Local boiling heat transfer characteristics of ammonia in a vertical plate evaporator

Ocean thermal energy conversion systems are expected to be the next-generation energy production systems. In these systems, a plate heat exchanger is used for improving the power generation efficiency, and ammonia or an ammonia/water mixture is used as a working fluid. In this study, boiling heat transfer coefficients of pure ammonia are measured oil a vertical flat PHE (a plate heat exchanger), for elucidating and characterizing the behavior of ammonia on a compact plate evaporator, a type of PHE The measurement results show that local boiling heat transfer coefficients increase with increasing vapor quality. Further, the effects of saturation pressure, mass flow rate, and average heat flux on the boiling heat transfer coefficient are elucidated. An empirical correlation for the local boiling heat transfer coefficient is derived using the Lockhart-Martinelli parameter. Further, a visualization experiment of boiling phenomena of ammonia is performed to elucidate the relation between boiling behavior and heat transfer. (C) 2009 Elsevier Ltd and IIR. All rights reserved.