ZhongLian
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- Date: 2023-04-24
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1. Scope*
1.1 This standard covers a test method for measurement of
thermal impedance and calculation of an apparent thermal
conductivity for thermally conductive electrical insulation
materials ranging from liquid compounds to hard solid mate
rials.
1.2 The term “thermal conductivity” applies only to homo
geneous materials. Thermally conductive electrical insulating
materials are usually heterogeneous and to avoid confusion this
test method uses “apparent thermal conductivity” for determin
ing thermal transmission properties of both homogeneous and
heterogeneous materials.
1.3 The values stated in SI units are to be regarded as
standard.
1.4 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 appro
priate safety, health, and environmental practices and deter
mine the applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accor
dance with internationally recognized principles on standard
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:2
D374 Test Methods for Thickness of Solid Electrical Insu
lation (Metric) D0374_D0374M
E691 Practice for Conducting an Interlaboratory Study to
Determine the Precision of a Test Method
E1225 Test Method for Thermal Conductivity of Solids
Using the Guarded-Comparative-Longitudinal Heat Flow
Technique
3. Terminology
3.1 Defifinitions of Terms Specifific to This Standard:
3.1.1 apparent thermal conductivity (λ), n—the time rate of
heat flflow, under steady conditions, through unit area of a
heterogeneous material, per unit temperature gradient in the
direction perpendicular to the area.
3.1.2 average temperature (of a surface), n—the area
weighted mean temperature.
3.1.3 composite, n—a material made up of distinct parts
which contribute, either proportionally or synergistically, to the
properties of the combination.
3.1.4 homogeneous material, n—a material in which rel
evant properties are not a function of the position within the
material.
3.1.5 thermal impedance (θ), n—the total opposition that an
assembly (material, material interfaces) presents to the flflow of
heat.
3.1.6 thermal interfacial resistance (contact resistance),
n—the temperature difference required to produce a unit of heat
flflux at the contact planes between the specimen surfaces and
the hot and cold surfaces in contact with the specimen under
test. The symbol for contact resistance is RI .
3.1.7 thermal resistivity, n—the reciprocal of thermal con
ductivity. Under steady-state conditions, the temperature
gradient, in the direction perpendicular to the isothermal
surface per unit of heat flflux.
3.2 Symbols Used in This Standard:
3.2.1 λ = apparent thermal conductivity, W/m·K.
3.2.2 A = area of a specimen, m2 .
3.2.3 d = thickness of specimen, m.
3.2.4 Q = time rate of heat flflow, W or J/s.
3.2.5 q = heat flflux, or time rate of heat flflow per unit area,
W/m2 .
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