In Situ Biofouling of Ocean Thermal Energy Conversion (OTEC) Evaporator Tubes

The Puerto Rico Center for Energy and Environmental Research designed, constructed and operated a facility for measuring in situ biofouling of simulated Ocean Thermal Energy Conversion (OTEC) evaporator tubes of various materials. The system consisted of two 5052 aluminum alloy and two titanium experimental modules mounted on a Landing Craft, Utility moored in 1100 m of water at a potential OTEC site two miles south of Punta Tuna, Puerto Rico. Continuous flow of ocean surface water was maintained through all modules, and the fouling resistance (R_f) for each instrumented tube was monitored regularly. During the first eight months of operation the tubes were cleaned three times with manually operated M.A.N. brushes. Initially, the rate of increase in R_f was greater for the aluminum units, but after the third cleaning all units had fouling rates near 4×10⁻⁶ m²-K/W-day (2×10⁻⁵ hr-ft²-°F/Btu-day). Each cleaning of the tubes reduced R_f to values betwen 9×10⁻⁶ and 20×10⁻⁶ m²-K/W (5×10⁻⁵ and 11×10⁻⁵ hr-ft²-°F/Btu).