Condensation is a ubiquitous natural phenomenon with both detrimental and beneficial implications. The key point to minimize its harmful effects while harnessing its potential for various applications is the spatial controlling of condensation. In recent years, using hygroscopic liquids for spatially controlling condensation has gradually emerged as a promising strategy. However, the underlying mechanisms and influencing parameters of controlling condensation with hygroscopic liquids remain insufficiently understood. In this paper, the effect of hygroscopic droplets in suppressing condensation on low-temperature surfaces, specifically -15 ℃ to 15 ℃, under different conditions, including substrate temperature, cooling time, droplet volume are studied. A typical hygroscopic liquid, dipropylene glycol, was employed to illustrate this issue. The results indicated that distinct ring-shaped dry zone forms around dipropylene glycol droplets on low-temperature surfaces, evidencing their efficacy in inhibiting condensation. Experiments and theoretical analysis reveal that the ratio of the dry-zone radius to the droplet radius is a function of substrate surface temperature, scaling as 1/( T dew - T c ). The results also show that cooling time has a negligible effect on this ratio over short periods. Furthermore, the ratio slightly decreases with increasing droplet volume at higher substrate temperatures, while remaining nearly constant at lower temperatures. These findings may enhance our understanding of the condensation inhibition effect of hygroscopic droplets and also provide valuable insights for potential applications in condensation control.
Anti-condensation is important in various fields, e.g., transportation, power transmission, internal drying of precision instruments. Vapor sink is an important manner to suppress the happening of water vapor condensation, and shows potentials in some special scenarios. However, the mechanism of anti-condensation by vapor sink is not well understood up until now. In this article, the effect of substrate temperature on the dry zone generated by vapor sink were systematically studied with experiments and theoretical analysis. First, the effect of hygroscopic solutions on the local humidity were measured. The results indicated that the local humidity level near the hygroscopic solutions was effectively suppressed, reducing the water vapor condensation. Second, the variation of the dry zone with the cooling substrate temperature was systematically studied. The results indicated that the dry zone exhibits a hyperbolic relationship with the substrate temperature. The dry zone changing under different humidity conditions and cooling time were also studied. The dry zone remained approximately unchanged over time in a short period. Finally, a simple yet effective model between the dry zone and substrate temperature was deduced. The theoretical results are in good agreement with the experimental data. Our study may deeper the understanding of condensation suppression via vapor sink and offer guidance to the design of anti-condensation or anti-icing surfaces.
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