Evaluation and visualization of refrigerant two-phase flow in distributor

This study aims at understanding flow distribution exiting thermostatic expansion valve and through distributor. It is well known that when two-phase flow goes through separation devices such as distributors and headers, mal-distribution is unavoidable due to different properties of liquid and vapor. However, it is possible to reduce mal-distribution by better design or creating proper working conditions. In this study, several parameters that may influence the flow distribution such as mass flow rate, distributor inlet quality, and orientation are studied. Refrigerant mal-distribution is quantified by comparing mass flow rate, quality, and cooling capacity in each circuit. To make the experiment results more applicable to real system, several aspects in this facility which are not exactly the same with real air conditioning system are analyzed, including the extra pressure drop due to mass flow meter and the different design of evaporator. What’s more, two-phase flow exiting thermostatic expansion valve and through distributor is visualized by high-speed camera to get a deeper understanding about what happened in this region. It was found that better distribution can be achieved at higher mass flow rate and lower distributor inlet quality, because flow velocity increases as mass flow rate gets higher, which contributes to form more homogeneous flow. And decrease in quality makes the two-phase flow closer to single phase. Orientation was found to have no influence on distribution, since the distributor is installed quite close to the exit of thermostatic expansion valve where the phase separation does not happen. The pressure drop due to mass flow meter was proved helpful to achieve better distribution, which means the performance of distributor was a little overestimated by experiments in this study. According to the visualization, flow regime at the inlet of distributor is somewhere between annular flow and homogeneous flow with variation of mass flow rate