U N I V E R S I T Y     O F     N E W    H A M P S H I R E






go to top


go to top


go to top


go to top

The focus of my research is to understand multiphase flows of Newtonian and viscoelastic fluids using analytical, numerical, and experimental tools. Two-phase systems with surface tension gradients and elastic effects are encountered in a variety of applications such as materials, polymer, and food processing, pharmaceuticals, and microfluidics. The prediction of two-phase flow of Newtonian fluids is difficult because the location of the interface between the two immiscible phases is not known a priori and needs to be determined as part of the solution. The interface between two fluid phases is often characterized by a single property, the interfacial tension. Variation of interfacial tension along an interface leads to tangential stresses that are known as Marangoni stresses. Temperature gradient or a gradient in concentration of surface-active agents (surfactants) along the interface leads to surface tension variation along the interface. This complicates the problem as the temperature or the concentration distribution of the surfactant needs to be determined before the shape of the interface can be predicted. Furthermore, if the bulk fluids exhibit viscoelasticity, they can store energy to some extent and display partial recovery upon removal of stress. The fundamental issues of how surface tension gradients affect free surface flows, how surfactants can be added to control flows, and how elasticity in the bulk phase changes the deformation and break up of a dispersed fluid phase are explored in confined domains such as a Hele-Shaw cell, a rectangular channel, or a cylindrical capillary.

Some of the ongoing projects in my research group are:

Capsule Dynamics in Channels

Manipulation of single cells in microfluidic devices has gained momentum in the last decade with the development of novel microdevices for in vitro fertilization, cell-culture studies, forensic analysis, and diagnosis of diseases such as cancer, diabetes, and malaria. The overall research objectives of this project are to determine: (a) the effect of inertia on the three-dimensional non-axisymmetric motion of capsules in channels, (b) the effect of a non-uniform confining wall on capsule dynamics, and (c) the effect of the presence of another capsule in the vicinity.

Motion of drops and bubbles in confined domains at finite Reynolds numbers

The deformation and breakup of drops in a confined fluid medium is a problem of great practical importance in a variety of natural and physical processes such as motion of blood cells in capillaries as well as a host of industrial applications such as polymer processing, two-phase flows in microfluidic devices. We are conducting a combined experimental and numerical study of the three-dimensional motion of a drop/bubble in capillaries and channels of varying length scales. Numerically, the coupling between the momentum balance and the surfactant balance in two-phase flows will be handled using a hybrid volume-of-fluid (VOF) algorithm developed in our group. Unlike the VOF method, the interface is tracked explicitly as a Lagrangian grid and this scheme ensures that the shape and the normals and curvatures at the interface are represented accurately. Hence, the numerical technique can model strongly deforming interfaces with large density and viscosity ratios. Many fluids of interest such as glass-forming liquids, polymer melts and solutions, and micellar solutions exhibit viscoelastic behavior. Unlike Newtonian fluids, viscoelastic materials have the ability to store energy to some extent and thereby display partial recovery upon the removal of applied stress. Many interesting two-phase phenomena such as two-dimensional cusps at the trailing end of bubbles and velocity discontinuity have been attributed to the elasticity of the fluid phases. Experiments and numerical studies of the effects of elasticity on the motion of fluid particles in confined domains is currently underway. Being able to predict the mobility and deformation of viscoelastic drops in confined domains helps us to choose appropriate operating conditions to stabilize (as in emulsions) or eliminate (as in polymer systems) fluid droplets in a bulk fluid medium.

Thermocapillary Flow in Double-layer Fluid Structures
Collaborator: A. Borhan, H. Haj-Hariri

Thermocapillary flows are of considerable technological importance in materials processing applications such as crystal growth particularly under microgravity conditions where the influence of buoyancy-driven convection is minimized. We numerically analyze the thermally-driven convection within a differentially-heated rectangular or cylindrical cavity containing two immiscible liquid layers in the absence of gravity. We have developed a single-layer model which accurately predicts the flow in the double-layer system even for large aspect ratios.

go to top


Graduate Students

Brian Zukas (PhD: Expected 2016)
Xiameng Liu (MS: Expected 2015)
Brett Kolmeister (MS: Expected 2016)

Undergraduate Students

Christopher Blais
Ana Lidia Dos Santos

Former Graduate Students

Brian Zukas (MS 2014)
Robert Carroll (PhD 2014)
Yuanyuan Cui (PhD 2011)
Weihua Li (MS 2011)
Michael O'Connor (MS 2009)
Vinod Bulusu (MS 2006)

go to top


Hemmati, S., Barkey, D. P, Gupta, N., and Banfield, R., ``Synthesis and characterization of silver nanowire suspensions for printable conductive media,'' ECS J. Solid State Sci. Technol., 4(4), P3075-P3079 (2015).

Carroll, R. M. and Gupta, N. R. ``Inertial and surfactant effects on the steady droplet flow in cylindrical channels,'' Phys. Fluids, 26, 122102 (2014).

Gupta, N. R., Haj-Hariri, H., and Borhan, A. , ``Effect of free surface heat transfer on thermocapillary flow in double-layer fluid structures,'' Heat Mass Transfer , 50, 333-339 (2014).

Cui, Y. and Gupta, N. R. ``Surfactant effects on drop formation in co-flowing fluid streams,'' Colloids and Surfaces A: Physicochem. Eng. Aspects, 393, 111-121 (2012).

Cui, Y. and Gupta, N. R. ``Drop formation in co-flowing fluid streams,'' Int. J. Trans. Phenomena, 12(3-4), 217-226 (2011).

Li, J., Bulusu, V., and Gupta, N. R., ``Buoyancy-driven motion of bubbles in square channels,'' Chem. Eng. Sci., 63(14), 3766-3774 (2008).

Gupta, N. R., Haj-Hariri, H., and Borhan A., ``Thermocapillary convection in double-layer fluid structures within a two-dimensional open cavity,'' J. Colloid Interface Sci., 315(1), 237-247 (2007).

Gupta, N. R., Haj-Hariri, H., and Borhan A., ``Thermocapillary Flow in Double-Layer Fluid Structures,'' Ann. N. Y. Acad. Sci., 1077, 395-414 (2006).

Jin, F., Gupta, N. R., and Stebe, K. J., ``The detachment of a viscous drop in a viscous solution in the presence of a soluble surfactant,'' Phys. Fluids, 18(2), 022103 (2006).

Gupta, N. R., Haj-Hariri, H., and Borhan A., ``Thermocapillary Flow in Double-Layer Fluid Structures: An Effective Single-Layer Model,'' J. Colloid Interface Sci., 293(1), 158-171 (2006).


Borhan, A. and Gupta, N. R., ``Capsule motion and deformation in tube and channel flow,'' in Modeling and Simulation of Capsules and Biological Cells, Ed. C. Pozrikidis, Chapman & Hall / CRC (2003).

go to top

Last Updated: February 24, 2015