EVALUATION OF THERMAL CONTACT CONDUCTANCE WITH SIMULATED ROUGH SURFACES

Abstract

Finite element (FE) modelling of rough surfaces is becoming increasingly common. Over the last four decades many experimental and theoretical models have been developed on thermal contact conductance across joints that take into account the surface effects. Unfortunately, no universal model exists to predict the thermal contact conductance (TCC) by measuring the actual contact area between any two contact surfaces using FEM software. To determine which of the available analytical models is appropriate for a situation, the thermal engineer must assess the surface conditions, addressing questions such as: are the surfaces flat or rough? Are oxides on the surface? What is the pressure distribution within the contact? What is the real contact area? For surfaces where these questions can be answers with a high degree of certainty, some of the analytical models validated by extensive lab tests can be reliably used to predict overall thermal contact conductance. One of the primary motivations for the measurement of surfaces and the development of surface metrology tools is the ability not only to characterize the physical attributes of a surface but also to understand the functional behaviour of that surface. In experimental models, TCC has been calculated on the basis of nominal area instead of real contact area (obtained by spots in contact), that is the reason to go for analytical modelling and another motivation to study surface effects. In this work, rough surface profile has been generated for different roughness values by using random number generation using universal FEM software and estimation of actual contact area has been done. A comparison has been made between the current results of real contact area and various pre-existing models. Using the calculated real contact area, TCC has been evaluated between the contacting rough surfaces under varying loading conditions. By feeding this TCC value, a temperature pattern has been obtained to understand the thermal effects.