• 한국수소및신에너지학회논문집
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• 제15권1호
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• pp.72-81
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• 2004

Study on the analysis of sodium spray fire using Gaussian drop size distribution, which redistributes a droplet spectrum with given mean diameter if its size classes with critical diameter(D>8mm) occur, was carried out. In this case, the oversized droplets were reduced to a stable diameter. Results calculated by the code using Gaussian drop size distribution were in better agreement with AI experimental results than those of NACOM and SPRAY code. The effect of variance on pressure in the test cell appeared greatly by introducing Gaussian function, which could represent various sodium droplet size distribution. The increase of the variance with mean droplet size resulted had an important effect upon the pressure in the test cell.

• 대한기계학회논문집B
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• 제30권10호
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• pp.942-949
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• 2006

A lumped model is proposed to predict liquid ejection characteristics of a thermally driven inkjet print head. The model is based on a two-dimensional heat conduction equation, an empirical pressure-temperature equation and a nonlinear hydraulic flow-pressure equation. It has been simulated through the construction of an equivalent R-C circuit, and subsequently analyzed using SIMULINK and a circuit simulation tool, PLECS. Using the model, heating and cooling characteristics of the head are predicted to be in agreement with the IR temperature measurements. The effects of the head geometry on the drop ejection are also analyzed using the nonlinear hydraulic model. The present model can be used as a design tool for a better design of thermal inkjet print heads.

• 한국유체기계학회 논문집
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• 제7권1호
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• pp.45-50
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• 2004

Two phenomena often encountered in liquid flow, which were completely absent in gas or vapor flow, were cavitation and flashing. These phenomena were of significant interest in any comprehensive discussion of control valves or contracted devices since their occurrence would affect the device sizing procedures, might introduce noise and vibration, and also may limit the life expectancy of device components and the immediate downstream piping. Thus, this study aimed to find the reduction method of occurred cavitation in system by the computer simulation. A derivative six model with different dimensions of cavity were adopted. From the results, it was found that the length of the cavity was mote important factor to reduce the pressure drop over the control valves or contracted devices than the depth of the cavity. And the pressures along the centerline of the contracted devices were dropped two times in the case of haying the large length (Lc=1.5D) of cavity.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제28회 춘계학술대회논문집
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• pp.175-178
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• 2007

The mode transition from cone-jet to dripping in colloid thruster operation has been analytically investigated. The transition has been predicted by the dynamic behavior of a liquid drop at the tip of the cone-jet. Conservation laws are applied to determine the upward motion of the drop, and an instability model of electrified jets is used to determine the jet breakup. Finally, for the first time, the analysis enables prediction of the transition in terms of the Weber number and electric Bond number. The predictions are in good agreement with experimental data.

• 대한설비공학회지:설비저널
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• 제17권5호
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• pp.590-597
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• 1988

Characteristics of flow regime transitions in inclined upwards gas-liquid two-phase flow have been investigated based upon a statistical analysis of instantaneous pressure drop curves through an orifice. The probability density functions of the curves indicate distinct patterns depending upon two-phase flow regime, which are very similar to those of horizontal two-phase. The dimensionless intensity of fluctuations of the pressure drops sharply change as the flow transitions such as plug-slug, pseudo slug-slug and annular-slug take place. The effects of inclination angle on the flow regime transitions have been also investigated. The results show that the method to identify the flow pattern based upon the statistical analysis of instantaneous pressure drops is suitable for inclined flow as well as horizontal flow.

• 설비공학논문집
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• 제16권12호
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• pp.1107-1116
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• 2004

In this paper, the effects of diverse parameters on the operation of loop heat pipe (LHP), such as particle diameter of sintered porous wick, wick porosity, vapor line diameter, thickness of wick and heating capacity were investigated by a theoretical analysis. A LHP has a wick only in its evaporator for the circulation of working fluid, and utilizes a porous wick structure of which pore size is very small to obtain a large capillary force. The working fluid is water and the material of sintered porous wick is copper. For these different parameters, capillary pressure, pressure drop in wick, pressure drops and temperature distribution were analyzed by a theoretical design method of LHP.

