• Journal of the Korean Geotechnical Society
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• v.26 no.7
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• pp.93-106
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• 2010

In performing a series of in-situ thermal response tests, the effective thermal conductivities of six vertical closed-loop ground heat exchangers were experimentally evaluated and compared one another, which were constructed in a test bed in Wonju. To compare thermal efficiency of the ground heat exchangers in field, the six boreholes were constructed with different construction conditions: grouting materials (cement vs. bentonite), different additives (silica sand vs. graphite) and the shape of pipe-sections (general U-loop type vs. 3 pipe-type). From the test results, it can be concluded that cement grouting has a higher effective thermal conductivity than bentonite grouting, and the efficiency of graphite better performs than silica sand as a thermally-enhancing addictive. In addition, a new 3 pipe-type heat exchanger provides less thermal interference between the inlet and outlet pipe than the conventional U-loop type heat exchanger, which results in superior thermal performance. Based on the results from the in-situ thermal response tests, a series of economic analyses have been made to show the applicability of the new addictives and 3 pipe-type heat exchanger.

• Resources Recycling
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• v.32 no.3
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• pp.18-25
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• 2023

Sericite was ground with or without additives (LiNO₃ or TiO₂) using a planetary mill. The resultant ground products included the average particle size of 2-3 ㎛ (sericite only or sericite+LiNO₃) and 0.5-0.6 ㎛ (sericite+TiO₂) were obtained within 10 minutes of grinding time. respectively. In the grinding of the sericite without any addictive, the particle size initially decreased, but, as grinding time elapsed thereafter, agglomerates were formed and D50 increased over 10 ㎛. In contrast, when the additive was added, the particle size decreased as the grinding time elapsed and any aggregation was relatively not noticeable, compared with the grinding of the sericite only. As a result of measuring the zeta potential for the raw or the ground samples, variation of the zeta potential values according to pH at the early stage of the grinding with the addictives was gentler than that at the final stage of grinding, which showed the relatively similar trend to the pH-zeta potential correlation in grinding of raw sericite. In addition, as a result of the disintegration experiment through ultrasonic excitation, D50 decreased rapidly only until the disintegration time of about 50 minutes.