Papers by Tugce Baser, Ph.D.
This study focuses on an evaluation of the subsurface temperature distribution during operation o... more This study focuses on an evaluation of the subsurface temperature distribution during operation of a Soil-Borehole Thermal Energy Storage (SBTES) system. The system consists of an array of five 9 m-deep geothermal heat exchangers, configured as a central heat exchanger surrounded by four other heat exchangers at a radial spacing of 2.5 m. In addition to monitoring the temperature of the fluid entering and exiting each heat exchanger, 5 thermistor strings are embedded in boreholes inside and outside of the array to monitor changes in ground temperature with depth. After 75 days of heat injection at a constant rate of 25 W/m, the heat loss from the system was monitored over a 4-month rest period. Although the heat injection rate is smaller than that expected in an actual SBTES systems (35-50 W/m), the average ground temperature increased by 7 °C at the end of heating. However, the average ground temperature was only 3 °C greater than the initial ground temperature at the end of the rest period due to lateral heat loss. The trends in subsurface temperatures during heat injection were consistent with the results from a simplified heat injection simulation, although they indicate that the thermal properties of the soil may be changing with time. An energy balance analysis indicates the number of boreholes in the array was too few to effectively concentrate the heat injected during the test within the array. Nonetheless, the results provide an experimental reference point between a single borehole and a larger SBTES system.
This paper focuses on the role of unsaturated soil mechanics in different thermal energy applicat... more This paper focuses on the role of unsaturated soil mechanics in different thermal energy applications in geotechnical engineering. These applications include ground-source heat exchangers in geotechnical engineering infrastructure (drilled shafts, diaphragm walls, etc.), injection of excess heat into near-surface thermally active geotechnical systems involving unsaturated soils (embankments, retaining walls with poorly draining backfill), and soil-borehole thermal energy storage systems. In addition to discussing the effects of temperature on soil properties, results from different physical modeling experiments on thermally active geotechnical systems are presented. The results indicate that consideration of inter-relationships between heat transfer, water flow, and mechanical effects leads to opportunities for improving heat transfer in unsaturated soils, as well as for improving the performance of geotechnical systems involving unsaturated soils.
This paper focuses on characterization of the heat-transfer and water-fl ow processes in physical... more This paper focuses on characterization of the heat-transfer and water-fl ow processes in physical models of borehole heat exchanger arrays in unsaturated soil layers. The overall goal is to develop a data set that can be used to validate the coupled thermo-hydraulic fl ow models needed to simulate the effi ciency of heat transfer in soil-borehole thermal energy storage systems. Two bench-scale physical models consisting of a triangular array of vertical heat exchangers within a layer of unsaturated silt were constructed in insulated cylindrical tanks to evaluate the impact of different boundary conditions on the heat-transfer and water-fl ow processes in the silt during heat injection into the array. In one model, the heat exchangers were placed at a radial location at 26% of the tank radius, while in the other model, the heat exchangers were placed on the inside of the tank wall. During circulation of heated fl uid through the heat exchangers, the changes in soil temperature and volumetric water content along the centerline of the array at different depths were measured using dielectric sensors. The thermal conductivity and specifi c heat capacity of the silt were also monitored using a thermal probe at the center of the silt layer at midheight. Permanent drying was observed for the soil within the array with the smaller spacing, while an increase in water content was observed in the array with a spacing equal to the container diameter. An increase in thermal conductivity of the soil was observed within *.
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Papers by Tugce Baser, Ph.D.