Pore-Level Modeling of Isothermal Drying of Pore Networks Accounting for Evaporation, Viscous Flow, and Shrinking

Microstructural Changes of Apples (Granny Smith) During Drying: Visual Microstructural Changes and Possible Explanation from Capillary Pressure Data

“…Results shown in Figures 5 and 6 confirm this assumption; as liquid content in the cell structure decreases, capillary pressure increases; when the liquid film is lower than 1 m, the value of capillary pressure considerably increases because of the disjoining pressure, whereas shrinkage increases even more. Segura and Toledo [5] developed a discrete drying model that considers shrinkage as a function of changes in capillary pressure and found that transport properties and drying curves are strongly dependent on shrinkage. Figure 7 shows the different drying stages and the morphology of the liquid fraction as drying progresses in order to illustrate the shrinkage process at pore-scale.…”

“…They suggested the existence of two drying zones in the porous structure: a wet region (liquid-filled and dominated by capillary flow) and a sorption region (dominated by vapor transfer and movement of bound water). These studies also put forward the following list of mechanisms: (1) liquid movement in capillary forces; (2) diffusion of liquid caused by differences in concentration, (3) surface diffusion in liquid layers absorbed at solid interfaces, (4) water vapor diffusion in air-filled pores caused by partial pressure differences, (5) water flow in total pressure differences, (6) flow caused by shrinkage and pressure gradients, (7) flow caused by gravity, and (8) flow caused by a vaporization-condensation sequence. These mechanisms are present at different stages of the drying process and their relative importance depends on drying conditions, pore geometry, pore topology, and wall composition of the porous medium [7] .…”

“…According to Rahaman and Perera [31] and Rahaman [9,28] , possible physical mechanisms that can play an important role during shrinkage are: (1) pore pressure, (2) glass transition, (3) moisture transport mechanisms, (4) matrix mechanical strength, (5) environmental pressure, (6) surface electrical charge, and (7) gravitational force. One of these authors mentions that the "surface tension causes collapse in terms of the capillary suction created by a receding liquid meniscus" [9] .…”

“…Liquid water contained in the porous structure is gradually removed by several mechanisms during drying. Some research studies have distinguished different drying mechanisms that occur at pore level [3][4][5][6][7] . They suggested the existence of two drying zones in the porous structure: a wet region (liquid-filled and dominated by capillary flow) and a sorption region (dominated by vapor transfer and movement of bound water).…”

Network models for capillary porous media: application to drying technology

“…The effective parameters, e.g., liquid permeability, are determined by numerical experiments on partially saturated pore network. In drying technology, the authors are currently developing this approach; some pioneering work can already be found in literature [3,7].…”