Research On Brayton Cycle Properties Of Helium-Xenon Mixed Working Fluid Based On Space Nuclear Power System

With the deepening of space exploration,higher requirements have been put forward on the power density and service life of spacecraft.Traditional energy is no longer suitable for high-power power system,and nuclear reactor power system has become a research hotspot in the world.In the high-power space nuclear power supply system,the Brayton cycle energy conversion system is an ideal thermoelectric conversion technology which can meet the needs of megawatt nuclear power system.In this paper,the space Brayton cycle with relatively mature technology and obvious advantages is taken as the research object.The core structure of the reactor is designed reasonably,and the thermodynamic model of the Brayton cycle is established with He-Xe gas mixture as the working medium.The key parameters were selected for the thermodynamic analysis of the cycle characteristics,and the genetic algorithm was used to optimize the cycle characteristics.Several specific components of the working medium were selected for specific performance analysis,and the feasibility of different components of the working medium for practical application was discussed from many aspects.In this paper,the reactor scheme of liquid metal cooled fast neutron reactor is chosen.The fuel element is of rod structure,the fuel is uranium dioxide pellets,a nd the cladding material is zirconium-4 alloy.There is a Be O reflection layer at both ends of the pellets,and a compression spring is installed at the upper end.The hexagonal structure inside the reactor core contains 360 fuel rods,cooled by liquid metal sodium and controlled by control drums.The core has an equivalent diameter of 43.8cm and a height of 48.18 cm.By comparing the physical properties of different inert gases,the binary mixture of helium and xenon was selected as the circulating working medium.The thermodynamic properties and transport properties of the binary mixture of helium and xenon were analyzed with the change of molar mass under different pressures and temperatures.On this basis,the thermodynamic model of the space Brayton cycle is established,and the function models of efficiency and specific work are derived from the mathematical models of the main components.Among the several parameter variables affecting cycle efficiency and specific work,the adiabatic coefficient,recuperator effectiveness and pressure loss coefficient will change with the change of working medium composition,so the above three parameters are selected as the key parameters of the cycle,while the rest parameters are given as the inherent parameters through known conditions.The influence of key parameters on cycle efficiency and specific work was analyzed with compressor pressure ratio as variable.The adiabatic coefficient has little effect on efficiency and specific work,while the recuperator effectiveness has a positive effect on efficiency and specific work,while the pressure loss coefficient will significantly reduce efficiency and specific work.The double-objective optimization of the cycle was carried out by using genetic algorithm,and the Pareto optimal solution set was obtained.The appropriate operating parameters could be selected according to different task requirements.Finally,the performance of pure helium gas,15.5g/mol He-Xe binary mixture and 40.9g/mol He-Xe binary mixture is compared in many ways,and it is shown that 40.9g/mol He-Xe binary mixture is the most suitable working fluid for the space Brayton cycle.