| Severe aerodynamic heat will be generated during the flight of hypersonic vehicle,and protection against aerodynamic heat is one of the difficulties of hypersonic technology.At present,the aerodynamic heat transfer in large area of hypersonic vehicle is mainly blocked and delayed by thermal insulation structure.With the development of hypersonic vehicle,the treatment of aerodynamic heat will not be limited to the traditional thermal protection methods.The use of thermoelectric conversion technology to convert aerodynamic heat into electrical energy and provide thermal protection for aircraft will be a new research direction.In this paper,the thermodynamic model of wall thermoelectric conversion system based on Rankine cycle is established to simulate the thermodynamic performance of wall thermoelectric conversion system under large area aerodynamic heat of hypersonic vehicle.The CFD numerical method is used to simulate the flow process in the wall heat exchanger and the expansion process in the scroll expander.By improving the other parts of the system,the rated and critical operating conditions of the system are determined,and the output performance of the system is evaluated.The main research contents are as follows:(1)By establishing a thermodynamic model of the wall thermoelectric conversion system based on Rankine cycle,the influence of evaporation pressure on the system performance with different working fluids is analyzed,and the influence of outer wall temperature on system performance and rake loss is studied.The evaporation pressure is positively correlated with the net output of the system and the thermal efficiency of Rankine cycle.The total efficiency and loss of the system is negatively correlated with the temperature of the outer wall of the hypersonic vehicle.At the same time,considering the performance of the system and the thermal protection requirements inside the hypersonic vehicle,the cycle conditions of the system are determined.(2)The vaporization effect and thermal protection effect of working fluid in wall heat exchanger are taken as performance evaluation indexes.The effects of different channel layers and different flow modes of working fluid on the performance of wall heat exchangers are analyzed,and the difference of heat transfer efficiency in wall heat exchanger is analyzed when water and cyclopentane are used as working fluids respectively.In this paper,cyclopentane is selected as working fluid,and the wall heat exchanger with three-layer channels is determined to be the optimal structure when working fluid flows forward.The work output of the scroll expander at different rotational speeds is analyzed by solving the tangential gas force.With the increase of rotational speed,the work output and the mass flow of system are increased almost linearly.The volume of the system increases with the increase of mass flow of the system.Therefore,the rated speed of the scroll expander should not be too high.(3)On the basis of the previous calculation,other parts of the system are determined,the system is perfected and the rated operating conditions of the system are determined.Under the rated working conditions,the specific power of the system is 23.49W/kg,and the total efficiency is 2.729%.Compared with the thermoelectric conversion device with thermoelectric unit embedded in heat insulation structure,the system designed in this paper improves the specific power,and can guarantee the rated power generation and provide better thermal protection effect for the hypersonic vehicle during the operation of the system.In addition,the system can be operated under the critical condition when the heat flow on the outer wall of hypersonic vehicle is 90 kW/m~2.The total efficiency of the system is 2.665%. |
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