Enhancement of Thermal Water Vapor Diffusion in Soil

Cass, A.; Campbell, Gaylon S.; Jones, T.L.

doi:10.2136/sssaj1984.03615995004800010005x

Cited by 251 publications

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“…q vp and q vT are vapor fluxes due to water potential gradient and temperature gradient respectively, D v is the vapor diffusivity of the soil, ρ vs is the saturated vapor density at soil temperature, T, h r is the relative humidity within the soil, h is the pressure head, s v is the slope of the saturated vapor pressure curve (dρ v /dT) and ζ is an enhancement factor for vapor flux in response to the temperature gradient [Cass et al, 1984].…”

Section: Mathematical Modelmentioning

confidence: 99%

An Evaluation of Unsaturated Flow Models in an Arid Climate

Dixon

1999

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An Evaluation of Unsaturated FlowModels in an Arid Climate by Jason DixonDr. James Cardle, Examination Committee Chair Professor of Civil and Environmental Engineering University of Nevada, Las VegasThe objective of this study was to evaluate the effectiveness of two unsaturated flow models in arid regions. The area selected for the study was the Area 5 Radioactive Waste Management Site (RWMS)at the Nevada Test Site in Nye County, Nevada. The two models selected for this evaluation were HYDRUS-1D [Simunek et al., 1998] and the SHAW model [Flerchinger and Saxton, 1989].Approximately 5 years of soil-water and atmospheric data collected from an instrumented weighing lysimeter site near the RWMS were used for building the models with actual initial and boundary conditions representative of the site. Physical processes affecting the site and model performance were explored. Model performance was based on a detailed sensitivity analysis and ultimately on storage comparisons. During the process of developing descriptive model input, procedures for converting hydraulic parameters for each model were explored. In addition, the compilation of atmospheric data collected at the site became a useful tool for developing predictive functions for future studies. The final model results were used to evaluate the capacities of the HYDRUS and SHAW models for predicting soilmoisture movement and variable surface phenomena for bare soil conditions in the arid vadose zone. The development of calibrated models along with the atmospheric and soil data collected at the site provide useful information for predicting future site performance at the RWMS.

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Section: Mathematical Modelmentioning

confidence: 99%

An Evaluation of Unsaturated Flow Models in an Arid Climate

Dixon

1999

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“…Experimental and modeling studies have established that in unsaturated porous media, vapor diffusion is enhanced relative to the diffusion of non-condensable gases by pore-level phase change effects (Philip and de Vries, 1957;Cass et al, 1984;Webb and Ho, 1998). Enhancement coefficients are poorly known for field-scale systems, and no such effects have been included in the present study.…”

Section: Fluid Propertiesmentioning

confidence: 99%

Multiphase fluid flow and heat transfer at Hanford single-shell tanks - a progress report on modeling studies

Pruess¹

2000

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“…Measurement of both buoyant gas flow and enhanced diffusion would require advection to be relatively unimportant. The enhanced binary diffusion coefficient is poorly understood in porous media where it has been studied for more than 40 years (Cass, Campbell, and Jones, 1984). The conditions for which it exists in a partially saturated fracture have not yet been identified.…”

Section: Drive: Implications For Fast Liquid Flow Pathsmentioning

confidence: 99%

Preferential Flow Paths and Heat Pipes: Results From Laboratory Experiments on Heat-Driven Flow in Natural and Artificial Rock Fractures, Level 4 Milestone Id: Spl6a5m4, WSB 1.2.3.12.2

Kneafsey¹

1997

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Water flow in fractures under the conditions of partial saturation and thermal drive may lead to fast flow along preferential localized pathways and heat pipe conditions. Water flowing in fast pathways may ultimately contact waste packages at Yucca Mountain and transport radionuclides to the accessible environment. Sixteen experiments were conducted to visualize liquid flow in glass fracture models, a transparent epoxy fracture replica, and a rockJreplica fracture assembly. Spatially resolved thermal monitoring was performed in seven of these experiments to evaluate heat-pipe formation. Depending on the fracture apertures and flow conditions, various flow regimes were observed including continuous rivulet flow for high flow rates, intermittent rivulet flow and drop flow for intermediate flow rates, and film flow for low flow rates and wide apertures. These flow regimes were present in both fracture models and in the replica of a natural fracture. Heat-pipe conditions indicated by low thermal gradients were observed in five experiments. Conditions conducive to heat-pipe formation include an evaporation zone, condensation zone, adequate space for vapor and liquid to travel, and appropriate fluid driving forces. In one of the two experiments where I heat pipe conditions were not observed, adequate space for liquid-vapor counterflow was not provided. Heat pipe conditions were not established in the other, because liquid flow was inadequate to compensate for imbibition and the quantity of heat contained within the rock. 1 . Introduction Heat released from high-level nuclear waste packages in a partially saturated environment can have major impacts on moisture distribution and migration. The tuff formations in the unsaturated zone at Yucca Mountain contain from 40 to 80% or more liquid water in the pore space, which will be vaporized as formation temperatures approach and exceed the boiling point at prevailing pressures. This will cause pressurization of the gas phase, which will drive vapor away from the heat source. In a fractured medium, the vapor is expected to flow primarily in the fractures. Condensation will take place as the vapor invades cooler rock, which will generate mobile water in the fractures. The water will flow under the combined action of gravity and capillary forces. It may, in part, return to the vicinity of the waste packages where it would again be subject to vaporization (Buscheck and Nitao, 1993). Mathematical modeling studies have indicated that vaporization may not be complete. Water flowing down (sub-) vertical fractures may partially escape vaporization, and may migrate considerable distances through fractured rock that is at above-boiling temperatures (Pmess, 1997). This raises the obvious concern that flowing condensate may contact waste packages, and provide a pathway for the transport of water-soluble radionuclides.The amount of water that could be generated by vaporization-condensation cycles is potentially very large. From the data given by Pruess and Tsang (1994) one can d...

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Enhancement of Thermal Water Vapor Diffusion in Soil

Cited by 251 publications

References 0 publications

An Evaluation of Unsaturated Flow Models in an Arid Climate

An Evaluation of Unsaturated Flow Models in an Arid Climate

Multiphase fluid flow and heat transfer at Hanford single-shell tanks - a progress report on modeling studies

Preferential Flow Paths and Heat Pipes: Results From Laboratory Experiments on Heat-Driven Flow in Natural and Artificial Rock Fractures, Level 4 Milestone Id: Spl6a5m4, WSB 1.2.3.12.2

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