Overview of metallic materials for heat exchangers for ocean thermal energy conversion systems

Candidate materials for use in ocean thermal energy conversion systems, OTECS, heat exchangers include aluminium, Cu-Ni, stainless steel and titanium alloys. These are considered in this review, and their advantages and disadvantages are highlighted and discussed. Aluminium alloys have shortcomings for the anticipated long life span of OTEC heat exchangers; however they may still offer an economic alternative in the form of short-life, disposable units of low initial capital cost. The long-term effects of exposure to ammonia and to erosion pose questions about the suitability of Cu-Ni alloys. Although stainless steel alloys provide a strong challenge for OTECS use, titanium exhibits better seawater performance, has good fabricability, and has an excellent service history in marine environments. These factors, together with current and projected developments promise major savings in materials usage, reduced OTECS structure sizes and increased efficiencies consequent on the use of titanium and its alloys.