Experimental investigation on two-phase flow pattern of ammonia inside 4 mm and 8 mm horizontal smooth tubes

Abstract

The two-phase flow patterns of ammonia in different scale channels are experimentally investigated in this study. The inner diameters of the tested tubes are 4 mm and 8 mm. The observed flow patterns in the two tubes include slug flow, stratified-wavy flow, annular flow, and annular flow with partial dryout. For both 4 mm and 8 mm tubes, the annular flow gradually expands to a wider vapor quality range with a rise in mass flux and a descent in saturation temperature at the cost of other flow patterns. The comparison of the flow patterns in the two tubes shows that the 8 mm tube has a wider range of annular flow. This is attributed to that the higher dominance of the surface tension force in the 4 mm tube is conductive to the liquid slug to holdup on the channel wall and consequently delay the transition to annular flow. The flow patterns in the two tubes have been compared to the flow pattern maps of Baker, Mandhane et al., and Wojtan et al.. The Wojtan et al. flow pattern map could give a superior prediction for the flow patterns in the 4 mm tube, whereas none of the three existing models accurately predict the flow patterns in the 8 mm tube.