Anugrah Singh

Slip velocity of concentrated suspensions in Couette flow

We present measurement of wall slip velocity in concentrated suspension of non-colloidal particles. The slip in non-colloidal concentrated suspension mainly arises from wall depletion effect since the non-hydrodynamic effects such as those arising from particle-wall interactions can be small. In this work, we provide a simple methodology for the determination of slip velocity, which requires less experimental work compared to other methods available for slip corrections. The experiments were carried out in a cylindrical Couette geometry of a rheometer. The rheological measurements were carried out first with serrated cup and serrated rotor geometry. Next, the serrated rotor was made smooth by a wax coating while the cup remained serrated. The serrated geometry offers no-slip boundary and the measured viscosity is the true viscosity of suspension, whereas smooth rotor showed significant slip at a higher concentration of particles and the measured viscosity was significantly lower. Comparing the wall shear ...

Fluid Flow and Particle Dynamics Inside an Evaporating Droplet Containing Live Bacteria Displaying Chemotaxis

Evaporation-induced particle deposition patterns like coffee rings provide easy visual identification that is beneficial for developing inexpensive and simple diagnostic devices for detecting pathogens. In this study, the effect of chemotaxis on such pattern formation has been realized experimentally in drying droplets of bacterial suspensions. We have investigated the velocity field, concentration profile, and deposition pattern in the evaporating droplet of Escherichia coli suspension in the presence and absence of nutrients. Flow visualization experiments using particle image velocimetry (PIV) were carried out with E. coli bacteria as biological tracer particles. Experiments were conducted for suspensions of motile (live) as well as nonmotile (dead) bacteria. In the absence of any nutrient gradient like sugar on the substrate, both types of bacterial suspension showed two symmetric convection cells and a ring like deposition of particles after complete evaporation. Interestingly, the droplet containing live bacterial suspension showed a different velocity field when the sugar was placed at the base of the droplet. This can be attributed to the chemoattractant nature of the sugar, which induced chemotaxis among live bacteria targeted toward the nutrient site. Deposition of the suspended bacteria was also displaced toward the nutrient site as the evaporation proceeded. Our experiments demonstrate that both velocity fields and concentration patterns can be altered by chemotaxis to modify the pattern formation in evaporating droplet containing live bacteria. These results highlight the role of bacterial chemotaxis in modifying coffee ring patterns.

Experimental investigation of interface deformation in free surface flow of concentrated suspensions

It is well known that during the free surface flow of concentrated suspension of non-colloidal particles, the suspension-air interface becomes highly corrugated. This surface corrugation changes the interfacial area which could have important implications in various applications involving heat and mass transfer across the interface. Surface corrugation in free surface flow has been studied in the past, but its mechanism is not fully understood. We report detailed experiments on quantitative measurement of the surface deformation of concentrated suspension of non-colloidal particles in open channel flow. The motion and location of the interface and the velocity field of the bulk flow beneath the free surface were measured using the particle image velocimetry technique. Experiments were performed to study the effect of particle size, particle concentration, and viscosity of suspending fluid on the corrugation. The interface fluctuation was found to increase linearly with the flow rate. The deformation of th...

Petroleum Reservoir Simulation of Two-Phase Flow

Numerical solution of governing equations of two-phase immiscible flow in porous media is presented. The mathematical equations are built by combining the conservation of mass with Darcys law which describes fluid flow through porous media. The resulting partial differential equations were solved using Implicit Pressure and Explicit Saturation method (IMPES). We have implemented the IMPES method in open source CFD toolbox OpenFOAM, which uses finite volume method to solve PDEs. The underlying advantage of using general purpose CFD solver for reservoir simulation is the possible extension of simulation technique to enhanced oil recovery methods involving simultaneous fluid flow, heat transfer, mass transfer and chemical reactions. Simulations were carried out for water displacing oil in homogeneous as well as heterogeneous reservoirs. The simulation method was validated by comparing the results with analytical solution and numerical solution of Matlab Reservoir Simulation Toolbox (MRST). The displacement efficiency and water breakthrough of various flooding patterns were evaluated.

Shear-induced migration of concentrated suspension through Y-shaped bifurcation channels

ABSTRACT Transport of suspension through bifurcation channels has many scientific and engineering applications, particularly in industrial and biological processes. At moderate concentrations, the shear-induced migration of particles in pressure-driven channel flow causes nonuniform concentration profile. The velocity profile also shows significant deviation from the Newtonian fluid behavior. The phenomenon of shear-induced migration has been well studied for straight channels and tubes, but there are few studies on channels with bifurcations. We have used the diffusive flux model to study the particle migration during transport of concentrated suspension of neutrally buoyant particles in Y-shaped two-dimensional (2D) bifurcation channels. The governing equations of continuity, momentum, and particle transport were solved to obtain the velocity and particle concentration profiles in the channel. The effect of particle size, bifurcation angle, bulk concentration, and flow rate on the velocity and concentration profile was studied. The velocity profile in the case of concentrated suspension differs significantly from that of Newtonian fluid of the same effective viscosity. Near the bifurcation section, the velocity profile for suspension flow is blunted, and at larger bifurcation angles peak-valley-peak–shaped profile is observed. The velocity and concentration profile in the inlet section remains symmetric, but significant asymmetry is observed in the daughter branches due to shear-induced particle migration.