• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.10
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• pp.1812-1817
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• 2008

A cooling system for microelectronics is becoming more important as its surface heat density is projected to reach that of the sun surface. The existing technologies using natural and forced convection are limited to solve the problems. Recently, an electrohydrodynamic driven flow is studied as one of the means to cope with this problems. A new method, utilizing a needle-centered nozzle electrode, has been proposed and investigated. The I-V characteristics of the nozzle electrode for deionized water and silicone oil were significantly different from that of without liquid, which might be due to the liquid drop covered on the nozzle tip by the EHD force acting near the needle tip. Results showed that the liquid pumping rate and flow efficiency of the nozzle electrode were very high, especially for the silicone oil. Theoretical analysis also showed the effectiveness of the needle electrode centered in the ceramic nozzle, which, however, can be a means as a liquid pump.

• Journal of Mechanical Science and Technology
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• v.14 no.4
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• pp.466-476
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• 2000

This paper presents atomization characteristics of a double impinging F -0-0- F type injector with four streams. A phase Doppler particle analyzer was employed to measure the droplet-size and water was used as the inert simulant liquid instead of reactive propellant liquids. The droplet mean diameter (SMD) and size distribution were measured to investigate the effects of the momentum ratio and pressure drop variations. This experimental results can be used during the preliminary design stage of a impinging stream type injector for liquid rockets.

• Journal of the Korean Society of Visualization
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• v.16 no.1
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• pp.48-53
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• 2018

In this study, the effect of injection pressure on the column diameter and droplet velocity of liquid jet with the weakly turbulent Rayleigh-like breakup mode is experimentally studied using digital microscopic holography (DMH). The injection nozzle has the diameter of $50{\mu}m$ and injection pressure is varied from 0.1 to 0.4 MPa. When the micro liquid jet is injected into still air, the double-pulsed holograms was recorded on a CCD sensor and numerically reconstructed in order to obtain well focused images. In this study, the liquid column diameter from $50{\mu}m$ orifice nozzle is shown to be changed slightly but the droplet velocity is increased proportionally as the injection pressure is increased.

• Journal of ILASS-Korea
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• v.4 no.4
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• pp.24-29
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• 1999

In the pressure swirl atomizer, the liquid is injected through tangential passages into a swirl chamber, from which it emerges with both tangential and axial velocity components to form a thin conical sheet at the nozzle exit. This sheet rapidly attenuates, finally disintegrating into ligaments and then drops. The purpose of this study is to measure the spray characteristics according to variation of viscosity of the spray produced by the pressure swirl atomizer. The nozzle tested here were especially designed for this investigation. The discharge coefficient is determined by measuring the volume flow rate with a flow meter and the cone angle of the liquid sheets issuing from the nozzle is obtained from series of photographs of the sheet for various liquid viscosity and injection pressure. And mean drop size is measured by image processing method. It is found that the geometrical characteristics of the nozzle and the variation of viscosity were the influential parameters to determine the spray characteristics such as the cone angle, discharge coefficients and SMD.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.6
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• pp.1948-1958
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• 1996

Experimental and theoretical studies on the air-assist coaxial atomizer have been continuously carried out for a long time. But now the importance of the theoretical study is tending to increase as with the development of computer. This study is concerned to the spray modelization, especially, the instability of the liquid jet surrounded by the air stream which flows with high velocity. To study the phenomena of the break up, we used the linear theory based on the classical Kelvin-Helmholtz theory for capillary wave at a simple interface and we investigated the variation of liquid core radius. As a result, we obtained that the drop diameter and the variation of the liquid core radius predicted by using our model are reasonable.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.5
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• pp.402-409
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• 2006

For the design of a liquid direct contact cooling system, thermal and hydraulic analysis has been carried out. Well-known Zukauskas correlations are used to estimate the Nusselt number between the liquid refrigerant columns and the inlet airflow. The inlet air velocity is set at a typical value used in an actual showcase. For a constant column number, the best nozzle arrangement is determined for the maximum heat transfer. Heat transfer increases as the transverse pitch of the refrigerant column decreases. Among all the cases dealt with in the present study, the staggered arrangement with 140-columns of $14{\times}10$ shows the best thermal peformance and the expected temperature drop is $27.8^{\circ}C$. The effect of downstream refrigerant columns on the overall thermal performance is investigated as well.

