This page calculates the temperature difference and the thermal contact conductance (thermal resistance) for an interface formed by two conforming, rectangular, rough surfaces as a function of contact pressure in the low pressure range.

Define the surface properties and the interface material , as well as the conductivity and the isothermal temperature applied to the medium surrounding the plate. the interstitial material can be either a gas or a liquid (gas parameter is zero). This page will calculate the temperature difference and the thermal resistance between the two surfaces.

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Material and State Conditions (Choose a defined materials or enter your own data)

Description Symbol Value Units
Contact Pressure of Surfaces P MPa
Width of Common Surface W m
Length of Common Surface L m
Heat Load on Surface 1 q W
Surface 1
Microhardness of Surface 1 HC1 MPa
Effective RMS Surface Roughness 1 sig1 micrometer
Thermal Conductivity of Surface 1 k1 W/(m oC)
Absolute Asperity Slope = 0.125 (sig1)0.402 m1 None
Surface 2
Microhardness of Surface 2 HC2 MPa
Effective RMS Surface Roughness 2 sig2 micrometer
Thermal Conductivity of Surface 2 k2 W/(m oC)
Absolute Asperity Slope = 0.125 (sig2)0.402 m2 None
Interstitial Material
Thermal Conductivity of Gap Substance k W/(m oC)
Gas Parameter (@ T0 = 50oC and P0 = 1 atm) (M0 0 for liquid) M0 m
Average Interface Thickness t m
Gas Temperature (needed if substance is a gas) Tg oC
Gas pressure (needed if substance is a gas) Pg kPa

Results for Thermal Grease Interface Resistance

Description Symbol Value Units
Microhardness used in Calculation HC MPa
Effective RMS Surface Roughness = (sig12+sig22)1/2 sig micrometer
Effective Mean Absolute Asperity Slope = 0.125 (sig)0.402 m None
Harmonic Mean Thermal Conductivity = 2k1k2/(k1+k2) ks W/(m oC)
Contact Conductive HTC1 = 1.25k1(m1/sig1)(P/H1)0.95 hc1 W/(m2 oC)
Contact Conductive HTC2 = 1.25k2(m2/sig2)(P/H2)0.95 hc2 W/(m2 oC)
Contact Conductive HTC = 1.25ks(m/sig)(P/HC)0.95 hc W/(m2 oC)
Gas Parameter = M0(T/T0)(Pg,0/Pg) Mg m
Effective Gap Thickness1 = 1.53sig1(P/H1)-0.097 Y1 m
Effective Gap Thickness2 = 1.53sig2(P/H2)-0.097 Y2 m
Effective Gap Thickness = 1.53sig(P/HC)-0.097 Y m
Gap Conductive HTC1 = kg/ (Y1+ M) hg1 W/(m2 oC)
Gap Conductive HTC2 = kg/ (Y2+ M) hg2 W/(m2 oC)
Gap Conductive HTC = kg/ (Y+ M) hg W/(m2 oC)
Joint Conductive HTC1 = hc1 + hg1 hj1 W/(m2 oC)
Joint Conductive HTC2 = hc2 + hg2 hj2 W/(m2 oC)
Joint Conductive HTC = hj W/(m2 oC)
Interface Thermal Resistance = 1/ (W*L*hj) rj oC/W
Temperature Difference = q/ (W*L*hj) T1-2 > oC
NOTE: HTC is Heat Transfer Coefficient


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