• Journal of Advanced Marine Engineering and Technology
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• v.40 no.9
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• pp.733-742
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• 2016

In recent years, gas engines fueled with LNG or synthetic gas have been attracting considerable attention for marine use owing to their potential to facilitate better fuel economy and to reduce emissions. It has been confirmed that gas engines using the Otto cycle, which involves premixed combustion, can satisfy Tier III regulations without the EGR or SCR system. The objective of this study is to acquire simulation technologies for predicting gas engine performances in industrial fields. Using the commercial software BOOST, the simulation is conducted on a gasoline engine rather than a marine engine due to the gasoline engine's easier accessibility. This study consists of two stages. In the first stage published previously, the optimal modeling techniques for representing the behavior of the gas in the intake and exhaust systems were determined. In the current study, we formulated a method to evaluate the combustion and heat transfer processes in the cylinder and to ultimately determine the major performance parameters, given that the analytical model derived from the previous stage has been applied. Through this study, we were able to determine a combustion and heat transfer model and a valve discharge coefficient that are less reliant on empirical data: we were also able to formulate a methodology through which relevant constants are decided. We confirmed that the values of transient cylinder pressure variation, indicated mean effective pressure, and air supply can be successfully predicted using our modeling techniques.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.15 no.5
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• pp.328-334
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• 2022

The process that one may consciously focuses on necessary stimulation among tremendous amount of stimulation through human sensory systems is called attention in psychology. It is known that the attention can be affected by many factors such as room temperatures, humidity level, etc. In the field of sports science, ice packs are widely used for recovery from exercise fatigue providing fast heat transfer by conduction. However, the effect on attention by so-called iced-pack-cooling has not been tested. This research focuses on the attention levels when one is provided with a special cooling pad on their dorsal and lateral cervices. 40 subjects were divided into four groups and their attention level was evaluated based on the exposure conditions of combinations in reading and light walking with and without the cooling pad. The Frankfruter Aufmerksamkeits-Inventar, FAIR was used to evaluate the attention levels; the performance index, quality index, and continuity index consist of the FAIR test indicating the selectiveness of the attention, correctness of the attention, and maintaining term of the attention, respectively. Analysis of variance was carried out for those variables and post-hoc if applicable. When visual attention is constantly used for reading and studying, application of conductive heat transfer by the cooling pads is significantly helpful for improvement in selectiveness of the attention and maintaining terms of the attention levels. Also, light walking yielded improvement in selectiveness of the attention and maintaining terms of the attention levels; however one should presupposedly consider the loss of reading time.

• Journal of the Korean Wood Science and Technology
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• v.41 no.6
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• pp.515-527
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• 2013

Building energy simulations which are mainly used in Korea have evaluated the building energy performance with the different thermal conductivity of construction materials. In order to evaluate the energy consumption accurately, the difference in thermal conductivity of the wood used in stud for wooden structure was confirmed from the each simulation. In addition, the thermal transmission of building members and the thermal bridge at the conjunction of building members according to thermal conductivity from each simulation programs were researched. The thermal conductivity of pine that has the largest variation among the energy simulations was applied to the thermal properties of studs in wooden structure. The maximum error between the maximum and minimum thermal transmission of roof, wall, and floor slab was $0.023W/m^2{\cdot}K$. Plus, that thermal bridge at Rafter junction on the roof, roof-wall joint, and floor slab-wall joint was $0.025W/m{\cdot}K$. The heat transfer image for changes in temperature and the heat exchange were analyzed by HEAT2 program. The distorted temperature lines were found around the insufficient insulated connection parts. It was predicted that the temperature at the distorted parts in the analyzed image was lower than that of the other portion of the other structures.

