Department of Chemical Engineering

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IIT Jodhpur

The triangle-well (TW) potential is a simple model which is able to capture the essence of the intermolecular attraction in real molecules. Transition matrix Monte Carlo simulations in the grand canonical ensemble (GC-TMMC) are performed to investigate the role of the range of attraction on the features of fluid phase equilibria. As the TW potential range increases, the vapour-liquid coexistence curves shift towards a higher temperature range with the critical temperature and pressure increasing, and the critical density values decreasing. These GC-TMMC results are in excellent agreement with the predictions of Gibbs ensemble Monte Carlo and replica exchange Monte Carlo (REMC) simulations reported in literature. Using the GC-TMMC method, the vapour pressures are also computed directly from the particle number probability distributions (PNPDs). It has been noted in literature that the surface tension values are computationally more expensive and difficult to determine than other coexistence properties using molecular simulations. The PNPDs from GC-TMMC simulations along with Binder's formalism allow for the calculation of the interfacial tension with relative ease. Also, our simulation generated results for the interfacial tension are in good agreement with the literature data obtained using REMC (via the virial route) and the plots of our interfacial tension values as a function of temperature are smooth unlike the literature data. © 2016 Elsevier B.V. All rights reserved.

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Chemical Physics

Prediction of fluid phase equilibria and interfacial tension of triangle-well fluids using transition matrix Monte Carlo

A distinctive and impactful idea has been materialized to develop high-performance mixed-matrix ultrafiltration (UF) membranes using non-solvent induced phase inversion technique, utilizing various optimized compositions of polymer - polysulfone (Psf) and bactericidal nanostructured material, i.e., silver nanoparticles (Ag-nps). Membranes in sheet-configuration with high void volumes were synthesized employing large amount of polyvinyl pyrrolidone (PVP) as porogen. The resultant porous morphology and surface chemistry, i.e., surface hydrophilicity and electrokinetic features were assessed by instrumental techniques. The notable separation performances were observed as the membranes exhibited very high solvent throughput with reasonable anti-microbial activity. It has been substantiated that the nanoparticles upon impregnation within such a benign matrix of polymer exerted more pronounced mechanistic role towards anti-microbial efficacy on Escherichia coli, since as a survival mechanism the bacteria undergoing flagellar locomotory motion started experiencing negative chemotactic responses under the modified circumstances. With an objective of applying the salient features of such membranes, the facile methodical attempt was utilized in fabricating a domestic water purification device, with the membrane in candle-configuration for treatment of environmentally relevant aquatic media. It has been corroborated that our impactful approach towards development of an efficient water purification methodology (solvent throughput: 2500 LMH/bar and bacterial rejection: 99.99%) confirms the significance of membrane technology as a green and sustainable process with provision of easy scale up, energy and cost efficiency. © 2016 Elsevier B.V.

Chemical Engineering Journal

High-throughput mixed-matrix membrane with superior anti-bacterial properties: A facile approach towards development of point-of-use water purification device

In this study, we discuss the preparations of cellulosic membranes from cellulose acetate (CA), cellulose triacetate (CTA) and cellulose acetate blend (CAB) [blending of CA and CTA] systems and their potential for concentration of simulated ammonium-diuranate (ADU) effluent solution (only uranium and ammonium nitrate) by FO. The membranes are prepared using casting solution of polymers in mixed solvent systems with gelling in ice-cold water followed by annealing in 80°C hot water. Prepared membranes are characterized in terms of separation performance (tested under brackish water reverse osmosis test condition), water contact angle and surface average roughness. The performance of the membranes are evaluated in terms of volume reduction factor using solution of 40,000 ppm of NH4NO3 and 20 ppm uranium as feed and 320000ppm of NH4NO3 as draw solution. It is found that the volume reduction factor increases in the order of CTA&lt;CAB&lt;CA membranes. The effect of different draw solutions on volume reduction for the same system using CA membrane is also evaluated. Almost no leaching of uranium is found to the draw solution side for all the membranes. Possibility of using the FO process in a simpler way (as membrane pouch) to concentrate this simulated ADU filtered solution has been ascertained. © , Copyright © Taylor & Francis Group, LLC.

