Abstract:
The objective of this study is to understand physical and numerical modelling aspects of two phase flow occurring in heat exchangers used in domestic refrigerators, and construct a computer model to simulate one dimensional two phase flow using the homogeneous flow model.This study is mainly composed in two parts. First part focuses on the two phase flow characteristics of refrigerants in tube: Flow regimes, pressure drop, void fraction and heat transfer correlations are investigated. Empirical correlations are evaluated and compared for a typical evaporator condition. Second part, introduces governing equations for 1-D two phase flow and describes the development of a finite difference type numerical scheme for a simulation of the transient behaviour of two phase flow in heat exchangers. A second order accurate numerical method, namely MacCormack, is applied for solving the equations. Simulation results are compared with the literature and similar flow characteristics are found. Although the presented model is second order accurate and easy to apply, it is too slow for use in an overall refrigeration system simulation. Also, it requires small CFL number and fine grid for some applications which means more execution time.Homogeneous flow model was the simplest model. An improved model, at least including slip effects should be preferred. For a complete system simulation, a simplified system of equation should be taken with an advanced implicit method.
