Fractal Prediction Model of Thermal Contact Conductance of Rough Surfaces

The thermal contact conductance problem is an important issue in studying the heat transfer of engineering surfaces, which has been widely studied since last few decades, and for predicting which many theoretical models have been established. However, the models which have been existed are lack of objectivity due to that they are mostly studied based on the statistical methodology characterization for rough surfaces and simple partition for the deformation formats of contact asperity. In this paper, a fractal prediction model is developed for the thermal contact conductance between two rough surfaces based on the rough surface being described by three-dimensional Weierstrass and Mandelbrot fractal function and assuming that there are three kinds of asperity deformation modes： elastic, elastoplastic and fully plastic. Influences of contact load and contact area as well as fractal parameters and material properties on the thermal contact conductance are investigated by using the presented model. The investigation results show that the thermal contact conductance increases with the increasing of the contact load and contact area. The larger the fractal dimension, or the smaller the fractal roughness, the larger the thermal contact conductance is. The thermal contact conductance increases with decreasing the ratio of Young＇s elastic modulus to the microhardness. The results obtained indicate that the proposed model can effectively predict the thermal contact conductance at the interface, which provide certain reference to the further study on the issue of heat transfer between contact surfaces.

Heat transfer analysis for the roller shell under the condition of periodic thermal shock

According to the actual working conditions of roller shell in the process ofcontinuous roll casting, the Fourier heat transfer law is used to conduct the simulating analysisfor the temperature distribution of the roller shell under the condition of periodic thermal shock.The temperature variation law inside the roller shell is studied during the process of continuousroll casting, and the steady temperature distributions of the roller shell at different castingvelocities have been obtained when the thermal contact conductance between the roller shell and thecasting strip is considered.

Transient temperature characteristics of friction clutch disc considering thermal contact conductance under sliding conditions

High temperatures are generated due to the sliding contacts between the rubbing surfaces of the friction clutch system.In this work,by considering the effective thermal contact conductance under sliding conditions,a simulation model of a two-dimensional transient temperature field of the clutch disc was developed.A numerical solution to obtain the surface temperature at different radii was presented based on the finite difference method.Compared with the experimental data,the proposed model for estimating the surface temperature is more accurate than the conventional prediction method.The results showed that the errors of the calculated temperatures at radii of 114 and 106 mm have obviously reduced by 12.98%and 12.60%,respectively.In addition,the influences of pressure and relative speed on the surface temperature were investigated.The temperature increases with the increase of the relative speed and pressure during the sliding period,and there is an interaction effect between pressure and speed on the surface temperature rise.

Investigation on Thermal Contact Conductance Based on Data Analysis Method of Reliability

The method of reliability is proposed for the investigation of thermal contact conductance （TCC） in this study. A new defini- tion is introduced, namely reliability thermal contact conductance （RTCC）, which is defined as the TCC value that meets the reliability design requirement of the structural materials under consideration. An experimental apparatus with the compensation heater to test the TCC is introduced here. A practical engineering example is utilized to demonstrate the applicability of the pro- posed approach. By using a statistical regression model along with experimental data obtained from the interfaces of the struc- tural materials GH4169 and K417 used in aero-engine, the estimate values and the confidence level of TCC and RTCC values are studied and compared. The results show that the testing values of TCC increase with interface pressure and the proposed RTCC model matches the test results better at high interface pressure.

Propagation of plane waves in thermoelastic cubic crystal material with two relaxation times

A problem concerned with the reflection and refraction of thermoelastic plane waves at an imperfect interface between two generalized thermally conducting cubic crystal solid half-spaces of different elastic and thermal properties with two relaxation times has been investigated. The generalized thermoelastic theory with two relaxation times developed by Green and Lindsay has been used to study the problem. The expressions for the reflection and refraction coefficients which are the ratios of the amplitudes of reflected and refracted waves to the amplitude of incident waves are obtained for an imperfect boundary and deduced for normal stiffness, transverse stiffness, thermal contact conductance, slip and welded boundaries. Amplitude ratios of different reflected and refracted waves for different boundaries with angle of emergence have been compared graphically for different incident waves. It is observed that the amplitude ratios of reflected and refracted waves are affected by the stiffness and thermal properties of the media.