• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.2 no.1
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• pp.49-62
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• 1990

The forced cooling system has been widely applied to passing more electric current in the underground power transmission cable technology. In this paper, the optimum cooling span of the in-trough-indirect water cooling method within an electric tunnel was investigated. A parametric study was performed for the cable currents, the coolant flow rates, and the coolant inlet temperatures. As a result, the temperature of the inlet air has been found as the most important parameter in determination of the optimum cooling span.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.6
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• pp.3708-3713
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• 2015

The objective of this study is to numerically investigate the heat transfer rate for evaluating the thermal performances of the stack thermal system using the commercial software. In order to perform this, the cooling performances of the stack system for fuel cell electric vehicle were tested under both driving road conditions including the general driving road and uphill driving road and operating conditions with and without of the air conditioning system. The heat transfer rate of the stack radiator for the stack system was increased with the increase of the inlet air flow velocity. The heat transfer rate of the stack radiator increased by 105.3% at the coolant flow rate of 20 l/min and 221.3% at the coolant flow rate of 120 l/min with the increase of the air flow velocity from 2 m/s to 10 m/s. $9.45^{\circ}C$ of inlet coolant temperature of the stack radiator at the severe driving condition of the slope of 8% and velocity of 50 km/h showed higher 85.3% than $5.1^{\circ}C$ of inlet coolant temperature at the general driving condition of the slope of 0% and velocity of 120 km/h. In addition, as the fuel cell electric vehicle with the air conditioning system operation was driving under severe uphill driving condition, the radiator coolant temperature for a stable stack operation could be exceeded over $70^{\circ}C$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.7
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• pp.1007-1014
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• 2003

This work deals with a controlled auto-ignition (CAI) single cylinder gasoline engine, focusing on the extension of operating conditions. The fuel is injected indirectly into electrically heated inlet air flow. In order to keep a homogeneous air-fuel mixing, the fuel injector is water-cooled by a specially designed coolant passage. Investigated are the engine performance and emission characteristics under the wide range of operating conditions such as 32 to 63 in the air-fuel ratio, 1000 to 1800 rpm in the engine speed, and 150 to 18$0^{\circ}C$ in the inlet air temperature. The compression ignition gasoline engine can be achieved that the ultra lean-burn with self-ignition of gasoline fuel by heating inlet air. For example. the allowable lean limit of air-fuel ratio is extended until 63 at engine speed of 1000 rpm and inlet air temperature of 17$0^{\circ}C$. It can be achieved that the emission concentrations of carbon monoxide, hydrocarbons and nitrogen oxide had been significantly reduced by CAI combustion compared with conventional spark ignition engine.

• Journal of Power System Engineering
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• v.10 no.1
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• pp.19-24
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• 2006

This work treats a controlled auto-ignition (CAI) single cylinder gasoline engine, focusing on the extension of operating conditions. The fuel was injected indirectly into electrically heated inlet air flow. In order to keep a homogeneous air-fuel mixing, the fuel injector was water-cooled by a specially designed coolant passage. The engine performance and emission characteristics were investigated under the wide range of operating conditions such as 40 in the air-fuel ratio, 1000 to 1800 rpm in the engine speed, 150 to $180^{\circ}C$ in the inlet-air temperature, and $60^{\circ}$ BTDC in the injection timing. The ultra lean-burn with self-ignition of gasoline fuel by heating inlet air was achieved in a controlled auto-ignition gasoline engine. It could be also achieved that the emission concentrations of carbon monoxide, hydrocarbons and nitrogen oxide significantly reduced by CAI combustion compared with conventional spark ignition engines.

• Journal of the Korean Society of Propulsion Engineers
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• v.2 no.3
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• pp.54-61
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• 1998

A numerical simulation is attempted for the regenerative cooling heat transfer processes of the liquid propellant rocket engine. The heat transfer from the combustion gases to the thrust chamber wall is called gas side heat transfer. This heat is conducted radially to the coolant through the carbon deposit and metallic wall of thrust chamber Finally, this heat is convected away by the coolant flowing along the passages in the thrust chamber. The equivalence of these three heat fluxes of the above processes is utilized to determine the coolant side wall temperature, gas side wall temperature and the heat flux. When the number and shape(width, height) of coolant passages, the shape(size) of thrust chamber, oxidant and fuel properties, coolant properties, oxidant/fuel mixture ratio, coolant inlet temperature, the thickness of carbon deposit formed along the thrust chamber wall during combustion are given, reasonable radial direction temperature distributions and heat fluxes along the thrust chamber axis are obtained.

