• Journal of Aerospace System Engineering
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• v.14 no.5
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• pp.26-32
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• 2020

In this study, a facility was constructed to supply liquid nitrogen to simulate combustion instability in a liquid rocket combustor. The pressurization and supply performances were predicted and verified through different experiments. The liquid nitrogen supply system was composed of a pressurized supply system, and a dome regulator was used to adjust the pressure of the pressurant. A cavitation venturi was used to control the mass flow rate of liquid nitrogen. The condition of liquid nitrogen supply was a mass flow rate of 2.55 kg/s and the venturi inlet pressure was above 100 bar. Based on the initial experiment, it was observed that the predicted amount of the pressurant was not sufficiently supplied and the target pressure was not supplied due to a drop in tank pressure. Through the modification of the established facilities, the target mass flow rate was successfully supplied and the cryogenic liquid nitrogen supply facility was verified.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.12
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• pp.3404-3412
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• 1994

The present study was undertaken to investigate the dry wear process and wear mechanism of the alumina ceramics in the purity variation which are used for the mechanical seal, roll, liner and dies. The wear test was carried out under different experimental condition using the wear testing device and in which the annular surface rubbed on dry sliding condition various sliding speed, contact pressure and sliding distance. In case of alumina purity 95%, there was speed range which wear loss increased rapidly owing to enlargement of heat impact force and temperature rise of wear surface. According as the alumina purity increased, wear loss decreased but alumina purity 85% with much void and defect had the most wear loss than any other alumina purity. The friction coefficient of sliding initial stage of wear curves has a large value but according to increase of sliding distance, it decreased owing to drop of the shear strength of wear surfaces.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.4
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• pp.463-470
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• 1985

In this study a parametric analysis for the rewetting temperature was made with 572 data obtained from the single tube experiment. The rewetting temperature was also evaluated by measuring the vaporization time of a liquid drop on a hot surface at the elevated pressures. The results showed that the rewetting temperature increased with flooding rate, inlet subcooling pressure and initial wall temperature, and decreased with increasing axial elevation. Based on the results obtained, the rewetting temperature correlation was suggested. From the comparison of correlated rewetting temperatures with measured values, it showed that the correlated values fell within .+-.5% error from the measured values.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.64-67
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• 2006

Drop-in tests were conducted using R290/R32 (31:69) or R290/DME (65:35) mixture in a ice-cream maker for possible replacement of R-502 and R-404A. At the standard room temperature ($20^{\circ}C$), the time required for initial ice-cream making was 4'7' for R290/32, 4'39' for R404A and 4'59' for R290/DME. The electric energy consumed was 436 kJ for R290/32, 425 kJ for R404A and 439 kJ for R290/DME. The mass flow rate as well as the temperature and pressure data are also provided.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.679-682
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• 2002

Energy dissipations in a general PHE flow are the compounded effects of the piled corrugate geometries and its wall pressure and temperature distributions. In addition, although the exchangers are substantial pieces of engineering equipment, they are composed of a very large number of nominally identical and small geometrical elements. In the present numerical study, the three-dimensionally complicated energy dissipation fields and those wall-shape-induced flow destabilization are investigated in the cross-corrugated passages, which result in high energy transports with comparatively low pressure drop. We revealed the critical conditions as $Re=157.3 for the wall-shape-induced flow destabilization in a general PHE element by initial value method, or shooting method, and compare its value to that of analytical solution of plane Poiseille flow, two-dimensional grooved flow and so on. We also observed the detailed variation of flow field and energy transportation with changes in time and flow variables such as Reynolds number. Lastly, we considered the flow natural frequency, or Strouhal number, with variation of hydrodynamic conditions for the best use of active control, such as forced mass flow rate pulsative flow, to enhance energy transportation.

