• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1833-1838
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• 2003

In the nuclear power plant, emergency core coolant system(ECCS) is furnished at reactor coolant system(RCS) in order to cool down high temperature water in case of emergency. However, in this coolant system, thermal stratification phenomenon can be occurred due to coolant leaking in the check valve. The thermal stratification produces excessive thermal stresses at the pipe wall so as to yield thermal fatigue crack(TFC) accident. In the present study, when the turbulence penetration occurs in the branch piping, the maximum temperature differences of fluid at the pipe cross-sections of the T-branch with thermal stratification are examine

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.5
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• pp.427-433
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• 2017

In the case of high-strength or low thermal conductivity material milling, tool breakage occurs easily because of the high friction temperature. Therefore, the effectiveness of the coolant supply is very important for proper tool cooling. As the manually adjustable joint mechanism nozzle is generally used for coolant supply, the cooling efficiency is very low. It also has a bad influence on the workspace environment because of coolant scattering. In this study, the milling characteristics of STS316L were investigated according to the coolant spray position based on the automatic adjustable system. Tool wear and surface roughness were measured according to the coolant spray position. Through these experiments, the effectiveness of the fabricated system was explained.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.735-740
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• 2001

In the nuclear power plant, emergency core coolant system(ECCS) is furnished at reactor coolant system(RCS) in order to cool down high temperature water in case of emergency. However, in this coolant system, it occurs thermal stratification phenomena in case that there is the mixing of cooling water and high temperature water due to valve leakage in ECCS. This thermal stratification phenomena raises excessive thermal stresses at pipe wall. Therefore, this phenomena causes the accident that reactor coolant flows in reactor containment in the nuclear power plant due to the deformation of pipe and thermal fatigue crack(TFC) at the pipe wall around the place that it exists. Hence, in order to fundamental identification of this phenomena, it requires the experimental research of modeling test in the pipe flow that occurs thermal stratification phenomena. So, this paper models RCS and ECCS pipe arrangement and analyzes the mechanism of thermal stratification phenomena by measuring of temperature in variance with leakage flow rate in ECCS modeled pipe and Reynold number in RCS modeled pipe. Besides, results of this experiment is compared with computational analysis which is done in advance.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.3
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• pp.179-185
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• 2014

Average temperature and temperature uniformity in a battery cell are the important criteria of the thermal management of the battery pack for hybrid electric vehicles and electric vehicles (HEVs and EVs) because high power with large size cell is used for the battery pack. Thus, liquid cooling system is generally applied for the HEV/EV battery pack. The liquid cooling system is made of multiple cooling plates with coolant flow paths. The cooling plates are inserted between the battery cells to reject the heat from batteries to coolant. In this study, the cooling plate with U-shaped coolant flow paths is considered to evaluate the effects of coolant flow condition on the cooling performance of the system. The counter flow and parallel flow set up is compared and the effect of flow rate is evaluated using CFD tool (FLUENT). The number of counter-flows and flow rate are changed and the effect on the cooling performance including average temperature, differential temperature, and standard deviation of temperature are investigated. The results show that the parallel flow has better cooling performance compared with counter flow and it is also found that the coolant flow rate should be chosen with the consideration of trade-off between the cooling performance and pressure drop.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.4
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• pp.446-453
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• 1997

The superconducting winding in rotor of a superconducting generator should be kept at extremely low temperature of 4-5 K to maintain the superconducting state. For this purpose the liquefied helium is used for the coolant and it is very important to analyze and design a cooling system making effective use of the coolant. In this paper, the typical heat exchanger of a superconducting generator with the flow passage is analyzed with regard to the thermal equilibrium. An experimental constant relevant to the flow condition in the flow passage is determined with heat exchange experiments in cryostat. Also a new heat exchanger with porous material is proposed and designed. Results of the numerical analysis for the temperature distributions for the torque tube and the coolant are reported and the efficiency of the heat exchanger is discussed from the viewpoint of amounts of coolant needed.

• Transactions of the Korean Society of Automotive Engineers
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• v.17 no.1
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• pp.72-79
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• 2009

Recently, the internal combustion engines have focused on reducing the $CO_2$ gas in order to cope with severe regulations for fuel economy. Therefore, various new technologies have been developed. Among them, cooling system is spotlighted because it has great effect on fuel economy. In this study, we measured the friction losses of engine parts according to engine speed and oil temperature. We also obtained optimized oil temperature which has the minimum friction losses. Then, we selected optimized oil temperature range and gave informations of friction losses for each engine parts. In addition, we analyzed relationship between coolant temperature and oil temperature by using engine performance test system. From this experiment, we obtained the database for relationship between coolant temperature and oil temperature. Then, we found the optimal temperature about engine oil. We analyzed BSFC and exhaust emissions by controlling the high coolant temperture. If we controlled coolant temperature more higher, BSFC has a little difference but exhaust emissions such as THC and CO have reduced. By using these experimental results, we predicted that IC engine have more low fuel consumption and exhaust emissions by optimized cooling control strategy.