• Journal of the Korean Society of Visualization
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• v.10 no.3
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• pp.21-24
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• 2012

Although the motion of the three-phase contact line on a solid substrate has been extensively studied thus far, the understanding of the dynamics of the contact line of liquid/liquid/gas phases is far from complete. Here we deposit a drop of isopropyl alcohol (IPA) on water and HFE-7100 whose free surfaces are exposed to air to observe the flow field around the contact line. By combining the shadowgraph and high-speed imaging techniques, we find that vortices are spontaneously generated at the contact line, which grow in size with time. The flow is attributed to the Marangoni stress that pulls a liquid of lower-surface tension toward a liquid surface having a higher surface tension. However, it is not still clear why the entrained lower-surface-tension liquid should whirl rapidly beneath the contact line. We also visualize the flow by the particle image velocimetry (PIV) to find out that the rotational velocity reaches the order of 1 mm/s near the free surface.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.85-88
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• 2011

In the trend of world wide environment preservation, researchers tried to find new environment friendly propellant instead of highly toxic propellant, Hydrazine. Among the candidates, ionic liquid propellants have lower toxicity, higher density, and higher specific impulse than Hydrazine. These ionic liquid propellants have high combustion chamber temperature, so catalyst supports such as gamma alumina cannot withstand in that temperature. Therefore, a catalyst that showed stable characteristic in high temperature is needed. Barium dopped alumina can be changed to Hexaaluminate in high temperature, and its characteristic in high temperature is superior than gamma alumina. Barium dopped Alumina is wet impregnated with Platinum and heated up to $1300^{\circ}C$ and $1400^{\circ}C$ for 2 hours. Those catalysts were examined by XRD, SEM, EDS, BET, and Drop test.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.4
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• pp.549-559
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• 1999

An experimental study was peformed to measure the viscosity of microencapsulated PCM slurries as the functions of its concentration and temperature, and also influence to its fluid dynamics. For the viscosity measurement, a rotary type viscometer, which was equipped with temperature control system, was adopted. The slurry was mixed with water and Sodium Lauryl Sulphate as a surfactant by which its suspended particles were dispersed well without the segregation of particles during the experiment. The viscosity was increased as the concentration of MicroPCM particle added. The surfactant increased 5% of the viscosity over the working fluid without particles. Experiments were proceeded by changing parameters such as PCM particles'concentration as well as the temperature of working fluid. As a result, a model to the functions of temperature for the working fluid and its particle concentration is proposed. The proposed model, for which its standard deviation shows 0.8068, is agreed well with the reference's data. The pressure drop was measured by U-tube manometer, and then the friction factor was obtained. It was noted that the pressure drop was not influenced by the state of PCM phase, that is solid or liquid in its core materials at their same concentration. On the other hand, it was described that the pressure drop of the slurry was much increased over the working fluid without particles. A friction factor was placed on a straight line in all working fluids of the laminar flow regardless of existing particles as we expected.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.3
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• pp.1005-1014
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• 1996

An experimental investigation has been carried out to examine the influence of injector design variables and operating conditions on the resultant drop size for triplet impinging streams injectors. The variables studied in this investigation are pressure drop, impinging angle, orifice length to diameter ratio, and impinging point distance. Droplet-size data are obtained using water as the propellant simulant by Malvern Particle Analyzer System. Drop size decreases with increasing impinging angle and pressure drop while other injector parameters remain constant at the same point. But it is found that there is no noticeable droplet-size change which results from change in orifice length to diameter ratio or impinging point distance within the investigated range.