Impact of wall hydrophobicity on condensation flow and heat transfer in silicon microchannels

Abstract

While microchannel condensation has been the subject of several recent studies, the critical impact of wall hydrophobicity on the microchannel condensation flow has received very little attention. The paper experimentally studies steam condensation in a silicon microchannel 286 μm in hydraulic diameter with three different wall hydrophobicities. It is found that the channel surface wettability has a significant impact on the flow pattern, pressure drop and heat transfer characteristic. Spatial flow pattern transition is observed in both hydrophobic and hydrophilic channels. In the hydrophobic channel, the transition from dropwise/slugwise flow to plug flow is induced by the slug instability. In the hydrophilic channel, the flow transition is characterized by the periodic bubble detachment, a process in which pressure evolution is found important. Local temperature measurement is conducted and heat flux distribution in the microchannel is reconstructed. For the same inlet vapor flux and temperature, the hydrophobic microchannel yields higher heat transfer rate and pressure drop compared to the hydrophilic channel. The difference is attributed to the distinction in flow pattern and heat transfer mechanism dictated by the channel hydrophobicity. This study highlights the importance of the channel hydrophobicity control for the optimization of the microchannel condenser.

Combined Visualization and Heat Transfer Measurements for Steam Flow Condensation in Hydrophilic and Hydrophobic Mini-Gaps

“…Mini-and microchannels offer opportunities for flow condensation enhancement over conventional-sized channels, and few studies have investigated dropwise condensation in mini-and microchannels. Fang et al [50] obtained 15% heat flux enhancement in a 286 lm diameter hydrophobic silicon channel with a contact angle of 123 deg and a hydrophilic channel with a contact angle of 25 deg. Derby et al [51] studied steam flow condensation in 1.06 mm mini-gaps of hydrophilic copper that measured 1.06 mm with a contact angle of 40 deg and TeflonAF TM coated channels with a contact angle of 120 deg.…”

Spray-on omniphobic ZnO coatings

“…[1][2][3][4][5][6][7][8] Many draw inspiration from the Lotus plant, 9 whose microstructure provides a self-cleaning mechanism through tiny air pockets that prevent penetration by water, leading to a Cassie-Baxter state 10 characterized by low contact angle hysteresis (CAH) and low tilt angle (i.e., roll-off or sliding angle). [1][2][3][4][5][6][7][8] Many draw inspiration from the Lotus plant, 9 whose microstructure provides a self-cleaning mechanism through tiny air pockets that prevent penetration by water, leading to a Cassie-Baxter state 10 characterized by low contact angle hysteresis (CAH) and low tilt angle (i.e., roll-off or sliding angle).…”

Near-Wall Liquid Layering, Velocity Slip, and Solid–Liquid Interfacial Thermal Resistance for Thin-Film Evaporation in Microchannels

“…The effect of the velocity slip is enhanced but the effects of the Kapitza resistance and the liquid layering are slightly reduced at smaller channel heights. Conventional thin liquid film models, which neglect the solid-liquid interfacial intermolecular bonding effects, also show that the surface hydrophobicity effects are more important at larger channel heights due to the reduced effect of the surface tension [10,[29][30][31].…”