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Performance and Economic Evaluation of Ground Heat Exchangers
Yoon, Seok,Cho, Nam Hyun,Go, Gyu Hyun,Lee, Seung Rae Trans Tech Publications, Ltd. 2013 Advanced materials research Vol.838 No.-
<P>This paper presents experimental study on the evaluation of thermal performance of U and W type ground heat exchangers (GHEs). These GHEs were installed in a partially saturated landfill ground which was composed of silt and clay in the runway area of Incheon International airport. Thermal performance tests (TPTs) were conducted for 100 hours under the continuous operation condition. Heat exchange rate of individual GHE was evaluated from the TPT results, and construction cost was also estimated. The required Borehole length of U and W type GHEs was calculated considering real construction condition from GLD (ground loop design) program.</P>
Thermal conductivity prediction model for compacted bentonites considering temperature variations
Yoon, Seok,Kim, Min-Jun,Park, Seunghun,Kim, Geon-Young Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.10
An engineered barrier system (EBS) for the deep geological disposal of high-level radioactive waste (HLW) is composed of a disposal canister, buffer material, gap-filling material, and backfill material. As the buffer fills the empty space between the disposal canisters and the near-field rock mass, heat energy from the canisters is released to the surrounding buffer material. It is vital that this heat energy is rapidly dissipated to the near-field rock mass, and thus the thermal conductivity of the buffer is a key parameter to consider when evaluating the safety of the overall disposal system. Therefore, to take into consideration the sizeable amount of heat being released from such canisters, this study investigated the thermal conductivity of Korean compacted bentonites and its variation within a temperature range of 25 ℃ to 80-90 ℃. As a result, thermal conductivity increased by 5-20% as the temperature increased. Furthermore, temperature had a greater effect under higher degrees of saturation and a lower impact under higher dry densities. This study also conducted a regression analysis with 147 sets of data to estimate the thermal conductivity of the compacted bentonite considering the initial dry density, water content, and variations in temperature. Furthermore, the Kriging method was adopted to establish an uncertainty metamodel of thermal conductivity to verify the regression model. The R<sup>2</sup> value of the regression model was 0.925, and the regression model and metamodel showed similar results.
Measuring thermal conductivity and water suction for variably saturated bentonite
Yoon, Seok,Kim, Geon-Young Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.3
An engineered barrier system (EBS) for the disposal of high-level radioactive waste (HLW) is composed of a disposal canister with spent fuel, a buffer material, a gap-filling material, and a backfill material. As the buffer is located in the empty space between the disposal canisters and the surrounding rock mass, it prevents the inflow of groundwater and retards the spill of radionuclides from the disposal canister. Due to the fact that the buffer gradually becomes saturated over a long time period, it is especially important to investigate its thermal-hydro-mechanical-chemical (THMC) properties considering variations of saturated condition. Therefore, this paper suggests a new method of measuring thermal conductivity and water suction for single compacted bentonite at various levels of saturation. This paper also highlights a convenient method of saturating compacted bentonite. The proposed method was verified with a previous method by comparing thermal conductivity and water suction with respect to water content. The relative error between the thermal conductivity and water suction values obtained through the proposed method and the previous method was determined as within 5% for compacted bentonite with a given water content.
Yoon, Seok,Lee, Seung-Rae,Go, Gyu-Hyun,Xue, Jianfeng,Park, Hyunku,Park, Dowon Techno-Press 2014 Geomechanics & engineering Vol.6 No.1
This paper presents an experimental and numerical study on the evaluation of a thermal response test using a precast high-strength concrete (PHC) energy pile and a closed vertical system with W-type ground heat exchangers (GHEs). Field thermal response tests (TRTs) were conducted on a PHC energy pile and on a general vertical GHE installed in a multiple layered soil ground. The equivalent ground thermal conductivity was determined by using the results from TRTs. A simple analytical solution is suggested in this research to derive an equivalent ground thermal conductivity of the multilayered soils for vertically buried GHEs. The PHC energy pile and general vertical system were numerically modeled using a three dimensional finite element method to compare the results with TRTs'. Borehole thermal resistance values were also obtained from the numerical results, and they were compared with various analytical solutions. Additionally, the effect of ground thermal conductivity on the borehole thermal resistance was analyzed.
Prediction of ground thermal diffusivity from thermal response tests
Yoon, Seok,Kim, Min-Jun Elsevier 2019 Energy and buildings Vol.185 No.-
<P><B>Abstract</B></P> <P>Ground-coupled heat pump (GCHP) systems are being increasingly utilized in recent years. There are several important parameters in the design of GCHP systems. As ground thermal conductivity is one of the most crucial parameters, it should be measured by conducting in-situ thermal response tests (TRTs). This paper presents the experimental results and analysis of thermal response tests to estimate the ground thermal conductivity and ground thermal diffusivity for three types of ground heat exchangers (GHEs), including U, 2U, and W-type ground heat exchangers (GHEs). Three different types of GHEs were installed in a dredged soil deposit, and continuous TRTs were conducted for 48 h. This study suggests a method to predict ground thermal diffusivity using the infinite line source model from the TRTs. Furthermore, soil samples were collected from different ground layers, and ground thermal properties were measured using laboratory tests. The equivalent ground thermal conductivity and ground thermal diffusivity measured through laboratory tests were compared with the in-situ TRT results that were newly derived in this paper. In addition, ground thermal diffusivity and ground thermal conductivity values that were obtained through research were used as input parameters in numerical analysis. The in-situ TRT results were numerically modeled using the finite element method.</P> <P><B>Highlights</B></P> <P> <UL> <LI> In-situ TRTs were conducted for 48 h with U, 2 U, and W type GHEs. </LI> <LI> The ground thermal diffusivity is derived by using an infinite line source model and regression analysis. </LI> <LI> The method to derive ground thermal diffusivity from in-situ TRTs was validated with laboratory test results. </LI> <LI> An in-situ TRT for W type GHE was numerically modeled by using ground thermal diffusivity and ground thermal conductivity as input parameters. </LI> </UL> </P>
Yoon, Seok,Lee, Seung-Rae,Kim, Yun-Tae,Go, Gyu-Hyun Techno-Press 2015 Geomechanics & engineering Vol.9 No.1
Saturated soil hydraulic conductivity is a very important soil parameter in numerous practical engineering applications, especially rainfall infiltration and slope stability problems. This parameter is difficult to measure since it is very highly sensitive to various soil conditions. There have been many analytical and empirical formulas to predict saturated soil hydraulic conductivity based on experimental data. However, there have been few studies to investigate in-situ hydraulic conductivity of weathered granite soils, which constitute the majority of soil slopes in Korea. This paper introduces an estimation method to derive saturated hydraulic conductivity of Korean weathered granite soils using in-situ experimental data which were obtained from a variety of slope areas of South Korea. A robust regression analysis was performed using different physical soil properties and an empirical solution with an $R^2$ value of 0.9193 was suggested. Besides that this research validated the proposed model by conducting in-situ saturated soil hydraulic conductivity tests in two slope areas.