恒壁温时污垢对管内对流换热过程热力学性能影响的分析

基于热力学第一、二定律 ,在恒壁温工况下分析了污垢对管内对流换热过程热力学性能的影响 ;提出了反映污垢对管内对流换热过程热力学性能影响的指标———单位传热量的熵增率 ;讨论了管内流体Reynolds数(无污垢时 )和量纲为 1的入口换热温差等参数对单位传热量熵增率的影响 .研究结果表明 ,该指标不仅能反映污垢对管内传热过程的影响 ,而且能反映污垢对管内流动过程的影响 ,而由污垢层导热所引起的熵产在管内传热过程总的熵产中占有重要的地位

ANALYSIS OF EFFECT OF FOULING ON THERMODYNAMIC PERFORMANCE OF CONVECTIVE HEAT TRANSFER PROCESS THROUGH DUCT WITH CONSTANT WALL TEMPERATURE

Fouling is considered as one of the important factors affecting the performance of heat transfer and flow process in heat transfer equipment.The existing studies neglect the simultaneous effect of fouling on heat transfer and flow performance and have not demonstrated the effect of fouling on the variation of irreversibility loss.This paper is based on the first and second laws of thermodynamics and the effect of fouling on the thermodynamic performance of convective heat transfer process through a duct with constant wall temperature is investigated analytically.A criterion evaluating the effect of fouling on the thermodynamic performance of convective heat transfer process--the entropy generation increase rate per unit heat flux is put forward.The effect of Reynolds number (not considering fouling) and dimensionless inlet temperature difference on the entropy generation increase rate per unit heat flux is discussed.The results show that the entropy generation increase rate per unit heat flux increases with the increase of Reynolds number and dimensionless inlet temperature difference, the entropy generation per unit heat flux caused by heat transfer decreases and that caused by viscous flow increases when fouling appears and mass flow rate is constant.The criterion put forward in this paper can not only illustrate the effect of fouling on heat transfer process, but also on flow process.In addition, the entropy generation caused by conduction of fouling plays an important role in total entropy generation of heat transfer process through a duct.The research reported in this paper provides a valid way to analyze quantitatively the effect of fouling on heat transfer and flow process performance.