Thermal Contact Conductance

Nowadays a new science direction has arisen from decades of experimental work carried out in 20th century-micromechanics of contact processes (deformation, heat transfer, electric conduction). To determine contact area a dynamic elastic-plastic deformation problem is to be solved even in the simplest case-butt contact of two rough surfaces under pressure. It is followed by the solution of spatial boundary heat transfer problem to obtain nonstationary temperature distribution for two bodies. In principal, this stage is not difficult to perform with finite element program ANSYS. Meanwhile the questions concerning deformation and conduction through oxide films of metals as well as directional effect remain. In the literature there are attempts to simulate thermal contact conductance numerically of such authors as M.K.Thompson, S.Lee et al, M. Ciavarella, M.M.Yovanovich and others. The disadvantages of existing spatial models are:-surfaces profiles has no random component;-only elastic or only plastic material behavior;-microroughness is not considered. In the present work the roughness before contact of two rough surfaces of copper bodies was presented as spatial two-level (roughness and microroughness) model with the use of fractal Weierstrass-Mandelbrot function. In quasistatic approach the 3D deformation and heat transfer problems of contacting bodies under pressure were solved within elastic-plastic material behavior. Contact ANSYS elements were used. Copper compression diagram was replaced by multilinear model of isotropic hardening. From the cycle of calculations real contact areas, shapes of contact spots, temperature and stress distributions were determined for the range of pressures. Good agreement with experimental data took place only when microroughness is considered. INTRODUCTION Chaosity and complex geometry of surfaces make great limits for structural and thermal numerical modeling. Nowadays according to [1-3] four directions for micromechanics modeling could be defined. 1. Multi-scale modeling. The whole of region is calculated using different mathematical models. 2. Combined multi-scale modeling. Part of region is calculated on one mathematical model, and other part is calculated using other mathematical model. 3. Multilevel one-scale modeling. A representative volume of low level geometry is calculated and the result is transferred as an initial condition in the geometry of higher level. All levels calculated on the only mathematical model 4. One-level one-scale modeling. Using the only mathematical and geometry model calculations are performed at macro and micro scales without their differentiation. The 1 st and 2 nd directions are needed when a model contains the regions under 100 μm. These are the problems of nanotechnology and solid body physics. The 3 rd direction has been developed since 90 th of 20 th century and is caused by computer performance limitations which exist so far. There is a range of continuum mechanics problems solved within the 4 th direction today [2,4]. And opportunities of the direction are rising because of its limits are also connected with today's computer performance. The advantages of this direction are: more accurate modeling of chaotic structures; absence of structure uncertainty in a region between levels; more accurate solution. In this work a thermal contact conduction modeling is carried out within one-level one-scale approach.

To study the heat transfer characteristics on pipe- concrete interface of a Reactor Vault (RV) model made of ordinary portland concrete with special additive. A mould to cast concrete is made using a wooden block of one square feet and pipe of 1 inch dia at the center. Thermocouples are arranged in the pipe. A heat transfer fluid at a higher temperature is circulated through the setup and the temperature readings are noted after attaining steady state. Experimental analysis is done, the values are verified using ANSYS software and the results are compared with other types of construction material.

A numerical model of heat conduction in vacuum through contact between two rough bodies made of commercial-purity AD1 aluminium is developed. To this end, the elastic-plastic contact deformation problem is solved accounting strain hardening. A method for consideration of surface initial cold work hardening and indentation size effect (ISE) is provided. Plastic characteristics of surface micro-volumes of material were taken from indentation results. Numerical realisation of the model in ANSYS finite element software is considered. Fractal surface models of two levels of roughness were used. Introduction of the second level roughness (microroughness) to the model was found to have considerable effect on the real contact area only when ISE is taken into account. An attempt to compare simulation results with data obtained with Shlykov's semi-empirical model was made.

... super-cooling, and poor stability in the phase-change characteristics under thermal cycling.7 For application as TIMs, organic PCMs are pre-ferred, due to their low tendency to cause ionic contamination, and are the ones addressed in this work. Prior work mostly used paraffin ...