Investigation On Heat Transport Across Solid Contact Interface For HTS Conduction Cooling

With the coming forth of high temperature superconductor and large capacity cryocooler, history of using cryogenic coolant(liquified He, H2,N2,etc.) as cold fountain in superconducting basic research and R.&D. has been changed. Conduction cooling by cryocooler has been used to various site where low temperature is necessary. Conduction cooling in low temperature works through heat transport between solids for the purpose of lowering temperature and thermal management. So therm op hysical properties of solids and contact heat transport in their mutual interfacial layer become key technical tache and basic scientific problem in conduction cooling. The task of Cryogenic system for conduction cooling high Tc superconductor provides is providing enough cooling capacity to counterpoise heat load and overcome thermal disturbance, and realizing the whole system miniaturization and integration with superconducting electrical system. The total amount of heat leakage and self-generating heat including joule heat, heat from magnetic hysteresis loss, vortex loss, etc. should be less than cooling capacity which cryocooler could give. It is necessary to implement thermodynamic optimizing design to make operating temperature, heat load, parts dimension, electricity parameter and operating cost match best. Interfacial heat transport properties have an important effect on thermal stability and operating temperature of superconducting system and main parts.With support of the National Technology Research and Development Program of P. R. C.(Item No.2002AA306331-4), the National Science Foundation of P. R. C.(Item No.51076013) and the Research Fund for the Doctoral Program of Higher Education of P. R. C.(Item No.20040487039), this paper conducts the investigation on characteristic and mechanism of solid interfacial heat transport in high temperature superconducting conduction cooling on the basic of micro-nano cryogenics.A cryogenic conduction cooling experiment system has been established. SMES magnet sample cooldown experiment by G-M cryocooler was conducted, its surface temperature distribution and cooldown properties have been obtained at low temperature. A concept of maximum allow contact interface resistance was proposed in thermal analysis for high temperature superconductive magnet cooled by cryocooler.AlN is widely used in power electronic devices, microelectronic integrated circuit device package optical electronic device heat management etc. thermal conduction parameter between AlN and superconductor, copper lead is of important value for thermal design of cryocooler cooling system, since AlN can be used for electric-isolating and heat-conducting pad of large current superconductive device and copper lead circuit. An experimental investigation has been carried on into contact interface thermal resistance between A1N with high heat conductivity and high electric isolation and OFHC on cryogenic conduction cooling setup. The A1N/OFHC thermal contact conductance and thermal conductivity of AlN were measured in range of40-140K.It shows that thermal contact conductance between A1N and OFHC increases as the temperature and the pressure load of contact interface increase. The temperature dependence of thermal conductivity of A1N can be explained by scattering characteristic of heat carrier, phonon.Modulated Laser photothermal test setup for cryogenic interface thermal resistance has been established. Investigations on contact interface thermal resistance of Bi2223/Cu and Cu/Al have been carried on. The experimental results are consistent with published literature, and it shows that modulated photothermal method is feasible to testing contact interface thermal resistance. From the point of view of micro-nanocryogenics, mode of heat transfer between solid contact interfaces is based on the conception of a3D low temperature interfacial thin layer with micron or nanometer thickness instead of a simple2D plane. Phonon transport is dependent on molecular crystal lattice, lattice fault, lattice defect, confine, etc. Phonon scattering mechanism in interfacial layer is very complex. Thermal wave phase and amplitude changes while passing through interfacial layer can be measured, transformed and checked by Modulated laser photothermal method. Local thermal contact conductance can be measured through acquiring local thermal wave phase or amplitude in the inter facial layer. Such laser photothermal measurement throws away limitations Measuring only average thermal contact conductance over contact surface, can give panorama feature of interface layer thermal contact conductance.Topographical-scattering model was put forward to predict cryogenic contact interface thermal resistance basing on AMM, DMM and topographical models from the point of views of micro-nano cryogenics. Such model gives an embodiment of the "three-dimensional boundary layer" concept, and makes a relative accurate calculation for "three-dimensional boundary layer" thermal resistance.