Chemical Engineering

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Shiv Nadar University

Three-phase segmented gas-liquid-liquid (G/L/L) flows in minichannels are important to several chemical process applications involving gas-liquid-liquid reactions. In the present work, we have investigated segmented G/L/L flows in a double T-junction minichannel, with cross-section of 0.95 mm × 1 mm, through high-speed imaging experiments and Volume-of-Fluid (VOF) simulations. The dynamics of bubble/slug formation at the 1st T-junction and importantly that of water drop/slug formation at the 2nd T-junction was simulated under different flow conditions (Caoil=2.63×10-3-1.101; Weair=4.24×10-4-2.62×10-3; Wewater=0.0431-7.14) and different surfactant concentrations (0.3 and 2 wt/wt.\%) in aqueous phase. The predicted formation mechanisms, three-phase flow regimes, and drop/bubble/slug lengths were compared quantitatively with the measurements. Different mechanisms of bubble/slug formation observed for the aforementioned range of the Caoil and Weair, and bubble/slug lengths were predicted in a satisfactory agreement with the measurements. The complex formation mechanism of water drops/slugs that was governed by viscous force exerted by continuous oil phase, inertial force exerted by water phase, interfacial tension force acting on the oil-water interface and also by incoming air bubbles/slugs; could be predicted in a satisfactory agreement with those observed in the experiments. Different three-phase flow regimes, e.g., drop-bubble, drop-slug and slug-slug, observed for different oil, air and water flow rates; and for different values of oil-water interfacial tensions are also predicted in satisfactory agreement with the measurements. The results reported in the present work help to understand the hydrodynamics of complex three-phase gas-liquid-liquid flows in minichannels, which in turn is crucial to device microreactor systems for process applications involving G/L/L flows. © 2018 Elsevier B.V.

(SoE) School of Engineering

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Chemical Engineering Journal

Volume-of-fluid simulations of gas-liquid-liquid flows in minichannels

There is an immense need for developing a simple, rapid, and inexpensive detection assay for health-care applications or monitoring environments. To address this need, a photonic crystal (PC)-based sensor has been extensively studied due to its numerous advantages such as colorimetric measurement, high sensitivity, and low cost. However, the response time of a typical PC-based sensor is relatively slow due to the presence of the inevitable upper residual layer in colloidal structures. Hence, we propose an ultra-fast responsive PC-based volatile organic compound (VOC) sensor by using a "nanoscale easy tear (NET) process" inspired by commercially available "easy tear package". A colloidal crystal-polydimethylsiloxane (PDMS) composite can be successfully realized through nanoscale tear propagation along the interface between the outer surface of crystallized nanoparticles and bulk PDMS. The response time for VOC detection exhibits a significant decrease by allowing the direct contact with VOCs, because of perfect removal of the residual on the colloidal crystals. Moreover, vapor-phase VOCs can be monitored, which had been previously impossible. High-throughput production of the patterned colloidal crystal-polymer composite through the NET process can be applied to other multiplexed selective sensing applications or may be used for nanomolding templates. © 2018 The Author(s).

Fulltext

Scientific Reports

Ultra-fast responsive colloidal-polymer composite-based volatile organic compounds (VOC) sensor using nanoscale easy tear process

In recent years, biodiesel, as a renewable and environment-friendly fuel has emerged as one of the most investigated bio-fuel with a goal to decrease our dependence on petroleum fuels and reduce environmental pollution. The current commercial technique of biodiesel production via transesterification is constrained by high operating cost and energy requirements, long residence time and limited conversion due to equilibrium limitations. On the other hand, the process intensification using the micro-reactor technology demonstrated an excellent performance ascribed to short diffusion distance and high surface area-to-volume ratio that can lead to high heat and mass transfer rates and improved mixing compared to the conventional reactors. This review provides an overview of the current status of biodiesel production in micro-reactors. It includes various types of micro-reactors used in the production of biodiesel, factors affecting the biodiesel production (i.e., temperature, residence time, alcohol to oil molar ratio, micro-channel size, inlet mixer type, internal geometries, co-solvent, catalyst type and concentration). This review also includes the factors affecting the liquid-liquid flow patterns and application of micro-reactor technology in the purification of biodiesel. Some of the critical observations from this review are, 1) inlet mixer type, channel size, and internal channel geometry (zig-zag, omega, and tesla shaped channels) have shown a significant effect on mixing in micro-channels. 2) In case of base-catalyzed transesterification, the biodiesel yield was found to increase up to the reaction temperature of 60–65 °C. 3) Homogeneous alkaline catalyst (NaOH, KOH, CH3ONa) was preferred for the feedstock with low free fatty acid content (&lt;1 wt\%). However, an acid catalyst with high concentration, a significant amount of methanol and long reaction time were required for high free fatty acid feedstock (&gt;1 wt\%). Therefore, the current research is more focused on the investigation of heterogeneous catalysts in micro-reactors to develop an ecologically friendly process for the production of biodiesel. 4) Also, the reaction temperature and inlet mixer type had shown a significant effect on liquid-liquid flow patterns. This review also addressed the following literature gaps; a numbering-up technique to increase the throughput; catalyst development for high free fatty acid feedstock; continuous production of biodiesel in micro-reactors with in-line purification step to meet the energy demand and quality standards. © 2018 International Energy Initiative

