• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.245-253
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• 2010

The present study shows some results of developing evaporative heat exchangers with mini-channels. Heat exchangers with three different water paths were manufactured and tested to compare performances of cooling and pressure drop. Among the three types of heat exchangers, Type 2 with full-etching was proved to be the best in the cooling performances for considered operating conditions, and thus it is recommended to adopt Type 2 for its simplicity of production and outstanding performance. However, Type 1 was shown to be better when it is operated at a high air inlet temperature condition. The developed evaporative heat exchanger will be installed in Environmental Control Systems(ECSs) for aerial vehicles, and it can be used effectively in case an ECS is not only limited in its weight and volume but also required to absorb heats without supplying water (or a coolant) for a certain period of time.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.5
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• pp.2628-2634
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• 2014

Vehicle washer heater system is more widely adopted to defrost a window or to clear the windshield glass in winter season. The washer heater system should be designed to heat up washer fluid rapidly to the target temperature for only a short time. A numerical analysis has been carried out to analyze the heat transfer characteristics with materials of inside parts in vehicle washer heater system with filler and flow path. ANSYS - FLUENT software is employed for the analysis. The axial symmetry model is three-dimensional and unsteady. It applies to the coupled method which is one of pressure based. Through this result, it was obtained to find the optimal material condition for the filler and flow path in washer system. For material of filler, the air with lower density was heated more rapidly rather than silicon carbide(SiC). For material of flow path, copper with the heat transfer coefficient of approximately four times greater than the nickel gives us higher efficiency. That is the reason why the heating time of methanol was reduced to make uniform temperature in washer heater system.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.5 no.2
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• pp.37-48
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• 1991

This paper shows the characteristics of sparkover discharge in flowing air ranging from O(Reynolds number, Re) to $10.52{\times}10^4$(Re). Also, we investigated changes of discharge pattern for constant input power by adjustment of the Reynolds number. Flowing air duct of this investigation is a circular tube. The flow at the experimented positions' section is described as fully development laminar flow. The important results obtained from this study are as follows. The sparkover discharge path of flowing air can be analyzed by the theories of flow field for air. The sparkover voltage shows nearly the maximum value when the Reynolds number of flowing air ranges $3{\times}10^4$ to $4{\times}10^4$The maximum sparkover voltages of flowing air are about 6.3[kV] higher than those of static air. The discharge pattern can be controlled by adjustment of the Reynolds number.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.4
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• pp.378-383
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• 2013

A butterfly throttle valve has been used to control the brake power of an SI engine by controlling the mass flow-rate of intake air in the induction system. However, the valve has a serious effect on the volumetric efficiency of the engine due to the pressure resistance in the induction system. In this study, a new intake air controlling valve named "Variable Geometry Throttle Valve(VGTV)" is proposed to minimize the pressure resistance in the intake system of an SI engine. The design concept of VGTV is on the application of a venturi nozzle in the air flow path. Instead of change of the butterfly valve angle in the airflow field, the throat width of the VGTV valve is varied with the operating condition of an SI engine. In this numerical study, CFD(computational fluid dynamics) simulation technique was incorporated to have an aerodynamics performance analysis of the two air flow controlling systems; butterfly valve and VGTV and compared the results to know which system has lower pressure resistance in the air intake system. From the result, it was found that VGTV has lower pressure resistance than the butterfly valve. Especially VGTV is effective on the low and medium load operating condition of an SI engine. The averaged pressure resistance of VGTV is about 49.0% lower than the value of the conventional butterfly throttle valve.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.8
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• pp.4802-4808
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• 2014

A plate-fin tube type heat exchanger has a lighter weight, approximately 30%, than the conventional circular-fin type condenser of household refrigerator. Because the low weight means low cost, it can have significant effects on the growth of related businesses if similar performance can be guaranteed. To check the possibility of the use of such a plate fin-tube condenser, experimental evaluations were performed in this study. Four different condensers including a conventional circular fin-tube condenser were used for the test. A well designed refrigerant supply system was used to supply similar conditions with a refrigerator, and the heat transfer rate and pressure drops of air side were measured precisely. As a result, the plate fin-tube type condensers showed a lower heat transfer rate of more than 13% than the conventional circular fin-tube type condenser, but the air side pressure drop was reduced and the heat transfer per unit weight was increased. Therefore, it shows the possibility of the use of a plate fin-tube type condenser after optimizing the air flow path and increasing the air flow to make a similar heat transfer rate.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.6
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• pp.883-892
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• 2002

