• Title/Summary/Keyword: Liquid subcooling

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An Analytical Study for Critical Mass Flowrate of Compressed Water (압축수의 임계유량에 관한 해석적 연구)

  • 김희동;김재형;한민교;박경암
    • Journal of the Korean Society of Propulsion Engineers
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    • v.7 no.1
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    • pp.57-65
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    • 2003
  • As a compressed water is rapidly expanded through a nozzle, two-phase flow of vapor and liquid is formed in the nozzle due to the flash evaporation. In the present study, critical flow of two-phase fluids is analysized using an Isentropic-Homogeneous-Equilibrium model and a Leung model. Calculation results show that the choke of the two-phase flow can be two different types of continuous and discontinuous chokings. For the stagnation pressure below 10 Mpa it is found that the continuous choking, which is similar to the choking phenomenon of single-phase gas flow, is possible only when the degree of subcooling is less than 10K.

An Experimental Investigation of Direct Condensation of Steam Jet in Subcooled Water

  • Kim, Yeon-Sik;Chung, Moon-Ki;Park, Jee-Won;Chun, Moon-Hyun
    • Nuclear Engineering and Technology
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    • v.29 no.1
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    • pp.45-57
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    • 1997
  • The direct contact condensation phenomenon, which occurs when steam is injected into the subcooled water, has been experimentally investigated. Two plume shapes in the stable condensation regime are found to be conical and ellipsoidal shapes depending on the steam mass flux and the liquid subcooling. Divergent plumes, however, are found when the subcooling is relatively small. The measured expansion ratio of the maximum plume diameter to the injector inner diameter ranges from 1.0 to 2.3. By means of fitting a large amount of measured data, an empirical correlation is obtained to predict the steam plume length as a function of a dimensionless steam mass flux and a driving potential for the condensation process. The average heat transfer coefficient of direct contact condensation has been found to be in the range 1.0~3.5 ㎿/$m^2$.$^{\circ}C$. Present results show that the magnitude of the average condensation heat transfer coefficient depends mainly on the steam mass fin By using dynamic pressure measurements and visual observations, six regimes of direct contact condensation have been identified on a condensation regime map, which are chugging, transition region from chugging to condensation oscillation, condensation oscillation, bubbling condensation oscillation, stable condensation, and interfacial oscillation condensation. The regime boundaries are quite clearly distinguishable except the boundaries of bubbling condensation oscillation and interfacial oscillation condensation.

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A study of heat transfer with Phase Change Material in heat storage system - Inward freezing in the vertical cylinder - (상변화물질을 이용한 축열조에서 열전달현상에 관한 연구 - 수직원통관 내에서 응고 열전달 -)

  • Lee, C.M.;Yim, C.S.;Iqbal, M.
    • Solar Energy
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    • v.13 no.2_3
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    • pp.53-64
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    • 1993
  • This study investigated heat transfer phenomena during the freezing of an initially superheated or non-superheated liquid in a cooled cylinder tube. Numerical and experimental method were performed to obtatin the temperature and velocity distribution, the shape of interface. Natural convection effects in the superheated liquid were confined and moderated a short freezing time. After natural convection ceases, heat conduction dominated in the whole paraffin, so Crystal and much-zone were found out in PCM. Initial superheating of liquid tended to morderatly diminish the frozen layer thickness at short freezing times but little effect on the these quantities at longer times. On the amount of frozen mass, Iintial liquid superheating is less affected than tube wall subcooling.

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Phenomenological Liquid Film Dryout Model for Upward Flow in Tubes and Annuli (원형 및 환상 채널에 흐르는 수직 상향류의 액막 건조 모델)

  • Hong, Sung-Deok;Chun, Se-Young
    • Proceedings of the KSME Conference
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    • 2001.06d
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    • pp.201-207
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    • 2001
  • We modeled the liquid film dryout(LFD) process for both tube and annulus which have uniformly heated vertical channels. We set phenomenological initial conditions in the model. The initial void fraction on the onset of the annular flow location is derived from the physical chum-to-annular flow criterion with the help of the drift-flux-model. The initial thermodynamic-equilibrium-quality is calculated by iteration with the flow quality to find the onset of the annular-flow location. Present model tends to predict very well at the lower exit quality but under-estimates at the higher exit quality. We found that the prediction error of the present model is gradually bigger as the inlet subcooling approaches near the saturation. We obtained excellent results for both tube and annulus channels as the mean of 0.97 and root-mean-square error of 11% for the number of 3883 experimental data on tubes, and of 0.96 and of 12% for 593 on annuli. The present model extended the applicable range to the relatively low exit quality region than previous LFD models.

