Enhancing filmwise and dropwise condensation using a hybrid wettability contrast mechanism: Circular patterns

摘要

Condensation surfaces using a wettability contrast mechanism is one of the effective methods to enhance heat transfer rate. The pattern design plays a critical role in realizing various contrast degrees of wettability. In this study, water vapor condensation of two series of hybrid circular-patterned designs were developed and experimentally characterized under the atmospheric pressure with the presence of non-condensable gasses (air). The outer surfaces of copper tubes in the horizontal orientation were used as the condensation surface with the designed patterns. The condensation heat transfer rates were compared to that of the complete dropwise condensation (DWC) and complete filmwise condensation (FWC), respectively. In the first series, the pattern design consists of hydrophobic (β) circular patterns formed on a less-hydrophobic (γ) background. The diameter of the patterns was varied to find an optimum configuration, which was observed with the pattern diameter and pattern distance at 1.5 mm and 0.5 mm, respectively. Significantly enhanced condensation rate was obtained compared to FWC. In the second series, the design consists of γ-patterns contrasting with a β-background, which is an inverse design of the first series in terms of wetting conditions. A parametric study was conducted to examine the influence of the pattern dimensions on the condensation. In the second series pattern designs, significant enhancements compared with both FWC and DWC were achieved. The optimal pattern was found to be at a diameter of 1.5 mm and gap of 1.5 mm, leading to a 79% higher heat transfer rate compared to that of the complete DWC.