• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2583-2588
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• 2008

In the present experimental study, the regime limit and pressure drop of dry-plug flow (dry wall condition at the gas portions of plug flow) in round mini-channels has been investigated. The air-water mixture was flowed through the round mini-channels made of Teflon, where the tube diameters ranged from 1.26 to 2.06 mm. For the present experimental range, with decreasing of the tube diameter, the transition between the plug and slug flows (wet and dry) happened at the higher gas superficial velocity region, which were in good agreement with the previous flow pattern maps tested. On the other hand, the transition between the wet- and dry-plug flows was little affected by the change of the tube diameter. In the pressure drop of dry-plug flows, among the correlations tested, the Lee and Lee's (2008) correlation best fitted the measured pressure drop data within the mean deviation of 10% for the present experimental range.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.5 no.3
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• pp.169-178
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• 1993

Performance charts of capillary tubes for R-134a are presented. The calculation is based on the one-dimensional, adiabatic flow through capillary tube. The length of capillary tube changes with inlet pressure, mass flux, inlet quality(or subcooling), and inside diameter. The length for R-134a is shorter by 12.5~23% than that for R-12 as mass flux varies, by 13~18.5% as inlet pressure changes, by 15~15.2% as inside diameter changes, and by 3.6~20% as subcooling(or quality) changes. In general, the length for R-134a is shorter than that for R-12 by 10~20%. Pressure drop per unit length for R-134a is greater than that for R-12 since specific volume of R-134a is larger that of R-12 and vapor pressure of R-134a is greater than that of R-12. Flash point of R-134a is ahead of that of R-12.

• 유체기계공업학회:학술대회논문집
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• 1999.12a
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• pp.301-308
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• 1999

The present study investigates numerically particle laden flow through compressor cascades and a rocket nozzle. Engines are affected by various particles which are suspending in the atmosphere. Especially in the case of aircraft aviating in volcanic, industrial and desert region including many particles, each components of engine system are damaged severely. That damage modes are erosion of compressor blading and rotor path components, partial or total blockage of cooling passage and engine control system degradation. Numerical prediction and experimental data, erosion rates are predicted for two materials - ceramic, soft metal - on compressor blade surface. Aluminum oxide ($Al_2O_3$) Particles included in solid rocket propelant make ablative the rocket motor nozzle and imped the expansion processes of propulsion. By the definition of particle deposition efficiency, characteristics of particles impaction are considered quantitatively Stoke number is defined over the various particle sizes and particle trajectories are treated by Lagrangian approach. Particle stability is considered by definition of Weber number in rocket nozzle and particle breakup and evaporation is simulated in a rocket nozzle.

• Nuclear Engineering and Technology
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• v.19 no.3
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• pp.198-204
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• 1987

A plant simulation code, MCSIM (Micro-Computer SIMulator), has been developed to simulate plant transient accidents for pressurized water reactors. Reactor coolant system is modeled using decoupled energy and momentum equations, drift flux two-phase flow model and integral momentum equation. A two-fluid pressurizer model is used to simulate the pressurizer dynamics. Pot Boiler model is used for steam generator, steady-state decoupled energy and momentum equations for secondary side system, and point kinetics equations for nuclear power calculation. For test of the present version of MCSIM, complete loss of flow and RCCA withdrawal accidents are calculated with MCSIM. The results are compared with those in FSAR of KNU 5 & 6.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.5
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• pp.1130-1137
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• 1988

Heat transfer characteristics of evaporative transpiration cooling was investigated experimentally in the range of coolant mass flux, 0.002kg/m$^{2}$.sec~0.015m$^{2}$.sec. Glass beads, sand and copper particles were used as porous media and distilled water was used as a conant. The existence of evaporation zone was confirmed on this experimental conditions and its length increases with increasing article size and with decreasing mass flux. In order to get the low surface temperature, porous materials with high thermal conductivity is preferred when the panicle sizes are same, and small particles with low porosity is effective in case of the same material. Due to the relatively small coolant mass flux, evaporative transpiration cooling system could be stable by the capillary effect.

• Journal of the Korean Society of Visualization
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• v.19 no.1
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• pp.28-35
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• 2021

In this study, an image processing method for the measurement of two-phase bubbly flow is developed. Shadowgraphy images obtained by high-speed camera are used for analysis. Some bubbles are generated as single unit and others are overlapped or clustered. Single bubbles can be easily analyzed using parameters such as bubble shape, centroid, and area. But overlapped bubbles are difficult to transform clustered bubbles into segmented bubbles. Several approaches were proposed for the bubble segmentation such as Hough transform, connection point method and watershed. These methods are not enough for bubble segmentation. In order to obtain the size distribution of bubbles, we present a method of splitting overlapping bubbles using watershed and approximating them to ellipse. There is only 5% error difference between manual and automatic analysis. Furthermore, the error can be reduced down to 1.2% when a correction factor is used. The ellipse fitting algorithm developed in this study can be used to measure bubble parameters accurately by reflecting the shape of the bubbles.

