Department of Chemical Engineering

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Abstracts of AIChe Annual Meet

Optimization Based Improved Water Recycle Strategies for Modern Oil Refineries

Atomistic molecular dynamics (MD) simulations are performed in order to derive thermodynamic properties important to understand the extraction of gadolinium (Gd3+) and uranium dioxide (UO2) with dibenzo crown ether (DBCE) in nitrobenzene (NB) and octanol (OCT) solvents. The effect of polystyrene graft length, on DBCE, on the binding behavior of Gd3+ and UO22+ is investigated for the first time. Our simulation results demonstrate that the binding of Gd3+ and UO22+ onto the oxygens of crown ethers is favorable for polystyrene grafted crown ether in the organic solvents OCT and NB. The metal ion binding free energy (ΔGBinding) in different solvent environments is calculated using the thermodynamic integration (TI) method. ΔGBinding becomes more favorable in both solvents, NB and OCT, with an increase in the polystyrene monomer length. The metal ion transferability from an aqueous phase to an organic phase is estimated by calculating transfer free-energy calculations (ΔGTransfer). ΔGTransfer is significantly favorable for both Gd3+ and UO22+ for the transfer from the aqueous phase to the organic phase (i.e., NB and OCT) via ion-complexation to DBCE with an increase in polystyrene length. The partition coefficient (log P) values for Gd3+ and UO22+ show a 5-fold increase in separation capacity with polystyrene grafted DBCE. We corroborate the observed behavior by further analyzing the structural and dynamical properties of the ions in different phases. © 2017 American Chemical Society.

Journal of Physical Chemistry B

Extraction of Gd3+ and UO22+ Ions Using Polystyrene Grafted Dibenzo Crown Ether (DB18C6) with Octanol and Nitrobenzene: A Molecular Dynamics Study

Identifying lower order models is desirable both for control design and prediction purposes. In a few cases, a lower order model can be further reduced so that it contains the fewest number of parameters. In this paper, a sparsity seeking optimization method is proposed to identify such parsimonious continuous time (CT) linear time invariant (LTI) models. Theoretical analysis of convergence of estimates is presented. Numerical results on a variety of systems show that the algorithm accurately estimates the model parameters. Further, Monte Carlo simulations are used to verify the statistical convergence properties of the parameter estimates. Identification of a reduced order CT LTI model of tanks in series system demonstrates the practical applicability of the proposed method. © 2018 Elsevier Ltd

Journal of Process Control

Identification of parsimonious continuous time LTI models with applications

Subspace identification techniques derive approximate models rather than models that are optimal with respect to a goodness of fit criterion. To obtain low rank models, a nuclear norm minimization method for estimating the system matrices of linear time invariant continuous time state-space models in the presence of measurement noise is proposed. In the proposed approach, Generalized Poisson Moment Functional (GPMF) method is used to circumvent the time-derivative problem which is inherent in continuous time models. To make the proposed algorithm consistent, instrumental variables (Hankel matrix of past inputs) are considered. The accuracy of the proposed method is demonstrated with the help of numerical simulations on a variety of systems. © 2018

Nuclear Norm Subspace Identification Of Continuous Time State-Space Models

The present research numerically explores the hydrodynamic and thermal characteristics due to mixed convection in the rectangular enclosure with one of the vertical wall moving and containing centrally placed heated elliptical block for steady state condition. In particular, the influence of different flow pertaining parameters, such as, the direction of moving vertical wall (either in positive –y or negative –y coordinate directions), aspect ratio of an elliptical cylinder (Er = 0.5, 1 and 2) are studied for the broad range of dimensionless parameters (Reynolds number: 1 ≤ Re ≤ 5000; Prandtl number: 1 ≤ Pr ≤ 100 and Grashof number: 0 ≤ Gr ≤ 105) by using finite volume method (FVM) and SIMPLE numerical approach. The analysis of physical insights of an enclosure is accomplished by systematic evaluation of the streamlines as well as isotherms profiles. In order to compare mean heat transfer from an elliptical cylinder with that of circular shape, normalized Nusselt number (NuN) is estimated. Heat transfer characteristics are more predominantly affected due to the direction of moving lid than the aspect ratio of the elliptical cylinder. Also, the enclosure with moving wall along positive –y direction tends to enhance heat transfer rate. Rather than a pure circular shape, the enclosure with heated elliptical block (Er≠1) shows a higher rate of convective heat transfer. © 2018 Elsevier Masson SAS

