Experimental Study of Two-phase Seperators for Vapor Compression Systems in Household Appliances

Two-phase separation offers an increase in refrigeration system efficiency with the added benefit of using a passive component. Although, a large amount research has been established in the refrigeration field for high mass flux systems, there is still ample opportunity to expand this application and knowledge in the refrigeration home appliances sector which require lower mass flux. The objective of this study was to evaluate the design of liquid-vapor gravity separators for low mass flux systems (1.5 – 3.5 lbm/ft^2hr). In the experimental method, the independent parameters varied were: Inlet Quality, Inlet Pressure, Inlet Mass Flow, Top Branch Flow Ratio and Separator Geometry. The dependent parameter was determined as, x_2, the Outlet Vapor Branch Quality. The two separator geometries which were designed, fabricated, and tested varied in aspect ratio, which is defined as the ratio of the height to the body diameter of the separator. The aspect ratio of the first geometry was 10, and it consisted of a tall separator height (4.125 in) with a narrow separator body diameter (0.423 in). The second geometry had an aspect ratio of 2, and it consisted of a short separator height (1.75 in) with a wide separator body diameter (0.742 in). The separator body was made of clear PVC tubing material in order visualize the flow conditions at different operating points. The results of the study showed that both geometries perform similarly. At low and high liquid Reynolds number, the flows characteristically show no significant vapor shearing and no vapor exiting through the liquid branch, as long as a liquid build-up was visually present in the separator; this indicates that vapor phase momentum is not high enough to penetrate through the high bulk viscosity of the liquid phase. Therefore, evaluating the vapor quality through the vapor branch was explicitly carried out by assuming the vapor quality through the liquid branch as 0. Thus, the results indicate that the primary factor to influence separation in this study was the balance maintained between the inlet quality and top branch flow ratio. Overall, separation was not highly sensitive to the rest of the factors in the tested ranges applicable to small scale refrigeration appliances. When inlet quality was greater than top branch flow ratio, no clear liquid-vapor interface was present and the mixture entering the separator was characteristic of misty flow, thus no liquid buildup was found within the separator.  However when the inlet quality was less than the top branch flow ratio, the liquid-vapor interface was visible and a liquid build-up was observed within the separator vessel