Evaporative heat and mass transfer from the free surface of a liquid wicked into a bed of spheres

Abstract

Evaporation of ethanol from square packed arrays of 3.95 mm diameter copper spheres in a transparent, enclosed chamber is investigated. The enclosure ensures that relatively saturated vapor conditions exist near the free surface. The desired heat flux is imposed on the copper substrate upon which the copper spheres are mounted, and the liquid level in the bed is maintained by wicking from a continuous supply of liquid provided by a syringe pump.Transparent windows in the enclosure allow for visualization of the evaporating liquid meniscus shape, which is recorded for different liquid feeding rates and heat fluxes. Experimentally measured meniscus profiles are compared to analytical results based on surface-energy minimization. A meniscus microregion is defined from the contact line to the length where the liquid thickness reaches 10 μm. An approximate kinetic theory-based analysis estimates that up to ~55% of the total meniscus mass transfer occurs in this microregion.

Advances in Fluid and Thermal Transport Property Analysis and Design of Sintered Porous Wick Microstructures

“…Iverson et al [30] experimentally quantified evaporation rates from sintered wick samples under conditions simulating heat pipe operation. Furthermore, Davis and Garimella [31] measured evaporative thermal resistance of wicks of different porosities under saturated vapor conditions, while Migliaccio and Garimella [32] mapped out the evaporative performance of an organized bed of copper spheres. Hanlon and Ma [33] performed experiments and developed a simple numerical model to delineate the role of thin-film evaporation in sintered media.…”

“…Evaporation from the thin-film region of a liquid meniscus has been shown in a number of prior studies (e.g., Refs. [32,56,57]) to be the dominant mode of phase-change heat transfer from thin wick layers. Ranjan et al [55] observed that an approximately 20% area of the meniscus near the triple line contributes to more than 80% of the overall evaporative heat transfer from the entire meniscus.…”