• Journal of Power System Engineering
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• v.8 no.3
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• pp.5-10
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• 2004

This work deals with a controlled auto-ignition (CAI) single cylinder gasoline engine, focusing on the extension of operating conditions. In order to keep a homogeneous air-fuel mixing, the fuel injector is water-cooled by a specially designed coolant passage. Investigated are the engine emission characteristics under the wide range of operating conditions such as 40 in the air-fuel ratio, 1000 to 1800 rpm in the engine speed, $150\;to\;180^{\circ}C$ in the inlet-air temperature, and $80^{\circ}$ BTDC to $20^{\circ}$ ATDC in the injection timing. A controlled auto-ignition gasoline engine which has the ultra lean-burn with self-ignition of gasoline fuel can be achieved by heating inlet air. It can be achieved that the emission concentrations of carbon monoxide, hydrocarbons and nitrogen oxides had been significantly reduced by CAI combustion compared with conventional spark ignition engine.

• Journal of ILASS-Korea
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• v.26 no.3
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• pp.135-141
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• 2021

High-efficient HEV Engine cooling systems reflects variable coolant temperature because it can decrease the hydrodynamic frictional losses of lubricated engine parts in light duty conditions. In order to safely raise the operating temperature of passenger cars to a constant higher level, and thus optimize combustion and all accompanying factors, a new thermostat technology was developed : the electronically map-controlled thermostat. In this work, various crystalline plastics such as polyphthalamide (PPA) and polyphenylenesulfide (PPS) mixed with various glass fiber amounts were introduced into plastic fittings of automotive electronic controlled thermostat for the purpose of suppressing influx of coolant into the element and undesirable opening during hot soaking. Skirt was installed around element frame of automotive electronic controlled thermostat for improving thermal sensitivity in terms of response time, hysteresis and melting temperature. To validate the effectiveness and optimum shape of skirt, thermal sensitivity test and three-dimensional CFD simulation have been performed. As a consequence, important improvement in thermal sensitivity with less than 3℃ of maximum coolant temperature between opening and engine inlet was obtained.

• Nuclear Engineering and Technology
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• v.55 no.8
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• pp.2757-2772
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• 2023

The fluid retention effect of the Volume Control Tank (VCT) leads to a long time delay in Reactor Coolant System (RCS) concentration during the boration process. A coupled model combining a lumped-parameter sub-model and a computational fluid dynamics sub-model is currently used to investigate the concentration dynamic characteristic of RCS during the boration process. This model is validated by comparison with experimental data, and the predicted results show excellent agreement with experimental data. We provide detailed fields in VCT and concentration variations of RCS to study the interaction between mixing in VCT and the transient responses of RCS. Moreover, the impacts of the inlet flow rate, inlet nozzle diameter, original concentration, and replenishing temperature of VCT on the RCS concentration characteristic are studied. The inlet flow rate and nozzle diameter of VCT remarkably affect the RCS concentration characteristic. Too-large or too-small inlet flow rates and nozzle diameters will lead to unacceptable long delays. In this work, the optimal inlet flow rate and nozzle diameter of VCT are 5 m³/h and 58.8 mm, respectively. Besides, the impacts of the original concentration and replenishing temperature of VCT are negligible under normal operating conditions.

• Nuclear Engineering and Technology
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• v.18 no.3
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• pp.209-217
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• 1986

The inlet coolant temperature reduction technique has been used to extend the load follow operation further in the end-of-cycle-life(EOL). In order to simulate the technique and calculate the nuclear characteristics of a PWR core according to the load follow operation, the three dimensional computing system has been established. The analysis was performed in both MINB and SPINR modes of typical 12-3-6-3 locad follow operation for the EOL of KNU-1 plant. Moreover, the capability of return-to-power has been also tested for those two modes with the system analysis by the RETRAN-02 code. The results show that it has no difficulty to extend the load follow operation further in the EOL by applying the inlet coolant temprature reduction, and also the spinning reserve capacity(SRC) increases by 13% in MINB mode and 14% in SPINR mode Bore that used by control rods only, for 14$^{\circ}$ F drop in the inlet temperature.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.12
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• pp.924-930
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• 2018

The objective of this study was to investigate heating performance characteristics of electric heat pump system in a fuel cell electric vehicle (FCEV). In order to analyze heating performance characteristics of electric heat pump system with plate-type heat exchanger using stack coolant to evaporate the refrigerant, R-134a, each component was installed and tested under various operating conditions, such as air inlet temperature of inner condenser and compressor speed. When the air inlet temperature of inner condenser was varied from $0.0^{\circ}C$ to $-20.0^{\circ}C$, heating capacity was not quite different due to similar temperature gap between inlet and outlet of inner condenser with electric-driven expansion valve (EEV). However, COP increased until certain EEV opening, especially under 45.0%, because of decreasing power consumption. According to the compressor speed variation from 2,000 to 4,000 RPM, heating capacity and COP were found to have opposite trend. In the future works, stack coolant conditions as the heat source for tested heat pump system were analyzed with respect to heating performance, such as heating capacity and COP.