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- Hansson, Klas, et al.
(författare)
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Water flow and heat transport in frozen soil : Numerical solution and freeze-thaw applications
- 2004
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Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 3:2, s. 693-704
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Tidskriftsartikel (refereegranskat)abstract
- A new method is presented to account for phase changes in a fully implicit numerical model for coupled heat transport and variably saturated water flow involving conditions both above and below zero temperature. The method is based on a mixed formulation for both water flow and heat transport similar to the approach commonly used for the Richards equation. The approach enabled numerically stable, energy- and mass-conservative solutions. The model was evaluated by comparing predictions with data from laboratory column freezing experiments. These experiments involved 20-cm long soil columns with an internal diameter of 8 cm that were exposed at the top to a circulating fluid with a temperature of −6°C. Water and soil in the columns froze from the top down during the experiment, with the freezing process inducing significant water redistribution within the soil. A new function is proposed to better describe the dependency of the thermal conductivity on the ice and water contents of frozen soils. Predicted values of the total water content compared well with measured values. The model proved to be numerically stable also for a hypothetical road problem involving simultaneous heat transport and water flow. The problem was simulated using measured values of the surface temperature for the duration of almost 1 yr. Since the road was snow-plowed during winter, surface temperatures varied more rapidly, and reached much lower values, than would have been the case under a natural snow cover. The numerical experiments demonstrate the ability of the code to cope with rapidly changing boundary conditions and very nonlinear water content and pressure head distributions in the soil profile.
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- Persson, Magnus, et al.
(författare)
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Time-domain reflectometry probe for water content and electrical conductivity measurements in saline porous media
- 2004
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Ingår i: Vadose Zone Journal. - 1539-1663. ; 3:4, s. 1146-1151
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Tidskriftsartikel (refereegranskat)abstract
- A new coated time-domain reflectometry (TDR) probe design is described and evaluated. In contrast to previous coated TDR probes, our probe may be used to measure both the dielectric constant (K-a) and bulk electrical conductivity (sigma(a)) in saline porous media. This was made possible by attaching two coaxial cables to a 0.27-m three-rod with a coated central rod. The shield of the first cable was to one of the outer rods and the conductor was connected to the coated central rod. The conductor and shield of the other coaxial cable were connected to each of the two outer rods, respectively. Thus, our probe consists of two unbalanced, two-rod probes. The probe is called coated-uncoated probe (CUP). Four prototypes with two different coating materials (i.e., polyolefin and kynar heat-shrink tubes) were evaluated. The probes were calibrated in several fluids having different K-a and sigma(a). The K-a measurement of the coated part the probe was successfully fitted to target K-a using a two-phase dielectric mixing model. Due to signal attenuation, measurements of K-a were not possible for sigma(a) higher than 9 dS m(-1) for the polyolefin-coated probes whereas the upper limits for the kynar-coated probes and the uncoated probe were 5 and 2.5 dS m(-1), respectively. Measurements of sigma(a) are only possible with the uncoated part. Measurements of K-a and sigma(a) were also taken during three upward infiltration experiments in sand using soil solution electrical conductivities of 0.01, 6.31, and 12.03 dS m(-1). For the uncoated part, K-a could not be measured when sigma(a) was higher than about 2 dS m(-1), whereas K-a measurements were possible using the coated part even when sigma(a) was 3 dS m(-1).
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