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Cool-down test of cryogenic cooling system for superconducting fault current limiter

  • Hong, Yong-Ju;In, Sehwan;Yeom, Han-Kil;Kim, Heesun;Kim, Hye-Rim
    • Progress in Superconductivity and Cryogenics
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    • v.17 no.3
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    • pp.57-61
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    • 2015
  • A Superconducting Fault Current Limiter is an electric power device which limits the fault current immediately in a power grid. The SFCL must be cooled to below the critical temperature of high temperature superconductor modules. In general, they are submerged in sub-cooled liquid nitrogen for their stable thermal characteristics. To cool and maintain the target temperature and pressure of the sub-cooled liquid nitrogen, the cryogenic cooling system should be designed well with a cryocooler and coolant circulation devices. The pressure of the cryostat for the SFCL should be pressurized to suppress the generation of nitrogen bubbles in quench mode of the SFCL. In this study, we tested the performance of the cooling system for the prototype 154 kV SFCL, which consist of a Stirling cryocooler, a subcooling cryostat, a pressure builder and a main cryostat for the SFCL module, to verify the design of the cooling system and the electric performance of the SFCL. The normal operation condition of the main cryostat is 71 K and 500 kPa. This paper presents tests results of the overall cooling system.

NEAL-WALL GRID DEPENDENCY OF CFD SIMULATION FOR A SUBCOOLED BOILING FLOW (과냉 비등유동에 대한 CFD 모의 계산에서의 벽 인접격자 영향)

  • In, W.K.;Shin, C.H.;Chun, T.H.
    • 한국전산유체공학회:학술대회논문집
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    • 2010.05a
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    • pp.320-325
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    • 2010
  • A multiphase CFD analysis is performed to investigate the effect of near-wall grid for simulating a subcooled boiling flow in vertical tube. The multiphase flow model used in this CFD analysis is the two-fluid model in which liquid(water) and vapor(steam) are considered as continuous and dispersed fluids, respectively. A wall boiling model is also used to simulate the subcooled boiling heat transfer at the heated wall boundary. The diameter and heated length of tube are 0.0154 m and 2 m, respectively. The system pressure in tube is 4.5 MPa and the inlet subcooling is 60 K. The near-wall grid size in the non-dimensional wall unit ($y_{w}^{+}$) was examined from 64 to 172 at the outlet boundary. The CFD calculations predicted the void distributions as well as the liquid and wall temperatures in tube. The predicted axial variations of the void fraction and the wall temperature are compared with the measured ones. The CFD prediction of the wall temperature is shown to slightly depend on the near-wall grid size but the axial void prediction has somewhat large dependency. The CFD prediction was found to show a better agreement with the measured one for the large near-wall grid, e.g., $y_{w}^{+}$ > 100.

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NEAR-WALL GRID DEPENDENCY OF CFD SIMULATION FOR A SUBCOOLED BOILING FLOW USING WALL BOILING MODEL (벽 비등모델을 이용한 과냉비등 유동에 대한 CFD 모의계산에서 벽 인접격자의 영향)

  • In, W.K.;Shin, C.H.;Chun, T.H.
    • Journal of computational fluids engineering
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    • v.15 no.3
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    • pp.24-31
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    • 2010
  • boiling flow in vertical tube. The multiphase flow model used in this CFD analysis is the two-fluid model in which liquid(water) and gas(vapour) are considered as continuous and dispersed fluids, respectively. A wall boiling model is also used to simulate the subcooled boiling heat transfer at the heated wall boundary. The diameter and heated length of tube are 0.0154 m and 2 m, respectively. The system pressure in tube is 4.5 MPa and the inlet subcooling is 60 K. The near-wall grid size in the non-dimensional wall unit for lqiuid phase ($y^+_{w,l}$) was examined from 101 to 313 at the outlet boundary. The CFD calculations predicted the void distributions as well as the liquid and wall temperatures in tube. The predicted axial variations of the void fraction and the wall temperature are compared with the measured ones. The CFD prediction of the wall temperature is shown to slightly depend on the near-wall grid size but the axial void prediction has somewhat large dependency. The CFD prediction was found to show a better agreement with the measured one for the large near-wall grid, e.g., $y^+_{w,l}$ > 300 at the tube exit.

