• Title/Summary/Keyword: Air Pressure Variation

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A Study on the Helical Flow of Newtonian and non-Newtonian fluid (뉴튼 및 비뉴튼 유체의 헬리컬 유동에 관한 연구)

  • Kim Young-Ju;Kim Chul-Soo;Hwang Young-Kyu
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.17 no.1
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    • pp.8-15
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    • 2005
  • This study concerns the characteristics of helical flow in a concentric and eccentric annulus with a diameter ratio of 0.52 and 0.9, whose outer cylinders are stationary and inner ones are rotating. Pressure losses and skin friction coefficients have been measured for fully developed flows of water and $0.2\%$ aqueous of sodium carboxymethyl cellulose(CMC), respectively, when the inner cylinder rotates at the speed of $0\~500$ rpm. The effect of rotation on the skin friction coefficient is significantly dependent on the flow regime. In all flow regimes, the skin friction coefficient is increased by the inner cylinder rotation. This study shows the change of skin friction coefficient and wall shear stress corresponding to the variation of rotating speed of the inner cylinder, radius ratio, eccentricity, and working fluids.

A Comparison Study on Drag Reduction Characteristics of Polymer and Surfactant as Drag Reduction Additive (고분자불질 및 계면활성제의 유동마찰 저감 특성 비교 연구)

  • Cho, Sung-Hwan;Ryu, Jae-Sung;Kim, Seong-Su;Jung, Sang-Hoon;Yoon, Seok-Mann
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.22 no.6
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    • pp.398-403
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    • 2010
  • The drag reduction(DR) of non-ionic surfactant and polymer according to the variation of fluid velocity, temperature and surfactant concentration was investigated experimentally. For this experiment, the kind of surfactant was non ionic amine-oxide and the kinds of polymer were polyacrylamide and xantan gum. An experimental apparatus equipped with one water storage tanks was built and two flow meters, two pressure gauges for data logging system was installed. Results showed that the kinds of polymer, polyacrylamide and xantan gum, had DR of below 20% for below 500 ppm in fluid temperature of $50{\sim}80^{\circ}C$. But the kind of surfactant, amine oxide, had DR of above 40% for 500~1000 ppm in fluid temperature of $50{\sim}80^{\circ}C$. As a result, amin oxide showed better materials to use to the district heating system.

A Study on an Integrated Drying Machine with Microwave at Vacuum Conditions (진공고주파를 이용한 일체형 건조기개발에 관한 연구)

  • Kim, Taehyung;Ko, Gwang-Soo;Park, Youn Cheol
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.26 no.9
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    • pp.441-446
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    • 2014
  • In Jeju province, the Citrus is widely spread crop which is the most popular fruit on the island. When the quality of a Citrus is not in a good condition or when its size exceeds or is lower than the set criteria, it is discarded as a waste. In this study, a drying machine for waste Citrus has been developed with 2.6 GHz microwave energy supply to the Citrus at vacuum environment. The vacuum environment of the drying chamber was maintained to reduce the energy supply to the Citrus by lowering the evaporating temperature of the water. The experiment was conducted with variation of the vacuum pressure, interior temperature of the drying chamber, and operating time of the microwave. As a result, the effect of the temperature was shown to be higher than the other two control methods, and it showed with 0.305 g/W evaporation efficiency.

Design Effect of Sealing Characteristics of Non-Contact Type Seal for High Speed Spindle (형상설계에 관한 고속주축용 비접촉 시일의 밀봉특성 연구)

  • 나병철;전경진;한동철
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1996.11a
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    • pp.610-614
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    • 1996
  • Sealing of lubricat-air mixture in the high performance machining conte is one of most the important characteristics to carry out enhanced lubrication. High speed spindle requires non-contact type of sealing mechanism. Evaluating an optimum seal design to minimize leakage is concerned in the aspect of flow control. Effect of geometry and leakage path are evaluated according to variation of sealing geometry, Velocity, pressure, turbulence intensity of profile is calculated to fina more efficient geometry and variables. This offers a methodological way of enhancement seal design for high speed spindle. The working fluid is regarded as two phases that are mixed flow of oil phase and air phase. It is more reasonable to simulate an oil jet or oil mist type high speed spindle lubrication. Turbulence and compressible flow model are used to evaluate a flow characteristic, This paper arranges a geometry of mostly used non-contact type seal and analyzes leakage characteristics to minimize a leakage on the same sealing area.

