Performance of the Heat Exchangers of a 100-kW (Gross) OTEC Plant

A power-generating test of the world’s largest (100-kW gross power) ocean thermal energy conversion (OTEC) demonstration plant was conducted from October through December 1981 in the Republic of Nauru in the central Pacific Ocean. Fluorocarbon-22 was selected as a working fluid. During the power-generating test, a maximum gross power output of 120-kW (31.5-kW net) was achieved. Continuous operation was maintained for ten days. This plant verified the results of various development tests that were conducted by the authors on the heat exchangers. The evaporator is a horizontal, shell-and-tube, pool-boiler with the titanium tubes enhanced by a flame-sprayed, porous copper coating on the outside. The condenser is a vertical shell-and-tube type with the titanium tubes fluted on the outside (working-fluid side). Overall heat transfer coefficients of approximately 4300 and 3000 W/m2K for the evaporator and condenser, respectively, were achieved at the seawater design velocity of 2 m/s.