• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.6
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• pp.1150-1155
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• 1992

The cooling characteristics of a hot steel plate by a laminar impinging water bar were investigated experimentally. The dynamic parameters investigated were nozzle height L between nozzle and the hot plate, flow rate Q, and initial cooling temperature. Because the boiling phenomena on a hot steel plate are unsteady and change discontinuously, it is difficult to analyze the cooling characteristics directly. In this study the cooling efficiency was estimated by using the temperature decay rates and expansion speed of the water cooling zone. Temperature in the water cooling zone decreased rapidly and the radius of the water cooling zone expanded nearly in proportion to square root of the cooling time. With increasing initial temperature of a hot steel plate, the cooling efficiency became descendent. The cooling curve in the case of L/D = 30 showed the largest temperature decay rate and excellent cooling performance.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.10
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• pp.1285-1295
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• 1999

An experimental study on heat transfer and flow characteristics of a circular impinging jet on a flat plate has been carried out. Of particular interests are the effects of nozzle wall thickness and nozzle exit pressure. Experimental apparatus has been designed to view heating plate coated by TLC from the opposite side of the nozzle in order to measure heat transfer rates for cases of very small nozzle to plate spacings. A visualization study of jet flows has also been performed. As the nozzle wall thickness increases at small nozzle to plate spacings, the effect of mixing is inhibited due to the confinement caused by the finite nozzle wall, consequently, heat transfer rates have been decreased. At small nozzle to plate spacings, heat transfer rates and nozzle exit pressures are increased together, therefore, enhancement of heat transfer at small nozzle to plate spacings should be considered in conjunction with the need of more fan power to generate the same Reynolds numbers.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.6
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• pp.751-757
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• 2001

An experimental study of impinging jet-flow structure has been carried out for a fully developed single circular jet impingement cooling on a flat plate, and the effect of the wall thickness at nozzle exit edge is investigated. Impinging jet flow structures have been measured by Laser-Doppler Velocimeter to interpret the heat transfer results presented previously by Yoon et al.(sup)(10) The peaks of heat transfer rate are observed near the nozzle edge owing to the radial acceleration of jet flow when the nozzle locates close to the impingement plate. The growth of the velocity fluctuations in the wall jet flow is induced by the vortices which originate in the jet shear layer, and consequently the radial distribution of local Nusselt numbers has a secondary peak at the certain radial position. As a wall of circular pipe nozzle becomes thicker for small nozzle-to-target distance, the entrainment can be inhibited, consequently, the acceleration of wall jet flow is reduced and the heat transfer rate decreases.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.1
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• pp.81-94
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• 1988

A series of experiments was performed in this study to investigate the boiling heat flux between an impinging water jet and a hot surface. Test variables were surface roughness, jet velocity, saturation temperature excess of surface, nozzle diameter and the gap distance between nozzle plate and the hot surface. In order to make the impinged cooling water a forced flow streaming a long the hot surface immediately after the initial impingement, the flat nozzle tip was extended to a circular flat plate having the same diameter as the hot surface. Utilizing the dimensionless parameter study on continuity, momentum and energy equations, 5 groups of variables involved in the nucleate boiling heat transfer were derived so that it is possible to estimate the increased heat flux by impinging water jet in a similar experimental work. For the case of saturated water being impinging onto a high temperature surface, an applicable correlation among dimensionless parameters describing the heat flux was found to be as follow.

• Particle and aerosol research
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• v.13 no.3
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• pp.111-118
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• 2017

Electrohydrodynamic (EHD) printing with the aid of strong electric fields can generate and pattern droplets that are smaller than droplets by other printing technologies. Conventional EHD printing has created two-dimensional (2D) patterns by moving its nozzle or a substrate in X and Y directions. In this study, we aimed to develop an EHD system that can create 2D patterns using a multielectrode array (MEA) without moving a nozzle or substrate. In particular, printing ink mixtures of biodegradable polymers and model dyes was patterned on a thin film made of another biodegradable polymer. Without movement of a nozzle and substrate, stable 2D patterning of minimum $6{\mu}m$ size over a range of about 1 mm away from the nozzle position was achieved by MEA control only. We also demonstrated the possibility of denser 2D pattering of the ink mixtures by moving a target substrate relative to MEA position.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.6
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• pp.693-700
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• 2003

