Suvankar Ganguly

Analysis of Entropy Generation During Mixed Convective Heat Transfer of Nanofluids Past a Square Cylinder in Vertically Upward Flow

The present work demonstrates entropy generation due to laminar mixed convection of water-based nanofluid past a square cylinder in vertically upward flow. Streamline upwind Petrov–Galerkin (SUPG) based finite element method is used for numerical simulation. Nanosized copper (Cu) and alumina (Al2O3) particles suspended in water are used with Prandtl number (Pr)1⁄4 6.2. The range of nanoparticle volume fractions considered is 0–20%. Computations are carried out at a representative Reynolds number (Re) of 100 with Richardson number (Ri) range 0.5<Ri< 0.5, both values inclusive. For both the nanofluids (Al2O3–water and Cu–water nanofluids), total entropy generation decreases with increasing nanoparticle volume fractions. It is found that for the present case of mixed convection flows with nanofluids, thermal irreversibility is much higher than that of frictional irreversibility. The Bejan number decreases with increasing nanoparticle volume fractions. [DOI: 10.1115/1.4007411]

Effective viscosity of nanoscale colloidal suspensions

A comprehensive model for predicting the effective viscosity of dilute suspensions of nanoscale colloidal particles is presented in this work. The physics of complex interparticle interaction mechanisms is considered in details to characterize the rheological features of the suspension (nanofluid), expressed in terms of the effective viscosity variations as functions of the particle fraction. This is accomplished by addressing the details of the agglomeration-deagglomeration kinetics in a spatio-temporally evolving manner, in tune with the pertinent variations in the effective particulate dimensions, volume fractions, as well as the aggregate structure of the particulate system. Detailed analysis of the results reveals a profound influence of the combined particle agglomeration and breakup features as well as the interparticle interaction potentials on the rheological characteristics of the nanofluid. Predictions from the model agree well with the experimental results reported in the literature.

Analysis of Entropy Generation During Mixed Convective Heat Transfer of Nanofluids Past a Rotating Circular Cylinder

The entropy generation due to mixed convective heat transfer of nanofluids past a rotating circular cylinder placed in a uniform cross stream is investigated via streamline upwind Petrov-Galerkin based finite element method. Nanosized copper (Cu) particles suspended in water are used with Prandtl number (Pr)=6.9. The computations are carried out at a representative Reynolds number (Re) of 100. The dimensionless cylinder rotation rate, a, is varied between 0 and 2. The range of nanoparticle volume fractions (phi) considered is 0 <= phi <= 5%. Effect of aiding buoyancy is brought about by considering two fixed values of the Richardson number (Ri) as 0.5 and 1.0. A new model for predicting the effective viscosity and thermal conductivity of dilute suspensions of nanoscale colloidal particles is presented. The model addresses the details of the agglomeration-deagglomeration in tune with the pertinent variations in the effective particulate dimensions, volume fractions, as well as the aggregate structure of the particulate system. The total entropy generation is found to decrease sharply with cylinder rotation rates and nanoparticle volume fractions. Increase in nanoparticle agglomeration shows decrease in heat transfer irreversibility. The Bejan number falls sharply with increase in alpha and phi.

Dispersion characteristics of blood during nanoparticle assisted drug delivery process through a permeable microvessel.

Nanoparticle assisted drug delivery holds considerable promise as a means of next generation of medicine that allows for the intravascular delivery of drugs and contrast agents. We analyze the dispersion characteristics of blood during a nanoparticle-assisted drug delivery process through a permeable microvessel. The contribution of molecular and convective diffusion is based on Taylors theory of shear dispersion. The aggregation of red blood cells in blood flowing through small tubes (less than 40 μm) leads to the two-phase flow with a core of rouleaux surrounded by a cell-depleted peripheral layer. The core region models as a non-Newtonian Casson fluid and the peripheral region acts as a Newtonian fluid. We investigate the influence of the nanoparticle volume fraction, the permeability of the blood vessel, pressure distribution, yield stress and the radius of the nanoparticle on the effective dispersion. We show that the effective diffusion of the nanoparticles reduces with an increase in nanoparticle volume fraction. The permeability of the blood vessels increases the effective dispersion at the inlet. The present study contributes to the fundamental understanding on how the particulate nature of blood influences nanoparticle delivery, and is of particular significance in nanomedicine design for targeted drug delivery applications.