International Journal of Thermal Sciences

Mixed convection characteristics in rectangular enclosure containing heated elliptical block: Effect of direction of moving wall

The role of polystyrene (PS) grafting to the dicyclohexano crown ether (DCHCE) in extracting the Gd3+ and UO2 2+ is evaluated for the first time using atomistic molecular dynamics (MD) simulations. The thermodynamic free-energy (ΔGBind) is calculated to understand the binding of Gadolinium (Gd3+) and Uranyl (UO2 2+) to the DCHCE in nitrobenzene (NB) and octanol (OCT) solvents. The results show that the binding free-energy is favorable for Gd3+ and UO2 2+ in NB, and unfavorable in OCT. In NB, the ΔGBind of Gd3+ and UO2 2+ increases by 2.3% and 3.1% respectively with an increase in the PS length from 0 to 3. On the contrary, in OCT, the ΔGBind of Gd3+ and UO2 2+ decreases by 2.4% and 3.4% with an increase in PS length of the grafted DCHCE. The transfer free-energy (ΔGTransfer) for both the ions viz., Gd3+ and UO2 2+, from the aqueous phase to an organic phase is also analyzed using NB and OCT as extractants. The ΔGTransfer for both ions shows encouraging extraction ability in NB while the extraction ability decreases using OCT as an extractant. The partition coefficient (log P) values show an increase with an increase in PS grafting length on the DCHCE using NB as an extractant, while an opposite behavior is observed in OCT. In particular, with increase in the PS length, for Gd3+ and UO2 2+, log P values in NB increase by 13% and 9.6% respectively; whereas log P values decrease by 27% and 10% in OCT. In the presence of acidic medium (3 M HNO3 solution) the ΔGTransfer values for both Gd3+ and UO2 2+ show ~6% and 9% increase with NB and OCT, respectively. The structural and thermodynamic solvation properties are in accordance with the observed ΔGBind, ΔGTransfer, and log P. © 2018 Elsevier B.V.

Journal of Molecular Liquids

Effect of polystyrene length for the extraction of Gd3+ and UO2 2+ ions using dicyclohexano crown ether (DCH18C6) with octanol and nitrobenzene: A molecular dynamics study

The present work examines the influence of location of the heated triangular block along the vertical centerline of cavity on mixed convection characteristics. The flow is assumed to be 2D, steady, laminar and for incompressible and Newtonian. The physical domain of study is top lid-driven square cavity. The top and bottom walls of cavity are thermally insulated; while the both vertical walls are exposed to ambient (Tc). The cavity contains equilateral triangular block (size of edge, b), maintained at isothermal temperature condition (TH(&gt;Tc)) along its geometric horizontal centerline. The change in the position of block is permitted along the vertical centerline (x=0.5,y) of cavity. Flow pertaining equations are solved by using finite volume method (FVM) and SIMPLE algorithm. The dependence of various relevant dimensionless parameter, such as, Reynolds number (Re=1—1000), Richardson number (Ri=0.01,1,10), blockage (B‾=0.1,0.2,0.3) and location (Ly=0.25,0.5,0.75) of triangular block on convection characteristics have been elucidated. Flow and thermal patterns in the cavity are analyzed by systematic evaluation of streamline and temperature contours. Followed by heat transfer characteristics are presented by studying variation of local as well as average Nusselt number. Average Nu values are presented in the form of tables for different values of Ri. Higher heat transfer rates can be achieved for centered block position (Ly=0.5) than remaining two (Ly=0.25,0.75). © 2018 Elsevier Ltd

International Journal of Heat and Mass Transfer

Mixed convection characteristic in a lid-driven cavity containing heated triangular block: Effect of location and size of block

