Reports on an investigation of the flow-boiling heat transfer from the inside of a smooth tube and a novel surface designed to improve boiling heat transfer. This surface consists of a perforated brass foil inserted into the smooth tube. Two fluids were investigated - pure R22 and a nonazeotropic mixture of 75% R143a and 25% R124 (by mass). The experiment was conducted in an apparatus consisting of a variable-speed compressor having a range of 500 to 3,000 rpm and a counterflow concentric-tube heat exchanger. The refrigerant circulates inside the central tube and water circulates in the annulus. For R22, the perforated foil insert increased the heat transfer coefficient of the smooth tube, particularly at lower qualities and heat fluxes, indicating augmentation of nucleate boiling. For this particular nonazeotropic refrigerant mixture, however, the perforated foil insert did not increase the heat transfer coefficient, which is most likely due to nucleate suppression in nonazeotropic refrigerant mixtures at the qualities observed in the tests.

KEYWORDS: heat flow, fluid flow, boiling, refrigerants, mixtures, non azeotropic, R143a, R124, performance, R22, experiment, variable speed motors, compressors, counterflow heat exchangers, tube in tube heat exchangers, heat exchangers, heat transfer coefficient