Thermal Resistance and Thermal Conductance

Introduction

Thermal resistance (R) and thermal conductance (C) of the materials are reciprocals of one another and can be derived from thermal conductivity (k) and the thickness of the materials. The C-Therm Trident Thermal Conductivity Instrument measures thermal conductivity and, therefore, paves the way to determine thermal resistance and thermal conductance.

On this page, we’re going to describe and explain how to get thermal resistance and thermal conductance from thermal conductivity.

Measure thermal Conductivity with Trident

Thermal Conductivity (k-Value)

Thermal conductivity is the time rate of steady-state heat flow through a unit area of a homogeneous material induced by a unit temperature gradient in a direction perpendicular to that unit area, W/m⋅K.

Where,

L – Thickness of the specimen (m)
T – Temperature (K)
q – Heat flow rate (W/m2)

Equation 1 – Thermal Conductivity

Thermal Resistance (R-Value)

Thermal resistance is the temperature difference, at steady state, between two defined surfaces of a material or construction that induces a unit heat flow rate through a unit area, K⋅m2/W. According to this definition and Equation 1, Equation 2, therefore, can be obtained.

As indicated in Equation 2, the value of the thermal resistance can be determined by dividing the thickness with thermal conductivity of the specimen. Thermal resistance testing uses a Heat Flow Meter to determine the resistance. Click here for more information on testing the thermal resistance of your sample.

Equation 2 – Thermal Resistance

Thermal Conductance

Thermal conductance is the time rate of steady state heat flow through a unit area of a material or construction induced by a unit temperature difference between the body surfaces, in W/m2⋅K. C-value, hence, is the reciprocal of the R-value and can be expressed as Equation (3).

Consequently, the value of the thermal conductance can be calculated by dividing the thermal conductivity with the thickness of the specimen.

Equation 3 – Thermal Conductance

Applications

Thermal resistance and thermal conductance can be conveniently calculated from the thermal conductivity and thickness of the material. The C-Therm Trident Thermal Conductivity Platform is a flexible, rapid, non-destructive, highly sensitive and cost effective instrument that can directly measure thermal conductivity and thermal effusivity of a wide variety of samples, easing the process of determining thermal resistance and thermal conductance.

Take a look below to learn more about how to measure thermal conductivity of specific applications and materials.

Next Step: Method Selection for Thermal Conductivity Measurement

There are many methods for measuring thermal conductivity – learn the benefits and limitations of each including:

FLEX Transient Plane Source (ISO 22007-2, and GB/T 32064)
Transient Line Source NEEDLE (ASTM D5334, and D5930)
Modified Transient Plane Source (ASTM D7984)

Method selection is critical to obtaining accurate, representative thermal conductivity data for your application. Learn more in downloading a free copy of the Method Selection Guide. Download here