BOILING HEAT TRANSFER AND PRESSURE DROP OF A REFRIGERANT FLOWING VERTICALLY DOWNWARD IN A SMALL RECTANGULAR TUBE

摘要

Experiments were performed on flow boiling heat transfer and two-phase pressure drop of a refrigerant R-410A flowing downward in a vertical small copper rectangular tube with 1.04 mm inside hydraulic equivalent diameter for the development of a high-performance heat exchanger using small tubes or multi-port extruded tubes for air conditioning systems. Local heat transfer coefficients were measured in a range of mass velocities from 30 to 200 kg m~(-2) s~(-1), heat fluxes from 1 to 16 kW m~(-2) and qualities from 0.05 to 1 at the evaporation temperature of 10℃. Pressure drops were also measured at mass velocities from 30 to 200 kg m~(-2) s~(-1) and qualities from 0.1 to 0.9 at the saturation temperature of 10℃ under the adiabatic condition. The characteristics of frictional pressure drop, heat transfer coefficient and dry-out quality were clarified by comparing the measurements with the data for the circular tube of 1.00 mm inside diameter previously obtained.