Water and Vapor Movement with Condensation and Evaporation in a Sandy Column

Abstract

The diffusion of warm, humid air into an initially cold, dry, sandy column was analyzed to study the movement of water vapor and liquid water under nonisothermal and low water content conditions. The analysis was performed using the HYDRUS‐1D code. While the water retention curve of sand was measured experimentally, the unsaturated hydraulic conductivity function was inversely estimated from the observed water content profiles in the column. The estimated unsaturated hydraulic conductivity function displayed a shape that reflected distinct processes of capillary pore water flow and film flow at high and low water contents, respectively. Four components of the total water flux, including thermal and isothermal liquid water and water vapor fluxes, were evaluated using the calibrated soil hydraulic properties. Evaporation and condensation rates were calculated based on water mass balance. Water vapor entered the soil column at the hot surface and condensed at the cold bottom. Subsequently, liquid water moved upward and evaporated at the moisture front in the middle of the column where the relative humidity decreased below unity. Liquid water and water vapor then circulated between the bottom and the moisture front, accompanied by condensation and evaporation processes. The impact of the enhancement factor in the thermal vapor diffusion term could not be clearly identified from available experimental water content profiles. Increases in liquid water flow and the evaporation rate could be compensated for by increases in vapor flow and the condensation rate. Additional data would be needed to fully evaluate the effect of the enhancement factor.

Vapor Flow Resistance of Dry Soil Layer to Soil Water Evaporation in Arid Environment: An Overview

“…Among the few studies, this overview selected four representatives (Table 1), including [22], [63], [67] and [68], to analyze advances and challenges in modeling Phase III soil water evaporation. Again, these representatives were overviewed in chronological order to highlight the continuous improvements of modeling techniques.…”

“…Sakai et al [67] set up a PdV model for six identical dune sand (90% of soil particles > 0.1 mm and 3% of soil particles < 0.02 mm) columns (height 10 cm and diameter 10 cm) using the HYDRUS-1D code [92], and used the model to reproduce the measured condensation dynamics. In the laboratory experiment, the tops of the columns were exposed to hot (37 °C) and moist air, while the closed bottoms of the columns were maintained at 20 °C by circulating constant-temperature water along the base of the columns using a water pump.…”

“…Sakai et al [67] set up PdV models for three 15-cm-long sand, silt, and silty clay soil columns and another 20-cm-long silt soil column using the HYDRUS-1D code with a grid spacing of less than 1.0 mm. A hypothetical constant or diurnal climate was used as the upper boundary condition, while zero water flux and a constant temperature of 25 °C were used as the lower boundary condition.…”

“…For Phase I and II, E tends to be maximal when total heat flux into the soil is greatest (e.g., seasonally in summer and daily at noon), whereas for Phase III, in contrast, E tends to be maximal when total heat flux out of the soil is greatest (e.g., seasonally in winter and daily at midnight). However, as pointed out by [26] and in my own research, due to wrong modeling premises (e.g., the traditional hydraulic functions are assumed to still be suitable for water potentials of <−1.5 × 10 4 cm) or insufficient and inclusive experimental (mostly laboratory soil-column) data, previous studies [22,23,[53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71] primarily examined and reported dynamics of Phase I and II evaporation. For this reason, the features presented by those researchers are unlikely to be found at any sites under naturally dry conditions, where most of the time a top DSL lies over underlying moist soils and Phase III dominates the soil water evaporation process.…”

A New Mechanism of Canopy Effect in Unsaturated Freezing Soils

“…Nassar and Horton (1989) [5] further extended Milly's work by including osmotic effects on liquid and water vapor movement. Sakai et al (2009) [6] presented a coupled model for water and vapor movement which considers condensation and evaporation effects under nonisothermal and low water content conditions.…”