• 제목/요약/키워드: subcooled flow boiling

검색결과 56건 처리시간 0.02초

Improvement of the MARS subcooled boiling model for a vertical upward flow

  • Ha, Tae-Wook;Jeong, Jae Jun;Yun, Byong-Jo
    • Nuclear Engineering and Technology
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    • 제51권4호
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    • pp.977-986
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    • 2019
  • In the thermal-hydraulic system codes, such as MARS and RELAP5/MOD3, the Savannah River Laboratory (SRL) model has been adopted as a subcooled boiling model. It, however, has been shown that the SRL model cannot take into account appropriately the effects of inlet liquid velocity and hydraulic diameter on axial void fraction development. To overcome the problems, Ha et al. (2018) proposed a modified SRL model, which is applicable to low-pressure and low-Pe conditions (P < 9.83 bar and $Pe{\leq}70,000$) only. In this work, the authors extended the modified SRL model by proposing a new net vapor generation (NVG) model and a wall evaporation model so that the new subcooled boiling model can cover a wide range of thermal-hydraulic conditions with pressures ranging from 1.1 to 69 bar, heat fluxes of $97-1186kW/m^2$, Pe of 3600 to 329,000, and hydraulic diameters of 5-25.5 mm. The new model was implemented in the MARS code and has been assessed using various subcooled boiling experimental data. The results of the new model showed better agreements with measured void fraction data, especially at low-pressure conditions.

FLOW BOILING HEAT TRANSFER FROM PLAIN AND MICROPOROUS COATED SURFACES IN SUBCOOLED FC-72

  • ;;유승문
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2001년도 춘계학술대회논문집D
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    • pp.181-188
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    • 2001
  • The present research is an experimental study of subcooled flow boiling behavior using flat, microporousenhanced square heater surfaces in pure FC-72. Two $1-cm^{2}$ copper surfaces, one highly polished (plain) and one microporous coated, were flush-mounted into a 12.7 mm square, horizontal flow channel. Testing was performed for fluid velocities ranging from 0.5 to 4 m/s (Reynolds numbers from 18,700 to 174,500) and pure subcooling levels from 4 to 20 K. Results showed both surfaces' nucleate flow boiling curves collapsed to one line showing insensitivity to fluid velocity and subcooling. The log-log slope of the microporous surface nucleate boiling curves was lower than the plain surface due to the conductive thermal resistance of the microporous coating layer. Both, increased fluid velocity and subcooling, increase the CHF values for both surfaces, however, the already enhanced boiling characteristics of the microporous coating appear dominant and require higher fluid velocities to provide additional enhancement of CHF to the microporous surface.

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Parameter Study of Boiling Model for CFD Simulation of Multiphase-Thermal Flow in a Pipe

  • Chung, Soh-Myung;Seo, Yong-Seok;Jeon, Gyu-Mok;Kim, Jae-Won;Park, Jong-Chun
    • 한국해양공학회지
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    • 제35권1호
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    • pp.50-58
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    • 2021
  • The demand for eco-friendly energy is expected to increase due to the recently strengthened environmental regulations. In particular, the flow inside the pipe used in a cargo handling system (CHS) or fuel gas supply system (FGSS) of hydrogen transport ships and hydrogen-powered ships exhibits a very complex pattern of multiphase-thermal flow, including the boiling phenomenon and high accuracy analysis is required concerning safety. In this study, a feasibility study applying the boiling model was conducted to analyze the multiphase-thermal flow in the pipe considering the phase change. Two types of boiling models were employed and compared to implement the subcooled boiling phenomenon in nucleate boiling numerically. One was the "Rohsenow boiling model", which is the most commonly used one among the VOF (Volume-of-Fluid) boiling models under the Eulerian-Eulerian framework. The other was the "wall boiling model", which is suitable for nucleate boiling among the Eulerian multiphase models. Moreover, a comparative study was conducted by combining the nucleate site density and bubble departure diameter model that could influence the accuracy of the wall boiling model. A comparison of the Rohsenow boiling and the wall boiling models showed that the wall boiling model relatively well represented the process of bubble formation and development, even though more computation time was consumed. Among the combination of models used in the wall boiling model, the simulation results were affected significantly by the bubble departure diameter model, which had a very close relationship with the grid size. The present results are expected to provide useful information for identifying the characteristics of various parameters of the boiling model used in CFD simulations of multiphase-thermalflow, including phase change and selecting the appropriate parameters.

계면면적 수송방정식을 적용한 이상유동 해석코드 개발 (CFD Code Development for a Two-phase Flow with an Interfacial Area Transport Equation)

  • 배병언;윤한영;어동진;송철화;박군�x
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2007년도 춘계학술대회B
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    • pp.2696-2701
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    • 2007
  • For the analysis of a two-phase flow, the interaction between two phases such as the interfacial momentum or heat transfer is proportional to the interfacial area. So the interfacial area concentration (IAC) is one of the most important parameters governing the behavior of each phase. This study focuses on the development of a computational fluid dynamics (CFD) code for investigating a boiling flow with a one-group IAC transport equation. It was based on the two-fluid model and governing equations were calculated by SMAC algorithm. For checking the robustness of the developed code, the experiment of a subcooled boiling in a vertical annulus channel was analyzed to validate the capability of the IAC transport equation. As the results, the developed code was confirmed to have the capability in predicting multi-dimensional phenomena of vapor generation and propagation in a subcooled boiling.

