Effect of microfouling on heat-transfer efficiency

The relationship between decreased heat transfer efficiency and the accumulation of corrosion and/or biofouling films on heat exchanger surfaces was investigated using sample tubes that were maintained under conditions simulating those of an Ocean Thermal Energy Conversion (OTEC) system. Seawater at Keahale Point, Hawaii and in the Gulf of Mexico flowed through 2.54 (internal diameter) aluminum, titanium, copper nickel, and stainless steel tubes at approximately 1.8 m/sec. All surfaces were colonized by microorganisms, though colonization of the Cu-Ni surface was initially retarded. Total film weight was greatest for the Al and Cu-Ni surfaces which were characterized by corrosion as well as microbial fouling. The total organic carbon: total nitrogen ratios of the fouling films from Ti, Al, SS and Cu-Ni, 4.2, 4.0, 4.8 and 7.9 respectively, remained constant throughout the experiment. The degradation of heat transfer efficiency due to the formation of fouling layers on Ti and SS is neither linear nor a simple exponential function. A microfouling model is proposed for corrosion resistant surfaces.