Characteristic of local boiling heat transfer of ammonia and ammonia / water binary mixture on the plate type evaporator

Power generation using small temperature difference such as ocean thermal energy conversion (OTEC) and discharged thermal energy conversion (DTEC) is expected to be the countermeasures against global warming problem. As ammonia and ammonia/water are used in evaporators for OTEC and DTEC as working fluids, the research of their local boiling heat transfer is important for improvement of the power generation efficiency. Measurements of local boiling heat transfer coefficients were performed for ammonia /water mixture (z = 0.9−1) on a vertical flat plate heat exchanger in a range of mass flux (7.5–15 kg/m² s), heat flux (15–23 kW/m²), and pressure (0.7–0.9 MPa). The result shows that in the case of ammonia /water mixture, the local heat transfer coefficients increase with an increase of mass flux and composition of ammonia, and decrease with an increase of heat flux.