Effect of mean void fraction correlations on a shell-and-tube evaporator dynamic model performance

Abstract

In this paper, the influence of different mean void fraction correlations on a shell-and-tube evaporator dynamic model performance has been evaluated. The model proposed is based on the moving boundary approach and includes the expansion valve modelling. Several transient tests, using R134a as working fluid, have been carried out varying refrigerant mass flow, inlet enthalpy and secondary fluid flow. Then, the model performance, using different mean void fractions, is analysed from the system model outputs (evaporating pressure, refrigerant outlet temperature and condensing water outlet temperature). The slip ratio expressions selected are: homogenous, momentum flux model, Zivi's, Chisholm's and Smith's correlations. The results of the comparison between experimental and model predictions depend on the transient characteristics and there is not a single slip ratio correlation that provides the best performance in all the cases analysed.