CONDENSATION OF REFRIGERANTS FLOWING INSIDE SMOOTH AND CORRUGATED TUBES

摘要

Because heat exchanger thermal performance has a direct influence on the overall cycle performance of vapor-compression refrigeration machinery, enhanced heat transfer surfaces are of interest to improve the efficiency of heat pumps and air conditioners. We investigated R-22 and a nonazeotropic refrigerant mixture (NARM) of 75% R-143a and 25% R-124 (by mass) to study their thermal performance in a condenser made of conventional smooth tubes and another condenser made of corrugated, or spirally indented, tubes. We investigated the condensing heat transfer and pressure drop characteristics in an experimental test loop model of a domestic heat pump system employing a variable speed compressor. The refrigerant circulates inside the central tube and the water circulates in the annulus. At refrigerant mass fluxes of approximately 275-300 kg/m{sup}2s, the measured irreversible pressure drop of the corrugated surface was 23% higher than that of the smooth surface for the R-22. At refrigerant mass fluxes of 350-370 kg/m{sup}2s, the irreversible pressure drop of the corrugated surface was 36% higher than that of the smooth surface for the NARM. The average heat transfer coefficient for the corrugated surface for R-22 was roughly 40% higher than that for the smooth tube surface at refrigerant mass fluxes of 275-295 kg/m{sup}2s. The average heat transfer coefficient for the corrugated surface for the NARM was typically 70% higher than that for the smooth tube surface at refrigerant mass fluxes of 340-385 kg/m{sup}2s.