• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.5
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• pp.579-589
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• 1985

The storage tank of the natural-circulation-solar-hot-water system equipped with flat-plate solar collectors is located at higher elevation than the solar collectors. Therefore, the heat loss from the system due to a reversed flow during the night-time is an important factor as well as the day-time thermal performance of the system. The thermal performance of the natural-circulation-solar-hot-water system with flat-plate solar collectors during the day-time depends mainly on the heat collecting efficiency of the solar collectors, whereas its thermal performance during the night-time depends on the system configuration , such as the elevation of the water storage tank with respect to the solar collectors and the piping connections between the storage tank and the solar collectors, as well as thermo-physical properties of the circulating fluid. In the present work, a computer program has been developed to simulate a typical natural-circulation-solar-hot-water-system, and a series of simulation tests have been carried out with the computer program to examine the thermal performance of the system during the day-time as well as the hight-time. In addition , a series of experiment have been conducted under a real sun condition using a natural-circulation-solar-hot-water-system constructed and installed at the KAIST building to compare with the results obtained from computer simulations.

• 한국해양학회지
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• v.13 no.2
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• pp.5-10
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• 1978

The coastal cold water near Ulsan, Korea, almost always appears in summer. From the results of some data analysis, it is found that this cold water has an important relation to the anticlockwise circulation appearing near the coast where the anticlockwise circulation turns its current direction from south to east.

• Journal of the Korean Solar Energy Society
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• v.31 no.5
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• pp.41-46
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• 2011

In the present work, a new freeze protection method has been proposed for a natural circulation system of solar water heater. Though electrothermal wire is popularly used for the purpose, there are freezing troubles by wire cut-off and excessive electric power consumption. In the experimental device, hot water in a storage tank was circulated by a small pump and used to heat the outdoor pipes if the cold water pipe surface temperature falls lower than a set point. As a result, It was observed that there was no hot water waste while the solar water heating system operated without freeze and burst.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.29 no.2
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• pp.77-100
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• 2024

Circulation, tides, currents, harmful algal blooms, water quality, and hypoxic conditions in Jinhae-Masan Bay have been extensively studied. However, these previous studies primarily focused on short-term variations, and there was limited detailed investigation into the physical mechanisms responsible for ocean circulation in the bays. Oceanic processes in the bays, such as pollutant dispersal, changes on a seasonal time scale. Therefore, this study aimed to understand how the circulation in Jinhae-Masan Bay varies seasonally and to examine the effects of tides, winds, and river discharges on regional ocean circulation. To achieve this, a three-dimensional ocean circulation model was used to simulate circulation patterns from 2016 to 2018, and sensitivity experiments were conducted. This study reveals that convective estuarine circulation develops in Jinhae and Masan Bays, characterized by the inflow of deep oceanic water from the Korea Strait through Gadeoksudo, while surface water flows outward. This deep water intrusion divides into northward and westward branches. In this study, the volume transport was calculated along the direction of bottom channels in each region. The meridional water exchange in the eastern region of Jinhae Bay is 2.3 times greater in winter and 1.4 times greater in summer compared to that of zonal exchange in the western region. In the western region of Jinhae Bay, the circulation pattern varies significantly by season due to changes in the balance of forces. During winter, surface currents flow southward and bottom currents flow northward, strengthening the north-south convective circulation due to the combined effects of northwesterly winds and the slope of the sea surface. In contrast, during summer, southwesterly winds cause surface seawater to flow eastward, and the elevated sea surface in the southeastern part enhances northward barotropic pressure gradient intensifying the eastward surface flow. The density gradient and southward baroclinic pressure gradient increase in the lower layer, causing a strong westward inflow of seawater from Gadeoksudo, enhancing the zonal convective circulation by 26% compared to winter. The convective circulation in the western Jinhae Bay is significantly influenced by both tidal current and wind during both winter and summer. In the eastern Jinhae Bay and Masan Bay, surface water flows outward to the open sea in all seasons, while bottom water flows inward, demonstrating a typical convective estuarine circulation. In winter, the contributions of wind and freshwater influx are significant, while in summer, the influence of mixing by tidal currents plays a major role in the north-south convective circulation. In the eastern Jinhae Bay, tidally driven residual circulation patterns, influenced by the local topography, are distinct. The study results are expected to enhance our understanding of pollutant dispersion, summer hypoxic events, and the abundance of red tide organisms in these bays.

• Journal of the Korean Society for Marine Environment & Energy
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• v.4 no.2
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• pp.3-14
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• 2001

In order to predict nutrient circulation in Hakata bay, we have developed an ecosystem model named the Sediment-Water Ecological Model (SWEM). The model, consisting of two sub-models with hydrodynamic and biological models, simulates the circulation process of nutrient between water column and sediment, such as nutrient regeneration from sediments as well as ecological structures on the growth of phytoplankton and zooplankton. This model was applied to prevent eutrophication in Hakata bay, located in western Japan. The calculated results of the tidal currents by the hydrodynamic model showed good agreement with the observed currents. Moreover, SWEM simulated reasonably well the seasonal variations of water quality, and reproduced spatial heterogeneity of water quality in the bay, observed in the field. According to the simulation of phosphorus circulation at the head of the bay, it was predicted that the regeneration process of phosphorus across the sediment-water interface had a strong influence on the water quality of the bay.