Energy for Sustainable Development

Biodiesel production in micro-reactors: A review

Turmeric oil was extracted from Curcuma Longa herb (turmeric root) using supercritical fluid extraction (SFE) process. Full-face central composite design was employed to optimize operating parameters of the process. These parameters were pressure, temperature, solvent flow rate, particle size and addition of co-solvent (ethanol) that varied as 20–40 MPa, 40–60 °C, 5–15 g/min, 0–0.8 mm and 0–15% of solvent rate, respectively. Turmeric oil yield found through Soxhlet extraction was 5.954 wt% of turmeric powder whereas through SFE, it varied from 2 to 5.3 wt%. Turmerone and curcumin were identified as principle compounds of turmeric essential oil, which were analyzed using Gas chromatography–mass spectrometry and Ultraviolet–visible Spectrophotometer, respectively. Experimental data of oil yield, Curcumin content and Turmerone content were fitted well in the Quadratic model. Optimized values of operating parameters for maximizing these responses were also predicted. Further, economic assessment of SFE of turmeric oil at industrial scale for 60 t/y production capacity was performed. © 2018 Elsevier Ltd

Journal of Cleaner Production

Influence of operating parameters on supercritical fluid extraction of essential oil from turmeric root

Luminescent trivalent europium(III) complexes Eu(CHPB)3·(H2O)2 (C1), Eu(CHPB)3·neo (C2), Eu(CHPB)3·batho (C3), Eu(CHPB)3·phen (C4) and Eu(CHPB)3·bipy (C5) have been synthesized by involving a β-diketone ligand 1-(5-chloro-2-hydroxyphenyl)-1,3-butanedione (CHPB) and four ancillary ligands like neocuproine (neo), bathophenanthroline (batho), 1,10-phenanthroline (phen) and 2,2-bipyridyl (bipy). All the synthesized complexes C1–C5 were investigated by adopting various techniques such as elemental (CHN) analysis, 1H NMR spectroscopy, IR spectroscopy, UV–visible, thermal analysis (TG/DTG) and photoluminescence (PL) spectroscopy. The luminescence of complexes C1–C5 gets intensified suggesting a favorable position of triplet state of ligand and coligand from the emitting levels of metal ion. The luminescence quantum efficiencies and Judd-Ofelt intensity parameter Ω2 of the complexes also determined which advocate higher polarizable ligand field around central metal ion. © 2017 Elsevier B.V.

Inorganica Chimica Acta

Judd-Ofelt characterization and energy transfer mechanism of highly luminescent europium(III) complexes with 1-(5-chloro-2-hydroxyphenyl)-1,3-butanedione

Supercritical fluid extraction (SFE) process is the sustainable green process for the extraction. Mathematical modeling of SFE process is carried out using mass transfer resistances, which vary with the types of solute. In this paper, the effect of matrices such as leaves, flower concrete, flower bud, herb plant, shrub seed and vegetable matter is studied on extraction yield through different models. These models are solved using COMSOL Multiphysics 5.2 solver and results are validated with that of literature. Experimental data of each type of solute matrix are fitted in various models and best suited model is predicted. © 2017 Taylor & Francis.

Separation Science and Technology (Philadelphia)

Selection of suitable model for different matrices of raw materials used in supercritical fluid extraction process

The stability of fibre spinning flow of a polymeric fluid is analysed in the presence of thermal effects. The spinline is modelled as a one-dimensional slender-body filament of the entangled polymer solution. The previous study (Gupta & Chokshi, J. Fluid Mech., vol. 776, 2015, pp. 268-289) analysed linear and nonlinear stability behaviour of an isothermal extensional flow in the air gap during the fibre spinning process. The present study extends the analysis to take in to account the non-isothermal spinning flow in which the spinline loses heat by convection to the surrounding air as well as by solvent evaporation. The nonlinear rheology of the polymer solution is described using the eXtended Pom-Pom (XPP) model. The non-isothermal effects influence the rheology of the fluid through viscosity, which is taken to be temperature and concentration dependent. The linear stability analysis is carried out to obtain the draw ratio for the onset of instability, known as the draw resonance, and a stability diagram is constructed in the plane. is the critical draw ratio, and is the flow Deborah number. The enhancement in viscosity driven by spinline cooling leads to postponement in the onset of draw resonance, indicating the stabilising role of non-isothermal effects. Weakly nonlinear stability analysis is also performed to reveal the role of nonlinearities in the finite amplitude manifold in the vicinity of the flow transition point. For low to moderate Deborah numbers, the bifurcation is supercritical, and the flow attains an oscillatory state with an equilibrium amplitude post-transition when DR>. The equilibrium amplitude of the resonating state is found to be smaller when non-isothermal effects are incorporated in comparison to the isothermal spinning flow. For very fast flows in the regime of high Deborah numbers, the finite amplitude manifold crosses over to a subcritical state. In this limit, the nonlinearities render the flow unstable even in the linearly stable regime of CD<DRc. © 2018 Cambridge University Press.

