Measurement of Thermal Resistance Due to Fouling on Heat Exchanger Surfaces

Fouling which occurs on power plant heat exchangers, particularly Ocean Thermal Energy Conversion plants, is a problem since these deposits reduce heat transfer efficiency. An apparatus to quantify the thermal resistance due to fouling, including low levels of fouling, has been developed and operated to acquire experimental data. The heat transfer monitor device developed utilizes a stable heat flux applied by direct electric heating to a circular tube in order to simulate flow characteristics of a shell and tube heat exchanger. The device serves to evaluate heat exchanger materials and antifouling or cleaning treatments in power plant applications. Several series of experiments were performed at a San Diego Bay location to determine the effect of materials, velocity, and low level chlorination on the fouling rate. Each experiment was run for a period of 6-10 weeks. The most dramatic reduction in fouling observed was afforded by chlorination dosed at 0.1 mg/1. Traditional control of fouling by chlorination may present toxicological problems to aquatic organisms in the receiving water. Minimizing the environmental impact of biofouling without delays and high costs as a result of the trial and error approach can be accomplished by measurement of the status of biofouling, or its effect on lowering heat transfer. The heat transfer monitor described herein seeks to provide this capability.