The heat transfer performance of a coiled tube heat exchanger for absorption refrigerators with the working pair of ammonia/water was experimentally studied. The effects of solution flow rate on the heat transfer coefficient was investigated in detail. To understand the effect of absorption on heat transfer, experiments without absorption phenomena were also carried out. It has been shown that the heat transfer coefficient of falling film, both with and without absorption, increases linearly to the solution flow rate in the experimental range. A heat transfer coefficient with absorption was found to be smaller than that without absorption. One reason for the reduction in the heat transfer coefficient seems to be uneven distribution or stagnation of liquid film caused by shear force at the liquid-vapor interface. Locally too-thick film and insufficient wetting of the surface result in a reduction in the heat transfer coefficient. In this experiment, it was difficult to explain clearly the effect of the driving pressure difference on the heat transfer coefficient. A nondimensional Nu-Re relation obtained from this study can be applied for sizing coiled tube heat exchangers.

Units: SI