• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.722-725
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• 2004

An experimental investigation was conducted to investigate the effects of the equivalence ratio and air mass flux on the combustion efficiency in a solid fuel ramjet used fuel grains which were highly loaded with boron carbide. Combustion efficiency increased with increasing equivalence ratio (grain length), and decreasing air mass flux. Higher inlet air temperature produced higher combustion efficiencies, apparently the result of enhanced combustion of the larger boron particles those bum in a diffusion controlled regime. Short grains which considered primarily of the recirculation region produced larger particles and lower combustion efficiencies. The result of the normalized combustion efficiency increased with inlet air temperature, is coincident with the result of the Brayton cycle thermal and the total efficiency relating to the heat input.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.6
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• pp.561-569
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• 2000

Single phase and condensation heat transfer characteristics of ammonia in a horizontal tube have been investigated experimentally The horizontal test section is composed of smooth SUS316 tube for refrigerant flow, surrounding annulus for water flow, and temperature and Pressure measuring sensors. For single phase test, subcooled ammonia mass flux was varied from 320 to 501 kg/mrs and temperature was varied from 18 to $47^{\circ}C$. For condensation test, mass flux and saturation temperature were varied from 86 to 128 kg/$m^2$s and 34 to $47^{\circ}C$, respectively. The equations of Gnielinski Soliman et al., Traviss et at., Cavallini and Zecchin, Shah, Chen et al., Tandon et al., and Chilli and Anand were compared with the experimental data. New correlations are proposed based on the experimental results and the absolute mean deviation of the experimental data becomes 1.0% for single phase test and 4.9% for condensation test.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.6
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• pp.912-920
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• 1999

The forced convective boiling heat transfer coefficients of R-407C were measured inside a horizontal tube 6.0mm I.D. and 4.0m long. The heat transfer coefficients increased according to an increase in heat flux at constant mass flux. Because nucleation was completely suppressed in the two-phase flow region with high quality, heat transfer coefficients in forced convective evaporation were higher than those in nucleate boiling region. Average heat transfer coefficients of R-407C were about 30 percent lower than the pure refrigerant correlation, due to mass transfer resistance at the gas-liquid interface. However, the total experimental data shows an agreement with the predicted data for ternary refrigerant mixtures with a mean deviation of 30%.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.5
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• pp.1011-1018
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• 1992

A series of experiment has been performed on the spray characteristics in a cylindrical confined space with the injection pressure taken as a parameter. By using a single-hole patternator and the Malvern particle sizer, the spray mass flux, drop size and volume concentration distributions along the radial and axial directions were obtained ; the line-of- sight data by Malvern particle sizer have been converted to the ring-of-sight data by using the tomographical transformation techniqe. The experimental results show that, due to the restriction on the ambient gas entrainment by the wall boundary, the effective spray angle is increasing. The spray drops were measured to be smaller in the confined space because of a large number of floating small drops by recirculation of the gas phase and the breakup of large drops by the wall collision. Also the details on the flow behavior of the confined spray are discussed.

• Journal of Ocean Engineering and Technology
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• v.30 no.4
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• pp.320-326
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• 2016

Rip current forecasts, based on intensity, are marked in four levels—notice, watch, warning, and danger. However, numerical results are represented by current vectors, whose magnitudes are then converted into predictive levels. In the present study, the rose diagram is adapted as a determinative forecasting index and examined for the case of an ideal rip channel consisting of surface, bottom, and averaged currents. Further, it is employed in the sensitivity analysis of wave-induced currents generated by wave conditions at the Haeundae Beach. The simulation of surface onshore and bottom undertow currents is accomplished by including a mass flux term in the wave-averaged continuity equation.

• Journal of the Korean Society of Visualization
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• v.1 no.1
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• pp.98-106
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• 2003

A PLLIF (Planar Liquid Laser Induced Fluorescence) technique has been known to be a useful tool for the measurement of the spray patterns for various spray injectors because it can obtain two-dimensional images with high spatial resolutions without any intrusion on the spray field. In case of dense spray, however, the secondary emission as well as the extinction of an incident laser beam or a fluorescence signal can cause errors in quantifying a mass distribution. Unfortunately, a like-doublet injector which has a dense spray zone at the center may not be a good example or the application of the PLLIF technique. Therefore, we took PLLIF data for the like-doublet injector with a 12 bit color CCD camera by varying laser power, and then assessed their accuracy by comparing with the data obtained with a mechanical patternator and a PDPA (Phase Doppler Particle Analyzer). The experimental results showed that the gray level of fluorescence signal increases nonlinearly due to a secondary emission at the dense spray zone but this nonlinearity can be avoided by reducing the incident laser beam power. In addition, the mass flux distribution of the spray could be obtained by using the mass concentration data from PLLIF technique and the velocity profiles of liquid drops, and this distribution showed good agreement with that of mechanical pattemator. Therefore, it is possible that the PLLIF technique can be successfully applied to finding the mass distributions of like-doublet injectors.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.4
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• pp.608-613
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• 2017

