相变换热单元动态过程的不可逆性分析

Irreversibility Analysis on a Phase Change Exchanger During Transient Processes

换热单元动态过程的热力学分析可为换热器的结构设计与运行参数调整提供依据。本文根据相变换热器的基本原理与质量、能量守恒方程,将相变换热器的工作过程用微分方程来表述,建立了典型相变换热单元的动态模型,得到了换热器动态过程的换热规律,进而研究了不同结构参数下换热单元动态过程的熵产变化规律。结果表明:与稳态过程相比,动态过程中产生了额外的熵产。提高金属热扩散率,降低金属壁面厚度,增加工作流体与金属壁面的换热阻力可以降低动态过程中的额外熵产。

Thermodynamic analysis on the transient processes of heat exchangers can be used for a reference and guidance for designs and operations.In this paper,a dynamic model of a phase change heat exchanger was developed based on the basic principle and mass,energy,and momentum conservation equations.The work processes of the phase change heat exchanger can be described by differential equations.The transient behaviors of phase change heat exchanger during the transient processes were obtained.Furthermore,the change law of entropy generation of the heat exchange unit under different design parameters during the transient processes was studied.Results show that the additional entropy generation is generated in the heat exchanger during the transient processes compared with stationary work conditions.And the additional entropy generation can be reduced by increasing the metal’s thermal diffusivity,reducing metal wall thickness,increasing heat transfer resistance between working fluid and metal wall.