• Journal of Energy Engineering
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• v.8 no.2
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• pp.233-241
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• 1999

A large-scale hot water production system using a natural circulation loop was developed. A computer simulation program was developed to design and evaluate thermal performance of the natural circulation system for hot water production. An experimental apparatus was set up and was tested against various conditions to exhibit a stable operating region of the natural circulation loop. When the system was a stable state for heating rate (695 ㎾) and feed water was circulated at 0.3 $\ell$/s constantly. A unstable state was checked by experiment and that time flow rate was oscillated with 0.4∼0.6 $\ell$/s. The result showed that the program can predict the thermal performance of the large-scale hot water system using the natural circulation loop and can be utilized to design the system.

• Journal of the Korean Society for Marine Environment & Energy
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• v.15 no.3
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• pp.257-262
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• 2012

This study was conducted to verify the performance of the solar water circulation apparatus that was installed in a semi-closed sea area of Tongyeong to improve the water quality through removing thermocline and oxygen depleted water mass, and to prevent the occurrence of red tides caused by eutrophication. From 8 weeks of experiments, we found that the thermocline in the semi-closed sea area has been removed gradually after installation of the apparatus. The initial temperature of surface and bottom was $27.9^{\circ}C$ and $23.8^{\circ}C$, respectively and it was changed to $22.1^{\circ}C$ in both depth. In case of DO concentration, there was a big gap between surface (5.49 mg/L) and bottom (2.61 mg/L) and was an oxygen depleted water mass in the bottom area at initial. However DO concentration in bottom layer has increased gradually after operation (6.19 mg/L) and the oxygen depleted water mass has removed. Due to the effects of seasonal variation and the operation of the solar water circulation apparatus for 8 weeks, COD concentration decreased from 5.61 mg/L to 2.36 mg/L in surface area, and from 6.08 mg/L to 1.73 mg/L in bottom area. Dissolved inorganic nitrogen concentration also decreased from 0.135 mg/L to 0.050 mg/L in surface area, and from 0.076 mg/L to 0.051 mg/L in bottom area. This research was conducted from July to September, and it might be possible that the variation of water quality was affected by both seasonal variation and the operation of the water circulation apparatus. Hence a further research is required to verify the performance of the water circulation apparatus itself and to monitor dissolved inorganic nitrogen and phosphorous concentrations as well as Chl-a.

• Journal of Environmental Health Sciences
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• v.34 no.3
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• pp.255-260
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• 2008

This study was conducted to analyse the effects of the UFCA for treating polluted water in a reservoir. The UFCA mixes water by circulation of surface and bottom water layers. The circulation supplies oxygen to bottom of the reservoir, resulting in water quality improvement. With a UFCA in use, we surveyed the changes of temperature, pH, transparency, depth, conductivity, DO, COD, BOD, T-N, T-P and Chlorophyll-a for 7 months from Feb. to Aug. in 2004 in our experimental reservoir. There was little difference in the surface and bottom temperatures of the reservoir because of water mixing by the UFCA. However, pH was changed from 7 to 9. The transparency of water was about 80 cm through the all periods. Conductivity was $150\;{\mu}S/cm$ in early Feb., but increased to $270\;{\mu}S/cm$ in early March. Little change was seen in DO with depth, but it was maintained above 6 mg/l in June and July. BOD increased from 2.1 to 12.2 mg/l. The study reservoir did not undergo any eutrophication during the period of our experiment, but the comparison reservoir had an algae-bloom. The COD in the experimental reservoir increased from 5.4 to 14.5 mg/l. The COD concentration of the experimental reservoir was higher than comparison reservoir at the beginning of the study but in August this situation was reversed. SS concentration increased from 13.5 to 23.5 mg/l in Feb., but it fell from between 8.5 to 11.2 mg/l in July. T-N was increased from 1.3 to 4.9 mg/l. It increased up to 3 times in the rainy season as compared to other components. However the comparison reservoir increased up to 40 times higher than the experimental reservoir in the same period. T-P increased from 0.04 to 0.17 mg/l. The ratio of T-N to T-P increased from 20:1 to 40:1 which means that T-P was a growth limiting factor for algae and aquatic plants. Chlorophyll-a increased from 20 to 120 mg/l, and its concentration was correlated with T-P, such that Chlorophyl-a concentration increased with increased of T-P concentration. The concentrations of COD, T-N, T-P and other parameters were higher in the experimental reservoir than in the comparison reservoir but this situation was reversed in July, when the most severe eutophication occurred. The results show that overall the experimental reservoir was greatly remedied by UFCA. The UFCA accelerated the degradation of aquatic organic materials through effective supply of air with up-flow and circulation of water. We conclude that the UFCA can be very effective in aspect of the remediation of water quality incontaminated reservoirs and lakes.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.4
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• pp.463-472
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• 1996

