Measurement Method And Experimental Study Of High Temperature Thermal Contact Resistance

High temperature thermal contact heat transfer at solid-solid interface widely exists in the field of spacecraft thermal protection,nuclear reactor cooling and heat treatment process.As the engineering application under these high temperature conditions often corresponds to ultra-high heat flux,the change of contact thermal resistance may lead to large temperature difference.It is particularly important to obtain accurate contact thermal resistance parameters for the reliability and safety design of devices or systems.Taking the hypersonic vehicle as an example,the outer surface temperature of the vehicle exceed 1000℃asired from aerodynamic heating.In order to ensure the safety of the vehicle,it is necessary to design a reliable thermal protection system.While,the performance of the thermal protection system is affected by the high temperature contact thermal resistance between the thermal protection materials and between the vehicle body material and insulation material,in addition to the thermal physical properties and structure size of the thermal protection materials.High temperature contact thermal resistance is one of the key parameters in the design of thermal protection system,which plays an important role in the performance of thermal protection system and the safety of aircraft.Therefore,it is urgently required to study the method and system to measure thermal contact resistance at high temperature,thus to accurately measure the thermal contact resistance and seek profitable thermal control solutions for practical high temperature engineering applications.In this paper,the research is focused in the test method and system of thermal contact resistance at high temperature.The steady state test method for high temperature thermal contact resistance was established,the distribution of the measurement error was completed,and the test system of high temperature thermal contact resistance was designed.A compound multilayer insulation structure was proposed which is available for reducing heat loss error of the test method.Then,the thermal contact resistance test system is developed,which involves the stable heating at high temperature,accurate measurement of heat flow,accurate measurement of interface temperature,high temperature thermal protection,accurate pressure loading and high vacuum maintenance.The data processing method to obtain the thermal contact resistance is provided,and the contact thermal resistance between HTA（Inconel 718 high temperature alloy）and C/Zr B₂-Si C（Carbon fiber reinforced zirconium diboride and silicon carbide based composite）at high temperature was measured.In addiation,a numerical method for accuractely predict the high temperature thermal contact resistance was established.The main research work of this paper includes the following aspects:1.High temperature thermal contact resistance test method and systemBased on the axial heat flow method described in ASTM D 5470,the test method of high temperature thermal contact resistance and the design scheme of measurement system were established.To ensure that the measurement error of contact thermal resistance is less than15%,the error distribution of the contact thermal resistance test system was carried out.The overall scheme and detailed design of key components of the system were given.In order to meet the requirements of thermal protection for the steady state contact thermal resistance test method at high temperature,a cylindrical composite multilayer insulation structure was designed,and an experimental system for testing the thermal characteristics of insulation materials at high temperature was established.The temperature distribution inside the insulation structure was measured,and the equivalent thermal conductivity of the insulation structure was calculated under the hot boundary temperature range of 800～1350 K.According to the principle of steady state test method,a thermal contact resistance test system was developed under high temperature conditions,which can measure the interface temperature up to 1000℃.The data processing method for obtaining the contact thermal resistance was proposed.The standard tungsten heat flow meter was used to measure the interface heat flow,and the high resolution thermal infrared camera was employed to measure the temperature of the contact surface.The error analysis was carried out by using the measured data,and the experimental measurement error of contact thermal resistance is 9.45%.With the estblished experimental system,the thermal conductivity of 99.9999%copper was measured by steady axial heat flow method.The reliability of the experimental system and test method was verified by comparing the measured experimental data with NIST standard value.2.The influence of temperature and pressure on thermal contact resistanceBased on the established high temperature contact thermal resistance measurement system,the thermal contact resistance of HTA–HTA,C/Zr B₂Si C–C/Zr B₂Si C and HTA–C/Zr B₂Si C were measured in the temperature range of 630～1100 K and pressure range of0.1～0.6 MPa.The one-dimensional axial heat flux can be effectively guaranteed by using the thin disk sample,according to the systematic heat loss error is less than 10%.The reliability of the test method was verified by temperature repeatability test and temperature cycle test.The measurement results show that thermal contact resistance decreases with increasing the interface temperature as the enhancement of radiative heat transfer.At the same time,thermal contact resistance decreases with increasing the interface pressure due to the increase of contact area,and the effects of pressure on thermal contact resistance is much lower at high temperature.In addiation,the new dimensionless parameters were obtained by correlating the experimental data with the dimensionless thermal contact resistance empirical model with the maximum correlation error is 3.03%.Compared with the existing dimensionless model parameters,the predicted contact thermal resistance changes faster with pressure,and the thermal contact resistance value is larger at high temperature.3.Numeical prediction model for high temperature thermal contact resistanceA finite element contact model was developed with the rough surfaces,which were generated from the optically measured surface topography of HTA and C/Zr B₂-Si C.The mechanical deformation was conducted account for the elastic-plastic mechanics,and the distribution of contact pressure and area with interface temperature（630～1100 K）and pressure（0.1～0.6 MPa）was given.Then the thermal analysis was completed in terms of the interface heat transfer condition with the solid spots conduction,far-field and near-field radiation.The results show that thermal contact resistance decreases from 1611 mm²K/W to488 mm²K/W when the interface pressure increases from 0.1 MPa to 0.6 MPa,as the solid spots conduction is sensitive to pressure.Also,thermal contact resistance decreases from 1611mm²K/W to 340 mm²K/W when the interface temperature increases from 630 K to 1100 K,due to the enhancement of heat transfer by radiation.And the thermal contact resistance account for solid conduction and radiation is reduced to 1/25 of that only considering solid conduction.Additionally,the accuracy of present method was effectively validated by comparing the numerical results with experimental data.