Flow Boiling Heat Transfer Characteristics of R32 inside a Horizontal Small-diameter Microfin Tube

摘要

This study experimentally investigated the flow boiling heat transfer and pressure drop characteristics of refrigerant R32 in a horizontal small-diameter microfin tube that had an outer diameter of 3.0 mm and an equivalent diameter of 2.6 mm. The test microfin tube had a helix angle of 10°, a fin height of 0.1 mm, and 25 fins. The flow boiling heat transfer coefficient and the pressure drop were measured against a mass velocities range of 100-400 kg/(m~2s), a heat flux range of 5-20 kW/m~2, and a saturation temperature of 15°C. The heat transfer coefficient was found to increase with an increase in the heat flux and the vapor quality in the pre-dryout region. The effect of tube diameter on heat transfer in small-diameter microfin tubes - tubes with equivalent diameters of 2.6 mm and 3.7 mm - that had the same number and height of fins, is significant in the forced convection and thin liquid film evaporation heat transfer dominant regions compared to the nucleate boiling dominant region.