• Journal of Ocean Engineering and Technology
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• v.15 no.3
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• pp.35-42
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• 2001

The characteristics of tidal circulation with the flow-control structures using the three-dimensional numerical model (POM, Princeton Ocean Model) of Chinhae Bay, Korea were investigated. To confirm th efficiencies of flow-control structures, the training wall and submerged training wall were constructed at the mouth and narrow channel in Chinhae Bay. On the basis of the present investigation, the tidal circulation induced by the construction of flow-control structures could enhance the water exchange improvement appropriately. And, th training wall at the central is more dominated than the other structures for the efficient of water exchange. The sites and types of structure and flow patterns seem to be very sensitive in tidal simulation and changes in flow fields.

• Water for future
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• v.23 no.1
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• pp.119-127
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• 1990

The concentration of cohesive suspended sediment is determined by the circulation of water and the material dispersion. The equations of the two-dimensional, depth-integrated dispersive transport are the Reynolds equation, continuity equation, and advection-dispersion equation based on the Fick's law. A finite difference method has been applied to two models of circulation and dispersion transport. The circulation model is solved by the explicit scheme and the dispersion transport model is solved by multi-operational scheme. It is investigated wheter advective terms are included when the equation of circulation is applied to the model. For advection-dispersion equation, it was also investigated about variations of suspended sediment concentration with respect to the critical shear stresses.

• Journal of Environmental Impact Assessment
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• v.21 no.1
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• pp.133-142
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• 2012

Convection Current Circulation System(CCCS) in stratified reservoir controls development of anaerobic condition and algal bloom during summer. In order to increase the CCCS effectiveness, we analyze diverse design parameters to make optimize the flow pattern in reservoir. In this study, we interpret the internal flow with installation and operation condition of CCCS based on CFD in reservoir. Design variables of CCCS is reservoir depth, stratification strength, distance of between CCCS and so on. Since reservoir depth and stratification strength in variables is depending on natural phenomenon, we evaluated current circulation effect by distance of CCCS and proposed the optimal design condition using CFD simulation. Flow and diffusion changes in water body was assessed by temperature and dye test. Changes in water floor temperature at 40m intervals was slowly descending over 37 hours. Dye diffusion simulation at 60m intervals, the radius of the spread between two devices were overlapped after 12 hours.

• Ecology and Resilient Infrastructure
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• v.6 no.2
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• pp.109-119
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• 2019

Eutrophication has occurred due to the inflow of various water pollutants in many Korean reservoirs with low depth, and algal blooms of surface layer and low oxygenation of deep layer have repeated every year. There are several existing technologies to alleviate the stratification of reservoirs, but it is difficult to apply them in field sites due to the necessity of electric power and low economic efficiency. In this study, a non-powered water circulation system using natural energy of wind and water flow has been developed, and two test-beds constructed in the reservoirs with different conditions and examined its field applicability. Through computational fluid dynamics (CFD) simulation, it has been shown that the water circulation system could induce the downward flow to mitigate the stratification between surface and deep layers, and its influence radius could reach about 30 m. As a result of long-term monitoring of the test-beds, various water quality improvement effects have been observed such as moderation of DO fluctuation by water circulation, reduction of DO supersaturation and prevention of excessive pH rising. In order to improve the applicability of the water circulation system, it is considered necessary to review countermeasures against flood and depth conditions of each reservoir.

• Journal of The Korean Society of Agricultural Engineers
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• v.62 no.4
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• pp.99-110
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• 2020

The objective of this study is to analyze the trend of changes in the water circulation rates under climate change by adopting the concept of WCR defined by the Ministry of Environment. With the need for sound water circulation recovery, the MOE proposed the idea of WCR as (1-direct flow/precipitation). The guideline for calculating WCR suggests the SCS method, which is only suitable for short term rainfall events. However, climate change, which affects WCR significantly, is a global phenomenon and happens gradually over a long period. Therefore, long-term trends in WCRs should also be considered when analyzing changes in WCR due to climate change. RCP (Representative Concentration Pathway) 4.5 and 8.5 scenarios were used to simulate future runoff. SWAT (Soil and Water Assessment Tool) was run under the future daily data from GCMs (General Circulation Models) after the calibration. In 2085s, monthly WCR decreased by 4.2-9.9% and 3.3-8.7% in April and October. However, the WCR in the winter increased as the precipitation during the winter decreased compared to the baseline. In the aspect of yearly WCR, the value showed a decrease in most GCMs in the mid-long future. In particular, in the case of the RCP 8.5 scenario, the WCR reduced 2-3 times rapidly than the RCP 4.5 scenario. The WCR of 2055s did not significantly differ from the 2025s, but the value declined by 0.6-2.8% at 2085s.