Lecture-6-Week No. 7 (June-14-2018).pdf

Soil grains water air filled voids vadose zone vs

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soil grains water air-filled voids
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Vadose Zone vs. Groundwater The physics of flow is different in the vadose zone. Vadose Zone Groundwater Component Soil, water and air Soil and water Phases Applies? Applies Darcy s Law K is dependent on θ K is constant Flow Controlled by changes in θ Elastic expansion & contraction ( α and β ) Storage Negative Positive Water Pressure
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Vadose Zone Flow and Storage Our goal is to understand how water moves in the vadose zone and continue developing tools we can use to quantify these processes. In order to understand the flow of multiple phases (termed multiphase flow) , it is important to understand the concepts of wettability , interfacial tension , and capillary forces . These concepts can be applied to a variety of systems. air and water - vadose zone oil and water - petroleum migration oil, gas, and water - oil spills in vadose zone, petroleum/natural gas migration
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When two immiscible fluids ( e.g., water and air) contact a solid surface, one will adhere more readily to the surface. This is referred to as the wetting phase because it wets the solid surfaces. The other phase is call the non-wetting phase . contact angle, λ air water The type of surface and fluids under consideration will control the wettability. We will deal exclusively with water-air-soil systems . Wettability
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Interfacial Tension, σ Refers to the phenomenon at the interface between two immiscible fluids . The molecules in one fluid will have a greater attraction for each other than they do for the opposing fluid. Also called surface tension in an air-water system. Molecules near the air-water interface feel a stronger force inward than outward. A body of water tends to have the minimum surface area for a given volume. air water
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Interfacial tension has units of energy/area or force/length. It is dependent on the two fluids that form the interface as well as the temperature. •σ air - water ≈ 0.072 N/m (@ 25C) We need to apply some force to increase the surface area of an air- water interface. This force is equal to the surface tension . F Du Noüy ring
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