• The Transactions of the Korean Institute of Power Electronics
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• v.4 no.3
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• pp.257-267
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• 1999

This paper deals with the water cooling system of HVDC(High Voltage Direct CUlTentJ. It is generally accepted that water is a veη effective medium to remove heat losses from any type of equipment. Because of this benefits the water cooling method is used in HVDC. The water cooling system consists of a heat exchanger, circulation pump and a connecting pipe. According to thYI1stor temperature level. thyristor junction temperature is controlled by controlling the f fan of exchanger. In this paper. the water cooling system of HVDC system is analyzed and estimated.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.4 no.4
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• pp.332-341
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• 1992

An absorption heat pump cycle has been modeled and simulated to analyze the system performance of water-cooled, series-flow, double-effect absorption heat pump, which can be applied to a direct gas fired cooling system with the medium range of cooling capacity (15RT level). Effect of absorption cooling system parameters, such as concentration difference, inlet temperature of cooling water, 1st generator temperature, leaving temperature differences of condenser and evaporator and efficiency of solution heat exchanger, has been investigated in the view of system cooling performance.

• Journal of The Korean Astronomical Society
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• v.37 no.5
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• pp.455-460
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• 2004

There have been many speculations about the presence of cosmic ray protons (CRps) in galaxy clusters over the past two decades. However, no direct evidence such as the characteristic $\gamma$-ray signature of decaying pions has been found so far. These pions would be a direct tracer of hadronic CRp interactions with the ambient thermal gas also yielding observable synchrotron and inverse Compton emission by additionally produced secondary electrons. The obvious question concerns the type of galaxy clusters most likely to yield a signal: Particularly suited sites should be cluster cooling cores due to their high gas and magnetic energy densities. We studied a nearby sample of clusters evincing cooling cores in order to place stringent limits on the cluster CRp population by using non-detections of EGRET. In this context, we examined the possibility of a hadronic origin of Coma-sized radio halos as well as radio mini-halos. Especially for mini-halos, strong clues are provided by the very plausible small amount of required CRp energy density and a matching radio profile. Introducing the hadronic minimum energy criterion, we show that the energetically favored CRp energy density is constrained to $2\%{\pm}1\%$ of the thermal energy density in Perseus. We also studied the CRp population within the cooling core region of Virgo using the TeV $\gamma$-ray detection of M 87 by HEGRA. Both the expected radial $\gamma$-ray profile and the required amount of CRp support this hadronic scenario.

• Journal of Power System Engineering
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• v.9 no.2
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• pp.88-92
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• 2005

The experiment of thermal performance about closed-wet cooling tower was conducted in this study. A closed cooling tower is a device similar to a general cooling tower, but with cooling tower replaced by a heat exchanger. The test section for this experiment has the process that the cooling water flows from the top of the heat exchanger to the bottom side in the inner part of the tube, and spray water flows in the gravitational direction in the outer side. Air comes in direct contact with the spray water at the outer side of the tube while passing from the lower the upper part having a counterflow to the spray water. The heat transfer pipe used in this experiment is a bare-type tube having an outer diameter of 15.88mm. The heat exchanger is consisted of seven rows and fifteen columns. In this experiment, thermal performance of the cooling tower is derived from overall heat transfer coefficients between the process fluid and sprayed water and volumetric overall mass transfer coefficient between sprayed water and air.

• Journal of Energy Engineering
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• v.10 no.4
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• pp.357-362
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• 2001

A bench type ammonia-water absorber heat exchange cycle was tested by varying the system charging concentration, refrigerating valve opening and weak solution flow rate. It was observed that the cooling capacity was increased as the system charging concentration was increased. Optimum system charging concentration was found for the coolong capacity of the system. The opening rate of refrigerant expansion valve had a direct influence on the refrigerant sub-cooling at the condenser outlet. Optimum sub-cooling was found to be 0~4$^{\circ}C$. As the weak solution flow rate increased the concentration of strong solution and the evaporating pressure decreased. There existed a optimum weak solution flow rate which maximized the cooling capacity and COP.