• Journal of Korean Society of Environmental Engineers
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• v.30 no.5
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• pp.507-516
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• 2008

This research was conducted to elucidate the effect of temperature on the nitrogen removal of municipal wastewater with waste-tire media. The experiments were carried out in laboratory-scale batch reactor and pilot-scale moving bed biofilm reactor filled at a 0.15 filling ratio with waste-tire media, respectively. In batch tests, specific nitrification rate(SNR) with media was 3.4 mg NH$_4^+$-N/g Mixed-Liquor Volatile Suspended Solid(MLVSS)$\cdot$hr, compared with 1.7 mg NH$_4^+$-N/g MLVSS$\cdot$hr without media. In pilot-scale test with media, total nitrogen removal efficiency increased from 53 $\pm$ 8% to 76 $\pm$ 5% as the temperature increased from 9$\sim$10$^{\circ}C$ to 20$\sim$24$^{\circ}C$. At the temperature of 9$\sim$10$^{\circ}C$, 10$\sim$20$^{\circ}C$, and 20$\sim$24$^{\circ}C$, the SNRs were 0.8 $\pm$ 0.5, 3.1 $\pm$ 1.9, and 3.4 $\pm$ 2.1 mg NH$_4^+$-N/g MLVSS$\cdot$hr and the specific denitrification rates(SDNR) were 0.6 $\pm$ 0.2, 1.1 $\pm$ 0.6, 1.4 $\pm$ 0.6 mg NO$_3^-$-N/g MLVSS.hr, respectively. The overall activities of biomass in anaerobic, anoxic, and oxic zones at 20$\sim$24$^{\circ}C$ increased to 22, 20, and 15%, compared with those at 9$\sim$10$^{\circ}C$, respectively. The activity distribution of Nitrosomonas and Nitrobacter also increased with the increase of temperature.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.6
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• pp.72-83
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• 2018

In this study, a series of CFD analyses were carried out for a hydrogen rocket combustor with a single shear coaxial injector. A hybrid RANS/LES approach was used for the turbulent combustion analysis with a two-dimensional axisymmetric configuration. Three reaction mechanisms, three spatial discretization methods, and three levels of grid resolution were compared to determine an appropriate CFD approach. The performance of the CFD prediction were investigated by comparing the wall heat flux with experimental data. Investigation of the flow field results provides an insight into the characteristics of the turbulent reacting flow of a rocket combustor with a shear coaxial injector.

• Journal of Energy Engineering
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• v.11 no.2
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• pp.114-121
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• 2002

Alkali metal compounds existed in original coal or sorbents are exhausted as vapor or small particle at the outlet of combustor when operating PFBC power plant. These compounds can be removed with dust removal equipment, but total generation efficiency will be decreased because of lower operating temperature of dust removal equipment. Alkali metal contained in vapor phase is initially deposited onto turbine blade results in serious corrosion. The concentration of alkali vapor in the PFBC flue gas is 20∼40 ppm which is dependent on mineral characteristics and composition as well as operating condition of PFBC. However, the allowance limit of alkali metal vapor is assigned as less than 50 ppb for gas turbine when coal or oil is used as fuel. Therefore, alkali metal vapor in PFBC or IGCC process should be removed by solid sorbents to prevent corrosion of turbine blade and improve plant efficiency. In the present investigation, powder of Bauxite, Kaolinite and Limestone is used in the preparation of cylinder-type pellet which is inserted into the pressurized alkali removal reactor for the alkali absorption experiment. Experimental results showed that the alkali removal efficiency in the order of Bauxite, Kaolinite and Limestone. Alkali vapor removal efficiency is related with reaction temperature, porosity of pellet and alkali vapor concentration of flue gas.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.45-49
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• 2011

The blow-down oxidizer feed system with self-pressurizing $N_2O$ has more advantages than the regulated system. However, it is difficult to predict the exhaust flow rate because there exist two phases in the $N_2O$ tank - liquid phase and gas phase, and the properties of $N_2O$ in storage tank are varied continuously during blow-down. In this paper, a method that can analyse simply the blow-down oxidizer feed system is studied. The properties of saturated $N_2O$ are found from the NIST data base, and mass flow through the orifice is modeled as NHNE. Cold flow test with hybrid rocket combustor is performed for the comparison where the results should found from the good agreement.