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1
Content available Analysis of wake structures in bubbly flowsusing Particle Image Velocimetry (PIV)
Lewandowski Björn, Fertig Micha, Kreke Georg, Ulbricht Mathias
Chemical and Process Engineering
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2019
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Vol. 40, nr 1
49–-55
EN
The flow structure around rising single air bubbles in water and their characteristics, such as equivalentdiameter, rising velocity and shape, was investigated using Particle Image Velocimetry (PIV) and Shadowgraphy in a transparent apparatus with a volume of 120mL. The effect of different volumetricgas flow rates, ranging from 4μL/min to 2 mL/min on the liquid velocity was studied. Ellipsoidalbubbles were observed with a rising velocity of 0.25–0.29 m/s. It was found that a Kármán vortex streetexisted behind the rising bubbles. Furthermore, the wake region expanded with increasing volumetricgas flow rate as well as the number and size of the vortices.
2
Content available remote Simutations of transient cavitating turbulent flow using unsteady frictional loss models
Urbanowicz K., Zarzycki Z.
Transactions of the Institute of Fluid-Flow Machinery
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2007
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nr 120
53-70
EN
The paper presents two key mathematical models of transient cavitating pipe flow, i.e. column separation model (CSM) and bubbly cavitation model (BCM). Both models investigated in the paper take into account unsteady frictional loss models. The equations describing the CSM and BCM models have been solved using first the method of characteristics and then the finite differences method. The results of numerical simulations have been compared with the results obtained in the experiments. Transients which took into account unsteady wall shear stress fit well the results of experiments in comparison with quasi-steady wall shear stress model.
3
Content available remote Simulation of condensation in a subcooled bubbly steam-water flow along a large vertical pipe
Lucas D., Prasser H.
Archives of Thermodynamics
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2005
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Vol. 26, no. 4
49-59
EN
Detailed experimental data obtained at the TOPFLOW facility for steam-water vertical pipe flow were used to test the complex interaction of local bubble distributions, bubble size distributions and local heat and mass transfer. Steam is injected into subcooled water and condenses during the upward flow. The model considers a large number of bubble classes (50). This allows the investigation of the influence of the bubble size distribution. The results of the simulations show a good agreement with experimental data. The condensation process is clearly slower, if large bubbles are injected (4 mm holes). Also the bubble break-up has a strong influence on the condensation process because of the change of the interfacial area. Some unsureness arises from the unknown interfacial area for large bubbles and possible uncertainties of the heat transfer coefficient.
4
Content available remote Modelling of heat transfer in bubbly flow in the turbulent boundary layer
Mikielewicz D.
Archives of Thermodynamics
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2001
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Vol. 22, nr 1-2
33-49
EN
In the work presented is a new approach to modelling the heat transfer in bubbly flow in the boundary layer. An approximate velocity distribution profile [1] is used in solution of energy equation. Presented have been two solutions to the problem, namely for a constant void fraction distribution, where an analytical temperature distribution has been obtained, and for a variable void fraction formulation, a more accurate solution, which is based on solution of three differential equations, namely: equation describing the lateral motion of bubbles, migration of gaseous phase and temperature distribution. It seems that the error incurred, in the case of small void fractions, between a constant and variable formulation is so small, that a simple analytical solution can be recommended for engineering purposes.
5
Content available remote Universal velocity profile for bubbly flow in the boundary layer
Mikielewicz D.
Archives of Thermodynamics
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2000
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Vol. 21, nr 3-4
117-132
EN
In the work presented is a new approach to modelling the bubble flow in a boundary layer. The approach is based on summation of the dissipation energy coming from the shearing turbulent flow in the absence of bubbles and the dissipation contribution from the bubble motion. As a result we obtain the shear stress of equivalent single phase turbulent flow. An approximate solution to the model has been given in a form of an explicit differential equation, which can be solved with assumption of constant or variable void fraction distribution. Velocity distributions calculated using the new model have been compared against the experimental data of turbulent bubble flows with small void fraction. A good consistency of calculations performed using a new model with experiment has been obtained.
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