换热器传热过程的熵产分析

Performance Analysis of Heat Transfer in the Heat Exchanger by Entropy Generation

本文从热力学第一及第二定律出发,分析换热器传热过程的熵产率,从而建立传热过程的熵产率关系式,并以此对换热器的传热及流动性能进行定量分析,进而寻找使熵产率为最小时的换热器的有关参数,为换热器的优化设计及校核提供最佳数据.

An analytic method by entropy generation has been developed for evaluating the performance of a heat exchanger. On the basis of the first and second ther-modynamic laws, the convective processes of cool and hot fluids in the heat exchanger have been analyzed and the equations for the entropy generation rate derived. The entropy generation equations reflecting the comprehensive performance of the fluid flow and the heat transfer can serve as objective functions in determining the optimal parameters for the thermal design of a heat exchanger. The physical meaning of the nondimensiocal entropy generation numbers presented in the equations is clear and the form is simple for engineering application. Based on the entropy analysis of two kinds of exchanger, the following conclusions can be drawn: (a) an exchanger will perform better only when the hot and cool fluids work in regions of the optimal Reynolds numbers; (b) with the same flow state and a given range of the Reynolds number, an exchanger with a smaller size of convective heat transfer will have relatively smaller entropy generation and is superior to that with a bigger size in performance.