OR-94-07-3 -- An Analytical Model of Condensation Heat Transfer of Nonazeotropic Refrigerant Mixtures in a Horizontal Tube PDF

Thermodynamic characteristics of the condensation of nonazeotropic refrigerant mixtures (NARMs) in a horizontal tube are discussed analytically. The composition of the axial vapour flow is found to approach that of the more volatile component in the downstream region of the condenser. A one-dimensional model of the condensation of NARMs in a horizontal tube is then formulated in which an annular flow pattern is assumed. Energy and mass balances as well as heat and mass transfer equations are presented for the axial vapour flow and the condensate liquid flow, respectively. The local diffusion flux in the liquid condensate is found to have little effect on the local condensed mass flux. On the contrary, the ratio of the local counter-diffusion flux of the more volatile component on the vapour side near the vapour-liquid interface to the local condensed mass flux is found to equal the mass fraction difference of the more volatile component between the interfacial vapour and the interfacial liquid. Simulation results of heat transfer and pressure drop are compared with experimental data, and good agreement is obtained. The comparisons also validate the fact that the degree of subcooling of the completely condensed liquid will be greater than the temperature difference between the bubble point of the mixture and the boiling point of the pure, more volatile component.

KEYWORDS: condensation, heat flow, non azeotropic, refrigerants, mixtures, thermodynamics, properties, horizontal, tubes, calculating, fluid flow, pressure drop, comparing, subcooling, temperature difference, performance