to This Standard:
5. Significance and Use
3.2.1 transient hot wire method, n—a method for measure-
5.1 This test method covers the measurement of thermal
ment of thermal properties wherein a thin wire is immersed in
properties for engine coolants (aqueous or non-aqueous) and
a liquid specimen that is contained in a sampling cell. An
related fluids.
instantofcurrentissentthroughthewire,heatingboththewire
and specimen. Immediately afterward, the resistance of the
5.2 Witheachsinglemeasurement,thethermalconductivity
wire is measured with respect to time, while the wire cools.A
(λ) and thermal diffusivity (α) are measured directly, and
temperature-time profile of the specimen is produced and from
volumetric heat capacity (VHC) is determined by the relation-
this profile, thermal properties are determined.
ship:
3.2.1.1 dry bath, n—a temperature control peripheral with a
VHC 5 λ⁄α (1)
central heating well that receives the sampling cell containing
5.3 The test method is transient and requires only a small
the liquid specimen for providing temperatures above ambient.
amount of specimen and a short duration of time (0.8 s) to run
3.2.1.2 heat exchanger and circulator, n—a temperature
a measurement. These attributes minimize heat convection in
control peripheral consisting of a refrigerated/heated circulator
the liquid.
for heating and cooling that is connected to a heat exchanger.
5.4 The brief application of current to the sensor wire adds
The heat exchanger has a central well that receives the
very little heat to the test specimen and ten repetitive tests may
sampling cell containing the liquid specimen, for providing
be applied at 30 s intervals without causing any significant
temperatures above and below ambient.
convection or temperature drift.
3.2.1.3 liquid, n—refers to the engine coolant or related
fluid sample. 6. Apparatus
6.1 Transient Hotwire Liquid Thermal Conductivity Mea-
4. Summary of Test Method
surement System:
4.1 A fluid to be tested is placed inside the sampling cell
NOTE 1—The descriptions and instructions contained herein are based
assembly that is part of the system apparatus. The temperature
upon familiarity with the ThermTest, Inc. THW Lambda Transient Hot
within the sampling cell assembly is regulated by the use of a
Wire LiquidThermal Conductivity Meter. Other equivalent systems may
temperature control peripheral. Regardless of the test
be suitable for this application.
temperature, the sample and the System sensor are allowed to
6.1.1 The apparatus for the test method (Fig. 1) consists of
equilibrate to approximately the same temperature. The sam-
a sampling cell assembly with platinum wire sensor inserted,
pling cell assembly may be pressurized by up to a gauge
and a controller containing a microprocessor. Unless the
pressureof241kPa(35psig).Thesensor,athinplatinumwire,
measurements are to be made at ambient temperature, the
is immersed in the liquid test sample. A current is introduced
apparatusalsoincludesatemperaturecontrolperipheral(either
intothewireovertheshorttesttimeof0.8sthatheatsboththe
a dry bath or heat exchanger and circulator type). In a typical
wireandtheliquidsample.Thetemperatureofthewireandthe
implementation of the System, a personal computer is used for
resistance of the wire decay rapidly once the current is
convenience and greater flexibility in operation, and software
removed.Theresistanceofthewireismeasuredwithrespectto
supplied by the manufacturer provides the user interface,
timeandatemperatureversustimeprofilefortheliquidsample
is created. From the temperature versus time profile, the
thermal conductivity and thermal diffusivity of the liquid http://www.thermtest.com.
Shown are the controller connected to the platinum-wire sensor with the sensor residing in the sampling cell, along with the liquid specimen. For non-ambient
temperature readings, the sampling cell inserts into a temperature control peripheral (not shown). The computer downloads data from the controller for storage and for
the creation of spreadsheets and reports.
FIG. 1 Transient Hot Wire Liquid Thermal Conductivity Apparatus
D7896 − 19
control of test sequencing, data acquisition, and options for 7.8 Pressure of up to 241 kPa (35 psig) psi may be applied
working with test results in a spreadsheet program. Specific to the sampling cell assembly. An inert gas (from an argon or
operating instructions are provided in the equipment manuals. nitrogen tank) is introduced into the sampling cell assembly
through a pressure regulator. The level of pressure introduced
6.2 Transient Hot Wire Sampling Cell Assembly:
is manually controlled and set to the desired level for the
6.2.1 Fig. 2 shows details of the sampling cell assembly.
measurement.(Warning—Usecarewhenapplyingpressureto
Fig. 3 shows what the hot wire sensor actually looks like.
thecell,andensuretheproperregulatorisusedfortheintended
7. Specimen and Test Preparations pressure range and type of inert gas to be used. See the
operating manual supplied with the equipment for more
7.1 The sampling cell must be clean and dry before the
information on applying pressure to the sampling cell.)
liquid to be tested is introduced into it.
