| dc.description.abstract | The coupled heat and mass transport in the vadose zone is essentially a multiphysics issue. Addressing this issue appropriately has remarkable impacts on soil physical, chemical and biological processes. That is, knowledge of heat, water and vapor transport in the shallow subsurface affects the soil evaporation pattern and rate, the contaminant volatilization and transport, and the greenhouse gas COv2 transfer and emission, as well as seed germination, plant growth and soil microbial activity. In addition, the 2007 Phoenix Mars Mission also included specifically designed instrument to measure soil thermal properties, soil temperature and moisture content due to the central significance of soil heat and water dynamics to understanding land-atmosphere exchange and the possible life environment on Mars.
Most coupled heat and water transport modeling to date has focused on the interactions between liquid water, water vapor and heat transport in homogeneous soils. Comparatively little work has been done on evaporation from layered dry soils that involves simultaneous heat and water transport under diurnal field condition. Moreover, the classic coupled heat and water model usually neglected physical processes such as adsorptive water retention, nonwetting phase air flow, etc., which were found to be significant under specific conditions. However, it is largely elusive so far on the transport parameterizations (e.g., relative air permeability) and their associated effects (e.g., extended full range water retention) on coupled heat and water transport modeling under highly transient field conditions.
In order to address the above mentioned limitations, this dissertation aims to develop and validate a predictive multiphysics modeling framework with associated improved transport parameterizations for coupled soil heat and water transport in the homogeneous and heterogeneous shallow subsurface. To this end, the following research work is specifically conducted: (a) propose improved parameterizations to better predict the nonwetting phase relative permeability; (b) explore the effects of full range water retention curve on coupled heat and water transport in homogeneous soils; and (c) investigate the nonisothermal evaporation characteristics from layered dry soils considering the additional adsorptive water retention.
The results of this study showed that: (a) the proposed modified nonwetting phase relative permeability models are much more accurate, which can be readily adopted for improved parameterization in the nonisothermal two phase flow models for structured soils evaporation; (b) considering the full range water retention is important for better soil moisture and evaporation prediction in homogeneous soils under dry conditions where water is very limited (e.g., arid and semiarid environments); and (c) the upper layer properties (layering thicknesses and sequences) and hydraulic characteristics (capillary and adsorptive water retention) have important impacts on overall evaporation water losses in layered soil profiles. | en |
