CONDENSATION OF NON-AZEOTROPIC REFRIGERANT MIXTURES INSIDE A VERTICAL TUBE

A theoretical model has been formulated and numerical calculations performed for the condensation of non-azeotiopic mixtures of refrigerants, which have been proposed as promising alternatives to the pure-substance ozone-depleting CFC's. While the preferred geometry for condensers in operating heat pumps is based on tubes, most of the theoretical models on mixtures condensation to-date have dealt with vertical plates. The purpose of this work has been to develop a numerical tool to enable prediction of heat and mass transfer during the condensation process inside vertical tubes. A physical model has been formulated, based on the governing equations for mass, momentum, energy and species conservation. Pertinent boundary conditions specify thermodynamic equilibrium between vapor and liquid at the interface and continuity in heat and mass fluxes. A numerical method was developed for solving the equations based on a finite volume technique. The computer program that was written can be used to solve the condensation problem of any binary refrigerant mixture inside a vertical tube. In this work, two mixtures were taken as examples, and the influence of mixture composition, vapor flowrate, temperature difference between the vapor and wall and varying wall temperature in the flow direction were studied. The results show that heat transfer is higher when the temperature glide of the mixture follows closely the change in wall temperature. Other conclusions are that the higher the vapor flow into the tube, the lower the concentration of the volatile component at the vapor-liquid interface and the larger the heat transfer.