7.2 If the liquid to be tested is aqueous and dilutions are
8. Procedure
required, follow the proc
...

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: D7896 − 14 D7896 − 19
Standard Test Method for
Thermal Conductivity, Thermal Diffusivity, and Volumetric
Heat Capacity of Engine Coolants and Related Fluids by
Transient Hot Wire Liquid Thermal Conductivity Method
This standard is issued under the fixed designation D7896; 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 use of a transient hot wire liquid thermal conductivity method and associated equipment (the
System) for the determination of thermal conductivity, thermal diffusivity and volumetric heat capacity of aqueous engine coolants,
non-aqueous engine coolants, and related fluids. The System is intended for use in a laboratory.
1.2 The System directly measures thermal conductivity and thermal diffusivity without the requirement to input any additional
properties. Volumetric heat capacity is calculated by dividing the thermal conductivity by the thermal diffusivity of the sample
measured.
1.3 This test method can be applied to any aqueous or non-aqueous engine coolants or related fluid with thermal conductivity
in the range of 0.1 to 1.0 W/m—K.
1.4 This test method excludes fluids that react with platinum.
1.5 The range of temperatures applicable to this test method is –20 to 100°C.100 °C.
1.6 This test method requires a sample of approximately 40 mL.
1.7 The System may be used without external pressurization for any fluid having a vapor pressure of 33.8 kPa (4.9 psia) or less
at the test temperature.
1.8 For a fluid having a vapor pressure greater than 33.8 kPa (4.9 psia) at the test temperature, external pressurization is required
(see Annex A2).
1.9 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this The values
given in parentheses after SI units are provided for information only and are not considered standard.
1.9.1 Exception—Inch-pound units are provided in 1.7, 1.8, 4.1, 7.8, and A2.1 for information.
1.10 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.
1.11 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:
D1176 Practice for Sampling and Preparing Aqueous Solutions of Engine Coolants or Antirusts for Testing Purposes
D5931 Test Method for Density and Relative Density of Engine Coolant Concentrates and Aqueous Engine Coolants by Digital
Density Meter
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
This test method is under the jurisdiction of ASTM Committee D15 on Engine Coolants and Related Fluids, and is the direct responsibility of Subcommittee D15.22
on Non-Aqueous Coolants.
Current edition approved Feb. 1, 2014June 1, 2019. Published June 2014June 2019. Originally approved in 2014. Last previous edition approved in 2014 as D7896–14.
DOI: 10.1520/D7896-14.10.1520/D7896–19.
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.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7896 − 19
3. Terminology
3.1 Definitions of Thermal Related Units:
3.1.1 density (ρ),n—the mass per unit volume of a substance under specific conditions of pressure and temperature. Unit: kg/m .
3.1.2 specific heat capacity (Cp),n—the amount of heat required to raise the temperature of a unit mass of material by 1°C.1 °C.
See Annex A1. Unit: J/(kg—K).
3.1.3 thermal conductivity (λ),n—rate of heat flow under steady conditions through unit area, per unit temperature gradient in
the direction perpendicular to the area. Unit: W/m—K.
3.1.4 thermal diffusivity (α),n—a measure of the ability of a substance to transmit a difference in temperature. Unit: m /s.
3.1.5 volumetric heat capacity (VHC),n—the amount of heat required to raise the temperature of a unit volume of material by
1°C.1 °C. Volumetric heat capacity is the thermal conductivity of a material divided by its thermal diffusivity. Unit: J/m —K.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 transient hot wire method, n—a method for measurement of thermal properties wherein a thin wire is immersed in a liquid
specimen that is contained in a sampling cell. An instant of current is sent through the wire, heating both the wire and specimen.
Immediately afterward, the resistance of the wire is measured with respect to time, while the wire cools. A temperature-time profile
of the specimen is produced and from this profile, thermal properties are determined.
3.2.1.1 dry bath, n—a temperature control peripheral with a central heating well that receives the sampling cell containing the
liquid specimen for providing temperatures above ambient.
3.2.1.2 heat exchanger and circulator, n—a temperature control peripheral consisting of a refrigerated/heated circulator for
heating and cooling that is connected to a heat exchanger. The heat exchanger has a central well that receives the sampling cell
containing the liquid specimen, for providing temperatures above and below ambient.
