• 한국연소학회:학술대회논문집
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• 2015.12a
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• pp.201-204
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• 2015

Recently, energy excessive consumption and environmental pollution are the social issued. The most efficient way to solve both energy excessive consumption and environmental pollution is existing combustion system improved. This study was part of the assume and commercial used existing waste heat recovery condensing boiler to low emission performance for exhaust gas recirculation(EGR) and thermal efficiency rise by applying the condensed water recirculation(CWR) conducted. The researchers applied the EGR and CWR develop a new concept for the condensed water recirculation waste heat recovery condensing boiler. Waste heat recovery condensing boiler applied to the condensed water recirculation thermal efficiency of the same conditions was increased by about 4.8~5.5% and pollution emission also decreased.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.12
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• pp.857-864
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• 2007

In the current residential building, hot water supply system consumes the second largest energy in order to make the thermal comport condition of residential space. The more residential environment improves the more the demand for hot water and water consumption is increasing gradually. So this study examines the possibility of applying the recirculation for individual hot water supply system compared with the existing method for waiting time for hot water, wasted water and energy consumption. The results are as follows. (1) In case of recirculation system method the waiting time for hot water can be reduced up to $69\sim85%$ in spring and fall period and so dose up to $77\sim85%$ in winter period. (2) The total wasted water has a little change compared with the existing method which can make the total wasted water reduced about $77\sim86%$. (3) The efficiency of hot water supply system can be improved, if the method which blocks the inflow of cold water is applied, when return pump is operated to recirculate hot water in recirculation system.

• Journal of Soil and Groundwater Environment
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• v.26 no.5
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• pp.39-48
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• 2021

Analysis of the change in water content and distribution was conducted according to the supply of recirculation water to a landfill. An excavation sample analysis showed that the recirculation water injection zone had water content 8.8% point higher than that of the non-injection zone, after 8 months of operation. And due to the influence of recirculation water supply by vertical wells in injection zones, the water content increases along with depth more clearly than non-injection zone. According to an electrical specific-resistivity survey after 13 months of operation, the water content got higher towards the bottom of the landfill. The water transmission coefficient is 8.72×10^-4 cm/sec for injection zones and 3.36×10^-5 cm/sec for the intermediate cover layer; analysis shows that the intermediate cover layer may affect the penetration velocity of water supplied by the horizontal injection tube. For the scientific design and operation of re-injection facilities, it was deemed necessary to follow-up research on the residence time and behavior of re-injection water considering the ratio of recirculation water supply in horizontal and vertical tubes, and pitcher coefficient of intermediate and waste layers.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.648-654
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• 2011

The feed-water piping system constitutes a complex flow impedance network incorporating dynamic transfer characteristics which will amplify some pulsation frequencies. Understanding pressure pulsation waves for the feed-water recirculation piping system with cavitation problem of flow control valve is very important to prevent acoustic resonance. Feed water recirculation piping system is excited by potential sources of the shock pulse waves by cavitation of flow control valve. The pulsation becomes the source of structural vibration at the piping system. If it coincides with the natural frequency of the pipe system, excessive vibration results. High-level vibration due to the pressure pulsation affects the reliability of the plant piping system. This paper discusses the piping vibration due to the effect of shock pulsation by the cavitation of the flow control valves for the recirculation piping of feed-water pump system in combined cycle power plants.

• Journal of Korean Society of Water and Wastewater
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• v.24 no.1
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• pp.5-14
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• 2010

A pilot-scale biological aerated filter (BAF) was operated with an anaerobic, anoxic and oxic zone at $23{\pm}1^{\circ}C$. The influent sCOD and total nitrogen concentrations in the feedwater were approximately 250 mg/L and 35 mg N/L, respectively. sCOD removal at optimum hydraulic retention time (HRT) of 3 hours with recirculation rates of 100, 200 and 300% in the column was more than 96%. Total nitrogen removal was consistently above 80% for 4 and 6 hours HRT at 300% recirculation. For 3 hours HRT and 300% recirculation, total nitrogen removal was approximately 79%. Based on fitting results, the kinetic parameter values on nitrification and denitrification show that as recirculation rates increased, the rate of ammonia and nitrate transformation increased. The ammonium loading rates for maximum ammonium removed were 0.15 and 0.19 kg $NH_3$-N/$m^3$-day for 100% and 200% recirculation, respectively. The experimental results demonstrated that the BAF can be operated at an HRT of 3 hours with 200 - 300% recirculation rates with more than 96 % removal of sCOD and ammonium, and at least 75% removal of total nitrogen.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.05a
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• pp.95-99
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• 2001

