• 한국환경과학회지
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• 제20권1호
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• pp.25-34
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• 2011

The new empirical static model was constructed on the basis of dimension analysis to predict the pressure drop according to the operating conditions. The empirical static model consists of the initial pressure drop term (${\Delta}P_{initial}$) and the dust mass number term($N_{dust}=\frac{{\omega}_0{\nu}_f}{P_{pulse}t}$), and two parameters (dust deposit resistance and exponent of dust mass number) have been estimated from experimental data. The optimum injection distance was identified in the 64 experimental data at the fixed filtration velocity and pulse pressure. The dust deposit resistance ($K_d$), one of the empirical static model parameters got the minimum value at d=0.11m, at which the total pressure drop was minimized. The exponent of dust mass number was interpreted as the elasticity of pressure drop to the dust mass number. The elasticity of the unimodal behavior had also a maximum value at d=0.11m, at which the pressure drop increased most rapidly with the dust mass number. Additionally, the correlation coefficient for the new empirical static model was 0.914.

• 한국연소학회:학술대회논문집
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• 한국연소학회 1999년도 제19회 KOSCO SYMPOSIUM 논문집
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• pp.209-217
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• 1999

A model for depicting the rocket engine combustion process is presented and basic experiments near a design point are provided with a FOOF type of unlike impinging injector for RP-I fuel and liquid-oxygen. The model is based on the assumption that the vaporization is the rate-controlling combustion process. The effects of initial drop size and initial drop velocity are systematically shown and discussed. It is seen that in the midst of considered parameters the change of initial drop size is more sensitive to the performance. The proposed model describes qualitative trends of combustion process well despite of its simplicity.

• Journal of Welding and Joining
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• 제15권3호
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• pp.47-55
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• 1997

Dynamic characteristics of the short circuit mode are investigated using the Volume of Fluid (VOF) method. When the initial molten drop volume, contact area and wire feed rate are given, rate change of the molten bridge profiles, pressure and velocity distributions are predicted. The electromagnetic force with proper boundary conditions are included in the formulation to consider the effects of welding current. It is found that the molten metal is transferred to the weld pool mainly due to the pressure difference caused by the curvatures in the initial stage, and electromagnetic force becomes dominant factor in the final stage of short circuit transfer. Necking occurs at the contact position between the molten drop and weld pool, and the initial molten drop volume and welding current have significant effects on break-up time.

• 대한기계학회논문집B
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• 제24권5호
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• pp.718-724
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• 2000

A model for depicting the rocket engine combustion process is presented and several experiments near a design point are provided with a FOOF type of unlike impinging injector for a propellant combination of Jet A-1 fuel and liquid-oxygen. The model is based on the assumption that the vaporization is the rate-controlling combustion process. The effects of initial drop size and initial drop velocity are systematically shown and discussed. It is seen that in the midst of considered parameters the change of initial drop size is more sensitive to the performance. The proposed model describes qualitative trends of combustion process well despite of its simplicity.

• 전기의세계
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• 제18권2호
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• pp.7-14
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• 1969

From the first customer located right at the substation to the last customer at the end of the line, voltage must be held within close limits, so the voltage regulation is more important than the thermal limit. On a typical distribution system during the peak load period, the voltage drop may be serious enough to cause unsatisfactory operation of home appliances in the residential area, and present many problems to manufacturing industries, where the voltage must be maintained within close limits to insure smooth operation. Among all the factors contributing to voltage drop in the distribution system, the voltage drop in the distribution transformer may account for 30% of this figure. If we can eliminate this factor, the power companies can provide better quality electricity to more customers with the existing distribution facilities, thus saving on initial investment costs. Taking all these problems into consideration, the author undertook the design of a capacitive transformer which would give zero voltage drop at rated load and at 80% lagging power factor while incorporating overload features to withstand 400% overload for at least 100 seconds. The following are the results obtained through design, manufacture and test of an initial experimental transformer built with these specific purposes.