We proposed a pyrometallurgical process to achieve gold alloy with an Au content of more than 80wt% from low grade (<35wt%) gold alloys. We performed the heat treatment at a temperature of $1200^{\circ}C$ for 5 hrs using Au35wt%-Ag5wt%-Cu60wt% gold alloys mixed with 1/2 weighed PbO and CaO flux by varying the ratio of PbO/(PbO+CaO) from 0 to 1. We investigated the change in content of the samples with energy dispersive X-ray spectroscopy (EDS) and time of flight secondary ion mass spectrometry (ToF-SIMS). The EDS results showed that the Au content increased from 35.0wt% in the PbO-only sample to 86.7wt% (in the PbO/(PbO+CaO) 1:1 sample), while the other samples achieved more that 84wt%. In addition, the 2/3 flux ratio sample showed the lowest Ag loss into the flux. In the ToF-SIMS results, the PbO only and CaO only fluxes had Au+ peak intensities of 349 and 37, respectively. Although the CaO-only flux might be more favorable considering the loss of Au into the flux, we concluded that the amount of Au lost into the flux could be ignored. Our results imply that that the pyrometallurgical process using a mixed flux is an effective hydrometallurgical process.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.5
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• pp.397-407
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• 2004

It is well known that some key parameters, such as evaporating temperature, refrigerant mass flow rate, face velocity and inlet air temperature, have significant influence on the evaporator performance. However performance studies related to a humid environment have been very scarce. It is demonstrated that the refrigerant mass flow rate, heat flux, water condensing rate and air outlet temperature of the evaporator significantly increase with air inlet relative humidity. As the air inlet relative humidity increases, the latent and total heat transfer rates increase, but the sensible heat transfer rate decreases. The purpose of this study is to provide experimental data on the effect of air inlet relative humidity on the air and refrigerant side pressure drop characteristics for a slit fin-tube heat exchanger. Experiments were carried out under the conditions of inlet refrigerant saturation temperature of 7 $^{\circ}C$ and mass flux varied from 150 to 250 kg/$m^2$s. The condition of air was dry bulb temperature of 27$^{\circ}C$, air Velocity Varied from 0.38 to 1.6 m/s. Experiments Showed that air Velocity decreased 8.7% on 50% of relative humidity 40% of that at degree of superheat of 5$^{\circ}C$, which resulted that pressure drop of air and refrigerant was decreased 20.8 and 8.3% for 50% of relative humidity as compared to 40%, respectively.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.1
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• pp.87-94
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• 2011

Characteristics of two-phase pressure drop in microchannels were investigated experimentally. The microchannels consisted of 9 parallel trapezoidal channels with each channel having $205\;{\mu}m$ of bottom width, $800\;{\mu}m$ of depth, $3.6^{\circ}$ of sidewall angle, and 7 cm of length. Pressure drops in convective boiling of Refrigerant 113 were measured in the range of inlet pressure 105~195 kPa, mass velocity $150{\sim}920\;kg/m^2s$, and heat flux $10{\sim}100\;kW/m^2$. The total pressure drop generally increased with increasing mass velocity and/or heat flux. Two-phase frictional pressure drop across the microchannels increased rapidly with exit quality and showed bigger gradient at higher mass velocity. A critical review of correlations in the literature suggested that existing correlations were not able to match the experimental results obtained for two-phase pressure drop associated with convective boiling in microchannels. A new correlation suitable for predicting two-phase friction multiplier was developed based on the separated flow model and showed good agreement with the experimental data.

• Membrane and Water Treatment
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• v.7 no.4
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• pp.297-311
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• 2016

Modeling and simulation of air humidification by hollow fiber membrane contactors are investigated in the current study. A computational fluid dynamic model was developed by solving the k-epsilon turbulence 2D Navier-Stokes equations as well as mass conservation equations for steady-state conditions in membrane contactors. Finite element method is used for the study of the air humidification under different operating conditions, with a focus on the humidity density, total mass transfer flux and velocity field. There has been good agreement between simulation results and experimental data obtained from literature. It is found that the enhancement of air stream decreases the outlet humidity from 0.392 to 0.340 (module 1) and from 0.467 to 0.337 (module 2). The results also indicated that there has been an increase in air velocity in the narrow space of shell side compared with air velocity wide space of shell side. Also, irregular arrangement has lower dead zones than regular arrangement which leads to higher water flux.