This work presents thermal lattice Boltzmann method simulation of magneto-hydrodynamic, buoyancy-driven convection in a partially differentially heated cavity (aspect ratio = 1) subjected to a magnetic field along the vertical direction, i.e. at 90°. Lattice Boltzmann method simulations are performed for three different cooler lengths (Lc = H/4, H/2, H) placed along the middle of one vertical wall for a wide range of Rayleigh and Hartmann numbers (103≤ Ra ≤ 105; Ha = 0, 60, 120) at fixed Prandtl number (Pr = 0.71, air). A partial heater is placed at the center of other vertical walls and its size is kept as half of the characteristic length (H/2). The physical insights of the systems are delineated by systematic analysis of stream function and temperature contours. Heat transfer characteristics of the cavity are elucidated by using averaged values of the Nusselt number. It is noted that average Nusselt number has a proportional dependence with cooler length and Rayleigh number, while it varied inversely with Hartmann number. Further, the functional dependence of average Nusselt number with cooler size, Rayleigh number, and Hartmann number is established for possible use in engineering design purpose. © 2018, © IMechE 2018.

Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science

Computational analysis of magneto-hydrodynamic natural convection in partially differentially heated cavity: Effect of cooler size

Photocatalytic reactors for the degradation of gaseous organic pollutants often suffer from major limitations such as small reaction area, sub-optimal irradiation conditions and thus limited reaction rate. In this work, an alternative solution is presented that involves a glass tube coated on the inside with (silver-modified) TiO2and spiraled around a UVA lamp. First, the spiral reactor is coated from the inside with TiO2using an experimentally verified procedure that is optimized toward UV light transmission. This procedure is kept as simple as possible and involves a single casting step of a 1 wt% suspension of TiO2in ethanol through the spiral. This results in a coated tube that absorbs nearly all incident UV light under the experimental conditions used. The optimized coated spiral reactor is then benchmarked to a conventional annular photoreactor of the same outer dimensions and total catalyst loading over a broad range of experimental conditions. Although residence time distribution experiments indicate slightly longer dwelling of molecules in the spiral reactor, no significant difference in by-passing of gas between the spiral reactor and the annular reactor can be claimed. Acetaldehyde degradation efficiency of 100% is obtained with the spiral reactor for a residence time as low as 60 s, whereas the annular reactor could not achieve full degradation even at 1000 s residence time. In a final case study, addition of long-term stable silver nanoparticles, protected by an ultra-thin polymer shell applied via the layer-by-layer (LbL) method, to the spiral reactor coating is shown to double the degradation efficiency and provides an interesting strategy to cope with higher pollutant concentrations without changing the overall dimensions. © 2017 Elsevier B.V.

Fulltext

Chemical Engineering Journal

Gas phase photocatalytic spiral reactor for fast and efficient pollutant degradation

Providing potable drinking water, with sufficient free residual chlorine to prevent microbial regrowth and contaminant by-product formation, is of utmost importance for municipal authorities. This work aims towards water quality control as it transports through water distribution networks. Presence of excessive chlorine (used as disinfectant worldwide) in water causes the generation of carcinogenic disinfectant by-products such as Tri-halo methane (THMs). On the other hand, lower chlorine levels in water results in microbial contamination. Hence, this leads to a two-point constraint control problem of maintaining free residual chlorine levels under the upper and lower bounds, by suitably optimizing the disinfectant dosage at booster stations. However, transport delay and complex interrelations present amongst the nodes in large water distribution network, makes it difficult to design a global feedback control system. Therefore, in this work we have proposed to decentralize the system by clustering demand nodes of the network based on concentration sensitivity matrix analysis. Further, input-output pairs for decentralized controllers were mapped with the knowledge of interactions between manipulating and control variables using partial correlation analysis. We also considered the results of partial correlation analysis to generate communication links which will be implemented for higher level co-ordinated decentralized control to account for dynamic, non-negligible interactions as disturbances to local control units. The proposed three step clustering-mapping strategy and mathematical formulation for two point control by optimized dosage is successfully verified for the steady state case on a prototype distribution example network. © 2020 CCWI 2017 - 15th International Conference on Computing and Control for the Water Industry. All rights reserved.