Numerical simulation of transport phenomena in electromagnetically stirred semi-solid materials processing

A continuum based integrated mathematical model is developed to analyse momentum, heat and solute transport during an electromagnetically stirred semi-solid materials processing operation. Separate conservation equations are solved to determine the solid phase velocity. Simultaneously, a solid fraction transport equation is solved to take into account the transport of fragmented dendrites and solidification of liquid phases present in the respective elemental volumes. Numerical simulations are performed to reveal the relative contributions of buoyancy and electromagnetic forces. The mathematical model is also tested by confronting present numerical results with reported experimental observations; an excellent agreement can be observed in this regard, thereby establishing the authenticity of the proposed formulation.

Effect of Channel Confinement on Mixed Convective Flow Past an Equilateral Triangular Cylinder

The present work investigates the mixed convective flow and heat transfer characteristics past a triangular cylinder placed symmetrically in a vertical channel. At a representative Reynolds number, Re = 100, simulations are carried out for the blockage ratios beta = 1/3; 1/4; and 1/6. Effect of aiding and opposing buoyancy is brought about by varying the Richardson number in the range -1.0 0: 75 is observed at beta = 1/3.

A Generalized Enthalpy-based Macro Model for Ternary Alloy Solidification Simulations

In this article, a generalized macroscopic mathematical model is developed to simulate the transport phenomena occurring during the solidification of ternary alloy systems. The model is essentially based on a fixed-grid, enthalpy-based control-volume approach. Microscopic features pertaining to complex thermosolutal transport mechanisms are incorporated through a novel formulation of latent enthalpy evolution, consistent with the phase-change morphology of general multicomponent alloy systems. Numerical simulations are performed for two different ternary steel alloys of apparently contrasting thermosolutal transport characteristics, and the resulting convection and macrosegregation patterns are analyzed in detail. The mathematical model is also tested by comparing the present numerical results with benchmark analytical solutions and experimental data reported in the literature for ternary alloy solidification systems, and excellent agreement is found in this regard.

Determination of the aggregate fractal dimensions in colloidal nanofluids

Owing to the significant technological implications of nanoscale colloidal suspensions (nanofluids), it is necessary to develop suitable techniques to characterize the nanostructured aggregates in suspension. In the present work, a fractal dimension approach is applied to characterize the agglomerate structure using image analysis by scanning electron microscope photographs of the nanoparticle aggregates. Aqueous suspensions of aluminum oxide nanoparticles (nanofluids) are used for the study. A simple and direct method of projected image manipulation has been used to calculate the aggregate fractal dimensions in colloidal nanofluid. The fractal dimension provides quantitative information about important morphological features of the aggregate structure. A functional relationship is established between the two-dimensional fractal dimension (df2) and the three-dimensional fractal dimension (df3). The present study demonstrates that the optical image analysis technique can be effectively used for fractal dimension analysis of colloidal nanoparticle aggregates.

Numerical analysis of particle transport during solidification using models based on stochastic differential equation

Abstract In the present work, a comprehensive theoretical model is developed to describe the particle transport mechanisms in a solidifying binary melt in the presence of random thermofluidic fluctuations offered by the surrounding fluid medium. The detailed transport phenomena in the particle and bulk phases are coupled together through a stochastic formalism, capturing the physical mechanisms and consequences of complex interparticle interactions and the associated growth and/or dissolution of the crystals. The equation of the motion of the particles is modelled using the theory of stochastic differential equations. Numerical simulation study reveals the statistically randomised nature of the evolution of particle phase, which otherwise cannot be captured from a purely deterministic viewpoint. The mathematical model is also tested by comparing present numerical results with reported experimental observations; a very good agreement can be observed in this regard, thereby establishing the authenticity of the proposed formulation.