Aniket S. Ambekar’s research while affiliated with Indian Institute of Technology Delhi and other places

Liquid spreading through a randomly packed particle-resolved bed influenced by capillary or inertial ( $AB_s \sim 1$ ), and gravitational force (moderately ( $AB_s \sim 0.1$ ) and strongly ( $AB_s \sim 0.01$ )) is investigated using the volume-of-fluid simulations. The relative contribution of governing forces at different stages of spreading is analysed using the time evolution of Weber ( $We_I$ ) and $AB_I$ numbers. We show that the dynamics of liquid spreading at $AB_s \sim 1$ is primarily governed by the inertial force in the beginning ( $AB_I > 1$ , $We_I > 1$ ) followed by the capillary force at $t/t^* \sim 1$ . This interplay of governing forces leads to inertia- and capillary-induced bubble entrapments at the void scale and promote lateral liquid spreading. When the $AB_s \sim 0.1$ , the $t/t^*$ for which the flow is governed by inertial ( $AB_I > 1$ , $We_I > 1$ ) and capillary forces ( $AB_I > 1$ , $We_I < 1$ ) decreases and the relative contribution of gravitational force is substantial at large $t/t^*$ ( $AB_I < 1$ ). This force balance leads to unified-void filling characterised by negligible bubble trapping and results in a decrease in the lateral spreading. Further decrease in the $AB_s$ to ${\sim } 0.01$ results in liquid spreading primarily governed by gravitational force ( $AB_I < 1$ ) with small contribution of inertial and capillary forces at the very beginning leading to trickling flow and a further decrease in lateral spreading. Finally, a regime map is proposed, which provides the relationship between different forces, void-scale events, and the resultant liquid spreading at $t/t^* \sim 1$ .

Packed beds are widely used to perform solid-catalyzed gas–liquid reactions, e.g., hydrodesulfurization, oxidation, and hydrogenation. The overall performance of packed beds is often governed by local liquid spreading. In the present work, the dynamics of liquid spreading through a randomly packed three-dimensional bed is investigated using particle-resolved volume-of-fluid simulations. The effect of particle surface-wettability ([Formula: see text]) at varying particle diameter ([Formula: see text]) on the relative contributions of forces governing the dynamics of liquid spreading is analyzed using the Ohnesorge ([Formula: see text]), Weber ([Formula: see text]), and [Formula: see text] (proposed in the present work) numbers. With the help of simulated liquid spreading and these numbers, we show that the contribution of inertial force is significant at the beginning of liquid spreading irrespective of [Formula: see text] as well as [Formula: see text] and promotes lateral liquid spreading ([Formula: see text] >1, [Formula: see text] >1). Once the dominance of inertial force diminishes, the capillary force leads to a substantial increase in the lateral spreading ([Formula: see text] > 1, [Formula: see text] < 1). In the final stages, the gravitational force dominates restricting the lateral liquid spreading ([Formula: see text] < 1). Furthermore, we have proposed a regime map constructed using [Formula: see text] and [Formula: see text], which provides a relationship between different forces and the resultant liquid spreading at breakthrough. We also show that the dominance of capillary force ([Formula: see text] >1, [Formula: see text] <1) results in the highest lateral spreading, whereas the flow dominated by inertial ([Formula: see text] >1, [Formula: see text] >1) and gravitational force ([Formula: see text] ≪ 1) leads to intermediate and least lateral liquid spreading, respectively.

Packed bed reactors are widely used to perform solid‐catalyzed gas‐phase reactions and local turbulence is known to influence heat and mass transfer characteristics. We have investigated turbulence characteristics in a packed bed of 113 spherical particles by performing particle‐resolved Reynolds‐averaged Navier–Stokes (RANS) simulations, Large Eddy Simulation (LES), and Direct Numerical Simulation (DNS). The predictions of the RANS and LES simulations are validated with the lattice Boltzmann method (LBM)–based DNS at particle Reynolds number (Rep) of 600. The RANS and LES simulations can predict the velocity, strain rate, and vorticity with a reasonable accuracy. Due to the dominance of enhanced wall‐function treatment, the turbulence characteristics predicted by the ε‐based models are found to be in a good agreement with the DNS. The ω‐based models under‐predicted the turbulence quantities by several orders of magnitude due to their inadequacy in handling strongly wall‐dominated flows at low Rep. Using the DNS performed at different Rep, we also show that the onset of turbulence occurs between 200≤Rep≤250.

In the present work, high-speed imaging experiments are performed to measure the time-evolution of two-phase oil-water flow, water-saturation, oil ganglia number and size distribution in a pseudo-3D porous medium. The corresponding pore-resolved simulations are performed using the Volume-of-Fluid (VOF) method and predictions are validated using the aforementioned measurements. The experimentally-validated VOF model is used to understand the effects of water-flooding velocity and interfacial tension [i.e. Capillary number (Ca)] on the pore-scale oil recovery mechanisms. The pore-resolved VOF simulations reveal that the drainage phenomenon is dominated by Haines-jump events at low Ca values. The increase in Ca values results in the decrease in the frequency of Haines-jump events and after the transitional Ca, the drainage phenomenon is no longer governed by Haines-jump events and is governed by viscous fingering. Finally, VOF simulations are used to analyze the effect of successive step changes in the interfacial tension on the oil recovery.

Imbibition of viscous fluids in capillaries is important in diagnostics, design of microfluidic devices and enhanced oil recovery. The imbibition of a viscous wetting fluid in a capillary follows Lucas-Washburn law. The Lucas-Washburn regime is only observed when the viscous forces are balanced by the capillary forces. This has been previously described for capillary driven flow as a function of the Ohnesorge number (Oh), the length imbibed by the fluid (x) and the radius (r), for a capillary initially filled with fluid of negligible viscosity, i.e., Ohxr∼1. We show using VOF simulations that, in a capillary of length L initially filled with a viscous fluid, the modified Lucas-Washburn law is observed only if the criterion OhLr∼1 is fulfilled. We use VOF simulations to show the deviation of capillary driven flow from the classical Lucas-Washburn behavior for OhLr∼0.1. VOF simulations for forced imbibition in the regime preceding the Lucas-Washburn regime for a single capillary show that with increase in the applied pressure, the advancement of the meniscus is faster. Forced imbibition dynamics in the interacting capillary geometry are also investigated in this study using VOF simulations. We observe that the leading meniscus in the interacting capillaries is significantly dependent on the applied pressures. We also show using VOF simulations that the wettability of the imbibing fluid plays a crucial role in determining the dynamics in an interacting capillary system.

Immiscible displacement of a non-wetting fluid by a wetting fluid is important for many fields for example, biomedical devices, paper micro-fluidics, oil reservoirs and water aquifers. In a multi-layered porous medium the displacement velocity and relative position of the layers with respect to each other is significant in determining the flow paths of the fluids. Earlier studies on two-layered porous medium indicate presence of different flow regimes in every layer depending upon the velocity. However, the effect of relative positioning of these layers in different flow regimes is still unknown. In the present work we experimentally show that at low velocity, a capillary regime is developed i.e. the wetting fluid front leads in the least permeable layer, while at high velocity the wetting fluid front leads in the highest permeability layer. At all flow rates, the least permeable layer is found to draw fluid from the high permeability layer due to capillary suction. We also show the effect of relative placement of the layers on the interphase dynamics.