Pranab Kumar Mondal

Entropy Generation Minimization in an Electroosmotic Flow of Non-Newtonian Fluid: Effect of Conjugate Heat Transfer

We investigate the entropy generation characteristics of a non-Newtonian fluid in a narrow fluidic channel under electrokinetic forcing, taking the effect of conjugate heat transfer into the analysis. We use power-law model to describe the non-Newtonian fluid rheology, in an effort to capture the essential thermohydrodynamics. We solve the conjugate heat transfer problem in an analytical formalism using the thermal boundary conditions of third kind at the outer surface of the walls. We bring out the alteration in the entropy generation behavior as attributable to the rheology-driven alteration in heat transfer, coupled with nonlinear interactions between viscous dissipation and Joule heating originating from electroosmotic effects. We unveil optimum values of different parameters, including both the geometric as well as thermophysical parameters, which lead to the minimization of the entropy generation rate in the system. We believe that the inferences obtained from the present study may bear far ranging consequences in the design of various cooling and heat removal devices/systems, for potential use in microscale thermal management.

Electroosmosis of Powell–Eyring fluids under interfacial slip

We investigate the EOF of a Powell–Eyring fluid through a slit microchannel, employing Navier slip boundary condition. Using an analytical scheme consistent with the homotopy perturbation method, we bring out the alteration in the underlying flow dynamics as attributable to the nonlinear interactions between fluid rheology and electrostatics over interfacial scales. We validate the approximate analytical solutions by comparing those with results from numerical analysis. We unveil a regime of phenomenal amplification in the net volumetric flow rate, realized as a consequence of an intricate interplay between interfacial electromechanics, slipping hydrodynamics, and the flow rheology. Our results may have far ranging consequences in the design of various biomicrofluidic devises/systems, which are often used for the manipulation of non‐Newtonain fluids.

Viscous dissipation effects on the limiting value of Nusselt numbers for a shear-driven flow through an asymmetrically heated annulus

In this study, an analytical investigation for analyzing the effects of viscous dissipation on the limiting Nusselt number for a hydro-dynamically fully developed laminar shear-driven flow through an asymmetrically heated annulus of two infinitely long concentric cylinders has been made, where the inner cylindrical rod is moving in an axial direction at a constant speed. On the basis of some common assumptions, an analytical framework has been devised to explore the effects of viscous dissipation on the heat transfer characteristics for the flow of Newtonian fluid, and, consequently, closed-form expressions for the limiting Nusselt numbers are evaluated. In the analysis, focus has been given on the viscous dissipative effect due to the shear produced by the movable inner cylindrical rod apart from the viscous dissipation due to internal fluid friction for the flow of a Newtonian fluid. The interactive effects of the Brinkman number and degree of asymmetry on the limiting Nusselt number are analytically investigated. It is observed from this study that the limiting Nusselt number becomes independent of Brinkman number when both the walls of the annulus are kept at an equal temperature. Moreover, the temperature profile in the conduction limit obtained with the consideration of viscous dissipation effect provides a boundary condition required for solving energy equation including the axial conduction in the fluid.

Erratum to: Thermodynamically Consistent Limiting Forced Convection Heat Transfer in a Asymmetrically Heated Porous Channel: An Analytical Study

Fluid transport and the associated heat transfer through porous media is of immense importance because of its numerous practical applications. In view of the widespread applications of porous media flow, the present study attempts to investigate the forced convective heat transfer in the limiting condition for the flow through porous channel. There could be many areas, where heat transfer through porous channel attain some limiting conditions, thus, the analysis of limiting convective heat transfer is far reaching. The primary aim of the present study is focused on the limiting forced convection analysis considering the flow of Newtonian fluid between two asymmetrically heated parallel plates filled with saturated porous media. Utilizing a few assumptions, which are usually employed in the literature, an analytical methodology is executed to obtain the closed-form expression of the temperature profile, and in the following the expression of the limiting Nusselt numbers. The parametric variations of the temperature profile and the Nusselt numbers in different cases have been shown highlighting the influential role of different performance indexing parameters, like Darcy number, porosity of the media, and Brinkman number of forced convective heat transfer in porous channel. In doing so, the underlying physics of the transport characteristics of heat has been delineated in a comprehensive way. Moreover, a discussion has been made regarding an important feature like the onset of point of singularity as appeared on the variation of the Nusselt number from the consideration of energy balance in the flow field, and in view of second law of thermodynamics.

Electroosmotic transport of immiscible binary system with a layer of non-conducting fluid under interfacial slip: The role applied pressure gradient.

We investigate the transport of immiscible binary fluid layers, constituted by one conducting (top layer fluid) and another non‐conducting (bottom layer fluid) fluids in a microfluidic channel under the combined influences of an applied pressure gradient and imposed electric field. We solve the transport equation governing the flow dynamics analytically and obtain the closed‐form expressions of the velocity fields. We bring out the alteration in the flow dynamics, mainly attributable to the non‐linear interaction between interfacial slip and the electrical double layer effect over small scales as modulated by the applied pressure gradient. In particular, we show the augmentation in the net volume transport rate through the channel, emerging from an intricate competition among electrical forcing, applied pressure gradient and the viscous resistance as modulated by the interfacial slip. We believe that the results of this study may be of immense consequence for the design of various microfluidic devises, which are often used for the manipulation of two immiscible fluids in different biomedical/biochemical processes.

