• Journal of the Korean Solar Energy Society
• /
• v.33 no.6
• /
• pp.12-18
• /
• 2013

Domestic solar hot water system can be divided into a passive type and an active type. In a passive type the storage tank is horizontally mounted immediately above the solar collectors. No pumping is required as the hot water naturally rises into the storage tank from the collectors through thermo-siphon flow. While, in an active type the storage tank is ground- or floor-mounted and is below the level of the collectors; a circulating pump moves water or heat transfer fluid between the storage tank and the collectors. We installed two types solar hot water systems consisting of the same storage tank and collectors at the same place, and were measured and compared typical operating characteristics under the same external conditions. In particular, the daily system performance was presented through the stirring test after the sunset. The results show that the amount of solar radiation obtained for an active type were less than a passive type on a cloudy day, because the operation of the circulation pump stops frequently took place on that day. However, on a sunny day, depending on the stable operation of the circulation pump, the amount of solar radiation obtained for an active type were increased than a passive type.

• Nuclear Engineering and Technology
• /
• v.40 no.6
• /
• pp.477-488
• /
• 2008

The objective of the paper is to analyze the thermally induced density wave oscillations in water cooled boiling water reactors. A transient thermal hydraulic model is developed with a characteristics-based implicit finite-difference scheme to solve the nonlinear mass, momentum and energy conservation equations in a time-domain. A two-phase flow was simulated with a one-dimensional homogeneous equilibrium model. The model treats the boundary conditions naturally and takes into account the compressibility effect of the two-phase flow. The axial variation of the heat flux profile can also be handled with the model. Unlike the method of characteristics analysis, the present numerical model is computationally inexpensive in terms of time and works in a Eulerian coordinate system without the loss of accuracy. The model was validated against available benchmarks. The model was extended for the purpose of studying the flow-induced density wave oscillations in forced circulation and natural circulation boiling water reactors. Various parametric studies were undertaken to evaluate the model's performance under different operating conditions. Marginal stability boundaries were drawn for type-I and type-II instabilities in a dimensionless parameter space. The significance of adiabatic riser sections in different boiling reactors was analyzed in detail. The effect of the axial heat flux profile was also investigated for different boiling reactors.

• Journal of Korean Society of Disaster and Security
• /
• v.14 no.2
• /
• pp.25-33
• /
• 2021

This technology is to let rainwater flow into a waterway that is located side gutter of a street with blocking garbage including cigarette butts at the same time. The first waterway is located beside the sidewalk and it enhances the water circulation in a city. This waterway is filled with aggregates and filter media, which removes fine dust that is washed out of the street and let water flow down to the earth. The second waterway is located beside the street and it retains rainwater temporarily with decreasing its flow speed. The second waterway shall reduce flooding damages by avoiding bottleneck situation in the street inlets and storm water pipelines which is the main causation of flooding in a city.

• Journal of Navigation and Port Research
• /
• v.40 no.1
• /
• pp.1-6
• /
• 2016

This study was conducted on a circulation system which can recycle waste water from EGCS(Exhaust Gas Cleaning System) using a wet scrubber that is used to treat air pollutants from ships. Though we developed a water treatment system that could remove effectively particulate matters and dispersed oil included in cleaning water for Ship Exhaust Gas Recycle System(DePM & DeSOx), we found that it is difficult to treat minutely dispersed oil only by means of centrifugal-typed purifier. Therefore, to this system, we applied a coalescer that coalesces emulsified minute oil particles in the 2nd phase of dispersion state after being filtered through the centrifugal-typed purifier. After we treated cleaning water drained out of Ship Exhaust Gas Recycle System(DePM & DeSOx) by using both purifier and coalescer, we found that particulate matters and dispersed oil were removed more than 55% and 99%, respectively, in comparison with those contained in cleaning water influent. Putting the results together, we conclude that the treated cleaning water can be recycled as normal cleaning water if this cleaning water treatment system is employed by the wet cleaning tower system for the reduction of air pollutants from ships.

• Journal of environmental and Sanitary engineering
• /
• v.15 no.2
• /
• pp.58-64
• /
• 2000

The photocatalytic removal of Ag(I) in water by $TiO_2$ at a various conditions, which are initial Ag(I) concentration, circulation flow rate, $TiO_2$ dosage and methanol concentration, was studied. A continuous flow system with a circular type reactor of the TiO2 suspensions with UV light through an photoreactor column was applied. The major results of this study were as follows; 1. First order kinetics was observed from the result at different initial concentration of Ag(I). As the initial Ag(I) concentration was incereased, the reaction rate was decreased. 2. The removal efficiency of Ag(I) increased with increasing the circulation flow rate and $TiO_2$ dosage. However, over $4{\ell}/min$ of circulation flow rate and $1.5g/{\ell}$ of $TiO_2$ dosage, increasing of the efficiency reached a plateau. 3. The addition of methanol as hole scavenger enhanced the removal efficiency of Ag(I) but the removal efficiency reached a plateau over some level of methanol. 4. It was found that $TiO_2$ photocatalysis was effective method to remove of Ag(I) from aqueous solution.

