SOME EFFECTS OF AIR-FLOW MALDISTRIBUTION ON PERFORMANCE OF A COMPACT EVAPORATOR WITH R134A

An experimental facility has been constructed to enable the effects of air flow non-uniformity on the transfer performance of refrigerant ev aporators to be investigated. This is based on an open-circuit wind tu nnel, which is equipped with a single component traversing LDA system, capable of determining local mean velocities and turbulence levels. T he refrigerant circuit uses R134a and has been designed to allow maxim um flexibility in setting test conditions. Preliminary results are pre sented from tests on a single circuit finned-tube evaporator with 33 t ubes, 300 mm long, arranged in an in-line matrix 4 rows deep, with 25 mm spacing. The height of the fin block was 225 mm, the fin spacing an d tube external diameter were 4 mm and 9.5 mm respectively. Contrary t o expectations, increases in heat transfer duty and overall heat trans fer coefficients were recorded as air how non-uniformities were artifi cially introduced, whilst a constant mean air velocity was maintained.