As a way to use energy effectively, the present study is aimed at investigating the performance characteristics of a Single Effect LiBr/Water Absorption Refrigerator using a low temperature driving heat-source. It was carried out by changing the driving heat-source temperature, the cold water outlet temperature(the refrigeration load), the cooling water inlet temperature, and the weak solution flow rate and this study compares the performance characteristics of refrigerator against the existence and non-existence of the Recirculation of the Weak solution which is used as a method to improve the performance of refrigerator. In case of Recirculation of the weak solution, more improved the Refrigeration Capacity and COP was obtained, and these effects became more larger in the high temperature of driving heat-source and large quantity of solution.

• The Korean Journal of Malacology
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• v.30 no.2
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• pp.127-134
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• 2014

Gonad maturation of Manila clam, Ruditapes philippinarum was induced in this study using a recirculation system over 8 weeks in early spring. Clams used in the experiment were collected in $15^{th}$ April 2010 from the west coast of Korea, as the surface water temperature remained $11^{\circ}C$. To induce gametogenesis and subsequent maturation seawater temperature was elevated $1^{\circ}C$ per day over 10 days to reach $20^{\circ}C$. For the experiment, clams were raised in 120 L quadrangle tank maintained with re-circulated seawater system over 57 days. Water quality parameters including the water temperature, salinity dissolved oxygen, ammonium ion and nitrate levels in the tanks were monitored daily. Mixture of concentrated microalgae including Tetraselmis, Isochrysis, Pavlova and Thalassiosira weissflogii was supplied to clams twice a day, and quantity of the daily ration was adjusted as 3% of clam body dry weight. Histology was applied to examine gonad maturation. Daily monitoring of the water quality parameters indicated that the recirculation system supplied suitable environment to Manila clam; the nitrogenous components stayed below toxic levels (< 0.2 mg/L). At the beginning of the study, clams were mostly in early developing stage. As the seawater temperature reached $20^{\circ}C$, 10 days after the experiment, 20% of clams reached late development at 12 days. First ripe clams were observed at 42 days and 40% of clams were in ripe and ready for spawning at the end of study, 57 days after the experiment. In this study, gametogenesis of Manila clam was successfully induced by elevating water temperature and supplying commercially produced microalgae in a recirculation tank system.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1667-1668
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• 2008

There are three main devices such as boiler producing steam, turbine driving generator and generator producing electricity. An electrical generator in power plant is driven and maintained its speed at rated by steam turbine which is coupled into generator directly. Turbine auxiliary devices such as condenser, deaerator, feed water heater, gland steam condenser, pump recirculation equipment, feed water pump, and so on should be operated well so that the steam turbine exert its maximum efficiency. There are many control loop such as hot well level and condenser recirculation, deaerator level, pegging steam pressure, feed water heater level, feed water pump recirculation. In this paper condenser level control and deaerator level control are going to be described.

• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.759-764
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• 2005

In this paper, numerical analysis of hydrogen recycle system has been conducted in order to enhance the efficiency of automotive fuel cell. Generally, the excess hydrogen is provided in the automotive fuel cell. Since the non-reaction hydrogen reduces automotive fuel cell efficiency, reuse of the non-reaction hydrogen can be helpful to improve the fuel cell performance. In case of PEM FC, the water vapor is provided to hydrogen from the cathode so that the mixture experiences phase change depending on the changes of pressure and temperature. The internal flow of the mixture in the hydrogen recirculation system of fuel cell was investigated for real flow conditions. The variation of performance, properties and mass fractions of mixture, hydrogen and water-vapor were investigated. This study was performed based on 80KW level automotive fuel cell's recycling system.

• Korean Chemical Engineering Research
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• v.57 no.4
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• pp.531-538
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• 2019

As the performance of PEMFC has been improved, the water and heat generated by reaction have increased so, the water and heat management of PEMFC is becoming more important. In this study, hydrogen recirculation was applied as the water management technique and the effect of recirculation flow rate, purge interval and duration on the performance of PEMFC was investigated. Anode pressure, fuel humidity and utilization, water discharge amount was measured to check the effect of purge conditions on performance. As the recirculation flow rate has increased, the performance of PEMFC became lower due to decrease of anode outlet pressure. According to the purge conditions, instantaneous voltage drop has occurred because of accumulated water. In frequent purge conditions, the performance of PEMFC gradually decreased due to fuel humidity control failure. Stable performance and high fuel utilization was achieved on this work by analyzing the effect of purge conditions.