Dropwise Condensation on Superhydrophobic Microporous Wick Structures

Abstract

Previous research in dropwise condensation (DWC) on rough microtextured superhydrophobic surfaces has demonstrated evidence of high heat transfer enhancement compared to smooth hydrophobic surfaces. In this study, we experimentally investigate the use of microporous sintered copper powder on copper substrates coated with a thiol-based self-assembled monolayer to attain enhanced DWC for steam in a custom condensation chamber. Although microtextured superhydrophobic surfaces have shown advantageous droplet growth dynamics, precise heat transfer measurements are underdeveloped at high heat flux. Sintered copper powder diameters from 4 μm to 119 μm were used to investigate particle size effects on heat transfer. As powder diameter decreased, competing physical factors led to improved thermal performance. At consistent operating conditions, we experimentally demonstrated a 23% improvement in the local condensation heat transfer coefficient for a superhydrophobic 4 μm diameter microporous copper powder surface compared to a smooth hydrophobic copper surface. For the smallest powders observed, this improvement is primarily attributed to the reduction in contact angle hysteresis as evidenced by the decrease in departing droplet size. Interestingly, the contact angle hysteresis of sessile water droplets measured in air is in contradiction with the departing droplet size observations made during condensation of saturated steam. It is evident that the specific design of textured superhydrophobic surfaces has profound implications for enhanced condensation in high heat flux applications.

Direct Simulations of Biphilic-Surface Condensation: Optimized Size Effects

“…The results of the existing simulations (Rose, 2002) and experiments (Alwazzan et al, 2017, Hoenig, and Bonner, 2018, O'Neill, and Westwater, 1984 are also shown in Fig. 6, with good agreement with the predictions of this study.…”

Dropwise Condensation on Hydrophobic Microporous Powder and the Transition to Intrapowder Droplet Removal

“…Further observations show that the departing droplet size appears to be the primary variable governing heat transfer, in addition to secondary explanations, such as the droplet growth mode, conduction resistance, and filmwise modes of condensation underneath the powder structures. These findings are in reference to [28], which the subsequent departing droplet size observations are exclusively based on. In this complementary study by Hoenig et al, the maximum departing droplet sizes were measured for several departing droplets located near the top of all of the condensation surfaces.…”

Review of Micro–Nanoscale Surface Coatings Application for Sustaining Dropwise Condensation

“…It was found that heat transfer coefficient greatly depends on microporous powder diameter. As the diameter decreases, htc increases; for a 4-µm diameter, 23% htc increment was reported as compared to bare surface [168]. However, the improvement is low as compared to other coating techniques.…”

“…The disadvantage of SLIPS are their durability; after a certain time, liquid infusion diminishes, and due to condensate pinning, htc decreases [166]. Attempts have been made to develop microporous surfaces along with SAMs [167,168]. It was found that heat transfer coefficient greatly depends on microporous powder diameter.…”