Visualization of refrigerant R600a (isobutane) boiling in horizontal tubes with bends

The flow patterns that prevail during two-phase flow inside the horizontal tubes, with bends of the evaporator of a refrigeration plant, are presented in this paper. The refrigerant used was R600a (Isobutane), The systems oil was mineral oil. The evaporator was a 16-row trombone shaped transparent glass coil with return bends of 180 degrees. The inside and outside tube diameters were 8mm and 12.5mm respectively. The total length of the tubing was 6394 mm. Several photographic techniques were considered and are discussed in the paper. The flow patterns reported include wavy stratified, wavy flow, wavy crest, semi annular, misty-annular, misty and superheated. Other flow patterns recorded were highly turbulent annular flow and oil ripples. All pressures quoted are absolute.