TWO-PHASE FLOW WITH AND WITHOUT PHASE CHANGE: SUSPENSION FLOWS - SOME QUESTIONS ANSWERED AND UNANSWERED

The present work deals with the numerical analysis of phase change effects and choked flow on the rotordynamic coefficients of cryogenic annular seals. The analysis is based on the “bulk flow” equations, with the energy equation written for the total enthalpy, and uses an estimation of the speed of sound that is valid for single- or two-phase flow as well. The numerical treatment of choked flow conditions is validated by comparisons with the experimental data of Hendricks (1987, “Straight Cylindrical Seal for High-Performance Turbomachines,” NASA Technical Paper No. 1850) obtained for gaseous nitrogen. The static characteristics and the dynamic coefficients of an annular seal working with liquid or gaseous oxygen are then investigated numerically. The same seal was used in previous analyses performed by Hughes et al. (1978, “Phase Change in Liquid Face Seals,” ASME J. Lubr. Technol., 100, pp. 74–80), Beatty and Hughes (1987, “Turbulent Two-Phase Flow in Annular Seals,” ASLE Trans., 30(1), pp. 11–18), and Arauz and San Andrés (1998, “Analysis of Two Phase Flow in Cryogenic Damper Seals. Part I: Theoretical Model,” ASME J. Tribol., 120, pp. 221–227 and 1998, “Analysis of Two Phase Flow in Cryogenic Damper Seals. Part 2: Model Validation and Predictions,” ASME J. Tribol., 120, pp. 228–233). The flow in the seal is unchoked, and rotordynamic coefficients show variations, with the excitation frequency depending if the flow is all liquid, all gas, or a liquid-gas mixture. Finally, the pressure ratio and length of the previous seal are changed in order to promote flow choking in the exit section. The rotordynamic coefficients calculated in this case show a dependence on the excitation frequency that differ from the unchoked seal.

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Non-local equilibrium two-phase flow model with phase change in porous media and its application to reflooding of a severely damaged reactor core

10.1063/1.4711167 ◽

2012 ◽

Cited By ~ 1

Author(s):

A. Bachrata ◽

F. Fichot ◽

M. Quintard ◽

G. Repetto ◽

J. Fleurot

Keyword(s):

Porous Media ◽

Phase Change ◽

Flow Model ◽

Two Phase Flow ◽

Local Equilibrium ◽

Reactor Core ◽

Phase Flow ◽

Two Phase ◽

Non Local

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A three-dimensional two-phase flow model with phase change inside a tube of petrochemical pre-heaters

Fuel ◽

10.1016/j.fuel.2012.09.065 ◽

2013 ◽

Vol 110 ◽

pp. 196-203 ◽

Cited By ~ 14

Author(s):

D.V.R. Fontoura ◽

E.M. Matos ◽

J.R. Nunhez

Keyword(s):

Phase Change ◽

Flow Model ◽

Two Phase Flow ◽

Three Dimensional ◽

Phase Flow ◽

Two Phase

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Liquid and Gas-Phase Distributions in a Jet With Phase Change

Journal of Heat Transfer ◽

10.1115/1.3250598 ◽

1988 ◽

Vol 110 (4a) ◽

pp. 955-960 ◽

Cited By ~ 19

Author(s):

Flavio Dobran

Keyword(s):

Phase Change ◽

Pressure Distribution ◽

Total Pressure ◽

Two Phase Flow ◽

Phase Flow ◽

Gas Velocity ◽

Flow Properties ◽

Two Phase ◽

Pipe Length ◽

Pressure Peak

A two-phase flow high-velocity jet with phase change was studied numerically. The jet is assumed to be created by the two-phase critical flow discharge through a pipe of variable length and attached to a vessel containing the saturated liquid at different stagnation pressures. The jet flow is assumed to be axisymmetric and the modeling of the two-phase flow was accomplished by a nonequilibrium model that accounts for the relative velocity and temperature difference between the phases. The numerical solution of the governing set of balance and conservation equations revealed steep gradients of flow properties in both radial and axial directions. The liquid phase in the jet is shown to remain close to the jet axis, and its velocity increases until it reaches a maximum corresponding to the gas velocity, and thereafter decreases at the same rate as the gas velocity. The effect of decreasing the pipe length is shown to produce a larger disequilibrium in the jet and a double pressure peak in the total pressure distribution. A comparison of the predicted total pressure distribution in the jet with the experimental data of steam–water at different axial locations is demonstrated to be very reasonable.

