Coating is one of the techniques used to avoid scaling or fouling on the surface of a plate heat exchanger in geothermal energy utilization. However, to date no satisfactory coatings and techniques have been developed. In this study, titania (TiO2), silica (SiO2), TiO2-fluoroalkylsilane (FPS), and SiO2-FPS coatings on the surfaces of heat transfer plates made of stainless steel were prepared by using liquid-phase deposition (LPD) and sol-gel methods. An experimental setup of the convection heat transfer in the plate heat exchanger using a data acquisition system was built to study the scaling behavior on the coated surfaces with a scaling solution of simulated geothermal water at 80°C. It was found that scaling inhibition was obtained on TiO2-FPS coatings prepared by using the LPD method. A certain amount of corrosion occurred on the TiO2 and TiO2-FPS coatings fabricated by using the sol-gel method. An increase in the scaling induction period and a decrease in the asymptotic thermal resistance for the SiO2 and SiO2-FPS coatings made by using the sol-gel method were not obtained; however, loose deposits on these coatings did break off and were washed away easily by the flow of the geothermal water.
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