%AKoyama, Shigeru
%AYu, Jian
%AIshibashi, Akira
%D1999
%IAmerican Society of Mechanical Engineers, New York, NY (US); Kyushu Univ., Kasuga (JP)
%J
%K32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION, MATERIAL SUBSTITUTION, REFRIGERANTS, BINARY MIXTURES, VAPOR CONDENSATION, TUBES, MATHEMATICAL MODELS, HEAT TRANSFER, MASS TRANSFER
%PMedium: X; Size: 8 pages, Paper AJTE99.6358
%THeat and mass transfer prediction of binary refrigerant mixtures condensing in a horizontal microfin tube
%XIn the face of the phase-out of HCFC22 for its effect on globe environment, the alternative refrigerant has been paid attention in the refrigeration and heat pump industry. In the present stage, it is found that any pure refrigerant is not a good substitute of HCFC22 for the system in use. The authors have to use binary or ternary refrigerant mixtures as the substitute to meet industrial requirement. But until now, although the heat transfer characteristics of the refrigerant mixtures can be measured in experiments and predicted in some degree, the mass transfer characteristics in condensation process, which is a main part in most systems, can not be clarified by both experimental and theoretical methods. In the present study a non-equilibrium model for condensation of binary refrigerant mixtures inside a horizontal microfin tube is proposed. In this model it is assumed that the phase equilibrium is only established at the vapor-liquid interface, while the bulk vapor and the bulk liquid are in non-equilibrium in the same cross section. The mass transfer characteristic in vapor core is obtained from the analogy between mass and momentum transfer. In the liquid layer, the mass fraction distribution is neglected, but the mass transfer coefficient is treated as infinite that can keep a finite value for the mass transfer rate in liquid phase. From the calculation results compared with the experimental ones for the condensation of HFC134a/HCFC123 and HCFC22/CFC114 mixtures, it is found that the calculated heat flux distribution along the tube axis is in good agreement with that of experiment, and the calculated values of condensing length agree well with the experimental ones. Using the present model, the local mass faction distribution, the diffusion mass transfer rate and the mass transfer characteristics in both vapor and liquid phase are demonstrated. From these results, the effect of mass transfer resistance on condensation heat transfer characteristics for binary refrigerant mixtures has been clarified.
%0Conference
United States TRN: IM200022%%91 DELTA English