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Forced Convection Boiling Heat Transfer from a Horizontal Cylinder to Subcooled Water

  • Lee, Sung-Hong;Lee, Euk-Soo
    • International Journal of Air-Conditioning and Refrigeration
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    • 제7권
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    • pp.79-90
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    • 1999
  • This investigation presents the experimental results of forced convection boiling heat transfer around a circular, electrically heated horizontal cylinder to subcooled water in cross flow. In these experiments, the following primary variables were included: heat flux, flow velocity, pressure and degree of subcooling at inlet. Local surface temperatures were measured at nine peripheral positions. Local surface temperature distributions are classified into four categories depending on the supplied heat flux. The effects of the boiling curve depending on the fluid velocity, degree of subcooling at inlet and pressure are presented.

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Thermo-hydrodynamic investigation into the effects of minichannel configuration on the thermal performance of subcooled flow boiling

  • Amal Igaadi;Rachid El Amraoui;Hicham El Mghari
    • Nuclear Engineering and Technology
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    • 제56권1호
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    • pp.265-274
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    • 2024
  • The current research focuses on the development of a numerical approach to forecast strongly subcooled flow boiling of FC-72 as the refrigerant in various vertical minichannel shapes for high-heat-flux cooling applications. The simulations are carried out using the Volume of Fluid method with the Lee phase change model, which revealed some inherent flaws in multiphase flows that are primarily due to an insufficient interpretation of shearlift force on bubbles and conjugate heat transfer against the walls. A user-defined function (UDF) is used to provide specific information about this noticeable effect. The influence of shape and the inlet mass fluxes on the flow patterns, heat transfer, and pressure drop characteristics are discussed. The computational results are validated with experimental measurements, where excellent agreements are found that prove the efficiency of the present numerical model. The findings demonstrate that the heat transfer coefficient decreases as the mass flux increases and that the constriction design improves the thermal performance by 24.68% and 10.45% compared to the straight and expansion shapes, respectively. The periodic constriction sections ensure good mixing between the core and near-wall layers. In addition, a slight pressure drop penalty versus the thermal transfer benefits for the two configurations proposed is reported.

마이크로채널에서 과냉 핵비등 시발점의 비정상 수치해석 (TRANSIENT SIMULATION OF SUBCOOLED ONSET OF NUCLEATE BOILING IN A MICRO-CHANNEL)

  • 이희준
    • 한국전산유체공학회지
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    • 제16권2호
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    • pp.88-93
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    • 2011
  • A numerical study of subcooled onset of nucleate boiling (ONB) in a micro-channel under pulsed heating using volume of fluids (VOF) model was conducted. The VOF simulation adopting the existing experimental condition is compared to the experimental data. The time to ONB was determined when the void fraction at the microheater surface first appeared. The theoretical superheat for homogeneous nucleation relatively predicts the transient ONB results of convective flow of water well based on local temperature distribution. It was found that once heat load increases at the heater, transient flow boiling starts to occur faster.

An Improved Mechanistic Model to Predict Critical Heat Flux in Subcooled and Low Quality Convective Boiling

  • Kwon, Young-Min;Chang, Soon-Heung
    • Nuclear Engineering and Technology
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    • 제31권2호
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    • pp.236-255
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    • 1999
  • An improved mechanistic model was developed to predict a convective boiling critical heat flux (CHF) in the vertical round tubes with uniform heat fluxes. The CHF formula for subcooled and low quality boiling was derived from the local conservation equations of mass, energy and momentum, together with appropriate constitutive relations. The model is characterized by the momentum balance equation to determine the limiting transverse interchange of mass flux crossing the interface of wall bubbly layer and core by taking account of the convective shear effect due to the frictional drag on the wall-attached bubbles. Comparison between the present model predictions and experimental CHF data from several sources shows good agreement over a wide range of How conditions. The present model shows comparable prediction accuracy with the CHF look-up table of Groeneveld et al. Also the model correctly accounts for the effects of flow variables as well as geometry parameters.

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Experimental Study on Single Bubble Growth Under Subcooled, Saturated, and Superheated Nucleate Pool Boiling

  • Kim Jeong-Bae;Lee Jang-Ho;Kim Moo-Hwan
    • Journal of Mechanical Science and Technology
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    • 제20권5호
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    • pp.692-709
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    • 2006
  • Nucleate pool boiling experiments with constant wall temperature were performed using pure R1l3 for subcooled, saturated, and superheated pool conditions. A microscale heater array and Wheatstone bridge circuits were used to maintain the constant wall temperature and to measure the instantaneous heat flow rate accurately with high temporal and spatial resolutions. Images of bubble growth were taken at 5,000 frames per second using a high-speed CCD camera synchronized with the heat flow rate measurements. The bubble geometry was obtained from the captured bubble images. The effect of the pool conditions on the bubble growth behavior was analyzed using dimensionless parameters for the initial and thermal growth regions. The effect of the pool conditions on the heat flow rate behavior was also examined. This study will provide good experimental data with precise constant wall temperature boundary condition for such works.

핵비등 열전달 효과를 고려한 내연기관 냉각수로의 CFD-FE 연성해석 기법 (Coupled CFD-FE Analysis Method for IC Engine Cooling Water Jacket under Subcooled Nucleate Boiling Conditions)

  • 이명훈;김동광;이상규;임동렬
    • 한국자동차공학회논문집
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    • 제14권5호
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    • pp.9-16
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    • 2006
  • The present study is to simulate coolant flow in IC engine cooling passages under subcooled nucleate boiling conditions and investigate thermal stress analysis of the solid part. To consider nucleate boiling heat transfer effect, Chen's empirical formula is used through user subroutine programing in CFD code and then nucleate boiling model is compared with Robinson's experimental results, which shows reasonable agreement. This Chen's nucleate boiling model is applied to single cylinder IC engine model and we do cylinder liner thermal stress analysis using commercial FEM code.