A numerical study has been carried out to investigate the flow and heat transfer from an aluminum foam heat sink in a confined channel. A uniform heat flux is given at the bottom of the aluminum foam heat sink, which is horizontally placed on the heated surface. The channel walls are assumed to be adiabatic. Cold air is supplied from the top opening of the channel and exhausted to the channel outlet. Comprehensive numerical solutions are acquired to the governing Wavier-Stokes and energy equations, using the Brinkman-Forchheimer extended Darcy model and the local thermal non-equilibrium model f3r the region of porous media. Details of flow and thermal fields are examined over wide ranges of the principal parameters; i.e., the Reynolds number Re, the height of heat sink h/H, porosity $\varepsilon$and pore diameter ratio $R_{H}$.

• Proceedings of the KAIS Fall Conference
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• 2010.11b
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• pp.824-827
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• 2010

본 논문은 전동형 모터의 Rotor의 자동 성형을 위한 자동화된 주조기 개발에 대한 결과이다. 개발된 자동화된 Rotor 전용 주조기는 수평형에 비해 금형의 크기가 약 1/2정도 이므로 금형 체결력이 반감되고, 기계 구조는 매우 작아진다. 그리고 Al용탕이 사출되는 과정에서 Spool -> Runner -> Gate -> Cavity(제품)에 이르기까지의 Runner를 최소화하여 재용융을 위한 에너지의 비용 절감을 할 수가 있다. 금형 구조가 간단하므로 금형비가 저렴하여 다품종 소량생산에 매우 유리하다. 개발제품은 수직형 구조로 알루미늄 용탕의 윗면의 공기가 금형의 유로 상측에 위치하므로 공기(gas)가 먼저 배출되어 사출(주조)후 Rotor 성형부에 남아 있는 기포가 최소화된다. 그러므로 충진도가 높아진다. Rotor 코아(규소강)가 크더라도 수직형은 금형내에 삽입(Inset)하기가 쉽고 또한, 제품의 착탈 부위와 사출부위가 다르기 때문에 작업성, 안전성이 우수하고 생산성이 매우 높다. 수직형은 충진 밀도가 매우 높고 밀도가 균일하기 때문 Rotor의 회전 소음, 진동에 대한 품질이 매우 우수하다. 따라서 고효율, 고품질의 전동모터 Rotor 제품 생산에 매우 효과적인 장비라 할 수 있다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.83-87
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• 2009

Ramjet engine is weak for low frequency combustion instability because of their long air flow passage. A model combustor which has fuel injector and V-gutter shaped flame holder was designed and fabricated in order to simulate a combustion mechanism of ramjet engine, and it could demonstrate combustion instability which might occur in ramjet combustor. The frequency of the instability was very similar to that of acoustic resonance frequency of combustor, and it proved that a typical combustion instability by thermo-acoustic coupling occurred.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.1
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• pp.93-101
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• 2000

In a gas-turbine engine, fan blades in flow path are confronted with many kinds of loading. The study of the excited force by the wake of struts has proposed and the possibility of fatigue failure about rotating fan blades by the excited force at the steady state is evaluated. Equations of the excited force of wakes has been derived at the steady state and the maximum pressure distributions measured at the transient state are proposed. Dynamic characteristics and the fatigue strength of fan blades by experimental test were obtained. To evaluate HCF(High Cycle Fatigue) damage of fan blades, FEM analysis was performed with a steady state harmonic response, which was followed by high cycle fatigue damage factor from goodman diagram.

• Applied Chemistry for Engineering
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• v.22 no.6
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• pp.664-671
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• 2011

The vacuum residue of petroleum refinery, i.e. asphalt, was modified through a non-catalytic air blowing process to prepare the semi-blown asphalt. Changes in composition, chemical structure, and physical properties of asphalt were examined. The result from the thin layer chromatography showed that the asphaltene content in asphalt was increased by the air blowing on account of the aromatization of aliphatic hydrocarbon and condensation. These changes in molecular structure were also confirmed by $^1H-NMR$, differential scanning calorimetry, and thermogravimetry. Because of the molecular structure changes, the penetration of asphalt was decreased and the softening point and the flash point of asphalt were increased.