Department of Chemical Engineering

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    Effects of overlapping electric double layer on mass transport of a macro-solute across porous wall of a micro/nanochannel for power law fluid
    (Wiley, 2017-03) Bhattacharjee, Saikat
    Effects of overlapping electric double layer and high wall potential on transport of a macrosolute for flow of a power law fluid through a microchannel with porous walls are studied in this work. The electric potential distribution is obtained by coupling the Poisson's equation without considering the Debye–Huckel approximation. The numerical solution shows that the center line potential can be 16% of wall potential at pH 8.5, at wall potential −73 mV and scaled Debye length 0.5. Transport phenomena involving mass transport of a neutral macrosolute is formulated by species advective equation. An analytical solution of Sherwood number is obtained for power law fluid. Effects of fluid rheology are studied in detail. Average Sherwood number is more for a pseudoplastic fluid compared to dilatant upto the ratio of Poiseuille to electroosmotic velocity of 5. Beyond that, the Sherwood number is independent of fluid rheology. Effects of fluid rheology and solute size on permeation flux and concentration of neutral solute are also quantified. More solute permeation occurs as the fluid changes from pseudoplastic to dilatant.
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    Experimental and modeling of fluoride removal using aluminum fumarate (AlFu) metal organic framework incorporated cellulose acetate phthalate mixed matrix membrane
    (Elsevier, 2017-12) Bhattacharjee, Saikat
    Selective adsorption of small sized contaminant by inorganic component incorporated in a polymeric membrane in addition to separation of total solids, iron, alkalinity and hardness makes mixed matrix membrane (MMM) a unique filtration medium. Significant separation of tiny pollutants along with high throughput at low operating pressure is the remarkable feature of MMM. Aluminum fumarate metal oxide framework (MOF), a super adsorbent for fluoride was included in cellulose acetate phthalate as base polymer to prepare a novel MMM for removal of fluoride from contaminated groundwater. The membranes were characterized by porosity, permeability, molecular weight cut off and contact angle. The morphology and the surface roughness were studied by scanning electron and atomic force microscope. The adsorption capacity of the membranes for fluoride varied from 107 to 179 mg g−1 for MOF concentration of 2 to 10 wt%. The fluoride rejection was more than 99% for 10% AlFu concentration. The life of the membrane was determined using a continuous cross flow setup with membrane area of 0.01 m2 and it was found to be 17 h for a feed concentration of 10 mg L−1 of fluoride in synthetic solution. Regeneration study and performance of the MMM in real life ground water samples were also investigated. The study provides a promising, scalable technology using MMM for fluoride mitigation by combining high throughput, selective separation of fluoride and general filtration including removal of total dissolved solids, hardness, alkalinity and iron.
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    Aluminium fumarate metal organic framework incorporated polyacrylonitrile hollow fiber membranes: spinning, characterization and application in fluoride removal from groundwater
    (Elsevier, 2018-02) Bhattacharjee, Saikat
    Novel mixed matrix hollow fiber membranes (MMM) were prepared by phase inversion technique using polyacrylonitrile (PAN) as base polymer and aluminium fumarate (AlFu) metal organic framework (MOF) as additive. The membranes were characterized in terms of surface morphology, surface charge, permeability, molecular weight cut off, porosity, pore size and contact angle. Permeability of the membrane increased from 3.5 × 10−10 to 4.5 × 10−10 m/Pa.s with increment of MOF concentration from 0 to 10 wt%. The contact angle of the corresponding membranes decreased from 80° to 51° indicating an increase in hydrophilicity. The MH10 (10 wt% concentration) membrane sustained up to 20, 19 and 17.5 h of operation with fluoride concentration of 4, 8 and 12 mg/l, respectively, at 35 kPa transmembrane pressure and 30 l/h cross flow rate with a membrane area of 0.026 m2. Regeneration study and performance of the MMM in real life ground water samples were also investigated. Filter performance was successfully predicted by a modified model available in literature.
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    Mass transport across porous wall of a microtube: a facile way to diagnosis of diseased state
    (Elsevier, 2018-03) Bhattacharjee, Saikat
    Mass transport characteristics of a neutral solute in a Casson fluid through a microtube with porous wall under the influence of both pressure and electric field are attempted in this work. The velocity and concentration fields were derived from first principles analytically. The expression of Sherwood number was obtained and impact of rheological parameters on Sherwood number was quantified. Influence of system parameters on solute transport characteristics in terms of permeation flux and concentration was established in detail. Finally, a theoretical method was developed to identify the diseased state by detecting the stagnation point in the microfluidic platform without any chemical reagents.
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    Combined concentration polarization and pore-flow modeling to predict the performance of a nanofiltration membrane for NaCI rejection
    (AIChE, 2018) Bhattacharjee, Saikat
    Membrane based filtration techniques are gaining importance day by day for its effectiveness and simplicity [1]. Different pressure driven techniques are exercised for membrane separation; nano filtration is one of them. Nano filtration membranes stand handy for different applications because of their thermal, chemical and mechanical stability [2]. High surface charge of these membranes help in separation of charged species from a solution. This particular property can be used to segregate any type of salt from water. Hence, it can be a useful technique for desalination of water which is a challenge for present day's world [3,4]. Modeling and simulation always provides useful lead to understand the underlying physical phenomenon behind a real life system. It also proves to be useful in scaling up the system and predict its performance in remote scenarios. Transport phenomena based membrane modeling is not a new field of study; a number of works have been reported till date which deals with it. Different studies have been done starting from prediction of different fouling mechanism [5,6] of membranes to prediction of flux for different processes [7,8]. In order to predict the flux and permeate concentration across the membrane a number of theoretical models have been proposed such as (a) osmotic pressure model [9 11]; (b) film theory [12 14]; (c) solution diffusion model; (d) Kedem-Katchalsky equation etc. Each of these models has their advantages and limitations also.
