Moisture Evaporation and Migration in Thin Porous Packed Bed Influenced by Ambient and Operating Conditions

Abstract

SUMMARYThe present paper investigates moisture migration in a thin porous bed filled with unconsolidated sand, unsaturated with water, and examines its cooling effect by water evaporation when used as a cooling device for room air-conditioning. An analytical model has been developed to simulate heat and moisture transport phenomena numerically and calculate the evaporation rate of water on which its cooling performance is dependent. For the case of a horizontal thin bed problem, with very small height and a relatively larger surface that is exposed to atmosphere air, one-dimensional, steady-state computation results have been obtained by focusing on the influence of ambient and operating conditions on the physical quantity fields in the porous packed bed.

Study of heat and moisture transfer in soil with a dry surface layer

“…Previously developed seven-field model [10,11,18] by current authors is used to describe simultaneous heat, moisture and gas migration in unsaturated porous media with phase change in wet region.…”

“…A formula to calculate the gaseous infiltrating conductivity K g corresponding to the liquid hydraulic conductivity K l , which can demonstrate the mechanisms of DarcyÕs drag resistance in terms of gaseous phase and the reaction of liquid to gaseous mixture, had been developed in the previous work [18]. At the same time, many researches [19,20] indicate that hydraulic conductivity K l is also influenced by temperature.…”

Volcanic ash decreases dehydration tolerance in the field cricket Gryllus bimaculatus (Orthoptera: Gryllidae)

“…While cricket dehydration tolerance (as adults) was reduced on soil only after continuous contact with Akadama soil (as nymphs and adults), adult crickets still experienced a reduction in dehydration tolerance after only nymphal exposure to volcano ash, suggesting some form of carryover effect. Because Akadama soil is porous and highly water retentive (Liu et al, 1997), dried Akadama soil may absorb moisture from its environment. If crickets are in contact with Akadama soil, dehydration tolerance might therefore be weak because the substrate acquires moisture from the surrounding environment.…”

Solar cooling with hydrophilic porous materials for reducing building cooling needs

“…Among the most studied natural materials for roof evaporative cooling applications is unconsolidated sand (Dos Santos and Mendes, 2013;Liu et al, 1997;Meng and Hu, 2005;Wanphen and Nagano, 2009). Sand is a low-cost, durable, and locally available material in most of the world.…”

“…In the last few years, the use of porous materials for the "free" integrated evaporative cooling of buildings has been started systematically to be studied mainly as a sustainable and alternative way to cool the roof surface of a building or the pavement of outdoor spaces by taking advantage of the properties of porous materials (Liu et al, 1997;Meng, 1996;Meng and Hu, 2005;Okada et al, 2008;Vardoulakis et al, 2011;Wanphen and Nagano, 2009). According to the principle of evaporation cooling of buildings with porous materials, stored water or night-sorbed moisture is evaporated during the hot day and the porous surface temperature is reduced due to the release of the latent heat.…”