Suppression of Frost Nucleation Achieved Using the Nanoengineered Integral Humidity Sink Effect

Abstract

Inhibition of frost formation is important for increasing efficiency of refrigeration systems and heat exchangers, as well as for preventing the rapid icing over of water-repellant coatings that are designed to prevent accumulation of rime and glaze. From a thermodynamic point of view, this task can be achieved by either increasing hydrophobicity of the surface or decreasing the concentration of water vapor above it. The first approach has been studied in depth, but so far has not yielded a robust solution to the problem of frost formation. In this work, we systematically explore how frost growth can be inhibited by controlling water vapor concentration using bilayer coatings with a porous exterior covering a hygroscopic liquid-infused layer. We lay the theoretical foundation and provide experimental validation of the mass transport mechanism that governs the integral humidity sink effect based on this coating platform as well as reveal intriguing sizing effects about this system. We show that the concentration profile above periodically spaced pores is governed by the sink and source concentrations and two geometrical parameters: the nondimensional pore size and the ratio of the pore spacing to the boundary layer thickness. We demonstrate that when the ratio of the pore spacing to the boundary layer thickness vanishes, as for the nanoporous bilayer coatings, the entire surface concentration becomes uniform and equal to the concentration set by the hygroscopic liquid. In other words, the surface concentration becomes completely independent of the nanopore size. We identified the threshold geometrical parameters for this condition and show that it can lead to a 65 K decrease in the nucleation onset surface temperature below the dew point. With this fundamental insight, we use bilayer coatings to nanoengineer the integral humidity sink effect to provide extreme antifrosting performance with up to a 2 h delay in nucleation onset at 263 K. The nanoporous bilayer coatings can be designed to combine optimal antifrosting functionality with a superhydrophobic water repelling exterior to provide coatings that can robustly prevent frost, rime, and glaze accumulation. By minimizing the required amount of antifreeze, this anti-icing method can have minimal operational cost and environmental impact.

Spatial Control of Condensation on Chemically Homogeneous Pillar-Built Surfaces

“…Similar focusing effects were reported by several groups, and lately by Sun and Rykaczewski, where micro-patches of hygroscopic liquid were used as sinks for water vapor, while the surrounding area was rendered water repellent by a hydrophobic surface chemistry. 42,43 In a FEM simulation Sun and Rykaczewski employed constant value boundary conditions at the surface of the hygroscopic liquid and a zero flux condition on the hydrophobic areas to explain the observed humidity sink effect. In Figure 5e, we present a simulation without the assumption of zero flux and find how an enhancement of the selectivity is present even for a conservative scenario without the hygroscopic effect.…”

Bubble formation in freezing droplets

“…Besides these studies on icing, many anti-icing methods are proposed to suppress the ice accretion, one of which is the application of nanoengineered surfaces. Researchers fabricated numerous surfaces with various structures and wettability and used them to delay the ice nucleation [15][16][17], reduce the ice adhesion [18,19], and even self-clean subcooled droplets or melting frost [20][21][22], and have achieved expected results.…”

Droplet re-icing characteristics on a superhydrophobic surface

“…9,10 Besides basic studies on icing, many anti-icing methods are proposed to suppress the ice accretion, one of which is the application of nanoengineered surfaces. 11,12 Researchers fabricated numerous surfaces with various structures and wettability with the purpose of delaying the ice nucleation, [13][14][15] retarding the ice propagation, 16,17 reducing the ice adhesion, 18,19 and even self-cleaning subcooled droplets or melting frost by a kind of self-jumping behavior, [20][21][22][23][24][25] and have achieved expected results.…”