• Nuclear Engineering and Technology
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• v.39 no.4
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• pp.257-272
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• 2007

Supercritical water-cooled reactors (SCWRs) are recognized as a Generation IV reactor concept. The Super LWR is a pressure-vessel type thermal spectrum SCWR with downward-flow water rods and is currently under study at the University of Tokyo. This paper reviews Super LWR safety. The fundamental requirement for the Super LWR, which has a once-through coolant cycle, is the core coolant flow rate rather than the coolant inventory. Key safety characteristics of the Super LWR inhere in the design features and have been identified through a series of safety analyses. Although loss-of-flow is the most important abnormality, fuel rod heat-up is mitigated by the "heat sink" and "water source" effects of the water rods. Response of the reactor power against pressurization events is mild due to a small change in the average coolant density and flow stagnation of the once-through coolant cycle. These mild responses against transients and also reactivity feedbacks provide good inherent safety against anticipated-transient-without-scram (ATWS) events without alternative actions. Initiation of an automatic depressurization system provides effective heat removal from the fuel rods. An "in-vessel accumulator" effect of the reactor vessel top dome enhances the fuel rod cooling. This effect enlarges the safety margin for large LOCA.

• Nuclear Engineering and Technology
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• v.51 no.2
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• pp.546-555
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• 2019

Since the first nuclear reactor first critical, nuclear systems has gone through four generations of history, and the fourth generation nuclear system will be truly realized in the near future. The notions of SVBR and lead-bismuth eutectic alloy coolant put forward by Russia were well received by the international nuclear science community. Lead-bismuth eutectic alloy with the ability of the better neutron economy, the low melting point, the high boiling point, the chemical inertness to water and air and other features, which was considered the most promising coolant for the 4th generation nuclear reactors. This study mainly focuses on the structural design optimization of the 4th-generation reactor coolant pump, including analysis of external characteristics, inner flow, and transient characteristic. It was found that: the reactor coolant pump with a central symmetrical dual-outlet volute structure has better radial-direction balance, the pump without guide vane has better hydraulic performance, and the pump with guide vanes has worse torsional vibration and pressure pulsation. This study serves as experience accumulation and technical support for the development of the 4th generation nuclear energy system.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.6
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• pp.84-93
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• 2018

Three-dimensional (3D) numerical simulations have been carried out to study how coolant injection conditions influence the cooling efficiency and projectile ejection performance in a mixture-gas ejection system (or gas-steam launch system). The 3D single-phase computational model was verified using a 1D model constructed with reference to the previous research and then a two-phase flow computation simulating coolant injection on to hot gas was performed using a DPM (Discrete Phase Model). As a result of varying the coolant flow rate and number of injection holes, cooling efficiency was improved when the number of injection holes were increased. In addition, the change of the coalescence frequency and spatial distribution of coolant droplets caused by the injection condition variation resulted in a change of the droplet diameter, affecting the evaporation rate of coolant. The evaporation was found to be a critical factor in the design optimization of the ejection system by suppressing the pressure drop while the temperature decreases inside the breech.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.3
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• pp.1-10
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• 1998

In this paper, we investigated the improvement of characteristics of knock, emission and fuel consumption rate by optimizing the location and size of water transfer holes in cylinder head gasket without change of engine water jacket design itself. The cooling system was modified in the direction of reducing the metal temperature in the head and increasing the metal temperature in the block. The optimization of water transfer holes in cylinder head gasket was obtained by "flow visualization test". The water transfer holes were concentrated in front side of the engine in order to reduce thermal boundary layer in the water jacket of No. 2 and No. 3 combustion changer in the cylinder head, which would have a large knock intensity, and increase thermal boundary layer in the water jacket of the cylinder block. When the modified coolant flow pattern was applied as proposed in this paper, the knock characteristic was improved. The spark timing was advanced up to 2$^{\circ}$ in low and middle speed range at a full load. In addition, HC emission at MBT was reduced by 5.2%, and the fuel consumption rate was decreased up to 1% in the driving condition of 2400 rpm and 250 KPa. However, since this coolant flow pattern mentioned in this paper might deteriorate the performance of vehicle cooling system due to the coolant flow rate reduction, a properly optimized point should be obtained. obtained.