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Effects of a Guide Fin Blade on the Flow Characteristics in a Ventilating Axial Fan (환기용 축류팬의 가이드핀 블레이드 형상변화에 따른 유동특성에 관한 연구)

  • Park, Hong-Kwang;Lee, Jee-Keun;Rho, Byung-Joon
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.19 no.12
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    • pp.874-882
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    • 2007
  • The effects of a guide fin blade on the flow characteristics in a ventilating axial fan were investigated experimentally. The guide fins were setup onto the pressure surface of the blade, and their effects on the flowrate were evaluated. Two types of the guide fin blade were designed. One is the stem fin blade, and the other is the radial fin blade. The stem fin is designed normal to the circumference of a circle, and the radial fin is designed along the circumference of a circle. The results from the guide fin blade fans are compared with that of the blade without guide fins. The position and the geometry of the radial fin setting up on the blade have an effect on the increase of flowrate with the minor sacrifice of rotational speed of the blades. The radial fin positioning at 0.84 times blade diameter shows highest performance in the flowrate. The increase of the blade weight resulting from applying the guide fins shows minor effect on the variation of rotational speed of the blades.

An Experimental Study on the Freeze Drying Process for Poly γ Glutamic Acid (폴리감마글루탐산의 동결 건조 과정의 실험적 연구)

  • Kang, Jisu;Sim, Yeon-Ho;Byun, Si-Ye;Chang, Young Soo;Kang, Byung Ha
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.27 no.12
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    • pp.645-651
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    • 2015
  • This paper presents an experimental study on the freeze drying process for poly ${\gamma}$ glutamic acid. The physical properties of poly ${\gamma}$ glutamic acid are measured during the freeze-drying process. The moisture contents of poly ${\gamma}$ glutamic acid according to the glass transient temperature are obtained by DSC (Differential Scanning Calorimetry) analysis. The end point of primary drying for the poly ${\gamma}$ glutamic acid with a thickness of 3 mm is obtained by measuring the thickness of the dried layer, the amount of moisture evaporation, the moisture content, and the pressure in the drying vacuum chamber during the freeze-drying process. By considering the variation in the glass transient temperature with respect to the moisture content of the material, a control schedule for the heating plate temperature is suggested during the secondary drying process.

Effects of supersonic condensing nozzle flow on oblique shock wave (超音速 노즐흐름에 있어서 凝縮이 傾斜衝擊波에 미치는 影響)

  • 강창수;권순범
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.13 no.3
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    • pp.547-553
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    • 1989
  • Last several stages of high capacity fossil power steam turbine and most stages of nuclear power steam turbine operate on wet steam. As a consequence, the flows in those cascades are accompanied by condensation, and the latent heat caused by condensation affects an oblique shock wave being generated at the vicinity of trailing of the blade. In the case of expanding of moist air through a suction type indraft wind tunnel, the effect of condensation affection the oblique shock wave generated by placing the small wedge into the supersonic part of the nozzle was investigated experimentally. In these connections, the relationship between condensation zone and reflection point of the incident oblique shock wave, angle between wedge bottom wall and oblique shock wave, and the variations of angles of incident and reflected shock waves due to the variation of initial stagnation relative humidity are discussed. Furthermore, the relationship between initial stagnation relative humidity and load working on the nozzle wall, obtained by measuring static pressure at the nozzle centerline, is discussed.

