Convective Boiling of R-22 in a Flat Extruded Aluminum Multi-Port Tube

Convective boiling heat transfer coefficients of R-22 were obtained in a flat extruded aluminum tube with D_h = 1.41 mm. The test range covered mass flux from 200 to 600 kg/m² s, heat flux from 5 to 15 kW/m² and saturation temperature from 5°C to 15°C. The heat transfer coefficient curve shows a decreasing trend after a certain quality (critical quality). The critical quality decreases as the heat flux increases, and as the mass flux decreases. The early dryout at a high heat flux results in a unique ‘cross-over’ of the heat transfer coefficient curves. The heat transfer coefficient increases as the mass flux increases. At a low quality region, however, the effect of mass flux is not prominent. The heat transfer coefficient increases as the saturation temperature increases. The effect of saturation temperature, however, diminishes as the heat flux decreases. Both the Shah and the Kandlikar correlations underpredict the low mass flux and overpredict the high mass flux data.