How liquid evaporation relies on the porosity of a surface

If two surfaces can hold the same fraction of liquid compared to their surface area — that is, they have the same porosity — how much do the size of the pores and the distance between them matter?

Evaporation from porous surfaces plays an important role in a wide range of fields, from the effects of soil surfaces on climate modeling to cooling applications in electronics. Hiroki Imai and Ikuya Kinefuchi studied how and why pore size affects evaporation flux from these types of surfaces.

“At first glance, one might expect the amount of evaporation to be independent of pore size, since the fraction of the surface area occupied by liquid is the same,” Kinefuchi said. “To answer this question, we analyzed the evaporation gas flow above porous surfaces.”

The researchers used simulations to analyze the gas flow generated by evaporation from the pores, comparing the effects of three orders of magnitude of pore spacing. They found that evaporation flux increases with pore sizes because of accelerations in vapor flow in the region immediately above the liquid surface.

In real systems, these pores do not operate on their own; their effects are compounded by contributions from surface wettability, geometry, thermal conductivity, and more. Imai and Kinefuchi plan to extend their simulations from 2D to 3D to better understand these interactions. They hope their work will help answer additional fundamental questions about evaporation dynamics, including what the velocity distribution of gas molecules is as they evaporate from a liquid surface.

Source: “Pore-scale effect on the non-equilibrium gas flow induced by evaporation from two-dimensional porous surfaces,” by Hiroki Imai and Ikuya Kinefuchi, Physics of Fluids (2026). The article can be accessed at https://doi.org/10.1063/5.0337128 .