Experimental investigation of the effects of hydrophobic surfaces on heat exchanger performance

In this study, the effects of hydrophobic coatings applied to plate wet surfaces on heat transfer, pressure drop, fouling, mechanical strength, pump power and heat exchanger performance were experimentally investigated by keeping the existing designs of gasketed plate heat exchangers constant. The Reynolds values were set to five different values equally spaced between 10000 and 30000. The temperature of the inlet fluid was set at 52, 62 and 72 ⁰C, respectively. In order to increase the hydrophobicity of the FEP (Fluorinated Ethylene Propylene) material, 3%, 7% and 10% by mass weighted of h-BN (Hexagonal Boron Nitride) nanoparticles were added in the solution. A cheap and easily applicable new hydrophobic coating solution which has high hydrophobic properties was synthesized. The wet surfaces of the plate were covered with a nanoparticle reinforced carbon-based polymer solution with four different hydrophobic properties: FEP, FH3 (FEP+3% h-BN), FH7 (FEP+7% h-BN) and FH10 (FEP+10% h-BN). The heat transfer, pressure drops, fouling, mechanical strength and pump power results obtained from the heat exchanger with hydrophobic surface coating were compared with the uncoated heat exchanger. The contact angles of the coated surfaces were measured as 95º, 121º, 135º and 113º, respectively. The contact angle increased due to high h-BN ratio, but when 10% by mass was added, the contact angle decreased with the increase in surface roughness and coating film thickness. It was observed that the efficiency of the heat exchanger increased in direct proportion to the degree of hydrophobicity. The highest efficiency value in hydrophobic heat exchanger was found in the FH7 coating and was determined as 0.543. It was determined that there was a decrease of approximately 17.14% in heat transfer with the hydrophobic coating. The pressure drops were 71.28% lower in the FH7 surface coated heat exchanger, which has the best hydrophobic property, compared to the heat exchanger without any coating process. In local losses, 25.5% improvement was achieved in the FH7 coated heat exchanger. Thanks to the hydrophobic surface coatings, the formation of fouling in the heat exchanger has been reduced by 82%. As a result of reducing the effects of fouling, 38.22% increase in heat transfer was achieved in the FH7 coated heat exchanger. The lowest coefficient of friction was determined as 0.21 in the FH7 coated heat exchanger, and 74.69% improvement was obtained in abrasion rates compared to the uncoated heat exchanger. The energy consumption of the circulation pumps has been reduced by 17.76% thanks to the FH7 coating.