Journal of Fluid Mechanics

Stability analysis of non-isothermal fibre spinning of polymeric solutions

Growing interest in hybrid organic-inorganic lead halide perovskites has led to the development of various perovskite nanowires (NWs), which have potential use in a wide range of applications, including lasers, photodetectors, and light-emitting diodes (LEDs). However, existing nanofabrication approaches lack the ability to control the number, location, orientation, and properties of perovskite NWs. Their growth mechanism also remains elusive. Here, we demonstrate a micro/nanofluidic fabrication technique (MNFFT) enabling both precise control and in situ monitoring of the growth of perovskite NWs. The initial nucleation point and subsequent growth path of a methylammonium lead iodide-dimethylformamide (MAPbI3·DMF) NW array can be guided by a nanochannel. In situ UV-vis absorption spectra are measured in real time, permitting the study of the growth mechanism of the DMF-mediated crystallization of MAPbI3. As an example of an application of the MNFFT, we demonstrate a highly sensitive MAPbI3-NW-based photodetector on both solid and flexible substrates, showing the potential of the MNFFT for low-cost, large-scale, highly efficient, and flexible optoelectronic applications. © 2018 American Chemical Society.

ACS Nano

Nanochannel-Assisted Perovskite Nanowires: From Growth Mechanisms to Photodetector Applications

Nanowires (NWs) with a high surface-to-volume ratio are advantageous for bio- or chemical sensor applications with high sensitivity, high selectivity, rapid response, and low power consumption. However, NWs are typically fabricated by combining several nanofabrication and even microfabrication processes, resulting in drawbacks such as high fabrication cost, extensive labor, and long processing time. Here, we show a novel NW fabrication platform based on "crack-photolithography" to produce a micro-/nanofluidic channel network. Solutions were loaded along the microchannel, while chemical synthesis was performed in the nanoslit-like nanochannels for fabricating silver nanobelts (AgNBs). In addition, the NW/NB fabrication platform not only made it possible to produce AgNBs in a repeatable, high-throughput, and low-cost manner but also allowed the simultaneous synthesis and alignment of AgNBs on a chip, eliminating the need for special micro- and/or nanofabrication equipment and dramatically reducing the processing time, labor, and cost. Finally, we demonstrated that the AgNBs can be used as chemical sensors, either as prepared or when integrated in a flexible substrate, to detect target analytes such as hydrogen peroxide. © 2017 The Royal Society of Chemistry.

Nanoscale

A cracking-assisted micro-/nanofluidic fabrication platform for silver nanobelt arrays and nanosensors

Effective surface-enhanced Raman scattering (SERS) detection requires substrates that are typically fabricated using expensive, low-throughput and time-consuming micro-/nanofabrication processes such as photolithography, electron-beam lithography and template- assisted methods Here, a novel micro-/nanofabrication technique for fabricating SERS substrates with hydrophobicity gradients is demonstrated. An inkjet printer enables injecting an AgNO3 solution onto a thiol-functionalized superhydrophobic Cu surface, upon which Ag micro/nanostructures are generated via replacement reactions in the droplet-injected areas. When a mixed solution of target analytes and Au-nanoparticles (Au-NPs) are placed on this substrate, the contact area decreases over time due to the evaporation of the solution and the hydrophobicity of the substrate. As a result, the analyte molecules and Au-NPs are delivered to the Ag micro-/nanostructure clusters, upon which the analyte and Au-NPs are simply and easily concentrated in situ. With the cooperation of Ag nanoplates and Au-NPs, two antibiotics at very low concentrations (e.g., 100 pM 6-aminopenicillanic acid and 50 pM penicillin G sodium) were successfully detected, confirming the higher SERS activity than that of Ag-nanoplate-assembled nanotube arrays or an Ag-NPs decorated graphene electrophoretic pre-concentration device. Hence, this rapid design-to-prototype method for substrates with adjustable wetting properties can be very useful for a SERS platform to detect various target analytes in biosamples. © 2016 Elsevier B.V.