Visualization of refrigerant two-phase flow before and through distributor and evaluation of its performance

This paper presents an evaluation of the performance of a refrigerant distributor with visualization of the two-phase flow. The distributor is a typical conical design w/o the orifice for about 4 kW R134a system. Three factors influencing two-phase flow distribution are varied: mass flow rate, distributor inlet quality, and orientation. We looked at the uniformity of mass flow rates, evaporator inlet qualities, and capacities of each circuit. The authors built a transparent distributor following the exact geometry of an original distributor to visualize two-phase flow regimes exiting the expansion device and entering the distributor. We related flow regimes with distributor performance. A high-speed camera is used to capture two-phase flow regimes. After acquiring results for a baseline situation, the authors applied two approaches in an attempt to improve flow distribution: The first is manual adjustment of the resistance of each circuit individually to achieve uniform mass flow rates, and the second is the homogenization of the flow regime before division by adding an orifice in the distributor before separation to four channels. The average deviations of capacity for each branch are 9% for the baseline case, 3.3% for manual adjusting, and only 1.6% for the homogenization approach, stressing the importance of that simple strategy.