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Solid state decomposition studies of Low and High Density Polyethylene (LDPE and HDPE) have been carried out in the present work. Thermo-gravimetric analysis (TGA) is utilized to determine the degradation kinetics for pure plastic samples at different heating rates. The distribution of activation energy values and rates estimated using various Iso-conversional methods have been selected on basis of correlation coefficients. For LDPE, isoconversional method of Friedman and for HDPE Flynn Wall Ozawa methods are used to estimate the distribution of activation energies having their mean values as 256.5 and 257.2 kJ/mol respectively. The inputs from Isoconversional methods are used to determine decomposition behavior with Criado method. Model based studies performed with Criado method identifies the solid-state degradation follows contracting volume-sphere (R3) model based on lower statistical parameter values. The identified decomposition model is validated by Coats Redfern method which also results in lower statistical parameter values. This is further validated through a best fit of extent of reaction profile against temperature, substantiating the solid-state decomposition model followed by given plastic fractions.

Bioreactors are of interest for value-upgrading of stranded or waste industrial gases. Reactor intensification requires development of low cost bioreactors with fast gas–liquid mass transfer rate. Here we assess published reactor technology in comparison with a novel downward bubble flow created by a micro-jet array. Compared to known technology, the advanced design achieves higher volumetric gas transfer efficiency (kLa per power density) and can operate at higher kLa. We measure the effect of four reactor heights (height-to-diameter ratios of 12, 9, 6, and 3) on the gas transfer coefficient kL, total interfacial area a, liquid residence time distribution, energy consumption, and turbulent hydrodynamics. Leading models for predicting kL and a are appraised with experimental data. The results show kL is governed by “entrance effects” due to Higbie penetration dominate at short distances below the micro-jet array, while turbulence dominates at intermediate distances, and finally terminal rise velocity dominates at large distances. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1399–1411, 2018

The main selection criteria for pumps in reprocessing applications is the absence of any moving parts or the moving parts not having any direct contact with the process fluid. There are different types of fluidic pumps such as vortex diode, reverse flow diode, etc. In this work, a new design of helical coil fluidic pump has been developed and demonstrated. Helical coils are widely used in process industries as heat exchangers, reactors, motionless mixers, etc. It is for the first time that the authors are proposing the use of helical coil as a fluidic pump based on its inherent property of high pressure drop as compared to a straight tube. The main objective of this work is to develop an alternate pumping system for reprocessing applications to replace the conventional air lift pump. The helical coil based fluidic diode pump was made up of SS 304 seamless pipe (pipe inner diameter is 9.5 mm) with a 36 mm diameter of helical coil and pitch of 14 mm. In this work, friction factor for the given helical coil was measured from pressure drop experiments. This information was also useful for understanding the transition of the laminar to turbulent region. In order to propose the operating region, the pumping capacity was measured for the helical coil based fluidic pump at different operating conditions. Experimental results show that the proposed hardware is able to pump up to 54 dm3/h. Recommendations have been made for proposing an optimum design. This article is protected by copyright. All rights reserved

Even though many experimental investigations are reported on this subject of liquid velocity patterns in bubble columns, most of the reported work is restricted to measurements at the near wall regions, columns without internals, and in low dispersed phase holdups. In the present work, a non-invasive Radioactive Particle Tracking (RPT) technique was employed to quantify the hydrodynamic parameters in 120 mm diameter bubble column with, and without vertical rod internals, using air/water system as the working fluids. The superficial air velocities cover a wide range of flow regimes: from 14 mm/s to 265 mm/s. Experiments were performed for four internals configurations with percentage obstruction area varied from 0 (without internals) to 11.7%. We report that the liquid phase hydrodynamics depends strongly on superficial gas velocity and internals. This article is protected by copyright. All rights reserved.