• 한국해양학회지
• /
• v.24 no.2
• /
• pp.96-108
• /
• 1989

Applying the numerical scheme developed by Semtner (1974), we investigate the circulation system in the Japan Sea in response to the air-sea interaction and the wind. In spite of blocking straits, resulting surface circulation pattern is similar to the schematic surface current chart introduced by Uda(1934) and Naganuma (1972); the northward flow along the Korean coast and the anticlockwise gyre in the northeastern part of the Japan Sea. Also the southward current flows along the Korean coast at depth of 100-200 m as similar to the North Korean Cold Current suggested by Kim and Kim (1983). And the sinking phenomenon of relatively saline water in the northeastern part of the Japan Sea is similar to the formation of the Japan Sea Proper Water.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.26 no.3
• /
• pp.242-253
• /
• 2020

This study examined the ef ects of freshwater discharge by artificial dikes from the Kanwol and Bunam lakes on the dynamics in the Chunsu Bay, Yellow Sea, Korea, during the summer season based on three-dimensional numerical modeling experiments. Model performances were evaluated in terms of skill scores for tidal elevation, velocity, temperature, and salinity and these scores mostly exceeded 90 %. The variability in residual currents before and after the freshwater discharge was examined. The large amount of lake water discharge through artificial dikes may result in a dramatically changed density field in the Chunsu Bay, leading to an estuarine circulation system. The density-driven current formed as a result of the freshwater inflow through the artificial dikes (Kanwol/Bunam) caused a partial change in the tidal circulation and a change in the scale and location of paired residual eddies. The stratification formed by strengthened static stability following the freshwater discharge led to a dramatic increase in the Richardson number and lasted for a few weeks. The strong stratification suppressed the vertical flux and inhibited surface aerated water mixing with bottom water. This phenomenon would have direct and indirect impacts on the marine environment such as hypoxia/anoxia formation at the bottom.

• Journal of Ocean Engineering and Technology
• /
• v.14 no.3
• /
• pp.20-28
• /
• 2000

Using the hydraulic and numerical model of semi-enclosed bay (Chinhae Bay), the efficiencies of flow-control structures on the seawater-circulation in the inner bay were investigated. Expecially, this study was confirmed the effectiveness of the flow-control structures at the mouth and narrow channel of Chinhae Bay through the experiments. The system of flow-control structures could enhance the water exchange improvement appropriately. The results of this study can be used as the long-term and integrated environmental impact assessment model in the inner bay.

• Journal of Wetlands Research
• /
• v.15 no.4
• /
• pp.535-541
• /
• 2013

The urbanization affects significantly on a natural water circulation system by increasing the imperviousness rate. It is also negatively affecting on urban temperature, environmental pollution, water quality, and aqua-ecosystems. The Korea MOE (Ministry of Environment) adapted a new environmental policy in order to reduce the impact of urbanization, which is the Green Stormwater Infrastructure (GSI) program. The GSI can be achieved by protecting conservable green spaces, enlarging more green spaces, and constructing more permeable pavements. The GSI is including many different techniques such as bioretention, rain garden, infiltration trench and so on. Also It is the infrastructures using natural mechanisms of soils, microorganisms, plants and animals on a water circulation system and pollutant reduction. In this research, a multi functional GSI technology with infiltration-filtration mechanisms has been developed and performed lab-scale tests to evaluate the performances about infiltration rate restoration and pollutant reduction. The most of pollutants including metals, organics and particulates were reduced about 50~90% due to water infiltration and storage functions. The clogging was found when the TSS loading rate was reached on $8.3{\sim}9.0kg/m^2$, which value is higher than the values in literatures. It means the new technology can show high performances with low maintenances.

• Land and Housing Review
• /
• v.15 no.1
• /
• pp.167-177
• /
• 2024

This study aimed to assess the efficacy of an adsorption process in removing organic matter and micropollutant residuals. After a full-scale water circulation system, the adsorption process was considered a post-treatment step. The system, treating anthropogenically impacted surface waters, comprises a hydro-cyclone, coagulation, flocculation, and dissolved air flotation unit. While the system generally maintained stable and satisfactory effluent quality standards over months, it did not meet the highest standard for organic matter (as determined by chemical oxygen demands). Adsorption experiments utilized two granular activated carbon types, GAC 830 and GCN 830, derived from coal and coconut-shell feedstocks, respectively. The assessment encompassed organic materials along with two notable micropollutants: acetaminophen (APAP) and acid orange 7 (AO7). Adsorption kinetics and isotherm experiments were conducted to determine adsorption rates and maximum adsorption amounts. The quantitative findings derived from pseudo-second-order kinetics and Langmuir isotherm models suggest the effectiveness of the adsorption process. The findings of this study propose the potential of employing the adsorption process as a post-treatment to enhance the treatment of contaminants that are not satisfactorily treated by conventional water circulation systems. This enhancement is crucial for ensuring the sustainability of urban water cycles.