In automotive air conditioning applications

parallel flow microchannel evaporators have become increasingly attractive owing to their compactness and high thermal performance per unit weight. However

a misdistribution of the refrigerant among the parallel microchannel tubes deteriorates the heat transfer performance of a microchannel evaporator and limites extensive promotion. Therefore

it is important to study the heat transfer characteristics of microchannel evaporator and how to improve the uniformity of refrigerant distribution. In this paper

an automotive air-conditioning test bench with R134a as refrigerant was set up. First

the heat transfer and exergy loss of the double-row and four-pass microchannel evaporator were analyzed. Then the surface of the evaporator is photographed by infrared camera Distribution image. As the evaporator inlet temperature increased from 21 ℃ to 42 ℃

the cooling capacity increased from 2.37 kW to 4.19 kW

while the evaporator exergy loss increased first and then decreased. And the exergy loss of the evaporator first increases and reaches a peak of 0.21 kW as the inlet air reaches 27 ℃

then decreases to a minimum value of 0.16 kW as the inlet air reaches 42 ℃. The σ value which represents the surface temperature distribution uniformity of the evaporator increases from 2.5 to 19.5 as the inlet air increases from 21 ℃ to 27 ℃. When the inlet air is 42 ℃

the value of σ decreases to 1.8. The surface temperature of the evaporator is the most uneven when the inlet air temperature is 27 ℃

and is most uniform when the inlet air temperature is 42 ℃. Therefore

the performance of the evaporator can be improved effectively at a relatively high air inlet temperature

and the rate of exergy loss and the value of σ decrease by 26.1% and 91.0%

respectively. Moreover

properly increase the compressor speed can effectively improve the surface temperature distribution uniformity of the evaporator.