3800 (RP-668) -- Spray Evaporation Heat Transfer of R-134a on Plain Tubes PDF

A test facility for performing spray evaporation tests was constructed and results are reported for refrigerant R134a with horizontal, plain-surface, copper alloy tubes. In addition, the effects of nozzle type, liquid feed rate, and tube diameter on heat transfer coefficients are demonstrated. Pool boiling experiments were also performed and a comparison was made with spray evaporation results under similar conditions. The test tubes used were 12.7mm (0.5 in.) and 19.1mm (0.75 in.) diameter copper tubes that were electrically heated by using inserted cartridge heaters. Average heat transfer coefficients were calculated by measuring the average surface temperature with wall-mounted thermocouples and the vapour space temperature with thermocouple probes. The 12.7mm (0.5 in.) diameter tubes performed better than the 191.1mm (0.75 in.) tubes, and the heat transfer performance was significantly affected by the liquid feed rate once dry-out effects became dominant. For the range of liquid feed rates evaluated, the heat transfer performance for spray evaporation was greater than the pool boiling performance at low heat fluxes and less at the higher heat fluxes.

KEYWORDS: spray nozzles, evaporation, heat flow, refrigerants, R134a, horizontal, tubes, copper, testing, heat transfer coefficient, experiment, comparing, calculating, measuring, surface temperature, wall mounted, thermocouples, probes, performance, fluid flow, flow rate