Thermal signatures of turbulent airflows interacting with evaporating thin porous surfaces

Evaporative drying of porous surfaces interacting with turbulent airflows is common in various natural (hydrology, climate) and industrial (food, paper, and building materials) applications. Turbulent airflows induce spatially-complex and highly intermittent boundary conditions that affect surface evaporation rates and associated near-surface thermal regimes. Such interactions are particularly significant during stage-I evaporation (vaporization plane at the surface) where turbulent eddies induce highly localized and intermittent variations in evaporative fluxes that leave distinct thermal signatures observable by infrared thermography (IRT). A theoretical framework supported by an experimental method was proposed to capitalize on measured thermal fluctuations of evaporating porous surfaces to determine airflow turbulence characteristics and evaporative fluxes. The study focuses on thin surfaces with low thermal capacity to illustrate experimentally direct links between characteristics of surface thermal fluctuations and momentum-based turbulent eddy residence times. For most practical applications, the method could be applied using rapid IR measurements from a single sensor aimed at the surface. The theoretical links between surface wetness and characteristics of surface temperature fluctuations offer opportunities for remote quantification of drying and energy exchange processes from engineered and natural porous surfaces.