An Experimental Study on the Energy Separation in the Geometric Setup of a Low Pressure Vortex Tube (저압용 vertex tube의 기하학적형상에 따른 에너지 분리특성에 관한 실험적 연구)

  • 오동진;류정인
    • Journal of Energy Engineering
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    • v.11 no.3
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    • pp.276-282
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    • 2002
  • The process of energy separation in a low Pressure vortex tube with compressed air as a work-ing medium is studied in detail. Experimental data of the temperature of the cold and hot air leaving the vortex tube are presented. The variation of the maximum wall temperature along the inner surface of the vortex tube and the temperature distribution in a vortex tube provide useful information about the location of the stagnation point of the flow field at the axis of the vortex tube. Analysis of the results enabled to find the optimum length of the vortex tube, the optimum shape of the Throttle and the usefulness of the Sleeve. In this study Outer tube is used for the exhaust application. The hot gas flow is turned 180$^{\circ}$and passes the out-side of the vortex tube a second time heating it. From this geometric setup of a vortex tube He effects of energy separation and the prediction of the ignition of Diesel Soot is presented by experimental data.

Unsteady Aerodynamic Characteristics depending on Reduced Frequency for a Pitching NACA0012 Airfoil at Rec=2.3×104

  • Kim, Dong-Ha;Chang, Jo-Won;Sohn, Myong Hwan
    • International Journal of Aeronautical and Space Sciences
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    • v.18 no.1
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    • pp.8-16
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    • 2017
  • Most of small air vehicles with moving wing fly at low Reynolds number condition and the reduced frequency of the moving wing ranges from 0.0 to 1.0. The physical phenomena over the wing dramatically vary with the reduced frequency. This study examines experimentally the effect of the reduced frequency at low Reynolds number. The NACA0012 airfoil performs sinusoidal pitching motion with respect to the quarter chord with the four reduced frequencies of 0.1, 0.2, 0.4 and 0.76 at the Reynolds number $2.3{\times}10^4$. Smoke-wire flow visualization, unsteady surface pressure measurement, and unsteady force calculation are conducted. At the reduced frequency of 0.1 and 0.2, various boundary layer events such as reverse flow, discrete vortices, separation and reattachment change the amplitude and the rotation direction of the unsteady force hysteresis. However, the boundary layer events abruptly disappear at the reduced frequency of 0.4 and 0.76. Especially at the reduced frequency of 0.76, the local variation of the unsteady force with respect to the angle of attack completely vanishes. These results lead us to the conclusion that the unsteady aerodynamic characteristics of the reduced frequency of 0.2 and 0.4 are clearly distinguishable and the unsteady aerodynamic characteristics below the reduced frequency of 0.2 are governed by the boundary layer events.

Study on Explosion Behavior of Air-born Rice Bran Dusts according to Ignition Energy (점화에너지 변화에 따른 쌀겨분진의 폭발 거동에 관한 연구)

  • 김정환;김현우;현성호;백동현
    • Fire Science and Engineering
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    • v.13 no.2
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    • pp.26-32
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    • 1999
  • We had investigated combustion pro야$\pi$ies of rice bran dusts. Decomposition of rice bran d dusts with temperature were investigated using DSC and the weight loss according to t temperature using TGA in order to find the thermal hazard of rice bran dusts, and the p properties of dust explosion in variation of their dust with the same particle size. Using H Hartman's dust explosion apparatus which estimate dust explosion by electric ignition after m making dust disperse by compressed air, dust explosion experiments have been conducted by v varying concen$\sigma$ation and size of rice br뻐 dust. According to the results for thermodynamic stability of rice bran dust, there are little change of initiation temperature of heat generation 때d heating value for used particle size. But i initiation temperature of heat generation decreased with high heating rate whereas d decomposition heat increased with particle size. Also, the explosion pressure was increased as t the ignition energy increased and average maximum explosion pressure was 13.5 kgv'cnt for 5 BJ/60 mesh and 1.5 뼈Ie미 dust concentration.

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