Preliminary Seawater Experiments with Open Cycle O.T.E.C. Spout Evaporation

Experiments with spout evaporator and direct contact condenser configurations have been performed at the Natural Energy Laboratory of Hawaii, using warm surface seawater at 25-28°C for the evaporator and cold deep ocean seawater at 7-8°C, obtained from 600 m depth, for the spray condenser. Flow rates of up to 250 1/min have been employed, through a spout of up to 5 cm diameter. Results show that the spout evaporator is 82-95 percent effective, and that steam evolution is initiated in subcooled boiling in the top part of the upcomer and in evaporation from small droplets, which are ejected violently from the boiling water at the spout mouth. The results are somewhat at variance with data obtained by others with high purity deaerated fresh water and with the existing mathematical model for spout evaporation, which was largely based on the same freshwater data. The differences are discussed in terms of bubble nucleation of heterogeneous nuclei present in the seawater, the easy deaeration of seawater as compared with fresh water, and the obvious limitations and simplifications inherent in the model. Implications of the results for future tests are discussed.