Begell House Inc.
Multiphase Science and Technology
MST
0276-1459
26
4
2014
VOID FRACTION AND WAKE ANALYSIS OF A GAS-LIQUID TWO-PHASE CROSS-FLOW
261-286
10.1615/MultScienTechn.v26.i4.10
Pedram
Hanafizadeh
Center of Excellence in Design and Optimization of Energy Systems, School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran
Mohammadreza
Momenifar
Center of Excellence in Design and Optimization of Energy Systems, School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran
A. Nouri
Geimassi
Department of Mechanical Engineering and Material Science, University of Pittsburgh, Pittsburgh, PA, 15261, USA
S.
Ghanbarzadeh
Department of Petroleum and Geosystems Engineering, The University of Texas at Austin, Austin, TX, 78712, USA
gas-liquid cross-flow
drag coefficient
flow regime
void fraction
Two-phase cross-flow takes place in a wide range of industrial equipment, including heat exchangers and measurement devices. The aim of this paper is to establish a numerical model and experimental methodology for comprehensive study and visualization of void fraction and wake region in gas-liquid cross-flow over immersed bodies with various cross-section geometries. Conservation of mass and momentum for both-phase free streams, along with constitutive relationships, were used for modeling turbulence. The input parameters for the numerical simulations were two-phase Reynolds number, free-stream void fraction, bubble size in the inlet, and cross-section geometry of prisms inserted in the two-phase flow path. Because the wake region and phase distribution around an immersed object are time-dependent, we report time average values of drag, lift, and pressure coefficients. The results show that drag and lift coefficients are strongly dependent on the two-phase Reynolds number; this dependency is a more moderate function of void fraction. The results are in good agreement with available empirical correlations and experimental work. Furthermore, experiments were conducted to visualize phase distribution and wake region in two-phase cross-flow. Comparison of the experimental and numerical results verifies the developed numerical model.
EFFECT OF THERMAL−HYDRAULIC PARAMETERS ON ENTROPY GENERATION IN A BOILING CHANNEL
287-303
10.1615/MultScienTechn.v26.i4.20
Saeed
Talebi
Department of Energy Engineering and Physics, Amirkabir University of Technology (Tehran Polytechnic), 424 Hafez Avenue, P.O. Box 15875-4413 , Tehran, Iran.
boiling channel
two-phase flow
entropy generation
critical heat flux
In this study, the optimization of local entropy generation for water/vapor-saturated two-phase flow in a vertical channel is conducted using entropy generation minimization. The contributions of heat transfer and pressure drop to entropy generation is considered. Appropriate models for estimating heat transfer and pressure drop in a boiling channel are applied. The drift flux model is used to predict the void fraction along the boiling channel. The effect of influential thermal-hydraulic parameters such as the inlet quality, induced power, power distribution profile, channel hydraulic diameter, and inlet mass flux on channel entropy generation is presented. The optimum channel hydraulic diameter is predicted as a function of the system pressure. Also, an appropriate critical heat flux model is applied to the boiling channel to insure safety margin evaluation. It is found that an increase in system pressure decreases the optimized channel hydraulic diameter. For each flow condition, there is a mass flux at which the entropy generation rate is maximized. It was also observed that the channel power distribution profile has an important effect on the entropy generation of a boiling channel. Uniform power distribution is preferred for both minimum entropy generation and a wider margin of safety.
BEST-ESTIMATE SIMULATIONS OF CONDENSATION-INDUCED WATER HAMMER IN HORIZONTAL PIPES WITH THE SYSTEM ANALYSIS CODE ATHLET
305-327
10.1615/MultScienTechn.v26.i4.30
Sabin Cristian
Ceuca
Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) gGmbH
H.
Austregesilo
Gesellschaft fur Anlagen- und Reaktorsicherheit (GRS) mbH, Forschungsinstitute, 85748 Garching, Germany
R.
Macian-Juan
Paul Scherrer Institut, 5232 Villigen PSI, Switzerland; and Department of Nuclear Engineering, TU Munchen, Boltzmannstrasse 15, D-85748 Garching, Germany
horizontal two-phase flow
direct contact condensation
condensation-induced water hammer
A newly developed hybrid heat transfer coefficient module has been developed, based on two individual surface renewal theory models and implemented into the German thermal-hydraulic system analysis code ATHLET (which stands for analysis of thermal hydraulics of leaks and transients). The new model is based on mechanistic assumptions and does not require special parameter tuning, thus increasing the predictive capabilities of the system analysis code. This model was validated against a full set of 33 experiments performed at the PMK-2 facility for the analysis of condensation-induced water hammer phenomena in a horizontal test section. The integral thermalhydraulic experimental facility has a similar design to the main steam line of a WWER nuclear power plant.
PNEUMATIC CONVEYING THROUGH A HORIZONTAL PIPE: NUMERICAL PRESSURE DROP
329-349
10.1615/MultScienTechn.v26.i4.40
Brundaban
Patro
National Institute of Technology Warangal, Telangana 506004, India
computational fluid dynamics
numerical modeling
Gidaspow drag model
restitution coefficient
granular temperature
The present paper predicts the numerical pressure drop in air−solid two-phase flows in a horizontal pipe with an internal diameter of 30 mm using four-way coupling. In four-way coupling, the dispersed-phase collisions are the significant momentum exchange mechanism. Using the present model, the predicted pressure drop in the two-phase flows is in satisfactory agreement with the published experimental data. It is observed that the pressure drop increases with an increase in the solids volume fraction, particle density, particle diameter, and inlet air velocity for particle diameters up to 50 µm. Finally, using nonlinear regression analysis, a correlation for the two-phase pressure drop is developed with an accuracy of ±10%. The correlation can be used to find the two-phase pressure drop in air−solid flows.
CONTENTS, VOLUME 26, 2014
351-353
10.1615/MultScienTechn.v26.i4.50