• Journal of Korean Society of Water and Wastewater
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• v.11 no.2
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• pp.76-93
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• 1997

Activated carbon is widely used for the treatment of water, wastewater and other liquid wastes. Biological activated carbon (BAC) process is water and wastewater treatment process developed in the 1970's. In addition to activated carbon adsorption, biodegradation organic pollutants occurs in the BAC bed where a large amount of aerobic biomass grows. This results in a long operation time of the carbon before having to be regenerated and thus a low treatment cost. Although the BAC process has been widely used, its mechanisms have not been well understood, especially the relationship between biodegradation and carbon adsorption, whether these two reactions can promote each other or whether they just simultaneously exist in the BAC bed. Also, the phenomenon of bioregeneration has been confused that previously occupied adsorption sites appear to be made available through the actions of microorganisms. And that, because biological process is influenced by low temperature, the mechanism of the BAC process is also effected by temperature variation in our country of winter temperature near the freezing point. Therefore, the objective of this study examines closely the mechanism of the BAC process by temperature variation using phenol as substrate. From this study, biological activated carbon is good substrate removal better than non adsorbing materials (charcoal, sand) as temperature variation, especially low temperature(near $5^{\circ}C$).

• The KSFM Journal of Fluid Machinery
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• v.18 no.1
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• pp.29-36
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• 2015

Recently, Stirling engines are emerging as a key device for power conversion of renewable energy or waste energy. This study develops a LTDSE(Low Temperature Differential Stirling Engine) using a water spray for higher heat transfer and performs load performance tests for various flow rates and temperatures of hot water spray for variable engine loads emulated by a mechanical friction device. Internal temperature and pressure, working frequency and inlet and outlet temperature of the supply water are measured. As a result, the increases in flow rate and temperature of hot water respectively enhance the power output, efficiency and the working frequency, while the increasing engine load leads to decreases in working frequency but increases in the pressure amplitude. Eventually, it is revealed there exists a maximum shaft power of the test engine.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.5 no.1
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• pp.7-11
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• 2009

The purpose of this study is to investigate the performance of a water heat source cascade heat pump system R717(Ammonia) is used for a low-stage working fluid while R134a is for a high-stage. In order to gain a high temperature supply water in winter season, the system is designed to perform a cascade cycle. In this study, two experiments were carried out. One is a system starting test from the low load temperature of $10^{\circ}C$. The other is a system performance investigation over the R717 compressor capacity changes. Experimental results show that when it starts from the low load temperature, the suction temperature of the low-stage compressor is higher than that of a high-stage. The system performance increases when a water source temperature or a low-stage compressor rotational frequency goes higher.

• Transactions of Materials Processing
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• v.31 no.4
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• pp.207-213
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• 2022

In this study, variations in the microstructure and hardness of a low-carbon SCM415 steel with austenitizing temperature and cooling rate are investigated. When the austenitizing temperature is lower than the A₁ temperature (738.8 ℃) of the SCM415 steel, the microstructures of both the air-cooled and water-cooled specimens consist of ferrite and pearlite, which are similar to the microstructure of the initial specimen. When heat treatment is conducted at temperatures ranging from the A₁ temperature to the A₃ temperature (822.4 ℃), the microstructure of the specimen changes depending on the temperature and cooling rate. The specimens air- and water-cooled from 750 ℃ consist of ferrite and pearlite, whereas the specimen water-cooled from 800 ℃ consists of ferrite and martensite. At a temperature higher than the A₃ temperature, the air-cooled specimens consist of ferrite and pearlite, whereas the water-cooled specimens consist of martensite. At 650 ℃ and 700 ℃, which are lower than the A₁ temperature, the hardness decreases irrespective of the cooling rate due to the ferrite coarsening and pearlite spheroidization. At 750 ℃ or higher, the air-cooled specimens have smaller grain sizes than the initial specimen, but they have lower hardness than the initial specimen owing to the increased interlamellar spacing of pearlite. At 800 ℃ or higher, martensitic transformation occurs during water cooling, which results in a significant increase in hardness. The specimens water-cooled from 850 ℃ and 950 ℃ have a complete martensite structure, and the specimen water-cooled from 850 ℃ has a higher hardness than that water-cooled from 950 ℃ because of the smaller size of prior austenite grains.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.3 no.2
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• pp.17-23
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• 2007

