Degree Type

Dissertation

Date of Award

2012

Degree Name

Doctor of Philosophy

Department

Agronomy

Major

Environmental Science

First Advisor

Robert Horton

Abstract

Coupled heat and water transfer in soil has been long recognized. The coupled transfer of heat and water near the soil surface and the temperature fluctuations and water contents that result are important for all biological, chemical, and physical processes that occur near the soil surface. Although advancements have been made in understanding coupled heat and water transfer processes in soil, deficiencies in our understanding continue to persist. The lack of soil water retention measurements at the dry end of the soil water retention curve (SWRC) limits our ability to accurately predict and simulate water movement at and near the soil surface. Furthermore, most studies neglect the effect of soil wettability and solutes on coupled heat and water transfer in soil. The overall purpose of this work is to improve our understanding of the effects of soil wettability and salinity on soil water retention and coupled heat and mass transfer in soil. The following three objectives were designed to accomplish this: (1) Measure soil water sorption including hysteresis at the dry end of the SWRC as it relates to soil wettability for two different soils; (2) Determine the effect of soil wettability on coupled heat and water transfer in response to thermal gradients; and (3) Determine the combined effects of soil wettability and soil salinity on coupled heat and mass transfer. The effect of soil wettability on soil water sorption, including relatively dry soil conditions, was measured. The effect of wettability was most noticeable at the driest end of the SWRCs for the silt loam and sand soils that were studied. Hysteresis was also found to exist in both relatively dry wettable and hydrophobic soils. Wettability and hysteresis should be considered when studying dynamics involved in water adsorption and desorption in relatively dry soils. The effect of soil wettability on coupled heat and water transfer in closed, instrumented soil columns was studied using wettable and hydrophobic soils. Soil moisture redistribution in response to the imposed temperature gradients was similar in the wettable sand and hydrophobic sand. Results indicated soil moisture redistribution under non-isothermal conditions was reduced in the hydrophobic silt loam when compared to the wettable silt loam. One week after the temperature gradients were imposed, net water transfer was reduced by 48% in the hydrophobic silt loam when compared to the wettable silt loam. After 28 days, net water transfer was reduced by more than 50% in the hydrophobic silt loam when compared to the wettable silt loam. These results indicated water vapor transfer was reduced in the hydrophobic silt loam when compared to the wettable silt loam. The combined effects of soil wettability and soil salinity on coupled heat and mass transfer were examined using two salinized wettable soils, sand and silt loam, and their salinized hydrophobic sand and silt loam counterparts. These experiments were conducted using closed, insulated, soil cells instrumented with thermo-time domain reflectometry probes (T-TDR) to provide in-situ measurements of temperature, soil volumetric water content (θ), and soil thermal conductivity (λ). Results showed that soil temperature and soil thermal conductivity distributions were influenced by soil moisture redistribution in response to the imposed temperature gradients. Soil volumetric water content distributions indicated water moved from the warm regions to the cold regions of the soil columns. Considerable salt accumulation occurred near the warm end of the wettable sand soil cell. This indicated liquid water flow occurred in the wettable sand. Minimal salt accumulation occurred near the warm end of the hydrophobic sand, wettable silt loam, and hydrophobic silt loam soil cells. Soil moisture redistribution in response to the imposed temperature gradients occurred as liquid water flow and water vapor flow in the wettable sand. Water vapor flow was the primary mechanism by which soil moisture redistribution occurred in the hydrophobic sand, wettable silt loam, and hydrophobic silt loam. The results of these experiments demonstrate the effects of soil wettability and soil salinity on soil water retention and coupled heat and water transfer in soil.

Copyright Owner

Dedrick DeWaun Davis

Language

en

Date Available

2012-10-31

File Format

application/pdf

File Size

91 pages

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