Advanced materials and surface engineering strategies for mitigating fouling and corrosion in geothermal heat exchangers

Geothermal heat exchangers (GHXs) are essential in binary Organic Rankine Cycle (ORC) plants and ground-source systems but suffer significant performance degradation due to scaling, fouling, and corrosion caused by aggressive geothermal brines. Silica and carbonate scaling can reduce heat transfer capacity by 30–50%, while carbon steel components exhibit corrosion rates of 0.1–0.4 mm/y in chloride-rich environments. Fouling behaviour follows an asymptotic, linear, or falling-rate trend, depending on whether crystallisation is diffusion- or reaction-controlled, thereby significantly affecting thermal resistance and pressure drop. This review evaluates degradation mechanisms and mitigation strategies, including chemical and mechanical descaling, corrosion-resistant alloys (PREN > 40), and advanced coatings. Thermal spray coatings (e.g., WC-CoCr, TiO 2 ) enhance erosion–corrosion resistance and improve heat transfer performance, while PECVD and liquid-phase deposited oxide coatings provide conformal antifouling protection and extended service intervals. A hybrid approach combining corrosion-resistant alloys with engineered surface coatings is identified as the most promising pathway to reduce oversizing, extend service life, and improve the economic viability of geothermal plants.