Role of Nonequilibrium Water Vapor Diffusion in Thermal Energy Storage Systems in the Vadose Zone

Abstract

Although siting of geothermal energy storage systems in the vadose zone may be beneficial due to the low heat losses associated with the low thermal conductivity of unsaturated soils, water phase change and vapor diffusion in soils surrounding geothermal heat exchangers may play important roles in both the heat injection and retention processes that are not considered in established design models for these systems. This study incorporates recently-developed coupled thermo-hydraulic constitutive relationships for unsaturated soils into a coupled heat transfer and water flow model that considers time-dependent, nonequilibrium water phase change and enhanced vapor diffusion to study the behavior of geothermal energy storage systems in the vadose zone. After calibration of key parameters using a tank-scale heating test on compacted silt, the ground response during 90 days of heat injection from a vertical geothermal heat exchanger

Impacts of Unsaturated Conditions on The Ultimate Axial Capacity of Energy Piles

“…Water flow in unsaturated soils under thermal gradients has been evaluated in several studies [13][14][15][16]. There are several mechanisms for thermally induced water flow in unsaturated soils.…”

“…The water content data at pro 0.6 m, 2.4 m, and 4.3 m at a from the surface were correc and (16). Time series of the Figures 3 and 4 the soil behavior during heating of the profiles of temperature and volumetr after equilibration (i.e., before axial energy pile) from the model and experi in Figure 5.…”

Temperature-Dependent Model for Small-Strain Shear Modulus of Unsaturated Soils

“…In many of the geotechnical and geoenvironmental applications mentioned above, changes in temperature may occur, which have an additional effect on the elastic moduli of unsaturated soils. Further, other geotechnical applications involving elevated temperatures include earthen structure-atmospheric interaction under a changing climate, storage of nuclear waste, energy piles, soil-borehole thermal energy storage systems, buried high voltage cables, and thermally active earthen structures (e.g., Gens and Olivella, 2001;Laloui and Di Donna, 2013;Robinson and Vahedifard, 2016;Vahedifard et al, 2015Vahedifard et al, , 20162017;2018a;McCartney et al, 2016;Başer et al, 2018;Thota et al, 2019;Shahrokhabadi et al, 2020). Several experimental studies have illustrated the effects of temperature on the shear strength, volume change and stiffness of saturated and unsaturated soils (e.g., Cekerevac and Laloui, 2004;Uchaipichat and Khalili 2009;Coccia et al, 2013;Alsherif and McCartney, 2015;Zhou and Ng, 2016;Ng et al, 2017).…”

Impact of temperature on the pullout of reinforcing geotextiles from unsaturated silt

“…One challenge encountered when incorporating geothermal heat exchangers into MSE walls is that heat transfer may lead to a change in the behavior of the soil and geosynthetic reinforcements, which must be understood before this technology is implemented in practice. As mentioned, thermally-induced flow of water is expected to occur in unsaturated soils from zones of high temperature (i.e., at the geothermal heat exchangers) to zones of lower temperature due to a combination of water phase change and enhanced vapor diffusion (i.e., Philip and De Vries 1957;Başer et al 2018). This will lead to a lower degree of saturation, increased suction, and increased 76 effective stress in the backfill soil at the locations of the heat exchangers (Coccia and McCartney 77 2013).…”