Two-phase, pressure drop, low mass flux, R600A, R134A, refrigerator evaporator
This study was conducted to evaluate pressure drop at extremely low velocity refrigerant flow through smooth circular evaporators in household refrigeration systems. Experimental data was taken at mass fluxes under 70 kg/m2s for two refrigerants, R134A and R600A, internal diameters of aluminum evaporators ranging from 0.186 inches (4.72 mm) to 0.317 inches (8.05 mm), U-bend internal radii ranging from 0.342 inches (8.69 mm) to 0.750 inches (19.05 mm) in horizontal and vertical orientations of evaporators. The geometry of the samples closely resembled a commonly used serpentine shape with multiple U-bends experiencing both, up- and down-flow of the refrigerant. Horizontal orientation test results with double the number of the U-bends suggest that horizontal U-bends (at least in tested geometries) at low mass fluxes less than 70 kg/m2s do not play a significant role in a total frictional pressure drop in horizontal evaporators. A Curvature Ratio study showed no two-phase frictional pressure drop dependence on the curvature ratio of the U-bends. Main geometrical properties affecting two-phase frictional pressure drop in evaporators at low flows are internal diameter of the tube and a total length of evaporator tube. And main physical properties of the refrigerant flow affecting two-phase frictional pressure drop in evaporators at low flows are the type of refrigerant and its mass flow rate. Experimental databank of nearly 100 points collected within this study can be used to extend the application of the currently available two-phase pressure drop correlations or to develop a new one specifically for low mass fluxes.