Fluid dynamics in a bubble column: New experiments and simulations

New high quality experimental data for the fluid dynamics of a bubble column are used to validate a baseline set of closure relations for bubbly flows. Development and validation of such closure relations is an important and active area of research, since they facilitate CFD simulations on industrial scales by means of the Euler–Euler two-fluid model. The new dataset features in particular large spatial and temporal resolution and high accuracy for a comprehensive set of observables and a range of different conditions. The closure model, which has been validated previously for a range of different conditions, is shown to agree with the new data quite well. In this way, the confidence in the model for predictive applications, such as optimization and scale-up of chemical engineering processes, is further enhanced.     

Mathematical modeling of gas desorption from a gas hydrate

In gas-gashydrate reservoirs the gas is in the free and bound states. The amount of gas bound in the hydrate depends on the thermodynamic conditions. Therefore, when these conditions are varied it is possible for gas to be released from the hydrate in the desorption regime up to total dissociation of the hydrate into gas and water. Below, the problem of extraction of free and bound gas in the desorption regime is considered.Ufa. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 5, pp. 118–125, September–October, 1996.     

Migration of a sphere suspended in viscoelastic liquids in Couette flow: experiments and simulations

The intrinsically coupled effects of the curvature of the flow-field and of the viscoelastic nature of suspending medium on the cross-stream lateral migration of a single non-Brownian sphere in wide-gap Couette flow are studied. Quantitative videomicroscopy experiments using a counterrotating device are compared to the results of 3D finite element simulations. To evaluate the effects of differences in rheological properties of the suspending media, fluids have been selected which highlight specific constitutive features, including a reference Newtonian fluid, a single relaxation time wormlike micellar surfactant solution, a broad spectrum shear-thinning elastic polymer solution and a constant viscosity, highly elastic Boger fluid. As expected for conditions corresponding to Stokes flow, migration is absent in the Newtonian fluid. In the wormlike micellar solution and the shear-thinning polymer solution, spheres are observed to migrate in the direction of decreasing shear rate gradient, i.e. the outer cylinder, except when the sphere is initially released close to the inner cylinder, in which case the migration is towards it. The migration is enhanced by faster relative angular velocities of the cylinders. Shear-thinning reduces the migration velocity, showing an opposite behavior as compared to previous results in planar shear flow. In the Boger fluid, within experimental error no migration could be observed, likely due to the large solvent contribution to the overall viscosity. For small Deborah numbers the migration results are well described by an heuristic argument based on a local stress balance.     

The buoyancy of a gas bubble in a tube filled with a viscous liquid

Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, Vol. 30, No. 6, pp. 98–105, November–December, 1989.     

Evaporation heat transfer of R-134a inside a microfin tube with different tube inclinations

An experimental investigation has been carried out to study the heat transfer characteristics during evaporation of R-134a inside a single helical microfin tube. The microfin tube has been provided with different tube inclination angles of the direction of fluid flow from horizontal, α. The experiments were performed for seven different tube inclinations, α, in a range of −90° to +90° and four mass velocities of 53, 80, 107 and 136 kg/m² s for each tube inclination angle during evaporation of R-134a. The results demonstrate that the tube inclination angle, α, affects the boiling heat-transfer coefficient in a significant manner. For all refrigerant mass velocities, the best performing tube is that having inclination angle of α = +90°. The effect of tube inclination angle, α, on heat-transfer coefficient, h, is more prominent at low vapor quality and mass velocity. An empirical correlation has also been developed to predict the heat-transfer coefficient during flow boiling inside a microfin tube with different tube inclinations.     

Radial oscillations of gas bubbles in liquids in the presence of a combustible gas component

Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.1, pp. 103–109, January–February, 1993.     

Possibility of identifying the viscoplastic properties of liquids in experiments with an oscillating-cup viscometer

Results of a numerical solution of the problem of oscillations of an oscillating-cup viscometer filled with a viscoplastic liquid are presented. It is shown that near the rotation axis, a stagnant zone arises, whose boundary changes position during the oscillations. The effect of the plastic properties of the liquid on the frequency and damping coefficient of oscillations of the viscometer is determined. A method of identifying the viscoplastic properties using observed oscillation parameters is proposed. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 6, pp. 59–63, November–December, 2006.     

Fully developed laminar flow of non-Newtonian liquids through annuli: comparison of numerical calculations with experiments

Experimental data are reported for fully developed laminar flow of a shear-thinning liquid through both a concentric and an 80% eccentric annulus with and without centrebody rotation. The working fluid was an aqueous solution of 0.1% xanthan gum and 0.1% carboxymethylcellulose for which the flow curve is well represented by the Cross model. Comparisons are reported between numerical calculations and the flow data, as well as with other laminar annular-flow data for a variety of shear-thinning liquids previously reported in the literature. In general, the calculations are in good quantitative agreement with the experimental data, even in situations where viscoelastic effects, neglected in the calculations, would be expected to play a role.