Geothermal energy is used in various forms, such as power generation, direct use, and geothermal heat pumps. High temperature geothermal energy sources have been used for power generation for more than a century. Recent technical advances in power generation equipments make relatively low temperature geothermal energy to be available for power generation. In these applications, lower temperature geothermal energy source makes smaller difference between condensing water temperature and it. Various condensing water temperatures were investigated in analyzing its influence on power generation performance. Condensing water temperature of organic Rankine cycle imposed greater influence on power generation and its performance in lower temperature geothermal power generation.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.266-271
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• 2001

In this study, the performance of the simultaneous heating & cooling water making system using R134a was investigated by simulation. The most important effect upon heating COP was intermediate pressure depending on input water temperature. With the input water temperature of $10^{\circ}C\;and\;20^{\circ}C$, optimum intermediate pressure were 923 and 1040kPa, respectively. At that optimum intermediate pressure, the maximum heating COP of the system operated between $0^{\circ}C$ evaporating temperature and $70^{\circ}C$ condensing temperature were 4.15 and 3.83. With installation of the subcoolers in high or low pressure section, the system COP was increased by reducing the refrigerant mass flow rate. Under the optimum pressure and $10^{\circ}C$ input water temperature, it was found that heating COP was maximized when the low-subcooler and high-subcooler capacity rate were taken by 14% and 13%, respectively.

• International Journal of Air-Conditioning and Refrigeration
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• v.17 no.1
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• pp.32-36
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• 2009

The ice storage system uses water for low temperature latent heat storage. However, a refrigerator capacity is increased and COP is decreased due to supercooling of water in the course of phase change from solid to liquid. This study investigates the cooling characteristics of the TMA-water clathrate compound including TMA (Tri-methyl-amine, $(CH_3)_3N$) of $20{\sim}25wt%$ as a low temperature latent heat storage material. The results showed that the phase change temperature and the specific heat is increased and the supercooling degree is decreased as the weight concentration of TMA increased. Especially, the clathrate compound containing TMA 25 wt% has the average phase change tempera ture of $5.8^{\circ}C$, the supercooling degree of $8.0^{\circ}C$ and the specific heat of 3.499 kJ/kgK in the cooling process. This can lead to reduction of operation time of refrigerator in low temperature latent heat storage system and efficiency improvement of refrigerator COP and overall system. Therefore, energy saving and improvement of utilization efficiency are expected.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.8
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• pp.690-696
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• 2003

This paper presents the heat recovery performance of water fluidized-bed heat exchanger. Temperature and humidity ratio of waste gas are considered as important parameters in this study. Therefore, the heat recovery rate through water fluidized-bed heat exchanger for exhaust gases with various temperatures and humidity ratios can be estimated from the results of this study. Mass flow ratio (the ratio of mass flow rate of water to that of gas) and temperature of inlet water are also considered as important operating variables. Increase of heat recovery rate can be obtained through either high mass flow ratio or low temperature of inlet water with resultant low recovered temperature. The heat recovery performance with the mass flow ratio of about up to 10 has been investigated. The effect of number of stages of water fluidized-bed on the heat recovery performance has been also examined in this study.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.10
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• pp.855-859
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• 2007

Hydrogen as an energy carrier in fuel cell offers perhaps the largest potential benefits of reduced emissions of pollutants and greenhouse gases. The generation of high-purity hydrogen from hydrocarbon fuels is essential for efficient operation of fuel cell. Reduction of carbon monoxide to an acceptable level of 10ppm involves high temperature and low temperature water gas shift (WGS), followed by selective oxidation of residual carbon monoxide. The WGS reactor was designed and tested in this study to produce hydrogen-rich gas with CO to less than 5000 ppm. In the water gas shift operation, gas emerges from the reformer is taken through a high temperature shift (HTS) catalyst to reduce the CO concentration to about $2{\sim}4%$ followed to about 5000 ppm via a low temperature shift (LTS) catalyst.

• Korean Journal of Ichthyology
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• v.23 no.2
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• pp.145-149
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• 2011

We studied any variations of skin mucus cells of Misgurnus mizolepis caused by inducing a great change of water temperature including high temperature- and low temperature-adapted groups and then compared them with a control group of normal water condition. The high temperature-adapted group showed no significant different in size and number of the mucus cell (P>0.01), whereas in the low temperature-adapted group, the surface area of mucus cell layer and shape of its mucus cell, and the number of mucus cell remarkably increased in all the skin regions of dorsum, lateral region and occiput (P<0.01). Returned to the same condition as the control group, the low temperature-adapted groups showed the same features that appear in the normal water condition (P<0.01). Based on these results, the skin mucus cells of M. mizolepis seems to be very sensitive to cold water temperature and therefore they may play a key role in assessment of its environmental conditions.