Seok Yoon

Identification of inhibitory metabolites in high density culture of recombinantBacillus megaterium PCK108

SummaryPropionic and isobutyric acids were found to be the major inhibitory metabolites for carboxymethyl(CM)-cellulase in high density culture of a recombinantBacillus megaterium pCK108. These organic acids accumulated significantly at the glucose feed rate of 12g/hr. They inhibited CM-cellulase production by about 80% even at 20mM and 10mM of propionic and isobutyric acids, respectively.

Life Cycle Cost Analysis for Ground-Coupled Heat Pump Systems Including Several Types of Heat Exchangers

Ground-Coupled Heat Pump (GCHP) systems are now popular in both residential and commercial applications because of their great advantages as compared to conventional electrical air conditioning systems. One of the most important problems in evaluating the GCHP systems is optimizing the Life Cycle Cost (LCC) of the systems. Yeung firstly proposed LCC optimization model to roughly estimate the LCC of GCHP systems with single U-type heat exchangers. However, in this optimization, only single U-type heat exchanger was considered. Moreover, the optimization did not take into account the eect of pipe sizes on the heat pump and neither considered the capacity of the heat pump. In this paper, a model of LCC optimization with new improvements was proposed to optimize the LCC of GCHP systems in consideration with the eect of pipe sizes and capacity of the heat pump for not only single U-type heat exchanger but also for double, triple U-type, and coil-type heat exchangers.

Performance and Economic Evaluation of Ground Heat Exchangers

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.

Comparison of Borehole Thermal Resistance Values of Ground Heat Exchanger Obtained by Several Methods

The Ground-Coupled or Source Heat Pump (GCHP/GSHP) system is increasingly being considered as an alternative to traditional cooling/heating system because it can reduce the emission of greenhouse gases. The GCHP/GSHP system uses sustainable ground temperature to emit heat during the summer and to extract heat during the winter. It is a ubiquitous system because it can be used at any time or place and semi-permanent energy. The geothermal system is composed of Ground Heat Exchanger (GHE), heat pump and load facilities. The GHE is embedded in a borehole, which is made up of GHE and grout. The borehole thermal resistance is the most important parameter in designing the geothermal system because it shows the quantity of heat transfer in the borehole. There are many methods to estimate the borehole thermal resistance. Thermal Performance Tests (TPTs) were conducted to directly measure the borehole thermal resistance of several kinds of GHEs. Then the experiment results and analytical results were compared in order to select the most accurate methods to evaluate the borehole thermal resistance.

Thermal Conductivity Estimation of Compacted Bentonite Buffer Materials for a High-Level Radioactive Waste Repository

Abstract A deep geological repository has been considered as one of the most appropriate options for the disposal of high-level radioactive waste (HLW), and it will be constructed in a host rock area at a depth of 500 to 1000 m below the ground surface. The geological repository system is based on the concept of an engineered barrier system, and it consists of a disposal canister with packed spent fuel, buffer material, backfill material, and intact rock. The buffer plays an important role to assure the disposal safety of HLW since it can restrain the release of radionuclides and protect the canister from the inflow of groundwater. Since an increased heat quantity is released from the disposal canister into the surrounding buffer material, the thermal conductivity of the buffer material constitutes a key parameter needed to analyze the entire disposal safety. Therefore, this study presents a thermal conductivity prediction model for compacted bentonite buffer material from Kyungju, which is the only bentonite produced in Korea. The thermal conductivity of the compacted bentonite buffer from Kyungju was measured using a hot-wire method according to varying degrees of saturation, dry density, and temperature. The measurements showed that the thermal conductivity was concurrently influenced by the degree of saturation, dry density, and temperature variation. A regression model was proposed to predict the thermal conductivity of the compacted bentonite buffer from Kyungju using the degree of saturation and the dry density as the dependent variables. An additional regression model was also introduced that incorporated the temperature variation as an additional dependent variable, and the two models were directly compared with each other.

A Prediction of Entrainment Growth Rate for Debris-flow Hazard Analysis Using Multiple Regression Analysis

Recently, landslide and debris-flow disasters caused by severe rain storms have frequently occurred. Landslides can be mobilized into debris-flows, and then they transport downwards with huge volumes of sediments in an extreme rainfall condition. It is necessary to analyze flow direction and route of debris-flow for the prevention of debris-flow disaster. Many numerical models have been developed to consider these properties of debris-flow, and DAN3D which is a continuum dynamic runout model is known to simulate real events of debris-flow in Korea. DAN3D considers volume increase of various sediments induced by an entrainment mechanism. However, it uses several user-prescribed parameters, and there is no clear method to determine the parameter values. Therefore, this research analyzed 35 previous debris-flow events in Korea and collected values of dependent and independent variables to decide the growth rate. Besides, a multiple regression analysis was conducted and an empirical solution with an value of 0.824 was suggested for the prediction of growth rate. In the solution, all statistical assumptions for the multiple regression analysis were satisfied.