• Title/Summary/Keyword: Moist Air

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A Computational Study of the Mach Disk in Under-Expanded Moist Air Jet (부족팽창 습공기 제트의 마하디스크 거동에 관한 수치적 연구)

  • Baek, Seung-Cheol;Kwon, Soon-Bum;Kim, Heuy-Dong
    • Proceedings of the KSME Conference
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    • 2003.11a
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    • pp.562-567
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    • 2003
  • A computational study is performed to clarify the characteristics of supersonic moist air jet issuing from a simple sonic nozzle. The effects of the initial supersaturation on the Mach disk diameter and location, the barrel shock wave and jet boundary structures are investigated in details. The axisymmetric, compressible, Navier-Stokes equations, coupled with droplet growth equation, are solved using a third-order MUSCL type TVD finite-difference scheme. It is found that the Mach disk diameter increases with an increase in relative humidity of moist air. while its location is not significantly dependent on the relative humidity. As the relative humidity increases, the barrel shock wave and jet boundary are more expanded due to the local static pressure rise of nonequilibrium condensation.

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A Study on the Effects of System Pressure on Heat and Mass Transfer Rates of an Air Cooler

  • Jung, Hyung-Ho
    • Journal of Mechanical Science and Technology
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    • v.16 no.5
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    • pp.696-702
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    • 2002
  • In the present paper, the effects of inlet pressure on the heat and mass transfer rates of an air cooler are numerically predicted by a local analysis method. The pressures of the moist air vary from 2 to 4 bars. The psychrometric properties such as dew point temperature, relative humidity and humidity ratio are employed to treat the condensing water vapor in the moist air when the surface temperatures are dropped below the dew point. The effects of the inlet pressures on the heat transfer rate, the dew point temperature, the rate of condensed water, the outlet temperature of air and cooling water are calculated. The condensation process of water vapor is discussed in detail. The results of present calculations are compared with the test data and shows good agreements.

A Study of the Passive Shock/Boundary Layer Interaction Control in Transonic Moist Air Flow (천음속 습공기 유동에서 발생하는 충격파와 경계층 간섭의 피동제어에 관한 연구)

  • Baek Seung-Cheol;Kwon Soon-Bum;Kim Heuy-Dong
    • Proceedings of the KSME Conference
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    • 2002.08a
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    • pp.161-164
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    • 2002
  • In the present study, a passive control method, using the porous wall and cavity system, is applied to the shock wave/boundary layer interactions in transonic moist air flow. The two-dimensional, unsteady, compressible Navier-Stokes equations, which are fully coupled with a droplet growth equation, are solved by the third-order MUSCL type TVD finite difference scheme. Baldwind-Lomax turbulence model is employed to close the governing equations. In order to investigate the effectiveness of the present control method, the total pressure losses of the flow and the time-dependent behaviour of shock motions are analyzed in detail. The computed results show that the present passive control method considerably reduces the total pressure losses due to the shock/boundary layer interaction in transonic moist air flow and suppresses the unsteady shock wave motions over the airfoil, as well. It is also found that the location of the porous ventilation significantly influences the control effectiveness.

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The Unsteady Cavity Flow Oscillation in Supersonic Moisture Air Stream (초음속 습공기 유동에서 비정상 공동유동의 진동)

  • Shin, Choon-Sik;Lee, Jong-Sung;Kim, Heuy-Dong;Setoguchi, Toshiaki
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2008.11a
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    • pp.341-344
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    • 2008
  • Numerical simulations have been carried out for a supersonic two-dimensional flow over open, rectangular cavities (length-to-depth ratios are L/D = 1.0) in order to investigate the effect of non-equilibrium condensation of moist air on supersonic flows around the cavity for the flow Mach number 1.83 at the cavity entrance. In the present computational investigation, a condensing flow was produced by an expansion of moist air in a Laval nozzle. The results obtained showed that in the case with non-equilibrium condensation for L/D = 1.0, amplitudes of oscillation in the cavity became smaller than those without the non-equilibrium condensation. Furthermore, the occurrence of the non-equilibrium condensation reduced the peaks of power spectrum density and the frequency of the flow field oscillation increased in comparison with the case of $S_0$ = 0.

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Study on the Flow of Briquette Gas in the Ondol Heating System (Chimney Draft of Low Temperature Moist Air) (온돌의 연탄개스유량에 관한 연구(1) (함습저온열기류의 굴뚝통풍력))

  • Min Man-Ki
    • The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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    • v.4 no.2
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    • pp.119-128
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    • 1975
  • Natural draft and flow which low temperature moist gas produces in the chimney of an Ondol heating system were numerically analysed. Among several factors involved inlet gas temperature has the strongest influence on the chimney performance and then next specific humidity of the gas. Thermal conductivity of the chimney wall, however, has little influence on the performance of such a low temperature chimney. Under given flow conditions there exists an optimum chimney height which gives a maximum flow rate for a given chimney diameter. This optimum value of chimney height inereases with increase in chimney diameter, inlet gas temperature and specific humidity.