• 한국재료학회지
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• 제19권2호
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• pp.111-114
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• 2009

For the fabrication of core-shell structure bimetallic lead-free solder balls, both the critical temperature ($T_{cr}$) for the phase separation of two immiscible liquid phases and the temperature coefficient of the interfacial tension between the two separated liquid phases are required. In order to obtain this information, the temperature dependence of the surface tension of 60%Bi-24%Cu-16%Sn(-REM) alloys was measured using the constrained drop method. The slope of the temperature dependence of the surface tension changed clearly at a critical temperature for the separation of two immiscible liquid phases. The critical temperature of the 60%Bi-24%Cu-16%Sn alloy was estimated to be 1097K. An addition of 0.05% Ce decreased the critical temperature to 1085K, whereas that of 0.05% La increased it to 1117K. It was found that the surface tension and its temperature coefficient of the 60%Bi-24%Cu-16%Sn alloy were slightly increased by the addition of 0.05% Ce and 0.05% La. In addition, additions of Ce and La increased the temperature coefficient of the interfacial tension.

• 설비공학논문집
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• 제8권2호
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• pp.198-207
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• 1996

It is well known that drag reduction in single phase liquid flow is affected by polymer material, molecular weight, polymer concentration, pipe diameter, and flow velocity. Drag reduction in two phase flow can be applied to the transport of crude oil, phase change system such as chemical reactor, pool and boiling flow, and to present cavitation which occurs in pump impellers. But the research of drag reduction in two phase flow is not sufficient. The purpose of the present work is to evaluate the drag reduction by measuring pressure drop, void fraction, mean liquid velocity, and turbulent intensity whether polymer is added in the horizontal two phase system or not. Experiment has been conducted in a test section with the inner diameter of 24mm and the length of 1,500mm. The polymer materials used are two kinds of polyacrylamide[PAAM] and co-polymer[A611P]. The polymer concentration was varied with 50, 100 and 200 ppm under the same experimental conditions. Experimental results showed that the drag reduction of co-polymer is higher than that of polyacrylamide. Mean liquid velocities increased as polymer was added, and turbulent intensity decreased inversely near the pipe wall.

• 한국분무공학회지
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• 제12권1호
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• pp.1-10
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• 2007

The low frequency combustion instability phenomena generated by pressure drop oscillation such as propellant shake in feed line are studied. To generate the flowrate oscillation by the pressure pulsation up to 400Hz without flow discontinuities and cavitations, a hydrodynamic mechanical pulsator of rotating disk type was produced. Injection pressure conditions are 5, 7 and 9 bar and pressure fluctuation frequency conditions are 0, 4, 6 and 8 Hz. When the injection pressure was oscillated by a mechanical pulsator, the spray shape was pulsated regularly. During the pulsated state of the spray with a mechanical pulsator, the spray characteristics, such as spray angle and liquid film thickness in orifice exit, were measured and compared with those in steady state without a mechanical pulsator. Though the mean injection pressure was fixed in the steady and fluctuating state, there were some differences in all measured values, i.e. liquid film thickness and spray cone angle, between both states.

• Journal of Advanced Marine Engineering and Technology
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• 제31권6호
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• pp.672-680
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• 2007

Apparatus of rotating disk and cup are widely used spray paintings and industrial boilers. This study was conducted experimentally to investigate the characteristics of liquid atomization in a rotating disk atomizer by means of viscous liquid mixed water and glycerin. The Purpose of this study are to observe breakup mechanism according to the variation of supplied flow rate $0.4{\sim}30 cm^3/s$ and rotating speed $200{\sim}4000rpm$, and to investigate three kinds of breakup Pattern such as drop ligament and film formation by comparing the transition flow rate. ligament number and ligament length to those of Tanasawa and Matsumoto's empirical formula. The results are as follows ; The higher it makes use of viscous liquid. the better it get the characteristics of breakup mechanism. Also When I compared practical value with experiential value at similar test conditions. it was shown similar tendency though were a little variation.