The evaporating heat transfer of R-22 in small tubes has been experimentally studied. The tubes in present work are single square tube and single round tube. The hydraulic diameter of the tubes is 1.67㎜. The experimental apparatus consists of a refrigerant pump, a condenser and a receiver, the small-tube test section, a subcooler of liquid refrigerant, a preheater for control of refrigerant quality at the inlet of test section. The heat flux is generated by heating wire wound on the outer wall of the test section. A set of five thermocouples are embedded at the wall of the test section to measure the wall temperature at five locations. The refrigerant flow rate is measured using a high-pressure rotameter. The pressure drop across the test section is measured using a differential pressure transducer.
For refrigerant mass flux of 384 ㎏/㎡s and 570 ㎏/㎡s, the inlet qualities are varied from 0.0 to 0.8 and the wall heat fluxes are varied from 4 ㎾/㎡ to 10 ㎾/㎡. The measured evaporating heat transfer coefficients in the small tubes are 620 ∼ 4760 W/㎡K, which are lower than those observed in the typical large-diameter circular tubes. The evaporating heat transfer coefficient in the square tube shows lower heat transfer coefficient than the round tube. The pressure drop increases with increasing quality.