• Journal of Chest Surgery
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• v.23 no.5
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• pp.864-870
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• 1990

This study was undertaken to evaluate current technique of extracorporeal circulation by analyzing the results in 73 cases. We performed standard cardiopulmonary bypass using Polystan roller pump, bubble[Polystan] and membrane[Cobe] oxygenator. There were 42 males and 31 females. We studied the changes of hemoglobin. hemodynamics, speed of cooling and warming, methods of cannulation and ACT. Arterial cannula was inserted on ascending aorta except for 7 cases of femoral cannulation. Preoperative hemoglobin was 13.2 gm% and this value dropped to 7.5 gm% during perfusion. Blood pressure of 113 mmHg in systolic dropped 57mmHg in 10 minutes of perfusion and became 98 mmHg at the end of perfusion. Initial drop of blood pressure was marked in pediatric patient. Mean cooling time was 19.4 min[0.54 Q /min] and warming time was 34 minutes[0.25 Q /min]. During perfusion, ACT was maintained above 600 sec and 44 patient did not need additional Heparin.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.5 no.2
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• pp.141-155
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• 1993

Thermodynamic properties of R-32 are calculated and its refrigeration performance is evaluated for the purpose the feasibility study of replacing R-22 with R-32. (1) Refrigeration effect of R-32 is superior to that of R-22 because heat of evaporation of R 32 is about 50% higher than that of R-22. However, COP of R-32 system is 10-30% lower than that of R-22 system. It is mainly attributed to the vapor pressore of R-32 being about 62% higher than R-22. (2) Since the pressure ratio and the specific heat ratio of R-32 system is higher than those of R -22, compressor discharging temperature rises as high as to $130-150^{\circ}C$. It may cause mechanical failure of compressor due to the breakdown of lubricant. Compressor should be improved to lower the temperature if R-32 is to replace R-22. (3) Averaged two-phase heat transfer coefficient of R-32 is about 10-20% higher than that of R-22. It may assume better heat exchanger effectiveness but not guarantee the better COP of R-32 system than R-22. (4) The high vapor pressure is the first reason to drop R-32 out of the line of R-22 alternative refrigerant. So, refrigerant mixtures based on R-32 are recommended to adjust the vapor pressure first and keep superior volumetric capacity of R-32.

• The Journal of the Acoustical Society of Korea
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• v.36 no.5
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• pp.314-320
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• 2017

A pressure relief valve is generally used to prevent piping systems from being broken due to high pressure gas flows. However, the sudden pressure drop caused by the pressure relief valve produces high acoustic energy which propagates in the form of compressible acoustic waves in the pipe and sometimes causes severe vibration of the pipe structure, thereby resulting in its failure. In this study, internal aerodynamic noise due to valve flow is estimated for a simple contraction-expansion pipe by combining the LES (Large-Eddy Simulation) technique with the wavenumber-frequency analysis, which allows the decomposition of fluctuating pressure into incompressible hydrodynamic pressure and compressible acoustic pressure. In order to increase the convergence, the steady Reynolds-Averaged Navier-Stokes equations are numerically solved. And then, for the unsteady flow analysis with high accuracy, the unsteady LES is performed with the steady result as the initial value. The wavenumber-frequency analysis is finally performed using the unsteady flow simulation results. The wavenumber-frequency analysis is shown to separate the compressible pressure fluctuation in the flow field from the incompressible one. This result can provide the accurate information for the source causing so-called acoustic-induced-vibration of a piping system.

• 한국생물공학회:학술대회논문집
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• 2003.10a
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• pp.384-387
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• 2003

We measured the inlet concentration of odorous gases from the food-waste composting facility for 90 days. In consequence of this survey, we ascertained that the gaseous concentration was detected $10{\sim}100ppm$ in operating time, but $0{\sim}10ppm$ in a shutdown of the facility. The initial removal efficiency of this biofilter was roughly represented 80%, however, 90% before and after twenty days. We have thought that this biofilter accomplished the treatment of those odorous gases effectively, because the pressure-drop was not exceeded a value of $20mmH_2O$ after 90 days.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.1
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• pp.33-41
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• 2011

A mathematical model of slip-in booster separation dynamics is described. A longitudinal 3-DOF(degree of freedom) 2-body dynamic model is developed to simulate the separation dynamics. Aerodynamic models of the missile and the exposed area of booster are built. And, gas generator pushing the booster out and internal channel pressure drop are modelled. To simulate the model, it is assumed that the missile can maintain the 1g level-fight condition during the separation. With this assumption, the interaction forces between missile and booster through the separation phases: phase 0: initial, phase 1: linear translation, and phase 2: free flight motion are defined. Using the simulation, missile flight conditions for slip-in booster`s safe separation, which can be represented by Mach vs. height envelope, are suggested.