• Journal of the Society of Naval Architects of Korea
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• v.52 no.3
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• pp.236-247
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• 2015

In this paper, the experimental equipments for ventilated supercavitation in cavitation tunnel is constructed and the basic data of ventilated supercavitation regard to the entrainment coefficient and Froude number is fulfilled. The experiments are conducted for the disk cavitator with injecting air and the pressure inside cavity and the shape of cavity are measured. As the entrainment coefficient increases while the Froude number is kept constant, the ventilated cavitation number decreases to a minimum value which decreases no more even with increasing the air entrainment. The minimum value of ventilated cavitation number, caused by the blockage effect, decreases according to increasing the diameter ratio of test section to cavitator. The cavity length is rapidly enlarged near the minimum cavitation number. In low Froude numbers, the cavity tail is floating up due to buoyancy and the air inside the cavity is evacuated from its rear end with twin-vortex hollow tubes. However, in high Froude numbers, the buoyancy effect is almost negligible and there is no more twin-vortex tubes so that the cavity shape becomes close to axisymmetric. In order to measure the cavity length and width, the two methods, which are to be based on the cavity shapes and the maximum width of cavity, are applied. As the entrainment coefficient increases after the ventilated cavitation number gets down to the minimum cavitation number, the cavity length still increases gradually. These phenomenon can be confirmed by the measurement using the method based on the cavity shapes. On the other hand, when the method based on the maximum width of cavity is used, the length and width of the cavity agree well with a semi-empirical formular of natural cavity. So the method based on the maximum width of cavity can be a valid method for cavitator design.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.7 s.94
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• pp.1841-1850
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• 1993

A simplified one-dimensional analysis has been performed to predict the local pressure distributions in Y-Jet twin-fluid atomizers. Fluid compressibility was considered both in the gas(air) and two-phase(mixing) ports. The annular-mist flow model was adopted to analyze the flow in the mixing port. A series of experiments also has been performed; the results show that the air flow rate increases and the liquid flow rate decreases with the increase of the air injection pressure and/or with the decrease of the liquid injection pressure. From the measured injection pressures and flow rates, the appropriate constants for the correlations of the pressure loss coefficients and the rate of drop entrainment were decided. The local pressures inside the nozzle by prediction reasonably agree with those by the experiments.

• 한국전산유체공학회:학술대회논문집
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• 2008.08a
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• pp.39.2-39.2
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• 2008

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2008.04a
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• pp.162-163
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• 2008

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.4
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• pp.475-482
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• 1998

In this paper, an experimental study was conducted to investigate the performance of the spherical ice particle production system which uses the technology of water spray in a vacuum chamber for increasing the heat transfer area. As a result, following conclusions were obtained. The diffusion-controlled evaporation model agreed relatively well with experiments. The spray flow rate influences the performance of the system rather than any other factors, for example, the spray nozzle position, the nozzle number. As the spray rate increases, the system efficiency increases. It is due to the entrainment of small droplets among the spray with the exhausted vapor. Thus the system should be designed and operated to prevent the entrainment. Assuming the compressor efficiency to be 70%, the COP of the system reaches highly up to 6 at a maximum spray rate. Under the conditions, however, the rigid ice layer is obtained because ice particles bond together with increase of the spray rate. Therefore, the spray rate should be controlled properly to make the spherical ice particles.

• 한국연소학회:학술대회논문집
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• 2004.06a
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• pp.118-123
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• 2004

The combustion characteristics of 0.03MW turbulent methane/oxygen diffusion flames have been investigated to give basic informations for designing industrial oxyfuel combustors. NOx reduction has become one of the most determining factors in the combustor design since 3-5% nitrogen is intrinsically included from the current oxygen producing processes. Flame lengths and NOx concentrations were measured by varying flow velocities with and without installing quarls. Flame stabilities are significantly enhanced by oxyfuel combustion in contrast to air-fuel combustion. Flame length decreases with increasing fuel or oxygen velocity because of the enhancement of turbulent mixing. NOx concentration was reduced with increasing flo velocities. This can be attributed to the entrainment of inert product gases into flame decreasing flame temperature. The installation of quarl on the burners rather increased NOx concentration since the quarl blocked the entrainment above the nozzles.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.4
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• pp.99-106
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• 2010

A piezo-driven injector was applied with a purpose to evaluate the effect of induced voltage on spray characteristics. For this, injection rate, macroscopic imaging, ambient gas entrainment and particle sizing were carried out. It was shown that initial slope of injection rate was steeper as induced voltage increased, while slope of injection rate became mostly constant with fully opened needle. From macroscopoic imaging, longer spray tip penetration was produced with higher induced voltage. Moreover, wider spray angle was detected in the early stage of spray development, when higher induced voltage was applied. Ambient air entrainment rate was increased and particle size was reduced with higher induced voltage.

• Journal of ILASS-Korea
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• v.15 no.2
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• pp.74-82
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• 2010

In order to understand the behavior of transient gaseous injection used in an LPG (Liquefied Petroleum Gas) engine, turbulent incompressible transient jets with butane and propane were measured and analyzed at pressures of 1.5 bar and 2.0 bar with injector diameters of 3 mm and 5 mm. Mie-scattering method with a tracer was used, and images were processed to investigate the behavior of butane and propane jets. Distances from the nozzle to transition region were measured as $L_e/d_{inj}$=4.35~19.4, where $L_e$ and $d_{inj}$ indicate respectively a distance from nozzle to transition point and nozzle diameter. Slits and tubes around jet at near-field were introduced to measure the effect of entrainment and the diameter of jet, which revealed that the entrainment of surrounding air is significant for developing jet diameter. When the entrainment is restricted, the behavior of jet became deviating from the baseline. It was found that the virtual origin located outside of a nozzle towards jet tip within the conditions of this work, and its location was estimated as $x_o/d_{inj}$=0.56~7.25, where $x_o$ is a distance from nozzle to virtual origin.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.5
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• pp.452-460
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• 2008

Anti-foaming agents and foam fences have been used to remove the foam at the outfall of power plants, but there are some problems as consumption of maintenance costs and insufficiency of effect. Therefore, development of the methods how to remove the foam by stable coastal structure has been required. In this study, numerical simulation of air entrainment was carried out to design the submerged outlet structure for reducing foam using curtain walls. The air entrainment rate and the discharge of entrained air change according to the shape of weir and curtain wall. Hence, it is necessary to design the optimum section through comparison of each case. The optimum section which has the maximum rate of foam reduction was determined by the simulation results. In addition, it was found that the flow velocity at the submerged outlet is to be smaller than 1 m/s and the submerged depth of curtain wall is to be taller than height of the submerged outlet section.

• Journal of Industrial Technology
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• v.17
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• pp.227-232
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• 1997

This study was conducted to evaluate durability of concrete which are increasingly demanded recently. Concrete durability properties incorporating waste foundry sand was performed with the variable of W/C ratio, Sand/Waste foundry sand ratio and Air entrainment-Non air entrainment. Cylinder specimens were made and subjected to freezing and thawing cycle at $-18^{\circ}C$ and $4^{\circ}C$. Dynamic modulus of elasticity were evaluated as F/T cycle increase. The results show that decreasing W/C ratio and AE concrete makes improved resistance of freezing and thawing improved. Especially, resistance of freezing and thawing is improved by Fine aggregate/Waste foundry sand ratio which is 50%, 25%, 0% in a row.