IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

It is desirable to reduce the time taken for sterilization without compromising on the criterion of the slowest heating zone (SHZ) in the container reaching the minimum prescribed temperature. In this study, the required sterilization times for food cans of equal volumes but different shapes ranging from full cone through truncated cones to full cylinder were investigated. Further, the effect of orientation of the can was also investigated by inclining these geometries from 0-180°. The non-Newtonian fluid (0.85% w/w CMC) was taken as the test food material and its laminar flow behavior analysed using computational fluid dynamics. It was observed that among these geometries the lowest sterilization time was observed for a vertically oriented upright full conical can. The cylinder gave lower sterilization time when oriented horizontally than vertically. The sterilization times of truncated conical cans were intermediate to those determined for full cone and cylinder. Even a small inclination in the orientation of the cans may lead to significant increase in the sterilization times due to decrease in the convective velocities. The slowest heating zone movement in both axial and radial directions was tracked for various geometries and typical results are presented. The convective velocities, volume of region above and the surface area below the slowest heating zone determine the time taken for sterilization. When geometry modifications are made for aesthetic reasons to the food container, the utilization of known sterilization times for the conventional cylindrical can of the same volume may be inappropriate for suitable thermal treatment. © 2005 Elsevier Ltd. All rights reserved.

Department Of Chemical Engineering

International Journal of Heat and Mass Transfer

Enhanced food sterilization through inclination of the container walls and geometry modifications

Mass transfer from solids, which has important applications in a number of chemical and pharmaceutical industries, has been studied experimentally and semiempirically under turbulent flow conditions, and correlations are available in the literature to calculate the mass-transfer coefficients from pellets, rotating cylinders and disks etc. However, mass transfer under laminar flow has not been sufficiently addressed. One of the difficulties here is the strong Reynolds number dependence of the flow pattern, for example, due to the onset of Taylor vortices for the case of a rotating cylinder. This problem is circumvented by using a computational fluid dynamics (CFD)-based solution of the governing equations for the case of a cylinder rotating inside a stationary cylindrical outer vessel filled with liquid. The parameters cover a range of Reynolds number (based on the cylinder diameter, and the tangential speed of the cylinder), Schmidt number and the ratio of the outer to inner cylinder diameters. The results confirm that the circumferential velocity profile is a strong function of the Reynolds number and varies from a nearly Couette-type flow at very low Reynolds numbers to a boundary layer-like profile at high Reynolds numbers. The onset of Taylor vortices has a strong effect on the flow field and the mass-transfer mode. The calculations show that the Sherwood number has a linear dependence on the Reynolds number in the Couette-flow regime, and roughly square-root dependence after the onset of Taylor vortices. Correlations have been proposed to calculate the Sherwood number taking account of these effects. © 2005 American Institute of Chemical Engineers.

GENERAL

AIChE Journal

Effect of Taylor Vortices on mass transfer from a rotating cylinder

A comprehensive techno-economic analysis, based on a systems concept approach, has been carried out, to study the performance and cost of integrated solar powered seawater desalination plants, named "Suryajal". In the first (technical) part of this paper, the energy requirement of a typical Seawater Reverse Osmosis (SWRO) system is estimated. Mathematical equations are developed that balances the energy input requirements of a SWRO plant to the energy output of Solar Photo Voltaic (SPV) Power plant. In the second (economic) part, a parametric study is carried out within a framework of six techno-economic operational scenarios. Regression equations are developed for SPV as well as SWRO plants. The specific capital cost trend of both SPV and SWRO plant are seen to decrease rapidly with size. The regression equations, with different financing options, are then used to analyze the trend of plant specific capital cost, and total investment required for integrated SPV-RO plants, as a function of fresh water production capacities, from 0.5 Million Litres per Day (MLD) to 300 MLD. Water costs as a function of capital cost, power cost and maintenance costs; as well as specific capital cost of integrated PV-RO plants, for different plant capacities, are estimated, with full capital cost recovery and without taking into account subsidies available for renewable energy systems. It is observed that plant specific capital cost as well as fresh water cost, fall rapidly and significantly down to current costs of river water, as plant capacity increases, for all techno-economic scenarios considered. It is concluded that seawater desalination, especially on large scales using solar photovoltaic power plants is a technically feasible, economically viable and environmentally friendly option for perennial supply of fresh water from the ocean.

Proceedings of the Solar World Congress 2005: Bringing Water to the World, Including Proceedings of 34th ASES Annual Conference and Proceedings of 30th National Passive Solar Conference

Solar photovoltaic powered seawater desalination plants

Homogeneous azeotropic distillation processes may exhibit multiple steady states under certain conditions. A methodology has been described for directly capturing all the multiple steady states as well as for generating the bifurcation diagram using the HYSYS process simulator in the steady-state mode. Initial guesses for generating the multiple steady states were based on the ∞/∞ approach of Bekiaris et al. (Ind. Eng. Chem. Res. 1993, 32, 2023) and the behavior of the composition-temperature profiles. The method was tested with different systems, feed locations, and compositions and was extended to nonideal stages using the overall efficiency approach. Conventional inside-out algorithms in the steady-state mode were found to capture the stable steady states only. Using stabilizing control, these algorithms could capture the unstable steady states as well. Their ability to incorporate Murphree efficiencies in the column specifications could, hence, be exploited. Preliminary results on the sustained oscillatory behavior on the higher branch are presented. © 2005 American Chemical Society.

Industrial and Engineering Chemistry Research

Multiple-steady-states identification in homogeneous azeotropic distillation using a process simulator

The enhancement of the dissolution rate of the sparingly soluble benzoic acid in aqueous solution by solid rotation, ultrasound and chemical reaction was investigated. The analysis indicated the strong influence of the ultrasound energy dissipation rate on the enhancement. The overall enhancements due to the three means were compared. The enhancement due to ultrasound was found to be much greater than mechanical rotation and comparable to that of chemical reaction. © 2004 Published by Elsevier B.V.

