Enhanced internal condensation of R1233zd(E) on micro- and nanostructured copper and aluminum surfaces

• Published in: International journal of heat and mass transfer Vol. 207; p. 124012
• Main Authors: Köhler Mendizábal, Johannes, Singh, Bakhshish Preet, Rabbi, Kazi Fazle, Upot, Nithin Vinod, Nawaz, Kashif, Jacobi, Anthony, Miljkovic, Nenad
• Format: Journal Article
• Language: English
• Published: United States Elsevier Ltd 15.06.2023; Elsevier
• Subjects: ENGINEERING
• ISSN: 0017-9310; 1879-2189
• DOI: 10.1016/j.ijheatmasstransfer.2023.124012

•Development of etched aluminum and copper oxide surfaces for two-phase heat transfer enhancement.•Internal flow condensation experimental facility for heat transfer coefficient and pressure drop characterization.•Enhancements demonstrated for high quality vapor internal condensation of R1233zd(E) refrigerant.•Enhancements demonstrated for low mass flux cases of internal condensation of R1233zd(E).•Experiments show higher quality-specific enhancements at lower Weber numbers, and lower Bond numbers. In-tube condensation of refrigerants is an important process which affects thermal efficiency in many applications, ranging from refrigeration and air conditioning to electronics thermal management. In-tube heat transfer and pressure drop are important to heat exchanger sizing and design. In this work, micro- and nanostructured surfaces are applied to the internal wetted areas of copper and aluminum mini-channels to enhance the condensation heat transfer coefficient of hydrofluorocarbon R1233zd(E) refrigerant. To achieve scalable nanomanufacturing, surfaces were uniformly structured by relying on hydrochloric acid etching of aluminum and chemical oxidation of copper. The etched aluminum surfaces exhibited a 150% increase in heat transfer coefficient compared to smooth aluminum channels at specific qualities, with a 66% heat transfer coefficient improvement for complete phase change from saturated vapor to saturated liquid. Copper oxide structures showed no discernable difference in thermal-hydraulic performance when compared to smooth copper channels. Critical dimensionless parameters governing the heat transfer enhancement were identified by varying the tube internal diameter (2.3 mm to 4.7 mm), refrigerant mass flux (50 to 300 kg/(m2·s)), and refrigerant quality (0 to 1). The dimensionless parameters include the Bond number normalized to the condensate film thickness, and the Weber number modified by the vapor friction factor. The relatively small increase in pressure drop (< 10%) associated with these surface enhancements further supports the promise of this method. The scalable and cost-effective techniques used to create these aluminum microstructures may reduce manufacturing cost when compared with current enhancement approaches such as extrusion, drawing, and welding.