• Proceedings of the KIPE Conference
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• 2014.11a
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• pp.62-63
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• 2014

전력용 변압기에서 강제송유 냉각방식을 채택할 경우 절연유 강제 순환을 위한 펌프가 필요한데, 매 설계 시 마다 유동해석 혹은 설계 프로그램을 통해 펌프를 선정하게 되면 상당한 시간이 소요된다. 이러한 시간적 손실을 줄이고자 유동해석 및 유체 이론에 근거하여 간단하게 엑셀 시트로 프로그램화 하였다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.10
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• pp.693-698
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• 2017

The 18650 battery cell is known to be reliable and cost effective, but it has a design limitation and low electric capacity compared to pouch-type cells. Because its economy is superior, an 18650-cell-type battery pack is chosen. A reliable temperature is very important in automobile battery packs. Therefore, in this study, the temperature stability of the battery pack is predicted using CFD simulation. Following 3C discharge tests, the results for the heat generation of the battery cell are compared to the simulation results. Based on these results, a natural convection condition, forced convection condition, direct cell-cooling condition, cooling condition on the upper and lower surfaces of the battery pack, and cooling condition using air channels are all simulated. The results indicate that the efficiency and the performance of the air-channel-type cooling system is good.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.297-302
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• 2000

Pipe cooling method is widely used for reduction of hydration heat and control of cracking in mass concrete structures. However, in order to effectively apply pipe cooling systems to concrete structure, the coefficient of flow convection relating the thermal transfer between inner stream of pipe and concrete must be estimated. In this study, a device measuring the coefficient of flow convection is developed. Since a variation of thermal distribution caused by pipe cooling has a direct effect in internal forced flows, the developed testing device is based on the internal forced flow concept. Influencing factors on the coefficient of flow convection are mainly flow velocity, pipe diameter and thickness, and pipe material. finally a prediction model of the coefficient of flow convection is proposed using experimental results from the developed device. According to the proposed prediction model, the coefficient of flow convection increases with increase in flow velocity and decreases with increase in pipe diameter and thickness. Also, the coefficient of flow convection is largely affected by the type of pipe materials.

• Proceedings of the KIEE Conference
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• 2003.10b
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• pp.104-106
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• 2003

In recent years for propulsion of cooling fan in cars are more used electrical motors than the engine direct coupled type. But the electrical motor which is now used has the brush and the commutator. Because of the brush and the commutator the electrical motor has short life time, low efficiency and mechanical- electrical noise. Therefore it is tried to develope brushless dc motor. The motor is located in the hot air from the radiator. The motor temperature increases high and the increasing of the motor temperature rolls big in its character. The cooling fan motor has relative small in size and input voltage is low. For 300 w output power must be the current of the motor high which causes high copper loss. In this paper will be tested and analysed characteristics of a dc motor which is now used for cooling fan and a BLDC motor will be designed with same character of the brushed motor and with considering of improvement of the efficiency. After design the motor should be analysed and tested.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.2
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• pp.123-134
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• 2012

A typical cooling system of an engine relies on a water pump that circulates the coolant through the system. The pump is typically driven by the crankshaft through a mechanical link with engine starting. In order to reduce the friction and warm-up time of an engine, the clutch-type water pump (CWP) was applied in 2.0 liter diesel vehicle. The clutch-type water pump can force cooling water to supply into an engine by the operation of an electromagnetic clutch equipped as the inner part of pump system. The onset of CWP is decided by temperature of cooling water and engine oil. And, the control logic for an optimal operation of the clutch-type water pump was developed and applied in engine and vehicle tests. In this study, the warm-up time was measured with the conventional water pump and clutch-type water pump in engine tests. And the emission and the fuel consumption were evaluated under NEDC mode in vehicle tests. Also, tests were carried out for the various temperature conditions starting the operation of CWP. From the results of the study, the application of CWP can improve the fuel consumption and $CO_2$ reduction by about 3%.