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    Hydrodynamics of electroosmotic flow in a microchannel with porous wall
    (2019-02) Bhattacharjee, Saikat
    Microchannel with porous wall has various microfluidic applications including iontophoresis, diagnostic devices, etc. In order to have an efficient and better design of such devices, exact quantification of velocity field in the microchannel needs to be established. In the present study, an analytical solution of velocity field in a microchannel with porous wall was obtained for a Newtonian fluid in case of a combined electroosmotic and pressure driven flow using perturbation technique. The velocity profile was reduced to well known solutions for three asymptotic cases, namely, purely electroosmotic flow and purely pressure driven flow in an impervious conduit as well as pressure driven flow with permeable wall. The pressure drop profile along the channel length was also generated. Effects of operating parameters, i.e., wall suction velocity, electrolyte concentration and channel half height on velocity and pressure fields were also investigated.
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    Electrohydrodynamic transport of non-symmetric electrolyte through porous wall of a microtube
    (Wiley, 2018-10) Bhattacharjee, Saikat
    Transport of salt through the wall of porous microtube is relevant in various physiological microcirculation systems. Transport phenomena based modeling of such system is undertaken in the present study considering a combined driving force consisting of pressure gradient and external electric field. Transport of salt is modeled in two domains, in the flow conduit and in the pores of porous wall of the microtube. The solute transport in the microtube is presented by convective-diffusive mass balance and it is solved using integral method under the framework of boundary layer analysis. The wall of the microtube is considered to be consisting of series of straight parallel cylindrical pores with charged inner surface. The solute transport through the pores is considered to be composed of diffusive, convective and electric potential gradient governed by Nernst-Planck equation. Transport in the microtube and pores is coupled through the osmotic pressure model for the solvent and Donnan equilibrium distribution for the solute. The simulated results agree remarkably well with the experimental data conducted by in-house experimental set up. The charge density of the porous wall is estimated through the minimization of errors involved between the experimental and simulated data for different operating conditions.
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    Integral method of analysis for combined concentration polarization and pore flow model for prediction of the performance of a nanofiltration membrane
    (ACS, 2019-09) Bhattacharjee, Saikat
    A coupled concentration polarization and pore flow model was used to predict the transport characteristics of a monovalent salt through a nanofiltration membrane. The concentration polarization in the flow channel was modeled using an integral method under the framework of boundary layer analysis. The extended Nernst–Planck equation was used to quantify the ion transport through the membrane pores. Ion partitioning across the solution phase and in the membrane pore was modeled using the Donnan exclusion principle including the steric hindrance. The membrane pore charge density was calculated for different membranes. The contributions of convection, diffusion, and electromigration toward the solute flux within the membrane pore were estimated. The calculated permeate flux and the solute concentration in permeate were compared with the experimental data available in the literature and were found to be in good agreement, indicating validation of the developed model.
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    Modelling the transport and adsorption dynamics of arsenic in a soil bed filter
    (Elsevier, 2019-12) Bhattacharjee, Saikat
    Arsenic is among the most hazardous contaminants present in drinking water. Recent increase in agricultural growth and fertiliser use in India and Bangladesh has led to the release of naturally occurring arsenic from the rocks, creating a major public health issue. A novel technology has been developed using naturally abundant laterite soil to filter arsenic, providing potable water to more than 5000 people. To upscale this technology and realise its full potential, a comprehensive understanding of the dependence of filter life on operating regime (flow rate, arsenic concentration and filter size) is essential. We present a mathematical model that characterises arsenic removal, circumventing the need for time-consuming experiments. The model incorporates inter- and intra-particle mass transport within the filter medium. The resulting model enables prediction of a filter lifetime in a specified role, such as on a domestic or community scale, and should assist in future filter deployment and maintenance.
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    Effect of electrolyte nature in mass transport of a neutral solute in a microtube with porous wall
    (AIChE, 2019-08) Bhattacharjee, Saikat
    Electroosmotic flow in a microchannel is an active area in microfluidics. Microchannels with porous wall are advantageous due to selective separation and enhanced mass transport. An economic and innovative method to fabricate hollow microtubes and their application in electrokinetics are illustrated. Effects of asymmetric electrolyte on mass transport of a neutral macrosolute in the microtube with porous wall are investigated. The combined velocity profile including both pressure-driven and electroosmotic flow is modeled for different electrolytes. It is found from the study that the addition of higher valency asymmetric electrolyte (3:1) increases transport of neutral solutes across the porous wall compared to its symmetric counterpart (1:1). The developed model was validated with the experimental results, using a cartridge having hollow microtubes with porous wall. This study would be helpful to select an appropriate electrolyte, improving the design, and performance prediction of microfluidic devices.