Ocean thermal energy conversion (OTEC) usually uses plate-type heat exchangers (PHEs) as an evaporator, condenser, and other devices. Generally, the heat transfer plate of PHEs is made of titanium because ammonia and seawater flow in PHEs as a working fluid and heat source. However, titanium is expensive and difficult to process; therefore, the use of low-cost materials is essential. The selection of materials for the heat transfer plates of a PHE is also a key factor affecting the OTEC performance. The suitability of aluminum alloy, Cu-Ni alloy, and stainless steel as materials for OTEC heat exchangers has been explored in some studies. The focus is on aluminum among other materials, because aluminum has better thermal conductivity than titanium, and its cost is also lower than that of titanium. The authors considered aluminum as an alternative to titanium. However, aluminum has low corrosion resistance for ammonia and seawater. To improve corrosion resistance, several coating methods are employed for aluminum, such as Polyether Ether Ketone (PEEK) resin or WIN KOTE® film, anodic oxidation, anodized and coated composite film; long-term immersion tests are conducted on ammonia. Anodic oxidation is identified as the best coating method to improve the corrosion resistance to ammonia. Therefore, anodic oxidation is employed in the aluminum coating method. Heat exchange and boiling experiments are performed on the apparatus used with ammonia to elucidate the thermal performance of aluminum alloy treated by anodic oxidation (1050 alloy) plate on the PHEs. In addition, the heat transfer performance is compared with three types of heat transfer surface shapes. As a result of the measurement of the overall heat transfer coefficient, the best configuration in these three plates is identified, and the overall heat transfer is almost the same as that of the titanium plate. In addition, the heat transfer coefficients of ammonia on these three plates are determined, and the value depends on the mass flow rate of ammonia. It is found that the anodized aluminum plate can be used as an evaporator, through which the ammonia flowed as a working fluid.
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Ocean thermal energy conversion (OTEC) usually uses plate-type heat exchangers (PHEs) as an evaporator, condenser, and other devices. Generally, the heat transfer plate of PHEs is made of titanium because ammonia and seawater flow in PHEs as a working fluid and heat source. However, titanium is expensive and difficult to process; therefore, the use of low-cost materials is essential. The selection of materials for the heat transfer plates of a PHE is also a key factor affecting the OTEC perform...
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