• Title/Summary/Keyword: Supercritical pressure

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Performance Characteristics of R134a Supercritical Heat Pump (R134a 냉매용 초임계 히트펌프의 성능 특성)

  • Choi, In-Soo
    • Journal of Power System Engineering
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    • v.18 no.4
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    • pp.60-65
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    • 2014
  • In this paper, cycle performance analysis for heating capacity, compression work and COP of R134a supercritical heat pump is presented to offer the basic design data for the operating parameters of the system. The operating parameters considered in this study include superheating degree, pressure and outlet temperature of gas cooler, compressor efficiency and evaporating temperature in the R134a supercritical heat pump system. The main results were summarized as follows : Superheating degree, pressure and outlet temperature of gas cooler, compressor efficiency and evaporating temperature of R134a heat pump system have an effect on the heating capacity, compression work and COP of this system. With a thorough grasp of these effect, it is necessary to design the supercritical heat pump using R134a. The prediction for COP of R134a supercritical heat pump have been proposed through multiple regression analysis.

Preparation of Micronized Anti-dandruff Agents Using Supercritical Carbon Dioxide (초임계 이산화탄소를 이용한 미립 항비듬제 제조)

  • Shin, Moon-Sam
    • Journal of the Society of Cosmetic Scientists of Korea
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    • v.34 no.3
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    • pp.209-215
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    • 2008
  • Iodopropynyl butylcarbamate and climbazole as anti-dandruff agents widely used in cosmetics and pharmaceutics were micronized using supercritical fluid. Supercritical carbon dioxide was selected due to relatively low critical temperature and critical pressure. Iodopropynyl butylcarbamate and climbazole were chosen because of their solubility in supercritical carbon dioxide. The rapid expansion of supercritical solution (RESS) experiments involved investigations of the effect of pressure, temperature on particle size and morphology.

Direct Numerical Simulation of Turbulent Heat Transfer to Fluids at Supercritical Pressure Flowing in Vertical Tubes (직접수치모사를 이용한 수직원형관내 초임계압 유체의 난류 열전달 특성 연구)

  • Bae, Joong-Hun;Yoo, Jung-Yul;Choi, Hae-Cheon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.11
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    • pp.1302-1314
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    • 2004
  • Turbulent heat transfer to $CO_2$ at supercritical pressure flowing in vertical tubes is investigated using direct numerical simulation (DNS). A conservative space-time discretization scheme for variable-density flows at low Mach numbers is adopted in the present study to treat steep variations of fluid properties at supercritical pressure just above the thermodynamic critical point. The fluid properties at these conditions are obtained using PROPATH and used in the form of tables in the simulations. The buoyancy influence induced by strong variation of density across the pseudo-critical temperature proved to play a major role in turbulent heat transfer at supercritical state. Depending on the degree of buoyancy influence, turbulent heat transfer may be enhanced or significantly deteriorated, resulting in local hot spots along the heated surface. Based on the results of the present DNS combined with theoretical considerations, the physical mechanism of this local heat transfer deterioration is elucidated.

Solubility Measurement and its Correlation of Disperse Dye in Supercritical HFC-134a (초임계 HFC-134a에 대한 분산염료의 용해도 측정과 모델링)

  • Park, Min-Woo;Bae, Hyo-Kwang
    • Korean Chemical Engineering Research
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    • v.40 no.6
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    • pp.715-718
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    • 2002
  • The supercritical dyeing process has been gaining the increasing importance because of environment reason. For further development of this process, it is needed to measure the solubility in supercritical fluids in the extensive ranges of temperature and pressure. In this study, using the semi-flow type apparatus consisted of supercritical fluid equilibrium cell, the solubility of disperse dye(C.I. disperse red 60) in supercritical HFC-134a has been measured at the temperatures of 383.2 K and 413.2 K, and in the pressure range of 50 bar to 160 bar. The solubility data are, with good agreement, correlated by an expanded liquid model which considers the supercritical fluid as compressed liquid.

Pressure Gradient of Supercritical CO2 in Vertical Tobacco Beds in Down Flow Condition (담배 고정층 반응기에서 하부로 흐르는 초임계 CO2의 압력 구배)

  • 이성철
    • Journal of the Korean Society of Tobacco Science
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    • v.18 no.1
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    • pp.92-99
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    • 1996
  • A mathematical model of the pressure gradient of supercritical CO2 in a vertical tobacco bed was developed in this study. In particular, the compaction of the tobacco as a function of temperature and CO2 flow is included in the model. Downflow of CO2 (low condition is described. At velocities in excess of 0.6 cm/sec at 7$0^{\circ}C$, there is a large increase in pressure gradient for beds deeper than about 0.5 m. The proposed model offers a better understanding of operating the process using supercritical CO2.

