组分迁移对R407C相变换热影响的理论分析

Theoretical Investigation on the Influence of Composition Shift on the Heat Exchange during the Phase Change Using R407C

为了研究组分迁移对非共沸工质在换热器中相变换热特性的影响,探明制冷剂和换热流体间的温差在换热器中的变化规律,进行了相应的理论分析。基于窄点理论和空泡模型,将换热器按等焓降划分为若干控制体,建立相应的数学模型,然后在给定工况下,计算出R407C在换热器内冷凝和蒸发的组分迁移情况,进而得到考虑组分迁移的非共沸工质温焓非线性关系,发现制冷剂和换热流体间的温差在换热器中的变化规律,再与未考虑组分迁移时作对比。结果发现,考虑组分迁移对窄点或最大传热温差及其在换热器中出现的位置、可用能损失的影响很大,在合理设计换热器时应给予考虑。

To investigate the influence of composition shift on the heat exchange characteristics of zeotropic refrigerants during the phase change in the heat exchanger,and understand the variance of temperature difference between refrigerant and heat transfer fluid,corresponding theoretical analysis is carried out.Based on the temperature pinch points and void fraction model,the heat exchanger is divided into some control volumes and a mathematical model of refrigerants condensation and evaporation is built up.Under a given work condition,the composition shift in the heat exchanger using R407C is calculated and furthermore,the nonlinear relationship between temperature and enthalpy with considering the composition shift is obtained.The variance of temperature difference between refrigerant and heat transfer fluid in the heat exchanger is foundand compared with that without considering the composition shift.The results show that the occurrence position of pinch points and the irreversible gain of entropy are significantly influenced by the composition shift,and it should be taken into consideration in the design of heat exchanger.