Experimental investigation on the thermal and entropic behavior of a vertical helical tube with none-boiling upward air-water two-phase flow

•Thermal and entropic characteristics of upward air-water two-phase flow in a vertical helical tube were studied.•The water superficial Dean number (Desl) was between 1000 and 4800.•The gas (air) superficial Dean number (Desg) was between 45 and 235.•Maximum increment of 35% was observed for heat transfer coefficient.•Maximum increment of %26 was observed for entropy generation. Helical tubes have great compact structure, two-phase flow stability and well thermal performance. The increment of applications which use two-phase flow in helical tubes, necessitates the investigation on thermal and entropic characteristics of two-phase flow in helically coiled tubes. The present study provides experimental results of heat transfer characteristics of upward air-water none-boiling two-phase flow in a vertical helically coiled tube. The helical tube was put under constant heat flux. The inlet, outlet, wall and ambient temperature of helical tube were measured for calculating the heat transfer coefficient and entropy generation. The water superficial Dean number (Desl) was between 1000 and 4800. Also, the gas (air) superficial Dean number (Desg) was between 45 and 235. The VF (volume fraction) fraction was between 0.11 and 0.55. Almost all investigated cases were at the range of slug and plug flow regimes. Results revealed that the air-water two-phase flow could increase the heat transfer coefficient. Increment of air superficial Dean Number increased the heat transfer rate and entropy generation. A maximum increment of 35% and %26 were observed for heat transfer coefficient and entropy generation respectively. Also it was revealed that increment of VF increases the Witte-Shamsundar efficiency.