3.2.1.3 liquid, n—refers to the engine coolant or related fluid sample.
4. Summary of Test Method
4.1 A fluid to be tested is placed inside the sampling cell assembly that is part of the Systemsystem apparatus. The temperature
within the sampling cell assembly is regulated by the use of a temperature control peripheral. Regardless of the test temperature,
the sample and the System sensor are allowed to equilibrate to approximately the same temperature. The sampling cell assembly
may be pressurized by up to a gauge pressure of 241 kPa (35 psig). The sensor, a thin platinum wire, is immersed in the liquid
test sample. A current is introduced into the wire over the short test time of 0.8 s that heats both the wire and the liquid sample.
The temperature of the wire and the resistance of the wire decay rapidly once the current is removed. The resistance of the wire
is measured with respect to time and a temperature versus time profile for the liquid sample is created. From the temperature versus
time profile, the thermal conductivity and thermal diffusivity of the liquid specimen are determined. Volumetric heat capacity is
determined by dividing the measured thermal conductivity by the measured thermal diffusivity of the specimen.
5. Significance and Use
5.1 This test method covers the measurement of thermal properties for engine coolants (aqueous or non-aqueous) and related
fluids.
5.2 With each single measurement, the thermal conductivity (λ) and thermal diffusivity (α) are measured directly, and
volumetric heat capacity (VHC) is determined by the relationship:
VHC5 λ⁄α (1)
Shown are the controller connected to the platinum-wire sensor with the sensor residing in the sampling cell, along with the liquid specimen. For non-ambient
temperature readings, the sampling cell inserts into a temperature control peripheral (not shown). The computer downloads data from the controller for storage and for
the creation of spreadsheets and reports.
FIG. 1 Transient Hot Wire Liquid Thermal Conductivity Apparatus
D7896 − 19
5.3 The test method is transient and requires only a small amount of specimen and a short duration of time (0.8 s) to run a
measurement. These attributes minimize heat convection in the liquid.
5.4 The brief application of current to the sensor wire adds very little heat to the test specimen and ten repetitive tests may be
applied at 30-s 30 s intervals without causing any significant convection or temperature drift.
6. Apparatus
6.1 Transient Hotwire Liquid Thermal Conductivity Measurement System:
NOTE 1—The descriptions and instructions contained herein are based upon familiarity with the ThermTest, Inc. THW Lambda Transient Hot Wire
Liquid Thermal Conductivity Meter. Other equivalent systems may be suitable for this application.
6.1.1 The apparatus for the test method (Fig. 1) consists of a sampling cell assembly with platinum wire sensor inserted, and
a controller containing a microprocessor. Unless the measurements are to be made at ambient temperature, the apparatus also
includes a temperature control peripheral (either a dry bath or heat exchanger and circulator type). In a typical implementation of
the System, a personal computer is used for convenience and greater flexibility in operation, and software supplied by the
manufacturer provides the user interface, control of test sequencing, data acquisition, and options for working with test results in
a spreadsheet program. Specific operating instructions are provided in the equipment manuals.
6.2 Transient Hot Wire Sampling Cell Assembly:
6.2.1 Fig. 2 shows details of the sampling cell assembly. Fig. 3 shows what the hot wire sensor actually looks like.
7. Specimen and Test Preparations
7.1 The sampling cell must be clean and dry before the liquid to be tested is introduced into it.
7.2 If the liquid to be tested is aqueous and dilutions are required, follow the procedures of Practice D1176 for proper sample
preparation.
7.3 If the liquid to be tested is non-aqueous, the liquid specimen is tested directly, without any changes or dilutions. Shake or
stir the liquid to assure that it is homogeneous.
7.4 If the liquid to be tested is non-aqueous, it should be assumed to be hygroscopic and its exposure to ambient air should be
as brief as possible.
7.5 Introduce approximately 40 mL of sample into the sampling cell. Important—make sure that the liquid level is 3 to 4 mL
below the threads that are clearly marked on the inner wall of the sampling cell. This allows room for possible thermal expansion
of the specimen while heating without any spillage or overflow, yet ensures full immersion of the sensor.
7.6 With the sample introduced, lower the sensor into the sampling cell. Remove any trapped air bubbles near the interface of
the sensor and specimen. Air bubbles can introduce errors and significantly degrade the resulting thermal properties measurement.
Tap the sampling cell to dislodge any air bubbles, and then screw the sensor onto the sampling cell.
The samp
...