Separation Science and Technology (Philadelphia)

Studies on Concentration of Simulated Ammonium-diuranate Filtered Effluent Solution by Forward Osmosis Using Indigenously Developed Cellulosic Osmosis Membranes

Human embryonic stem cells (hESCs) have been routinely treated with bone morphogenetic protein and/or inhibitors of activin/nodal signaling to obtain cells that express trophoblast markers. Trophoblasts can terminally differentiate to either extravillous trophoblasts or syncytiotrophoblasts. The signaling pathways that govern the terminal fate of these trophoblasts are not understood. We show that activin/nodal signaling switches the terminal fate of these hESC-derived trophoblasts. Inhibition of activin/nodal signaling leads to formation of extravillous trophoblast, whereas loss of activin/nodal inhibition leads to the formation of syncytiotrophoblasts. Also, the ability of hESCs to form bona fide trophoblasts has been intensely debated. We have examined hESC-derived trophoblasts in the light of stringent criteria that were proposed recently, such as hypomethylation of the ELF5-2b promoter region and down-regulation of HLA class I antigens. We report that trophoblasts that possess these properties can indeed be obtained from hESCs. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

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Journal of Biological Chemistry

Activin/nodal signaling switches the terminal fate of human embryonic stem cell-derived trophoblasts

In this study, zinc oxide nanoparticles were synthesized using electrochemical method. Zinc was used as electrode whereas oxalic acid in aqueous solution was used as an electrolyte. A L9 (34) Taguchi optimization methodology was used to find out the individual and interactive effect of all four independent experimental parameters namely pH (pHo): 5-8, oxalic acid concentration (m): 0.05-0.15 M, conductivity (k): 20-30 (mS/cm) and operating voltage (Vo): 5-8 V. These experimental parameters were optimized so as to maximize the productivity (g) and correspondingly find out specific energy consumption (kW h/kg) and specific electrode consumption (kg/kg). At the optimum condition of pHo = 5, m = 0.05 M, k = 30 (mS/cm) and Vo = 8 V, values of productivity, SENC and SELC were found to be 1.03 g, 3.79 kW h/kg and 1.76 kg/kg, respectively. Nanoparticles synthesized at optimum conditions have been further characterized by scanning electron microscopy, X-ray diffraction and UV-Visible diffuse reflectance spectroscopy techniques so as to confirm its ZnO nature. © 2015 Elsevier B.V. All rights reserved.

Journal of Alloys and Compounds

Zinc oxide nanoparticles synthesis by electrochemical method: Optimization of parameters for maximization of productivity and characterization

The conformational structure of dilute atactic-poly(methacrylic acid) (PMA) solution in binary water-ethanol mixture was investigated by molecular dynamics simulations, over 0-0.9 ethanol (co-solvent) fraction. The radius of gyration 〈Rg〉, torsion angle distribution, intra-chain hydrogen bonds (H-bonds), and H-bonds for PMA-water, PMA-ethanol and water-ethanol, atom-atom and atom-group pair radial distribution functions were analysed. An increase in the ethanol fraction leads to chain expansion. The non-monotonic variation of 〈Rg〉, commensurate with the experimentally observed behaviour of intrinsic viscosity [η], takes place by H-bonding effects between PMA, water and ethanol, as driven by the differences in the chemical structure of water and ethanol. The PMA repeat units are closer to the CH2 groups as compared with CH3 groups of ethanol, in the nearest coordination shell. Water as compared with ethanol is able to coordinate closer to the PMA repeat unit centre of mass. Intra-chain H-bonding depreciates with an increase in the ethanol content in solution. The changes, across the ethanol fraction range, in chain dimensions and of predicted intrinsic viscosity by the simulations, compare well with experimental results in the literature. © 2015 Taylor & Francis.

