MODELING OF A HELICALLY COILED HFC134a EVAPORATOR

Abstract

A computer simulation model has been developed for the performance analysis and design optimization of a helical coil and cylindrical shell type evaporator working with HFC-134a by using the appropriate empirical correlations of heat transfer coefficient and pressure drop in the helical tubes as available in the literature. This model is based on a numerical method of cell discretization of shell side and tube side of the evaporator. The local values of variables are calculated and the mass, momentum and energy balance is applied to each small cell. The whole sequential and iterative procedure to satisfy the boundary conditions has been transformed in the computer codes. The model has been validated by comparing with the actual results of an experimental study which is also a part of this work. A detailed analysis of the effects of varying input parameters of both fluids on the performance of evaporator was carried out with the help of this model. It also gives the optimum values of mass velocity of refrigerant and the helical tube diameter against the available flow conditions of refrigerant and of external fluid and the required degree of vapor superheat at the exit of evaporator. Thus it provides an easy solution in both the cases of either the performance optimization of an existing evaporator or the design optimization of a new evaporator. The inherent errors in the outcome of correlations for heat transfer, pressure drop and refrigerant properties are the limitations of this model.