Measurements of heat-transfer coefficients of nonazeotropic refrigerant mixtures condensing inside horizontal tubes

Some preliminary observations from previous system tests on a refrigeration facility using a mixture of R-12/R-114 indicated a reduction in condensing heat-transfer coefficients with the mixture in comparison to either constituent operating alone. Further exploration of this phenomenon involved a glass tube condenser constructed previously for observation of the flow regimes during the condensation process. The study, which is documented by this report, was pursed still further with a copper-tube condenser constructed only for the purpose of measuring heat-transfer coefficients and correlating them with the flow regimes previous observed. In tests that duplicated the flow regimes of the earlier work, the previous results were confirmed in that a low heat-transfer coefficient prevails in the early stage of the condenser, for both a single refrigerant and a mixture. It is in the midrange of the condenser that the mixture experiences its greatest reduction in coefficient in comparison to either constituent. Stratified flow prevails in the midrange of the condenser, so that liquid/vapor slip, if it does occur, would be most prominent in this section. Attempts to measure liquid and vapor concentrations to establish the existence of slip were not successful. From an application standpoint, heat-transfer enhancers such as turbulence promoters shouldmore » be considered for this midsection of the condenser. 27 refs., 79 figs.« less