Zhaorong He

Industrial heat exchangers are widely used in industries such as petrochemicals, energy and power, and food processing, making them one of the most important pieces of heat and mass transfer equipment in industry. During operation, a layer of fouling often adheres to the heat transfer surfaces, which reduces the heat transfer coefficient of the equipment and increases the thermal resistance of the surfaces. Additionally, fouling can corrode the material of the heat transfer surfaces, compromise their integrity, and even lead to perforations and leaks, severely impacting equipment operation and safety while increasing energy consumption and costs for enterprises. The application of anti-fouling coatings on surfaces is a key technology to address fouling on heat transfer surfaces. This paper focuses on introducing major types of anti-fouling coatings, including polymer-based coatings, “metal material + X”-type coatings, “inorganic material + X”-type coatings, carbon-based material coatings, and other varieties. It analyzes and discusses the current research status and hotspots for these coatings, elaborates on their future development directions, and proposes ideas for developing new coating systems. On the other hand, this paper summarizes the current research on the main factors—surface roughness, surface free energy, surface wettability, and coating corrosion resistance—that affect the anti-fouling performance of coatings. It outlines the research hotspots and challenges in understanding the influence of these three factors and suggests that future research should consider the synergistic effects of multiple factors, providing valuable insights for further studies in the field of anti-fouling coatings.

Polyalphaolefins (PAOs) are regarded as superior lubricants, but the biodegradability of the very low-viscosity PAO2/PAO4 has been ignored over a long history, despite being inherently biodegradable (PAO2/PAO4 biodegradation rate >20% by OECD guidelines). Previous studies typically concentrated on a single viscosity grade of PAO with additives, seldom engaging in comparative research efforts involving multiple low-viscosity grades of neat PAO concurrently. This study compares PAO2/PAO4 with non-biodegradable PAO6 regarding rheology and lubricating film formation. PAO2/PAO4 are Newtonian fluids with ≤10% viscosity fluctuation at high shear rates, while PAO6 shows a viscosity fluctuation of ≥15% at high shear rates. Viscosity–temperature equations are derived. An optical interference method measures lubricating film thickness. PAO2/PAO4 films are less sensitive to speed/load changes. PAO2 mainly works in boundary lubrication. Interference images show possible unique EHL characteristics of PAOs. The Hamrock–Dowson formula overestimates PAO6 film thickness at high speeds.

Fouling is one of the common problems in heat-transfer applications, resulting in higher fouling resistance, and lower heat-transfer coefficient. This paper introduces the design and fabrication of an Fe–Al coating with micro/nanostructures on low-carbon steel by electrical discharge coating (EDC) technology to improve the antifouling property. The Fe–Al coating with micro/nanostructures is characterized by a large number of micro/nanostructures and superior anti-fouling property, which is attributed to its hydrophobic surface. The antifouling property, fouling induction period and contact angle of the Fe–Al coating with micro/nanostructures increase with the increasing gap voltage. Compared with the polished surface of low-carbon steel, the Fe–Al coating with micro/nanostructures extends the induction period from 214 to 1350 min, with a heat flux of 98 kW·m⁻². After 50 adhesion tests, the contact angle of the Fe–Al coating with micro/nanostructures decreases from 6.81% to 27.52%, which indicates that the Fe–Al coating with micro/nanostructures is durable and suitable for industrial applications.