• Clean Technology
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• v.25 no.3
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• pp.189-197
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• 2019

In this study an optimization of the preparation conditions of activated carbon with a ternary metal ion material to treat $H_2S$, which is classified as a representative odor substance, was carried out. For a metal ion material for enhancing the adsorption performance of hydrogen sulfide, performance enhancement was confirmed by combining Li and Fe or a ternary combination (K, Li, Fe) based on KI, which is a substance promoting hydrogen sulfide adsorption performance. Also, it was determined by XRD analysis that the reaction of each active substance with $H_2S$ was because of binding. The adsorption performance increased more than 3 times with heat treatment of the adsorbent with nitrogen compared with heat treatment with air. The maximum adsorption constant ($q_m$) value of the optimum adsorbent was 97.07, which is 6 times higher than that of the existing K-based impregnated activated carbon. It was confirmed that the objective adsorption amount ($0.3g\;g^{-1}$) was secured by an equilibrium between the mass transfer rate and adsorption rate. From the results, it was confirmed that the performance improvement was noticeable even when activated carbon with a reagent grade activated carbon particle size was modified. It was confirmed that the adsorption performance exists at high relative humidity levels of 60 and 100%, and the optimized preparation can be applied to a wet process such as a scrubber downstream.

• Journal of Electrical Engineering and Technology
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• v.13 no.6
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• pp.2402-2411
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• 2018

Fluoronitriles-$CO_2$ gas mixtures are promising alternatives to $SF_6$ in environmentally-friendly gas-insulated transmission lines (GILs). Insulating gas heat transfer characteristics are of major significance for the current-carrying capacity design and operational state monitoring of GILs. In this paper, a three-dimensional calculation model was established for a GIL using the thermal-fluid coupled finite element method. The calculated results showed close agreement with experimentally measured data. The temperature distribution of a GIL filled with the Fluoronitriles-$CO_2$ mixture was obtained and compared with those of GILs filled with $CO_2$ and $SF_6$. Furthermore, the effects of the mixture ratio of the component gases and the gas pressure on the temperature rise and current-carrying capacity of the GIL were analyzed. Results indicated that the heat transfer performance of the Fluoronitriles-$CO_2$ gas mixture was better than that of $CO_2$ but worse than that of $SF_6$. When compared with $SF_6$, use of the Fluoronitriles-$CO_2$ gas mixture caused a reduction in the GIL's current-carrying capacity. In addition, increasing the Fluoronitriles gas component ratio or increasing the pressure of the insulating gas mixture could improve the heat dissipation and current-carrying capacity of the GIL. These research results can be used to design environmentally-friendly GILs containing Fluoronitriles-$CO_2$ gas mixtures.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.8
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• pp.287-297
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• 2020

This study examined ways of improving the internal insulation performance of aging university buildings, and to enhance the convenience of occupants in university buildings and the insulation effect of aging buildings. This research was conducted to solve the problem of continuous requests for improving the insulation performance of office workers in the Nehemiah Hall building of Handong University. The results showed that the internal temperature of Nehemiah Hall was low compared to the internal temperature of the adjacent building. Considering the characteristics of the building, the university chose insulating materials under the theme of internal insulation. The experiment was conducted by installing internal wall insulation used in the market by producing a model room that miniaturized the university professor's office. Based on the experimental results, an economic evaluation was conducted to analyze the insulation effect by measuring the heating time and actual heat transmission coefficient. An economic evaluation was conducted by experiment and theory and on a winter and summer basis. According to the research, when an Isopink (30 T) was introduced as an internal insulation material in 60 offices of Nehemiah Hall, it could save up to 1,071,600 won in total during the winter season and 109,200 won during the summer season.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.7
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• pp.462-469
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• 2008