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Water Condensation and Two-Phase Flow Modeling for a Plate Heat Exchanger Channel

Volume 8: Heat Transfer, Fluid Flows, and Thermal Systems, Parts A and B ◽

10.1115/imece2007-41635 ◽

2007 ◽

Author(s):

Charlotte Wilhelmsson ◽

Jinliang Yuan ◽

Bengt Sunden

Keyword(s):

Phase Change ◽

Two Phase Flow ◽

Plate Heat Exchanger ◽

Water Phase ◽

Phase Flow ◽

Governing Equations ◽

Two Phase ◽

Plate Heat ◽

Total Enthalpy ◽

Vapour Condensation

There are water vapour condensation and two-phase flow in plate heat exchangers when they are used as condensers. Water phase change and flow dynamics modelling is an important but complicated task due to large change in water physical/transport properties across the water liquid-vapour interface boundary. In particular, singular-link behaviour in governing equations is present due to the large step change in the density when computational fluid dynamics (CFD) is employed. Conventional methods using ensemble averaged parameters such as void fraction are impossible to be applied to cases where high-resolution calculations and detailed analysis are required. In this study, a CFD approach is employed to model water vapour condensation and two-phase flow in a channel relevant for plate heat exchanger parallel plates. The developed model is based on the governing equations which are directly solved for the entire single- and two-phase fields. The water phase change and two-phase flow are treated by employing a water liquid-phase fraction factor based on the total enthalpy in each computational cell. The factor is defined as the ratio of the total enthalpy differential to the latent heat of condensation. The thermal-physical properties, such as density, viscosity and conductivity of the two-phase region, are calculated and updated based on the calculated value of the liquid-phase fraction factor until a converged result is reached. It is concluded that, among others, the inlet vapour velocity has significant effects on the water phase change and two-phase flow in the channel, in terms of liquid-water fraction factor distribution.

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Computational Fluid Dynamics Modeling of Flow Boiling in Microchannels With Nonuniform Heat Flux

Journal of Heat Transfer ◽

10.1115/1.4037343 ◽

2017 ◽

Vol 140 (1) ◽

Cited By ~ 13

Author(s):

Daniel Lorenzini ◽

Yogendra K. Joshi

Keyword(s):

Fluid Dynamics ◽

Heat Flux ◽

Computational Fluid Dynamics ◽

Phase Change ◽

Two Phase Flow ◽

Flow Boiling ◽

Cfd Modeling ◽

Temperature Phase ◽

Phase Flow ◽

Two Phase

The computational fluid dynamics (CFD) modeling of boiling phenomena has remained a challenge due to numerical limitations for accurately simulating the two-phase flow and phase-change processes. In the present investigation, a CFD approach for such analysis is described using a three-dimensional (3D) volume of fluid (VOF) model coupled with a phase-change model accounting for the interfacial mass and energy transfer. This type of modeling allows the transient analysis of flow boiling mechanisms, while providing the ability to visualize in detail temperature, phase, and pressure distributions for microscale applications with affordable computational resources. Results for a plain microchannel are validated against benchmark correlations for heat transfer (HT) coefficients and pressure drop as a function of the heat flux and mass flux. Furthermore, the model is used for the assessment of two-phase cooling in microelectronics under a realistic scenario with nonuniform heat fluxes at localized regions of a silicon microchannel, relevant to the cooling layer of 3D integrated circuit (IC) architectures. Results indicate the strong effect of two-phase flow regime evolution and vapor accumulation on HT. The effects of reduced saturation pressure, subcooling, and flow arrangement are explored in order to provide insight about the underlying physics and cooling performance.

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