Performance Investigations On Radiation Cooler Of Free-piston Stirling Engine

In recent years,space exploration is undergoing a prosperous period,which gives rise to requirements for longer implementation cycle of the mission.Thus,the demands on energy are increased for spacecraft implementing space exploration.Free-piston Stirling engine is a closed cycle piston engine with external heating.It is of advantages on long life,high reliability,high efficiency and high specific power,and especially suitable for space application.Therefore,it is very important to research on the free-piston Stirling engine applied for thermal power generation in space.In this thesis,we firstly carry on the preliminary design of the structure of 200 W effective power free-piston Stirling engine,and determine the basic parameters of heat exchanger system.Based on the preliminary design methodology of free-piston Stirling engine,in conjunction with the ideal adiabatic model and Simple analysis method,visualization software using MATLAB is developed for design of free-piston Stirling engine.The main design parameters of the engine are optimized and analyzed by using the software and the global optimal design parameters are obtained by multi-objective optimization design method.In order to make grid numbers of model be acceptable and computing period be moderate in numerical computation,design of 15 W effective power Stirling engine is implemented and heat-pipe radiation cooler is performed based on the design parameters.Secondly,the physical model of heat pipe radiation cooler in the free-piston Stirling engine is established for the optimum design parameters.And oscillation flow of working fluid in engine cylinder is simulated by using the dynamic mesh technology of the FLUENT software.The characteristics of dynamic heat transfer and flow resistance of the radiation cooler are analyzed.It is found that the phase of the periodic total heat transfer in the evaporation section of the heat pipe is slightly lagging behind that of average velocity and slightly ahead of that of average temperature.When the heat transfer performance of evaporation section is the best under a different windward and tailwind distance of heat pipe in radiation cooler,the overall efficiency of the engine also is the best.By appropriately reducing the windward and tailwind distance of the heat pipe,heat transfer of per pair of heat pipe is balanced,which makes distribution of the heat transfer uniform.With the increasing of pair numbers of heat pipes,the heat transfer of evaporation section is lower at the close to the outlet of cooler.Finally,the cooling efficiency influenced by surface emissivity,radiant plane thickness and material of radiation cooler are investigated.The results show that the heat flux per unit area Q_out/A increases linearly with the increase of surface emissivity;but the quality per unit heat flux M/Q_out is inversely proportional to surface emissivity.The temperature distribution and cooling efficiency on the radiation surface are analyzed optimally based on the condition of radiation heat flux.When the total radiation heat flux is fixed,radiation cooler have optimum ratio of radiant surface length-width for different radiant plane thickness under the priority of M/Q_out.Compared with titanium alloy and pure aluminum as the radiant plane material,M/Q_out of magnesium alloy materials is half of that of the titanium alloy materials,but also less than that of pure aluminum material.Therefore,magnesium alloy is the most suitable material for the radiant plane.