A regenerative evaporative cooler has been fabricated and tested for the evaluation of cooling performance. The regenerative evaporative cooler is a kind of indirect evaporative cooler comprised of multiple pairs of dry and wet channels. The air flowing through the dry channels is cooled without any change in the humidity and at the outlet of the dry channel a part of air is redirected to the wet channel where the evaporative cooling takes place. The regenerative evaporative cooler fabricated in this study consists of the multiple pairs of finned channels in counterflow arrangement. The fins and heat transfer plates were made of aluminum and brazed for good thermal connection. Thin porous layer coating was applied to the internal surface of the wet channel to improve surface wettability. The regenerative evaporative cooler was placed in a climate chamber and tested at various operation condition. The cooling performance is found greatly influenced by the evaporation water flow rate. To improve the cooling performance, the evaporation water flow rate needs to be minimized as far as the even distribution of the evaporation water is secured. At the inlet condition of $32^{\circ}C$ and 50%RH, the outlet temperature was measured at $22^{\circ}C$ which is well below the inlet wet-bulb temperature of $23.7^{\circ}C$.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.1
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• pp.28-35
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• 2016

The in-situ thermal response test for the design of a ground heat exchanger of geothermal heat pumps have difficulty in predicting the outlet temperature according to the variation of conditions due to the expense and time. This paper suggests a 3-D CFD analysis method to predict the heat transfer performance of vertical type ground heat exchanger, which is mostly used in national, and the outlet temperature and the slope of two in-situ thermal response tests were compared to test the proposed CFD reliability. The results of CFD analysis showed that the outlet temperature was predicted to within $0.5^{\circ}C$ of the actual value and the slope was predicted to within 1.6%. The reliability of the CFD analysis method was confirmed using this process, and the outlet temperature prediction of the two in-situ thermal response tests was obtained by changing ${\pm}20%$ of the flow rate and the effective thermal conductivity conditions, respectively. The results of CFD analysis showed that the outlet temperature of Case 1 was 28.0 (-20%) and $29.6^{\circ}C$ (+20%) for the flow rate variation and $29.6^{\circ}C$ (-20%) and $28.0^{\circ}C$ (+20%) for the effective thermal conductivity variation, and the outlet temperature of Case 2 was 28.4 (-20%) and $29.8^{\circ}C$ (+20%) for the flow rate variation and $29.7^{\circ}C$(-20%) and $28.4^{\circ}C$(+20%) for the effective thermal conductivity variation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.5
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• pp.389-397
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• 2014

An absorption chiller-heater using only a natural refrigerant hardly causes any environmental pollution. In an absorption chiller-heater, the performance of its high-temperature generator, which uses exhaust gases, is essential to achieving superior system performance. To investigate the performance of such a high-temperature generator, a laboratory-scale high-temperature generator working with exhaust gases was designed and tested. Changes in the performance of the high-temperature generator as a function of inlet conditions of the absorbing solution, such as air inlet temperature and mass flow, were investigated. It was observed that when the air mass flow rate ratio was increased from 80% to 120%, the heat capacity was increased by 30%, 33%, 34%, and 37%, respectively. Additionally, when the air inlet temperature was elevated from $170^{\circ}C$ to $210^{\circ}C$ for absorption solution concentrations of 56%, 55%, 545, and 53%, the heat capacity increased by 140%, 160%, 220%, and 224%, respectively.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.5
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• pp.403-410
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• 2007

In this study, natural refrigerants and their mixtures that can supplement and replace R12 and R134a in automobile air-conditioners are studied. R134a is currently used as the refrigerant in new motor vehicle air conditioners, replacing the ozone depleting refrigerant R12. Although R134a has no ozone depletion potential, it has a relatively large global warming potential, approximately 1300 times that of $CO_2$ over a 100 year time horizon. For this reason, performance of natural refrigerants and their mixtures containing R152a, RE170 (Dimethylether, DME) and R600a (Isobutane) are measured under 2 different temperature conditions. They were tested in a refrigerating bench tester with an open type compressor. The test bench provided about 4 kW capacity and water and water/glycol mixture were employed as the secondary heat transfer fluids. Test results show that the coefficient of performance (COP) of these refrigerants is up to 21.55% higher than that of R12 in all temperature conditions. Overall, these fluids provide good performance with reasonable energy savings without any environmental problem and thus can be used as long term alternatives for automobile air-conditioners.