Effect of Channel Geometry on Ammonia Boiling Heat Transfer of a Plate-Type Evaporator

The ocean thermal energy conversion (OTEC) is attracted attention as one of the promising renewable energy. OTEC uses small temperature difference between surface and deep sea water. Plate-type heat exchangers, or evaporators, are usually used for OTEC to obtain vapor for electric generator. Ammonia is used for OTEC as a working fluid. It is important to improve thermal performance of an evaporator for the OTEC. Channel dimension is one of the important factors to improve heat transfer performance of an evaporator. In this study, the measurement and comparison of local heat transfer coefficient for three channels are experimentally performed. The experiments are conducted for a range of mass flux (5 and 7.5 kg/m²s), heat flux (10 to 25 kW/m²), and pressure (0.7 and 0.9 MPa). The results show that the heat transfer coefficient increases as decreases channel height. The modified emprical correlation for a plate-type evaporator is proposed.