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Solubility of Ibuprofen in Supercritical Carbon Dioxide (초임계 이산화탄소를 이용한 Ibuprofen의 용해도 측정)

  • Kim, Young Ae;Chu, Junho;Lim, Jong Sung;Kim, Hwayoung;Lee, Youn-Woo
    • Clean Technology
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    • v.11 no.3
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    • pp.147-152
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    • 2005
  • For estblishing the best technique for the micronization of Ibuprofen using supercritical fluids, the solubility should be known. The solubility of Ibuprofen in supercritical carbon dioxide was measured by observing the cloud point. The cloud point was observed using high pressure equipment equipped a variable volume view cell between temperature of 35, 40 and $45^{\circ}C$. The solubility data was correlated by the Peng-Robinson equation of state Solute physical properties, such as critical temperature (Tc), critical pressure (Pc) and acentric factor (${\omega}$) were estimated by the some group contribution method. As pressure was increased, the solubility increased at constant temperature. The retrograde phenomenon by a solute vapor pressure and a density of solvent was observed at the pressure of around 150bar. It was found that $CO_2$ can be used as a supercritical solvent in micronization of ibuprofen by RESS.

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An Experimental Study on Flame Spread in an One-Dimensional Droplet Array (일차원 액적 배열하에서 화염 퍼짐에 관한 실험적 연구)

  • Park, Jeong;Shin, Hyun Dong;Kobayashi, Hideaki;Niioka, Takashi
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.23 no.1
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    • pp.131-139
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    • 1999
  • Experimental investigations on flame spread in droplet arrays have been conducted under supercritical ambient pressures of fuel droplet. Flame spread rates are measured for n-Decane droplet of diameters of 0.75 and 1.0mm, using high speed images of OH chemiluminescence up to 3.0MPa. The pattern of flame spread is categorized into two: a continuous mode and an intermittent one. There exists a limit droplet spacing, above which flame spread does not occur. Flame spread rate with the decrease of droplet spacing increases and then decreases after takin& a maximum. It is also seen that there exists a limit ambient pressure, above which flame spread does not occur. Flame spread rate decreases monotonically with the increase of ambient pressure. Exceptionally, In the case of a small droplet spacing, flame spread with the increase of ambient pressure is extended to supercritical pressures of fuel droplet. This is caused by enhanced vaporization with the increase of ambient pressure. Consequently, in flame spread with droplet droplet spacing, the relative position of flame to droplet spacing plays an important role. The monotonic decrease with ambient pressure is mainly related to the reduction of flame radius in subcritical pressures and the extension to supercritical pressures of flame spread is caused by the reduction of ignition time of unburnt droplet due to the enhanced vaporization at supercritical pressures.

Environmentally Assisted Cracking of Alloys at Temperatures near and above the Critical Temperature of Water

  • Watanabe, Yutaka
    • Corrosion Science and Technology
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    • v.7 no.4
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    • pp.237-242
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    • 2008
  • Physical properties of water, such as dielectric constant and ionic product, significantly vary with the density of water. In the supercritical conditions, since density of water widely varies with pressure, pressure has a strong influence on physical properties of water. Dielectric constant represents a character of water as a solvent, which determines solubility of an inorganic compound including metal oxides. Dissociation equilibrium of an acid is also strongly dependent on water density. Dissociation constant of acid rises with increased density of water, resulting in drop of pH. Density of water and the density-related physical properties of water, therefore, are the major governing factors of corrosion and environmentally assisted cracking of metals in supercritical aqueous solutions. This paper discusses importance of "physical properties of water" in understanding corrosion and cracking behavior of alloys in supercritical water environments, based on experimental data and estimated solubility of metal oxides. It has been pointed out that the water density can have significant effects on stress corrosion cracking (SCC) susceptibility of metals in supercritical water, when dissolution of metal plays the key role in the cracking phenomena.

Coal pyrolysis behaviors at supercritical CO2 conditions

  • Hakduck Kim;Jeongmin Choi;Heechang Lim;Juhun Song
    • Advances in Energy Research
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    • v.8 no.4
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    • pp.265-273
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    • 2022
  • In this study, a product gas yield and carbon conversion were measured during the coal pyrolysis. The pyrolysis process occurred under two different atmospheres such as subcritical (45 bar, 10℃) and supercritical CO2 condition (80 bar, 35℃). Under the same pressure (80 bar), the atmosphere temperature increased from 35℃ to 45℃ to further examine temperature effect on the pyrolysis at supercritical CO2 condition. For all three cases, a power input supplied to heating wire placed below coal bed was controlled to make coal bed temperature constant. The phase change of CO2 atmosphere and subsequent pyrolysis behaviors of coal bed were observed using high-resolution camcorder. The pressure and temperature in the reactor were controlled by a CO2 pump and heater. Then, the coal bed was heated by wire heater to proceed the pyrolysis under supercritical CO2 condition.

Design of pressure and flowrate control systems for a supercritical extraction process (초임계 추출 공정의 압력 및 유량 제어계 구성)

  • 김원철;김홍식;이광순
    • 제어로봇시스템학회:학술대회논문집
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    • 1988.10a
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    • pp.471-475
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    • 1988
  • Pressure and flowrate control systems for a supercritical extraction process are designed and analyzed. To do this, the dynamic model was first set up using the performance equations of control valves, CO2 compressor and the state equation of the supercritical fluid. Using this model, optimum pairs of manipulated and controlled variable which give least steady stat interaction are determined though the relative gain analysis.

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