Chemical Engineering Journal

Enhancement of solid dissolution process

Reactive distillation combines reaction with separation in a single column thereby increasing conversion for equilibrium limited reactions, minimizing side reactions and saving on recycle and capital costs. KATAPAK®-SP provides the flexibility in varying the ratio of the reaction zone relative to the separation zone depending on process requirements. The current study provides pressure drop and holdup data for KATAPAK®-SP 12 packing contained in a 100mm diameter column. Correlations are provided for both the dry gas and irrigated pressure drop. The gas loading point was correlated to the liquid flow rate. Flow pattern studies were conducted to estimate the saturation capacity of the packed bed as well as to determine the apportioning of the total liquid flow between the reaction and separation layers. A correlation for the dispersed phase liquid holdup is developed based on the operating variables, equipment parameters and a flow distribution parameter estimated from the flow pattern studies. The holdup and pressure drop correlations were extended to the post-loading region. © 2004 Elsevier B.V. All rights reserved.

Holdup and pressure drop studies in structured packings with catalysts

The α/β barrel fold is adopted by most enzymes performing a variety of catalytic reactions, but with very low sequence similarity. In order to understand the stabilizing interactions important in maintaining the α/β barrel fold, we have identified residue clusters in a dataset of 36 α/β barrel proteins that have less than 10% sequence identity within themselves. A graph theoretical algorithm is used to identify backbone clusters. This approach uses the global information of the nonbonded interaction in the α/β barrel fold for the clustering procedure. The nonbonded interactions are represented mathematically in the form of an adjacency matrix. On diagonalizing the adjacency matrix, clusters and cluster centers are obtained from the highest eigenvalue and its corresponding vector components. Residue clusters are identified in the strand regions forming the β barrel and are topologically conserved in all 36 proteins studied. The residues forming the cluster in each of the α/β protein are also conserved among the sequences belonging to the same family. The cluster centers are found to occur in the middle of the strands or in the C-terminal of the strands. In most cases, the residues forming the clusters are part of the active site or are located close to the active site. The folding nucleus of the α/β fold is predicted based on hydrophobicity index evaluation of residues and identification of cluster centers. The predicted nucleation sites are found to occur mostly in the middle of the strands. © 2001 Wiley-Liss, Inc.

Department Of Biotechnology

World University root node

Proteins: Structure, Function and Genetics

Clusters in α/β barrel proteins: Implications for protein structure, function, and folding: A graph theoretical approach

A 5 cm internal diameter Karr reciprocating plate column has been operated in countercurrent liquid-liquid flow in the absence of mass transfer and with mass transfer of i-propanol from the dispersed phase (Isopar M) to the continuous phase (water). The effect of mass transfer is to increase the drop diameter, while the holdup is reduced and axial dispersion is increased. Although an unstable density gradient was created by the mass-transfer process, earlier models developed under non-mass-transfer conditions, based on Kolmogoroffs isotropic turbulence theory, were not applicable in describing the enhancement in axial mixing. It was concluded that the density gradient effect was masked by the effect of the larger drops which were formed because of mass-transfer-induced coalescence. Mass-transfer coefficients for the dispersed phase were found to show the same trends as the Handlos and Baron oscillating drop model.A 5 cm internal diameter Karr reciprocating plate column has been operated in countercurrent liquid-liquid flow in the absence of mass transfer and with mass transfer of i-propanol from the dispersed phase (Isopar M) to the continuous phase (water). The effect of mass transfer is to increase the drop diameter, while the holdup is reduced and axial dispersion is increased. Although an unstable density gradient was created by the mass-transfer process, earlier models developed under non-mass-transfer conditions, based on Kolmogoroff's isotropic turbulence theory, were not applicable in describing the enhancement in axial mixing. It was concluded that the density gradient effect was masked by the effect of the larger drops which were formed because of mass-transfer-induced coalescence. Mass-transfer coefficients for the dispersed phase were found to show the same trends as the Handlos and Baron oscillating drop model.

Effects of mass transfer on the hydrodynamic behavior of a Karr reciprocating plate column

Chemical Engineering Science

Formation of tailed drops in liquid-liquid extraction

Axial dispersion coefficients were measured in the continuous phase in a 5-cm-dia. Karr column, operated cocurrently with the system kerosene(d)-water(c). The effect of unstable density gradient in the continuous phase was studied by injecting a steady stream of sodium chloride solution as a tracer near the top of the column. The effects of energy dissipation due to unstable density gradient, mechanical agitation, and the flow of the dispersed phase were investigated as the three principal variables, and two plate spacings (2.55 and 5.10 cm) were also employed. The axial dispersion results were correlated in terms of a weighted power-law model based on Kolmogoroff's mixing length concept and incorporating contributions due to each of the three modes of energy dissipation. Axial mixing was significantly increased in the presence of unstable density gradients even though these contributed very little (typically less than 1 mW/kg) to the total specific energy dissipation rate.

Effect of Unstable Density Gradients on Back-Mixing in a Reciprocating Plate Column

Unsteady axial mixing due to addition of a batch of sodium chloride solution at the top of a water-filled tube (2.63 cm i.d.) has been studied by measuring the developing concentration profile and the advancing front with dye added to the brine. Data have also been obtained with added baffle plates, with the use of a viscous aqueous solution, and in smaller diameter (1.48, 1.91 cm) tubes. Results can be approximately correlated by means of a model based on unsteady one-dimensional turbulent dispersion. Laminar flow affects the behavior of the advancing front at which the salt concentration is lowest.