The effect of the configuration of the nozzle and the impinging surface on the characteristics of the hole-tones has been experimentally investigated. It is found that the plate-tone is a special case of hole-tones, where the hole diameter is zero. The jet velocity range for hole-tones is divided into the low velocity region associated with laminar jet and the high velocity region with turbulent jet. The frequency of the tone is that for the shear layer instability at the nozzle exit or that attainable by a cascade of vortex pairing process with increase of the impinging distance. When the distance is longer than one diameter the frequency decreases to the terminal value near the preferred frequency of the column mode instability, in the range 0.23< $St_d$<0.53, where $St_d$ is the Strouhal number defined by $fd/U_J$, f the frequency, d the nozzle diameter, and $U_J$ the exit velocity. While the convection speed of the downstream vortex, in the present study, is almost constant at low-speed laminar jet, it increases with distance at high-speed turbulent jet. As the frequency increases, the convection speed decreases in the low frequency range corresponding to the preferred mode, in agreement with the existing experimental data for a free jet.

• Fire Science and Engineering
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• v.32 no.3
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• pp.35-41
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• 2018

Experiments were performed on 140 ml hexane pool fire extinguishment using a twin-fluid nozzle. For this pool fire, the area of the fire source (round shape of 80 mm in diameter) was $0.005027m^2$ and the measured heat release rate was 2.81 kW. The flow rates of water and gas (air and nitrogen) supplied to the twin-fluid nozzle were 156-483 g/min (~0.156-0.483 l/min) and 30-70 l/min, respectively. In the present experimental ranges, the high gas flow rate conditions led to the successful extinguishing of the pool fire. Under the low gas flow rate conditions in the extinguishment regime, the extinguishment time was long and the estimated water consumption was high. Under high gas flow rate conditions, however, the water flow rate conditions did not appear to have a great impact on the extinguishment time and estimated water consumption. On the other hand, in the present experimental ranges, the types of supply gas did not appear to affect the extinguishable flow rate condition, extinguishment time, and estimated water consumption. Finally, using the present experimental results with previous ones using a single-fluid nozzle, the water consumption of twin-fluid and single-fluid nozzles for extinguishing a 140 ml hexane pool fire were preliminarily compared and discussed.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.1
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• pp.81-84
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• 2004

A water-cooled calorimeter chamber with 8 cooling channels based on KSR-III sub-scale chamber has been designed and manufactured. One dimensional empirical correlation has been used at the design stage and full three-dimensional CFD analysis has been conducted to confirm the cooling condition for hot fire test is safe. Predicted heat flux is accurate around the nozzle throat when the thermal resistance of carbon deposit is considered. However relatively large difference is observed in chamber part.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.353-356
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• 2006

Convective heat transfer coefficient was measured around a secondary jet ejected into the supersonic flow field. Wall temperature distribution was measured on the surface, which the constant heat flux condition is applied. According to jet to freestream momentum ratio, the secondary flow was penetrated into the supersonic flow field. During the test, two dimensional thermal image of a wall temperature is taken by an infra-red camera. Experiments were performed under the testing condition of freestream Mach number of about 3, stagnation pressure of 630 kPa and Reynolds number of $3.0{\times}10^6$.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.6
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• pp.89-95
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• 2000

To obtain an exact flow loss in piping systems is very important in the face of efficiency anticipation and work control of plant. The object of this study is to get the flow loss through the experiment for sudden expansion and contraction part of circular pipe nozzle. The experiment in this study is performed after getting the flow loss factor for sudden expansion and contraction through preliminary experiments. It is confirmed that the results of this study agreed with the approximated equation of Ikeda and Matsuo. It is proved that flow loss factor ${\zeta}_3$for sudden expansion and contraction part of circular pipe is dependent on $L/D_1$in these experimental conditions.