Quantification of flow distribution and heat capacity potential of a microchannel evaporator

Maldistribution of fluid among the ports reduces the heat capacity of a microchannel heat exchanger. It is essential to understand the maldistribution mechanism to optimize the design of the heat exchanger. Quantifi-cation of the distribution helps analyze the maldistribution issue. This study proposes a method to quantify the flow distribution and capacity potential in the microchannel heat exchangers by integrating a microchannel heat exchanger model and infrared thermography. The method calculates the liquid and vapor mass flow rate at the inlet of each microchannel tube by comparing the wall temperature of a heat exchanger from simulation and the infrared image. The method is validated with tests of a 49-tube horizontal microchannel evaporator with R134a. The exit region of the top tubes has an extremely high surface temperature, which forms a superheat region. More liquid flows to the tubes located at the center of the heat exchanger. The total mass flow rate is low when the tube has a long superheat region. The heat capacity of the tested evaporator has 9.6-21.3% improvement potential when uniformly distributed. When the refrigerant outlet superheats of the evaporator is lower, the improvement potential is higher. In the superheat region, the heat flux is much lower than the average value. This quantification method provides a tool for a more profound investigation of the maldistribution issue of a microchannel evaporator, and it can be expanded to heat exchangers with different structures.