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一、引言 目前对换热器的热工性能已有数十种评价指标,最常用的如温度效率E,换热器效率ε,水当量比R及传热单元数NTU等。但它们是把传热与阻力这二大因素分开来考虑,又不考虑能量的质方面的因素。Bejan着重考虑了过程的不可逆性,提出熵增单元数N_5,综合考虑了传热的数量、质量及阻力。然而N_5的概念还不够直观明确,而且不易找到优化值。
I. INTRODUCTION At present, there are dozens of evaluation indexes for the thermal performance of heat exchangers. The most commonly used ones are temperature efficiency E, heat exchanger efficiency ε, water equivalent ratio R and number of heat transfer units NTU. However, they consider the two major factors of heat transfer and resistance separately, without considering the qualitative aspects of energy. Bejan considered the irreversibility of the process and proposed the entropy increasing unit number N_5, considering the quantity, mass and resistance of heat transfer. However, the concept of N_5 is not yet intuitive and clear, and not easy to find the optimal value.