Abstracts - KTH Mechanics

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102 Experimental study of the effect of gas injection on oil-water phase inversion in a vertical pipe M.Descamps ∗ , R.V.A.Oliemans ∗ ,G.Ooms ∗ , R.F.Mudde ∗ and R.Kusters † In the case of a single-phase (water) flow through a vertical pipe it has been shown that the efficiency of the gas-lift technique increases, when the bubble size of the injected gas is reduced 1 . It is not clear whether this also holds for an oil-water flow through a vertical pipe, as in that case phase inversion between the two liquids can occur. This is particularly relevant for the oil industry, since the gas-lift technique is widely used for oil (with water) production. The phase inversion phenomenon has been investigated by various authors both experimentally 2 and numerically 3 , but very little is known about the influence of gas injection on this phenomenon. Therefore, an experimental study has been made of the influence of gas injection on the phase inversion between oil and water flowing through a vertical pipe. Particular attention was paid to the influence on the critical concentration of oil and water at which phase inversion occurs and on the pressure drop increase over the pipe during phase inversion. By using different types of gas injectors also the influence of the bubble size of the injected gas on the phase inversion was studied. It was found that gas injection does not significantly change the critical concentration, but the influence on the pressure drop at the point of inversion is considerable (see figure 1). Local measurements of the phase concentration and bubble size may provide an explanation. ∗J.M. Burgerscentrum for Fluid <strong>Mechanics</strong>, Delft University of Technology, Kramers Laboratorium, Prins Bernhardlaan 6, 2628 BW Delft, The Netherlands † Shell International Exploration and Production B.V., Kessler Park 1, 2288 GS, Rijswijk ZH, The Netherlands 1Guet et al., AICHE J. 49, 2242 (2003) 2Ioannou et al., Exp. Therm. Fluid Sci. 29, 331 (2005) 3Brauner and Ullmann, Int. J.Multiphase Flow 28, 1177 (2002) pressure gradient (Pa/m) 11000 10500 10000 9500 9000 Total pressure gradient U = 0.98 m/s m U = 1.96 m/s m U = 2.94 m/s m Water in Oil Oil in Water 8500 0 20 40 60 water fraction (%) 80 100 Pressure gradient (Pa/m) 11500 11000 10500 10000 9500 9000 8500 8000 0 20 40 60 80 100 Water cut (%) Shell Donau Loop : Oil−Water−Air vertical upward flow U = 2.94 m/s m GVF = 2.56 % Liquid−liquid Nozzle injector Conical porous injector Circular porous injector Figure 1: Pressure gradient as function of water volume fraction for an oil-water without (left) and with (right) gas injection.
Microbubble Drag Reduction in a Taylor-Couette System K. Sugiyama ∗ ,E.Calzavarini ∗ and D. Lohse ∗ We investigate the effect of microbubbles on a Taylor-Couette system by means of direct numerical simulations. In particular, the effect of axially rising bubbles on the modulation of the highly organized vortices in the wavy vortex flow regime (i.e. Re = 600 − 2500) is addressed. We employ an Eulerian-Lagrangian algorithm with a gas-fluid (two-way) coupling based on the point-force approximation 1 . Added mass, steady drag, lift, and gravity are taken into account in the modeling of the motion of the single bubble. Our results show that microbubbles are responsible for a reduction of the torque exerted by the system, and therefore of the drag. In figure 1 we show the behavior of the normalized torque, as a function of Reynolds number, and a comparison with a recent series of experimental data obtained by Murai et al. 2 Our analysis suggests that the physical mechanism for the torque reduction is due to the appearance of an axial flow, induced by rising bubbles, that is able to break the highly dissipative Taylor wavy vortices in the system. This effect is in principle similar to the one produced by an axial driving force applied to a single phase Taylor- Couette flow. However, we demonstrate that the bubble addition is more efficient in injecting energy into the flow. We finally show that the lift force acting on the bubble is crucial in this process. When neglecting it, the bubbles accumulate preferentially near the inner cylinder and the bulk flow is no longer modified. ∗ Department of Applied Physics, University of Twente, 7500 AE Enschede, The Netherlands. 1 Mazzitelli, Lohse and Toschi, J. Fluid Mech. 488, 283 (2003). 2 Murai et al., Proc. of 2nd Int. Symp. on Seawater Drag Reduction (2005). Torque Reduction Ratio 0.25 0.20 0.15 0.10 0.05 0.00 DNS Experiment TRR=1−Tmultiphase/Tsingle phase 1000 2000 3000 4000 Re(=ΩiRi(Ro−Ri)/ν) Figure 1: Torque reduction ratio, defined as the torque reduction due to the bubble addition normalized by the torque in the single phase flow, versus the Reynolds number for the Taylor-Couette system. The symbol • shows the present DNS. The symbol × shows the experimental data at the gas flow rate of 1.17 · 10 6 m 3 /sinRef. 2. The inner and outer cylinder radii are Ri = 60mm and Ro = 72mm, respectively. 103
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EFMC6 KTH Electronic version Abstra
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Uncertainty Quantification in Large
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Flow Separation from a Free Surface
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LIST OF AUTHORS Tuzi R. 11 Wolters
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Abstracts - KTH Mechanics

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