Showing papers by "Sanjoy Banerjee published in 2013"

Interfacial rheology of asphaltenes at oil-water interfaces and interpretation of the equation of state.

Abstract: In an earlier study,(1) oil–water interfacial tension was measured by the pendant drop technique for a range of oil-phase asphaltene concentrations and viscosities. The interfacial tension was found to be related to the relative surface coverage during droplet expansion. The relationship was independent of aging time and bulk asphaltenes concentration, suggesting that cross-linking did not occur at the interface and that only asphaltene monomers were adsorbed. The present study extends this work to measurements of interfacial rheology with the same fluids. Dilatation moduli have been measured using the pulsating droplet technique at different frequencies, different concentrations (below and above CNAC), and different aging times. Care was taken to apply the technique in conditions where viscous and inertial effects are small. The elastic modulus increases with frequency and then plateaus to an asymptotic value. The asymptotic or instantaneous elasticity has been plotted against the interfacial tension, in...

Air–water gas transfer and near-surface motions

Abstract: Rates of gas transfer between air and water remain difficult to predict or simulate due to the wide range of length and time scales and lack of experimental observations of near-surface fluid velocity and gas concentrations. The surface renewal model (SR) and surface divergence model (SD) provide the two leading models of the process, yet they remain poorly tested by observation because near-surface velocity is difficult to measure. To contribute to evaluation of these models, we apply new techniques called interfacial particle imaging velocimetry (IPIV) and three-dimensional IPIV (3D-IPIV) for measuring water velocities within a millimetre of a moving deformable air–water interface. The latter technique (3D-IPIV) simultaneously measures the air–water interface topography. We apply these techniques to turbulent open-channel water flows and wind-sheared water flows with microscale breaking waves. Additional measurements made for each flow condition are bulk turbulent length scales, bulk turbulent velocity scales, air–water gas transfer rates, friction velocities, and wave characteristics. We analyse these data to test the surface divergence models for interfacial gas transfer. The first test is of predictions from the Banerjee (Ninth International Heat Transfer Conference, Keynote Lectures, vol. 1, 1990, pp. 395–418, Hemisphere Press) surface divergence model for gas transfer for homogeneous isotropic turbulence interacting with a planar free surface. The second test is of predictions from the McCready, Vassiliadou and Hanratty (AIChE J., vol. 32(7), 1986, pp. 1108–1115) surface divergence model, as applied in both open-channel flow and wind-sheared wavy flows. We find the predictions of the Banerjee and McCready et al. models to agree with the experimental data taken for open-channel flow conditions. On the other hand, for wind-driven flows with wind waves we find disagreement between the McCready et al. predictions and our direct measurements of the gas transfer coefficient. The cause of the disagreement is investigated by Lagrangian tracking of surface divergence of surface water patches, and by analysis of the corresponding Lagrangian time series with advection–diffusion concepts. A quantitative criterion based on surface divergence strength and lifetime is proposed to distinguish the effectiveness of each near-surface motion toward causing interfacial gas transfer. Capillary waves are found to contribute to surface divergence but to have too short a time scale to cause interfacial gas transfer. As wind speed increases, the presence and intensity on the air–water interface of capillary waves and other ineffective near-surface motions is diminished by the rise of turbulent wakes from microscale breaking waves thus causing the disagreement of the surface divergence model’s predicted transfer rates with measurements. A model of air–water gas transfer that combines the surface renewal and surface divergence models is formulated and found to agree with the data from both open-channel flows and wind-driven flows without requiring an empirical coefficient.

Search for the rare decay Bs0→μ+μ-

Abstract: We perform a search for the rare decay B-s(0) -> mu(+) mu(-) using data collected by the D0 experiment at the Fermilab Tevatron Collider. This result is based on the full D0 Run II data set corr ...

Management of Gas Pressure and Electrode State of Charge in Alkaline Batteries

Abstract: An inventive, new system that measures gas composition and pressure in the headspace of an aqueous electrolyte battery is described. The system includes a microcontroller that can use the composition and pressure information to connect a third electrode to either the anode(s) or the cathode(s) in order to balance the state of charge between the two. Results have shown that such a system can control the gas pressure inside a sealed flooded aqueous electrolyte battery to remain below 20 kPa (3 psi) and greatly extend the useable life of the battery.

Application of Coupled Lattice Boltzmann and Phase-Field Methods for Multiphase Flow Simulations

Abstract: Coupling of lattice Boltzmann (LB) and phase-field (PF) methods is discussed for simulation of a range of multiphase flow problems The local relaxation and shifting operators make the LB method an attractive candidate for the simulation of the single-phase as well as multiphase flows For simulating interface dynamics, LB methods require to be coupled with an appropriate scheme representing interfacial dynamics To this end, we have used a model based on the order parameter, which could be either an index function or a phase-field variable, and coupled it with a LB solver for the simulation of various classes of complex multi-physics and multiphase flows The LB method is used to compute the flow-field, and, in the case of electrodeposition process modeling, the electro-static potential-field The application of such a coupled LB-PF is illustrated by the solution of a variety of examples Finally, fast simulation of such a coupled algorithm is achieved using the state-of-art numerical solution acceleration techniques involving preconditioning and multigrid approachesCopyright © 2013 by ASME