基于He-N_2混合工质的闭式Brayton循环系统及设备的优化设计

Optimal Design of a Closed Brayton Cycle System Based on He-N_2 Working Fluid

对以He-N_2混合气体为工质的闭式Brayton循环系统进行了优化分析,获得循环最高效率下系统各组成设备的性能参数。以此优化结果为目标,设计了轮机和换热器的初步方案。以纯氦气工质时轮机和换热器的成本为基准,利用设备成本与几何参数之间的近似关系,获得不同氦气摩尔分数下轮机和换热器的相对成本。通过Brayton循环中轮机与换热器的成本权重分配,得到不同氦气摩尔分数下Brayton循环的相对总成本。结果表明:当氦气摩尔分数为50%～60%时,存在一个相对总成本的最小值,与纯氦气时相比,其相对总成本降低了12%左右,这对于闭式Brayton循环系统工质的选择具有一定的指导意义。

Based on optimization and analysis of a closed Brayton cycle system with He-N2 as the working fluid, performance parameters of various components in the system were obtained under the condition when highest system efficiency is reached. On above basis, a preliminary design was carred out for the components including turbomachineries and heat exchangers. Taking the costs of turbomachineries and heat exchangers as the reference data for the cycle with pure helium working medium, relative costs of these components were calculated at different mole fractions of helium by using approximate relations between the equipment cost and their geometric parameters. According to the weight ratio of the costs of turbomachineries and heat exchangers, the relative total costs of the Brayton cycle with different molar ratios of helium were then obtained. Results show that when the mole fraction of helium gas lies in 50%-60%, there exists a minimum value of relative total cost, 12% lower than the pure helium case, which provides a better choice of working medium for closed Brayton cycle systems.