Heat Transfer Analysis on the Rapid Solidification Process of Atomized Metal Droplets (분무된 금속액적의 급속응고과정에 관한 열전달 해석)

  • 안종선;박병규;안상호
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.9
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    • pp.2404-2412
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    • 1994
  • A mathematical model has been developed for predicting kinematic, thermal, and solidification histories of atomized droplets during flight. Liquid droplet convective cooling, recalescence, equilibrium-state solidification, and solid-phase cooling were taken into account in the analysis of the solidification process. The spherical shell model was adopted where the heterogeneous nucleation is initiated from the whole surface of a droplet. The growth rate of the solid-liquid interface was determined from the theory of crystal growth kinetics with undercooling caused by the rapid solidification. The solid fraction after recalescence was obtained by using the integral method. The thermal responses of atomized droplets to gas velocity, particle size variation, and degree of undercooling were investigated through the parametric studies. It is possible to evaluate the solid fraction of the droplet according to flight distance and time in terms of a dimensionless parameter derived from the overall energy balance of the system. It is also found that the solid fraction at the end of recalescence is not dependent on the droplet size and nozzle exit velocity but on the degree of subcooling.

Experimental Study on Condensation Heat Transfer Characteristics of Special Heat Transfer Tubes (응축용 특수 전열관의 열전달 특성에 관한 연구)

  • 한규일;박종운;권영철;조동현
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.13 no.9
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    • pp.827-835
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    • 2001
  • In this study, condensation heat transfer characteristics were conducted with special heat transfer tubes of SH-C type. Experiments were carried out the saturated vapor temperature of 334K and the wall subcooling of 1.5-4.5K. The refrigerant was R-113 and the enhanced tubes used in the present study were SH-CDR, SH-CYR and SH-CHR. The experimental results showed that the condensation heat transfer coefficients of SH-C type tubes were about 23-66% higher than those of a low integral-fin tube. It was visualized that the condensed liquid on the outer surface of SH-C type tubes flowed continuously down unlike a low integral-fin tube and a plain tube, due to a 3-D extending fin on the outer surface of SH-C type tubes. As a result, the thermal resistance of the condensed liquid decreased and the heat transfer coefficient increased. Also, the enhancement ratio of SH-CDR tube was the highest, and it was about 9-11 times as compared to that of a plain tube.

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TRIGGERING AND ENERGETICS OF A SINGLE DROP VAPOR EXPLOSION: THE ROLE OF ENTRAPPED NON-CONDENSABLE GASES

  • Hansson, Roberta Concilio
    • Nuclear Engineering and Technology
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    • v.41 no.9
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    • pp.1215-1222
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    • 2009
  • The present work pertains to a research program to study Molten Fuel-Coolant Interactions (MFCI), which may occur in a nuclear power plant during a hypothetical severe accident. Dynamics of the hot liquid (melt) droplet and the volatile liquid (coolant) were investigated in the MISTEE (Micro-Interactions in Steam Explosion Experiments) facility by performing well-controlled, externally triggered, single-droplet experiments, using a high-speed visualization system with synchronized digital cinematography and continuous X-ray radiography. The current study is concerned with the MISTEE-NCG test campaign, in which a considerable amount of non-condensable gases (NCG) are present in the film that enfolds the molten droplet. The SHARP images for the MISTEE-NCG tests were analyzed and special attention was given to the morphology (aspect ratio) and dynamics of the air/ vapor bubble, as well as the melt drop preconditioning. Energetics of the vapor explosion (conversion ratio) were also evaluated. The MISTEE-NCG tests showed two main aspects when compared to the MISTEE test series (without entrapped air). First, analysis showed that the melt preconditioning still strongly depends on the coolant subcooling. Second, in respect to the energetics, the tests consistently showed a reduced conversion ratio compared to that of the MISTEE test series.