• 설비공학논문집
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• 제5권3호
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• pp.179-186
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• 1993

The characteristics of pressure-drop oscillations(PDO) in boiling channel are studied experimentally. The effects of initial and boundary conditions on PDO are investigated in terms of oscillation period and amplitude. The period and amplitude of PDO are increased with the increase in the compressible volume in surge tank and heat input. However the amplitude of PDO is decreased with fluid temperature under low subcooling condition. Higher initial insurge flowrate resulted in almost invariant oscillation period but lower amplitude. At higher heat input the oscillation of heater wall temperature is significant, whose period is the same as that of pressure-drop instability.

• Journal of Welding and Joining
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• 제27권1호
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• pp.59-64
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• 2009

In order to determine the One-Drop One-Pulse(ODOP) condition of the pulsed gas metal arc(GMA) welding, the drop detaching phenomenon during the peak time is investigated using the force-displacement model. The drop detaching criterion is established based on the displacement of the pendant drop, and the forces exerted on the drop are calculated using the Modified Force Balance Model(MFBM). The effects of wire melting on the drop size and force are included in the force-displacement model. While the peak current has most significant effects on the drop detaching time, the initial drop mass prior to the peak time also influences drop transfer. The calculated results show good agreements with the experimental data, which implies that the ODOP condition can be predicted using the force-displacement method.

• 한국자동차공학회논문집
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• 제21권6호
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• pp.72-80
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• 2013

For the proper cooling of in-wheel motor, the cooling channel should have the characteristics which are low pressure drop and adequate cooling oil supply to motor part. In this study, the flow performance of cooling channel for in-wheel motor was evaluated and the shape of the channel was optimized. First, the pressure drop and flow distribution characteristics of the initial channel model were evaluated using numerical analysis. Also, by the result of analysis and design modification, 4 design parameters of the channel were selected. Second, using the Taguchi optimal method, the cooling channel was optimized. In the method, nine models with different levels of the design parameters were generated and the flow characteristics of each models was estimated. Base on the result, the main effect of the design parameters was founded and optimized model was obtained. For the optimized model, the pressure drop and oil flow rate were about 0.196 bar and 0.207 L/min, respectively. The pressure drop decreased by about 0.3 bar and the oil flow rate to the motor part increased by about 0.2 L/min compared to the initial model.

• 반도체디스플레이기술학회지
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• 제9권1호
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• pp.23-28
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• 2010

In this paper, wafer drop from wafer guide mechanism, which is one of the serious problems in water transfer robot, is analyzed, and new wafer guide mechanisms are proposed to minimize this drop. Three types of new wafer guide mechanisms are proposed: roller type, gear type and L-shape rocker type. We choose one of the proposed mechanism, which is roller type, and verified this mechanism through real transfer experiment. Wafer picking up test is conducted with initial aligning error for simulating the wafer drop. Number of drop is compared between conventional mechanism and proposed mechanism. As a result, we can find the proposed mechanism can reduce the number of wafer drop dramatically.

• 한국도로학회논문집
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• 제17권4호
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• pp.33-40
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• 2015

PURPOSES: Evaluation of the wind speed effect on the temperature drop of an asphalt mixture during construction, by using the transient heat transfer theory and dominant convective heat transfer coefficient model. METHODS: Finite difference method (FDM) is used to solve the transient heat transfer difference equation numerically for various wind speeds and initial temperature conditions. The Blasius convective heat transfer coefficient model is adapted to account for the effect of wind speed in the temperature predictions of the asphalt mixture, and the Beaufort number is used to select a reasonable wind speed for the analysis. As a function of time and depth, the temperature of the pavement structure is predicted and analyzed for the given initial conditions. RESULTS : The effect of wind speed on the temperature drop of asphalt mixture is found to be significant. It seems that wind speed is another parameter to be accounted for in the construction specifications for obtaining a better quality of the asphalt mixture. CONCLUSIONS: It is concluded that wind speed has a significant effect on the temperature drop of the asphalt layer. Although additional field observations have to be made to reflect the effect of wind speed on the construction specifications, it appears that wind speed is a dominant variable to be considered, in addition to the atmospheric temperature.