Contact line dynamics of electroosmotic flows of incompressible binary fluid system with density and viscosity contrasts

We consider electrically driven dynamics of an incompressible binary fluid, with contrasting densities and viscosities of the two phases, flowing through narrow fluidic channel with walls with predefined surface wettabilities. Through phase field formalism, we describe the interfacial kinetics in the presence of electro-hydrodynamic coupling and address the contact line dynamics of the two-fluid system. We unveil the interplay of the substrate wettability and the contrast in the fluid properties culminating in the forms of two distinct regimes—interface breakup regime and a stable interface regime. Through a parametric study, we demarcate the effect of the density and viscosity contrasts along with the electrokinetic parameters such as the surface charge and ionic concentration on the underlying contact-line-dynamics over interfacial scales.

Entropy analysis for the Couette flow of non-Newtonian fluids between asymmetrically heated parallel plates: effect of applied pressure gradient

The current study discusses the irreversibility analysis for the Couette flow of non-Newtonian fluids between two asymmetrically heated parallel plates for two different flow configurations viz., under the application of a weak pressure gradient and for a relatively strong pressure gradient. The plates are kept at different constant temperatures, while the effect of viscous dissipation is included in the analysis. The study explores the combined consequences of the rheological effect of the fluids, the movement of the upper plate, and the magnitude of the externally applied pressure gradient on the irreversibility generation rate of the system as manifested by the variation of the volumetric entropy generation number, irreversibility distribution ratio, and the Bejan number. Intricate interplay between the effects of fluid friction and heat transfer in dictating the irreversibility of the system is highlighted for different degrees of asymmetrical wall heating and upper-plate velocity. The study further shows that, for a given degree of asymmetrical wall heating, the irreversibility generation rate alters with the alteration in the rheological behaviour of the fluid.

Pulsating flow driven alteration in moving contact-line dynamics on surfaces with patterned wettability gradients

The contact line dynamics over surfaces patterned with wettability gradients under pulsating flow condition are of essential importance in application areas ranging from the design of smart and effective microfluidic devices to the understanding of blood flow dynamics in narrow conduits. In the present study, we probe the capillary filling dynamics in a pulsatile flow environment, in an effort to explore the underlying flow physics. Presenting the results of frequency assisted contact line motion of two immiscible fluids over surfaces patterned with wettability gradients, we show how the interfacial dynamics are affected by the interplay of both the surface characteristics and flow pulsation. Our results reveal that the competition between two control parameters, the frequency and the amplitude of the imposed flow pulsation, may effectively be tuned to control the capillary filling dynamics significantly. The study, we present here, also suggests that by suitably tuning the control parameters, it is possible to control the capillary residence time over engineered locations which may, in turn, facilitate improved mixing and/or design of chemically active reaction stations.

Effect of thermal asymmetries on the entropy generation analysis of a variable viscosity Couette–Poiseuille flow

The influence of viscous dissipation on forced convective heat transfer and entropy generation rate in the conduction limit for a variable-viscosity flow between asymmetrically heated parallel plates is studied in an analytical framework consistent with perturbation method. The study considers a flow of Newtonian fluid under the simultaneous action of an applied pressure gradient and an axial movement of the upper plate. The present study emphasizes on the effect of dissipative heat produced by the movable upper plate as well as viscous heating generated due to applied pressure gradient on the underlying thermo-hydrodynamic transport. A few non-dimensional parameters such as dimensionless upper plate velocity, degree of asymmetry parameter and Brinkman number have been defined and their influential role on the variation of temperature profile, the Nusselt number and entropy generation number has been discussed in detail. The study shows that the variation of Nusselt number exhibits an unbounded swing, which, in turn, leads to appearance of the point of singularities at some cases of asymmetrical plate heating. Finally, the source of appearance of point of singularities has been discussed in view of the energy balance, and from the second-law analysis of thermodynamics.

Towards the minimization of thermodynamic irreversibility in an electrically actuated microflow of a viscoelastic fluid under electrical double layer phenomenon

We discuss the entropy generation minimization for electro-osmotic flow of a viscoelastic fluid through a parallel plate microchannel under the combined influences of interfacial slip and conjugate transport of heat. We use in this study the simplified Phan-Thien–Tanner model to describe the rheological behavior of the viscoelastic fluid. Using Navier’s slip law and thermal boundary conditions of the third kind, we solve the transport equations analytically and evaluate the global entropy generation rate of the system. We examine the influential role of the following parameters on the entropy generation rate of the system, viz., the viscoelastic parameter (eDe2), Debye–Huckel parameter κ ¯ , channel wall thickness (δ), thermal conductivity of the wall (γ), Biot number (Bi), Peclet number (Pe), and axial temperature gradient (B). This investigation finally establishes the optimum values of the abovementioned parameters, leading to the minimum entropy generation of the system. We believe that results of thi...