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Behaviors of Mach Disk in Underexpanded Supersonic Moist Jet (초음속 습공기 제트에서 발생하는 마하디스크의 거동)

  • 백승철;김희동;권순범
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2003.05a
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    • pp.87-90
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    • 2003
  • It has been well known that the major feature of compressible flow fields might be different depending on their formation processes. The objectives of the present study is to investigates the effect of jet development on the time history of supersonic jet flow field, accompanying nonequilibrium condensation. Especially, the behaviors of Mach disk diameter and location in a supersonic moist air jet are presented in terms of nozzle pressure ratio and initial relative humidity. The relative humidity of moist air is controlled at the nozzle supply, and the nozzle pressure ratio is varied to obtain the moderately underexpanded flows at the exit of the nozzle, installed in an indraft wind tunnel. It is found that at the same pressure ratio the Mach disk diameter increases with the initial relative humidity, while moves further upstream. Furthermore, the values of Mach disk diameter and location for increasing pressure ratio show larger than those for increasing.

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Classification of Precipitation Type Using the Wind Profiler Observations and Analysis of the Associated Synoptic Conditions: Years 2003-2005 (윈드프로파일러 관측 자료를 이용한 장마철 강수 형태 분류와 관련된 종관장의 특성 분석: 2003년-2005년)

  • Won, Hye-Yeong;Jo, Cheon-Ho;Baek, Seon-Gyun
    • Atmosphere
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    • v.16 no.3
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    • pp.235-246
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    • 2006
  • Remote sensing techniques using satellites or the scanning weather radars depend mostly on the presence of clouds or precipitation, and leave the extensive regions of clear air unobserved. But wind profilers provide the most direct measurements of mesoscale vertical air motion in the troposphere, even in the context of heavy precipitation. In this paper, the precipitation events during the Changma period was classified into 4 precipitation types - stratiform, mixed stratiform/ convective, deep convective, and shallow convective. The parameters for the classification of analysis are the vertical structure of reflectivity, Doppler velocity, and spectral width measured with the wind profiler at Haenam for a three-year period (2003-2005). In addition, the synoptic fields and total amount of precipitation were analyzed using the Global Final Analyses (FNL) data and the Global Precipitation Climatology Project (GPCP) data. During the Changma period, the results show that the stratiform type was dominant under the moist-neutral atmosphere in 2003, whereas the deep convective type was under the moist unstable condition in 2004. The stratiform type was no less popular than the deep convective type among four seasons because the moist neutral layer was formed by the convergence between the upper-level jet and the low-level jet, and by the moisture transport along the western rim of the North Pacific subtropical anticyclone.

Experimental Study on Stream Turbine Cascade Flow (증기터빈 익렬유동에 관한 실험적 연구)

  • 권순범;윤의수;김병지
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.8
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    • pp.2177-2183
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    • 1994
  • The rapid expansion or condensible gas such as moist air of steam gives rise to nonequilibrium condensation. As a result of irreversibility of condensation process in the supersonic cascade flow of low pressure steam turbine, the entropy of the flow is increased, and the efficiency of the turbine is decreased. In the present study, to investigate the flow of moist air in 2-dimensional cascade made as the configuration of the tip section of the last actual steam turbine moving blade, the static pressure at both sides of pressure and suction of blade are measured by static pressure taps and the distribution of Mach number on both surfaces of the blade are obtained by using the measured static pressure. Also, the flow field is visualized by a schlieren system. From the experimental results, the effects of the stagnation temperature and specific humidity on the flow properties in a 2-dimensional stationary cascade of a practical steam turbine blade are clearly identified.

A Study on the Onset of Condensation in a Supersonic Nozzle of Constant Expansion Rate (팽창율이 일정한 초음속 노즐흐름의 응축개시에 관한 연구)

  • 김병지;권순범;이은수
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.2
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    • pp.463-469
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    • 1990
  • A rapid expansion of moist air of condensible gas through a supersonic nozzle gives rise to condensation of nonequilibrium and equilibrium processes. Because most of the effects of condensation on the flow are caused by process of nonequilibrium condensation, it is very important to know the onset. condition of nonequilibrium condensation. In the present study, the relation between the initial relative stagnation humidity and the onset Mach number, for the case of the similarity law suggested by Zierep and Lin. Furthermore, the present theoretical result number is compared with the experimental, numerical and other results.