Experiments were carried out to study the operation characteristics of a regenerator with a thermo-syphon pump and a surface-flame burner for a lithium bromide (LiBr)-water absorption heat pump. A cylindrical-shape metal-fiber burner and commercial grade propane were used. The emission of carbon monoxide and nitric oxide was measured by a combustion gas analyzer. Ther regeneration rate of water vapor as a refrigerant was measured. It could be as a reference value showing the performance of the regenerator. The circulation rate of the LiBr-water solution was also measured from both the tanks for the weak-and the strong-solution. Using a refractometer, the LiBr concetration in the solution was calculated from the measured refractory index of the solution. Temperature of the solution and the condensed water was recorded at several points in the experimental apparatus with thermocouples, using a personal computer. This data collecting system for measuring temperature was calibrated with a set of standard thermometers. The generating rate of water vapor as refrigerant increased linearly with heat supplied. It was about 4.0g/s with the heat supplied at a rate of 16,500kcal/h. The circulation rate of LiBr solution also increases with the heat supplied. The difference in LiBr concentrations between the weak and the strong solution was in the range of 1 to 5% when the concentration of the strong solution was about 60%. It was dependent upon both the heat supplied and the circulation rate of the solution. The initial concentration and the level of the LiBr solution in the regenerator were measured and recorded before experiments. The effect of them on the generating rate of water vapor and the circulation rate of the solution was also studied. The generating rate of water vapor was not strongly dependent upon both the level of the LiBr solution and the initial LiBr concentration. However, the concentration difference of the solution increases with the initial level of the LiBr solution.

• KIEAE Journal
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• v.4 no.2
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• pp.49-56
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• 2004

This study intends to propose the fundamentals of 'Ecovillage' design by researching into the cycle system of material of 'Crystalwaters' which is having been in charge of a leading role of GEN since 1996 (GEN was formed in 1996) as Ecovillage in Australia. First, to secure the water resources, we can store up rain and the water of valley, and dam. Second, we are able to use the natural filter apparatus, do tree-planting of roof to gain better quality of water. Third, it is to save the energy as supplying water. For it, we make the best of a gravity that is one of the cycle principle of water. Forth, to build a Dam can make a site of scenic beauty, do the role of recreation place and provide against emergencies (a fire, drought) as well as make a mild climate. Fifth, it can reduce the environment load because of sewage and garbage as making it compost. This is possible by treating biologically using composting apparatus of the dry or wet process. Sixth, it is to reduce the environmental pollution as to discharge seperating a recycable waste, an organic matter being able to make it compost. Finally, first of all, environmentally friendly inhabitant consciousness from lifestyle and production style plays an importent part for water cycle and the ecological cycle of waste and sewage.

• Economic and Environmental Geology
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• v.31 no.3
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• pp.265-271
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• 1998

In the hydrologic and hydrochemical studies of natural waters, oxygen and hydrogen isotope compositions of waters are very important to elucidate the origin and circulation pattern of water in the hydrologic system. The hydrogen isotope analysis of waters usually has been undertaken through the reduction of water to form hydrogen gas using pure metals (in general, zinc and uranium). In 1996, a new apparatus (H/Device) was developed to prepare the water samples (by the reduction with Cr metal) without some intrinsic problems that may yield incorrect and/or inaccurate data, and was installed at 1997 in the Center for Mineral Resources Research (CMR) in Korea University. However, the optimistic conditions of preparation and analysis of samples has not been established. In this paper, we introduce the efficiency of H/Device to obtain accurate hydrogen isotope values of water, and discuss both the optimum conditions including the effective reduction time and the probable mixing (memory) effect between successive samples. We obtained large amounts of a laboratory working standard (KUW; Korea University Water) with the average ${\delta}D_{SMOW}$ value of $-42.1{\pm}1.0$‰ $(1{\sigma})$.

