On the Mechanism of Drying of Granular Beds

Evaporation from porous surfaces into turbulent airflows: Coupling eddy characteristics with pore scale vapor diffusion

“…[5] Evaporation from porous or perforated surfaces differs from evaporation from free water surfaces due to pore scale diffusive processes at the surface-air boundary layer that give rise to complex vapor concentration fields that, in turn, induce nonlinear behavior between surface wetness and evaporative flux [Suzuki and Maeda, 1968;Schl€ under, 1988;Assouline et al, 2010;Shahraeeni et al, 2012]. These nonlinear interactions are exemplified by the fact that despite gradual surface drying and a receding drying front, evaporation rates from porous surfaces under low atmospheric demand (<5 mm/d) may remain remarkably constant for extended periods (the so-called stage-I evaporation) [Suzuki and Maeda, 1968;Schl€ under, 1988;Shokri et al, 2008;Shahraeeni et al, 2012].…”

“…These nonlinear interactions are exemplified by the fact that despite gradual surface drying and a receding drying front, evaporation rates from porous surfaces under low atmospheric demand (<5 mm/d) may remain remarkably constant for extended periods (the so-called stage-I evaporation) [Suzuki and Maeda, 1968;Schl€ under, 1988;Shokri et al, 2008;Shahraeeni et al, 2012]. Our study focuses on stage-I evaporation defined as the period during which the vaporization plane remains at the surface and supplied by continuous liquid pathways [e.g., Yiotis et al, 2004;Shahraeeni et al, 2012;Or et al, 2013].…”

“…Our study focuses on stage-I evaporation defined as the period during which the vaporization plane remains at the surface and supplied by continuous liquid pathways [e.g., Yiotis et al, 2004;Shahraeeni et al, 2012;Or et al, 2013]. For relatively high evaporative demand (>5 mm/d), even when capillary flows to the surface are not limiting, evaporation rates may decrease continuously reflecting limitations to vapor exchange across the air boundary layer [e.g., Suzuki and Maeda, 1968;Schl€ under, 1988;Yiotis et al, 2007;Shahraeeni et al, 2012].…”

“…[7] In a pioneering study, Suzuki and Maeda [1968] modeled vapor transport from an array of pores under different airflow regimes. The governing equation in their model is similar to that used by Brutsaert [1975], namely considering steady advection along the surface (along mean airflow direction) supplemented by a 1-D (vertical) diffusion into the airflow.…”

“…The governing equation in their model is similar to that used by Brutsaert [1975], namely considering steady advection along the surface (along mean airflow direction) supplemented by a 1-D (vertical) diffusion into the airflow. Due to the typically large Peclet number for these two modes of transport, Suzuki and Maeda [1968] neglected vapor diffusion in the direction of flow in favor of using an advection term only. This assumption was unwarranted could lead to significant underestimation of evaporative fluxes from porous surfaces as was shown recently by Haghighi et al [2013].…”