不可逆半导体固态热离子制冷器性能分析和优化

建立了考虑外部有限速率传热过程和热源间热漏的不可逆半导体固态热离子制冷器模型,基于非平衡热力学和有限时间热力学理论导出了热离子制冷器的制冷率和制冷系数的表达式;对比分析了不可逆热离子制冷器与可逆热离子制冷器的发射电流密度特性、电极温度特性以及制冷系数特性;研究了不可逆系统的制冷率与制冷系数最优性能,得到了制冷率和制冷系数的最优运行区间;通过数值计算,详细讨论了外部传热以及内部导热、热源间热漏损失、热源温度、外加电压、半导体材料势垒等设计参数对热离子装置性能的影响。在总传热面积一定的条件下,进一步优化了高、低温侧换热器的面积分配以获得最佳的制冷率和制冷系数特性。结果表明,由于存在内部和外部的不可逆性,热离子装置的发射电流密度及制冷系数都会明显降低;不可逆半导体固态热离子制冷器的制冷率与制冷系数特性呈扭叶型;合理地选外加电压、势垒等参数,可以使制冷器设计于最大制冷率或最大制冷系数的状态。

Performance analysis and optimization for irreversible semiconductor solid-state thermionic refrigerator

A model of an irreversible semiconductor solid-state thermionic refrigerator considering external finite rate heat transfer and the heat leakage between two heat reservoirs is established in this paper. The general expressions for cooling load and coefficient of performance (COP) of the thermionic refrigerator are derived based on the theory of finite time thermodynamics and non-equilibrium thermodynamics. Performance characteristics of emitted current density, electrode temperature and COP for the irreversible thermionic refrigerator are compared with those for an idealized endoreversible thermionic refrigerator. The cooling load and COP performance are optimized and the optimum regions of cooling load and COP are determined. The influences of external heat transfer and design parameters such as internal heat conduction, heat leakage between reservoirs, heat reservoir temperature, applied voltage and potential barrier on the performance of the thermionic refrigerator are analyzed by detailed numerical calculations. Moreover, for the fixed total heat transfer surface area of two heat exchangers, the ratios of the heat transfer surface area of the hot side heat exchanger to the total heat transfer surface area of the heat exchangers are optimized for maximizing the cooling load and COP of the refrigerator, respectively. It is found that the emitted current density and COP of the device are all reduced due to the internal and external irreversibilities. The characteristic curves of cooling load versus COP are loop-shaped ones. By properly choosing the values of the design parameters such as applied voltage and potential barrier, the irreversible thermionic refrigerator can be designed to operate at maximum cooling load or maximum COP point.