• Journal of the Korean Society of Safety
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• v.35 no.3
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• pp.96-104
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• 2020

The numerical simulations were conducted to investigate the thermal-fluid phenomena occurred inside the experimental apparatus during a PCCS, used to remove heat released in accidents from a containment of light water nuclear power plant, operation. Numerical simulations of the flow and heat transfer caused by wall condensation inside the containment simulation vessel (CSV), which equipped with 18 vertical heat exchanger tubes, were conducted using the commercial computational fluid dynamics (CFD) software ANSYS-CFX. Shear stress transport (SST) and the wall condensation model were used for turbulence closure and wall condensation, respectively. The simulation using the actual size of the apparatus. However, rather than simulating the whole experimental apparatus in consideration of the experimental cases, calculation resources, and calculation time, the simulation model was prepared only in CSV. Selective simulation was conducted to verify the effects of non-condensable gas(NC gas) concentration, CSV internal pressure, and wall sub-cooling conditions. First, as a result of the internal flow of CSV, it was observed that downward flow due to condensation occurred surface of the vertical tube and upward flow occurred in the distant place. Natural convection occurred actively around the heat exchanger tube. Due to this rising and falling internal flow, natural circulation occurred actively around the heat exchanger tubes. Next, in order to check the performance of built-in condensation model using according to the non-condensable gas concentration, CSV internal flow and wall sub-cooling, the heat flux values were compared with the experimental results. On average, the results were underestimated with and error of about 25%. In addition, the influence of CSV internal pressure and wall sub-cooling was small, but when the condensate was highly generated due to the low non-condensable gas concentration, the error was large compared to the experimental values. This is considered to be due to the nature of the condensation model of the CFX code. However, in spite of the limitations of CFD, it is valid to use the built-in condensation model of CFD for PCCS performance prediction from a conservative perspective.

• Journal of Navigation and Port Research
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• v.31 no.10
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• pp.879-884
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• 2007

This study is to observe the change of temperature and relative humidity for various vegetables in vacuum precooling system. The materials for experiments were the lettuce, chinese cabbage, pak choi and cabbage. The experimental apparatus was constructed of vacuum chamber, vapor/water separator, water tank, pumps ejecting and cooling water circulation, refrigerator unit, cooling coil for water cooling, Hygrometer and Data logger measuring of the temperature change. The experiments were operated in 20torr and recorded every 3 minutes. It was found that the cooling temperature and speed of vegetables are depending on the percentage of its water content. The more water contains, the faster cooling speed and the lower cooling temperature.

• Nuclear Engineering and Technology
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• v.56 no.3
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• pp.1066-1080
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• 2024

SMART100 has a containment pressure and radioactivity suppression system (CPRSS) for passive containment cooling system (PCCS). This prevents overheating and over-pressurization of a containment through direct contact condensation in an in-containment refueling water storage tank (IRWST) and wall condensation in a CPRSS heat exchanger (CHX) in an emergency cool-down tank (ECT). The Korea Atomic Energy Research Institute (KAERI) constructed scaled-down test facilities, SISTA1 and SISTA2, for the thermal-hydraulic validation of the SMART100 CPRSS. Three separate effect tests were performed using SISTA1 to confirm the heat removal characteristics of SMART100 CPRSS. When the low mass flux steam with or without non-condensable gas is released into an IRWST, the conditions for mitigation of the chugging phenomenon were identified, and the physical variables were quantified by the 3D reconstruction method. The local behavior of the non-condensable gas was measured after condensation inside heat exchanger using a traverse system. Stratification of non-condensable gas occurred in large tank of the natural circulation loop. SISTA2 was used to simulate a small break loss-of-coolant accident (SBLCOA) transient. Since the test apparatus was a metal tank, compensations of initial heat transfer to the material and effect of heat loss during long-term operation were important for simulating cooling performance of SMART100 CPRSS. The pressure of SMART100 CPRSS was maintained below the design limit for 3 days even under sufficiently conservative conditions of an SBLOCA transient.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.1
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• pp.37-43
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• 2015

Evaporative cooling is a very effective way for exhaust heat recovery that uses both latent heat and sensible heat. This study investigated the performance of a heat recovery system using evaporative cooling. The experimental apparatus comprised a plastic heat exchanger, a water spray nozzle, an air blowing fan, a water circulation pump, and measuring sensors for the temperature, humidity, and flow rate. The effectiveness of the sensible heat recovery without evaporation was measured and compared with that of the total heat recovery with evaporation. The effectiveness of the sensible and total heat recoveries decreased as the air flow rate increased, and a much higher effectiveness was obtained with the counterflow arrangement in both cases. For total heat recovery, the effectiveness increased with the water flow rate, and the parallel flow arrangement was found to be more sensitive to the water flow rate than the counterflow arrangement.