Simulation of Concentration Shift for Multi-component Zeotropic Fluids

摘要

The use of a multi-component zeotropic fluid can result in concentration shift, which can be observed from the difference between the measured circulation concentration and the system bulk concentration. Recently the number of applications using zeotropic working fluids have been increased sharply, particularly with refrigeration and air conditioning systems zeotropes have been considered as important working fluids to replace CFCs and HCFCs to solve the ODP and GWP issues. Since it is closely related to system performance, modeling and predicting of concentration shift will have a great importance to the related industry, as well as to scientific research. This paper will deal with modeling of concentration shift of zeotropic refrigerant fluids circulating in constrained channels for an air conditioning system. A computer simulation program was created, which included detailed models for the system. Emphasizes have been concentrated on simulating the concentration shift phenomena according to its physical nature. Various void fraction models were tested for the vapour-liquid two phase flow regime. Component fractionation extend was evaluated for both evaporation and condensation. It was found that slip flow companied by the component fractionation is the main reason contributed to the concentration shift for zeotropic fluids circulating in constrained channels. The simulation results were compared with experimental results and the validity was confirmed. The simulation models can be useful for calculating circulating concentration associated with vapour liquid two phase flow of zeotropic fluids inside pipes and annular channels.