Molecular Simulation

Influence of hydrogen bonding on the structural transition of poly(methacrylic acid) chain in water-ethanol solution by molecular dynamics simulations

A thermal lattice Boltzmann method is utilized for the numerical simulation of the natural convection heat transfer phenomena inside a differentially heated square cavity. Numerical simulations are performed to elucidate the combined effects of Prandtl number (0.71 ≤ Pr ≤ 100) and Rayleigh number (104 ≤ Ra ≤ 106) on heat transfer and fluid flow characteristics inside the cavity. Detailed insights are gained by the evaluation of isotherms, stream functions and vorticity profiles. For higher Prandtl and Rayleigh numbers, streamlines become more confined to hot wall with the loss of symmetry. Similarly, isotherms patterns become more stratified towards the hot wall. The centre-line velocity and temperature profiles are also analyzed. Further, the heat transfer rate is estimated in terms of average Nusselt number. It suggests a proportional increase in the average Nusselt number with the increasing values of Prandtl number for considered range of Rayleigh numbers. Finally, the numerical data for the average Nusselt number are presented in the form of a correlation for their best utilization in design and engineering practices. © 2015 Canadian Society for Chemical Engineering.

Canadian Journal of Chemical Engineering

Two-dimensional lattice Boltzmann simulation of natural convection in differentially heated square cavity: Effect of Prandtl and Rayleigh numbers

Natural convection characteristics of a partially heated open ended square cavity have been investigated numerically by using an in-house computational flow solver based on the passive scalar thermal lattice Boltzmann method (PS-TLBM) with D2Q9 (two-dimensional and nine-velocity link) lattice model. The partial part of left wall of the cavity is heated isothermally at either of the three different (bottom, middle and top) locations for the fixed heating length as half of characteristic length (H/2) while the right wall is open to the ambient conditions. The other parts of the cavity are thermally isolated. In particular, the influences of partial heating locations and Rayleigh number (103≤ Ra≤106) in the laminar zone on the local and global natural convection characteristics (such as streamline, vorticity and isotherm contours; centerline variations of velocity and temperature; and local and average Nusselt numbers) have been presented and discussed for the fixed value of the Prandtl number (Pr=0.71). The streamline patterns show qualitatively similar nature for all the three heating cases and Rayleigh numbers, except the change in the recirculation zone which is found to be largest for middle heating case. Isotherm patterns are shifted towards a partially heated wall on increasing Rayleigh number and/or shifting of heating location from bottom to top. Both the local and average Nusselt numbers, as anticipated, shown proportional increase with Rayleigh number. The cavity with middle heating location shown higher heat transfer rate than that for the top and bottom heating cases. Finally, the functional dependence of the average Nusselt number on flow governing parameters is also presented as a closure relationship for the best possible utilization in engineering practices and design. © 2015, Korean Institute of Chemical Engineers, Seoul, Korea.

Korean Journal of Chemical Engineering

Lattice Boltzmann analysis of effect of heating location and Rayleigh number on natural convection in partially heated open ended cavity

A newly developed hydroxamic acids functionalized acrylic based solid phase sorbent, named as poly-acryl hydroxamic acid (PHOA) is used as an extractant for the recovery of uranium from nuclear waste solution. Various parameters such as sorbent solubility in different medium, effect of various cations on U(VI) sorption, desorption performance of different eluents with respect to U(VI) sorption has been investigated in detail. U(VI) sorption behaviors of the sorbent were studied in different concentration of competitive ions such as Mg2+, Fe3+, and NO3 − and it was found that the sorbent was capable of removing the U(VI) efficiently in the presence of high concentration of these ions. © , Copyright © Taylor & Francis Group, LLC.

Separation and Recovery of Uranium from Wastewater Using Sorbent Functionalized with Hydroxamic Acid

This work presents the lattice Boltzmann simulation of natural convection in an open ended square cavity subjected to partial heating. The size of heater is half of characteristic length and placed at middle location of one vertical wall. Numerical simulations are performed for three different fluids of industrial, scientific as well as domestic field, viz., air (. Pr = 0.71), dichloro-difluoro-methane (. Pr = 4.5) and water (. Pr = 7). The influence of the partial heater on heat and hydrodynamic characteristics of an open ended cavity have been elucidated. It is observed that isotherms become more confined toward the partially heated portion of wall with the increase in Prandtl number. The heat transfer rate shows linear increase with the Prandtl number, i.e., enclosure containing water shows higher heat transfer rate followed by R-12 refrigerant and air. The numerical results are summarized by the empirical correlation relating Nusselt number with Rayleigh and Prandtl numbers. © 2014 Taiwan Institute of Chemical Engineers.