Influence of 0° helix angle micro fins on flow and heat transfer of R32 evaporating in a horizontal mini multichannel flat tube

The heat transfer and pressure drop characteristics of R32 were experimentally investigated for flow boiling in a mini multichannel flat tube with 0° helix angle micro fins that are aligned with the flow direction. The micro-fin tube has an inner diameter of 1.7 mm with thirteen 0.16 mm high fins. The working conditions were mass fluxes of 100-400 kg m−2 s−1, heat fluxes of 10-40 kW m−2 and saturation temperatures of 10-20 °C. The results show that in the micro-fin tube with 0° helix angle, the flow boiling heat transfer coefficient of R32 increases with increasing mass flux, heat flux and saturation temperature. The heat transfer is affected by two dryout points, but the fins delay the totally dryout point. The pressure drop increases with increasing mass flux and heat flux or decreasing saturation temperature. The critical vapor qualities for the pressure drop in the micro-fin tube are lower than in the smooth tube. The 0° helix angle fins enhance the heat transfer for R32 flow boiling in the tube by 60% while increasing the pressure drop by 40% on average compared with a smooth tube.