How does surface coating treatment of low temperature evaporators improve corrosion resistance and heat transfer performance?
Release Time : 2025-10-08
Low-temperature evaporators, core equipment in evaporation and concentration processes, require surface coatings that enhance corrosion resistance and heat transfer performance. In the chemical, pharmaceutical, and food processing industries, low-temperature evaporators are often subject to corrosion from high-salinity solutions, acidic/alkaline media, and complex organic matter, while simultaneously maintaining efficient heat transfer in low-temperature environments. Optimizing coating materials and processes can significantly extend equipment life and reduce energy consumption.
Corrosion issues in low-temperature evaporators primarily stem from the characteristics of the media and the operating environment. For example, desalination evaporators are exposed to chloride-containing solutions for extended periods, which can easily cause pitting and crevice corrosion. In electroplating wastewater treatment, acidic media can accelerate the dissolution of the metal substrate. Furthermore, at low temperatures, condensate films easily form on the evaporator surface, further exacerbating the risk of corrosion. Traditional carbon steel evaporators are prone to perforation in corrosive media, leading to leaks and downtime. Ordinary stainless steel coatings can also suffer from localized corrosion in high-salinity environments. Therefore, developing coating technologies that combine corrosion resistance with high heat transfer performance is a critical need.
Graphene composite nanocoatings offer an innovative solution for low-temperature evaporators. This coating achieves zero-dead-angle coverage, including micropores and crevices, through a nanodeposition process, solving the corrosion protection challenges of complex structures difficult to address with traditional spray coatings. Graphene's high thermal conductivity (over 800 W/m·K in the horizontal direction) significantly improves the coating's heat transfer efficiency, while its high emissivity (up to 0.96) enhances radiative heat transfer. In low-temperature evaporators, this coating not only withstands thermal shocks ranging from -60°C to 300°C but also maintains stable heat transfer performance by reducing surface heat storage. For example, in the treatment of high-salinity wastewater from the coal chemical industry, evaporators using graphene coatings can operate efficiently for months without noticeable performance degradation.
Optimizing heat transfer in low-temperature evaporators requires a balanced approach to corrosion resistance and thermal resistance control. Traditional anti-corrosion coatings, while insulating the medium, can increase thermal resistance and reduce heat transfer efficiency. Graphene coatings, with their unique two-dimensional structure, form a dense anti-corrosion layer while maintaining extremely low thermal resistance. While its vertical thermal conductivity is lower than its horizontal one, it still significantly outperforms conventional coating materials. Furthermore, the coating's surface is hydrophilic, accelerating the shedding of condensed water and reducing liquid film thickness, thereby lowering convective heat transfer resistance. In vacuum low-temperature evaporation systems, this design helps maintain efficient heat transfer within the evaporator, ensuring stable evaporation of wastewater at temperatures between 35°C and 50°C.
Sacrificial anode and cathodic protection technology can form a synergistic corrosion protection system with coating treatment. In low-temperature, multi-effect seawater desalination units, the high temperature, humidity, and salinity inside the evaporator are prone to electrochemical corrosion. By adding a zinc- or aluminum-based alloy sacrificial anode, corrosion is preferentially applied to the anode material, protecting the evaporator substrate. Combined with a graphene coating, this provides dual protection: the coating blocks direct contact with the medium, while the sacrificial anode dissipates corrosion current. This combination performs exceptionally well in marine environments or for high-salinity wastewater treatment, significantly extending the evaporator's service life.
The flow channel design of a low-temperature evaporator significantly influences coating performance. Spiral flow channels enhance refrigerant turbulence and improve heat transfer coefficients, but also increase the risk of coating wear. The graphene coating's high adhesion (Grade 1) and strong bonding strength (up to 15 MPa) ensure long-term stability in complex flow channels. Furthermore, the serrated fin design increases air turbulence, improving air-side heat transfer efficiency, while the coating's smooth surface reduces air resistance, further optimizing heat transfer performance. In a low-temperature heat pump evaporator, this design improved the air-side heat transfer coefficient by approximately 15% while maintaining the coating's integrity.
Practical application cases have validated the effectiveness of coating treatment. A wastewater treatment plant in a chemical park employed a 2205 stainless steel evaporator coated with a graphene composite coating. The equipment operated stably with complex wastewater, increasing treatment efficiency by 30% and reducing operating costs by 20%. In another case study, a vacuum low-temperature wastewater evaporator, combined with a graphene coating and an intelligent defrost device, achieved months of trouble-free operation and 100% condensate compliance. These practices demonstrate that coating treatment is not only a corrosion prevention measure but also a key technology for improving the overall performance of low-temperature evaporators.