Effect of conical distributors on evaporator and system performance

摘要

This thesis presents the results of the study to experimentally examine effects of the distribution of refrigerant and air in the evaporator using a conical distributor on system COP and capacity. Several conditions at the distributor inlet are varied including quality, mass flux, and orientation in gravity and the resulting superheat profiles of the evaporator circuit outlets are recorded. To examine possible effect of cone misalignment feeder tubes are switched in several steps and the data shows that there is imbalance in both the evaporator and distributor. It is observed that the imbalanced refrigerant distribution does not change over various operating conditions and is the result of complex interactions between the distributor and the evaporator. Valves are installed on the feeder lines to create an ideal refrigerant distribution, indicated by uniform superheats at the outlets of the evaporator circuits, by adding a pressure drop in order to quantify the reduction in COP and capacity due to imperfect distribution. Using the valves to make the outlet superheat profile uniform improves the system and recovers most of the lost performance.Additionally, the air distribution is made poor by blocking parts of the evaporator face. The impact of air imbalances on system performance is smaller than those of refrigerant. COP declines faster than capacity. Blocking entire refrigerant circuits rapidly deteriorates performance, compared to the same blockage area spread over all circuits. Moreover, the performance of the evaporator in terms of UA, LMTD, epsilon, and NTU, declines faster than overall system performance in terms of COP and capacity.