Bioreactors are of interest for gas-to-liquid conversion of stranded or waste industrial gases, such as CO, CH4 , or syngas. Process economics requires reduction of bioreactor cost and size while maintaining intense production via rapid delivery of gases to the liquid phase (i.e., high kL a). Here, we show a novel bioreactor design that outperforms all known technology in terms of gas transfer energy efficiency (kL a per power density) while operating at high kL a (i.e., near 0.8 s-1 ). The reactor design uses a micro-jet array to break feedstock gas into a downward microbubble flow. Hydrodynamic and surfactant measurements show the reactor's advanced performance arises from its bubble breakage mechanism, which limits fluid shear to a thin plane located at an optimal location for bubble breakage. Power dissipation and kL are shown to scale with micro-jet diameter rather than reactor diameter, and the micro-jet array achieves improved performance compared to classical impinging-jets, ejector, or U-loop reactors. The hydrodynamic mechanism by which the micro-jets break bubbles apart is shown to be shearing the bubbles into filaments then fragmentation by surface tension rather than "cutting in half" of bubbles. Guided by these hydrodynamic insights, strategies for industrial design are given. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2710, 2019.

Simulation of flow patterns in eleven industrial crystallizers (standard Messo, Cerny direct contact, Swenson draft tube baffled, Swenson walker, Swenson evaporative, Oslo cooling, Oslo Krystal, APV Kestner, Batch Vacuum, stirred tank with disc turbine, and stirred tank with pitched blade impeller) have been carried out using computational fluid dynamics (CFD). Population balance modelling (PBM) is coupled with CFD to obtain better results. In all the cases, the crystallizer volume was 100 liter and the power consumption per unit volume was 1 kW/m3. The simulation results have been presented in terms of mean velocity components, turbulent kinetic energy and dissipation rate. On the basis of the flow patterns, these eleven crystallizers have been compared for crystal size distribution (CSD). It was found that Swenson Evaporative, Krystal and Batch Vacuum provide relatively low CSD.

Crystallization processes in a 500 mL stirred tank crystallizer with computational fluid dynamics (CFD) and population balances toward estimating how crystal size distributions (CSDs) are influenced by flow inhomogeneities was explored. The flow pattern and CSD are presented here though extensive phase Doppler particle analyzer measurements and CFD predictions for three different impeller designs (disc turbine, pitched blade turbine, and Propeller) and each rotated at three different speeds (2.5, 5, and10 r/s). As crystallization processes in practice could involve break-up and aggregation of crystals, some selected break-up and aggregation kernels are incorporated. Extensive comparison of simulations with experimental data showed consistent trends in the proper quantitative range. An attempt has also been made to develop scaling laws: (a) mean particle size with average power consumption per unit mass and (b) particle-size distribution with the turbulent energy dissipation distribution. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3596–3613, 2014

Measurements of temperature patterns in an inductively coupled plasma (ICP) have been carried out experimentally. Plasma torch was operated at different RF powers in the range of 3–14 kW at near atmospheric pressure and over a wide range of sheath gas flow rate (3–25 lpm). Measurements were made at five different axial positions in ICP torch. The chordal intensities were converted into a radial intensity profile by Abel Inversion technique. Typical radial temperature profile shows an off-axis temperature peak, which shifts toward the wall as the power increases. Temperatures in the range of 6000–14,000 K were recorded by this method. The temperature profiles in the plasma reactor were simulated using computational fluid dynamics (CFD). A good agreement was found between the CFD predictions of the flow and temperature pattern with those published in the literature as well as the temperature profiles measured in the present work. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3647–3664, 2014

Carbon nanotubes have been synthesized from acetylene and methane in a fluidized bed by using ferrocene as the catalyst dispersed over carbon black support material. The agglomerate size of carbon black, loading of catalyst, total gas flow rate, partial pressure of reactant gas, temperature of synthesis, and time of synthesis have been varied to understand their effects on the yield of carbon nanotubes. A reaction mechanism consisting of eleven steps and the rate equations for these steps have been proposed. Formation of carbon molecules on the catalyst surface was found to be the rate controlling step in the temperature range of 700–807°C, with an activation energy 47 kJ mol−1, while diffusion through pores in the carbon black was found to be the rate controlling step in the temperature range of 807–1000°C with an activation energy of 7.6 kJ mol−1. A continuous deactivation of the catalyst, represented by an exponential decay, was observed. The products have been characterized by thermogravimetry, electron microscopy, and Raman spectroscopy. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2882–2892, 2014

The production of petroleum coke (petcoke) in the refineries is progressively peaking up because of the trend of processing heavy crudes and in turn, a renewed interest in delayed coking process. Therefore, an efficient, economical, and environmentally safe utilisation of petcoke has become imperative in the current petroleum refining scenario. Gasification of petcoke has emerged as one of the attractive options and is gaining increasing attention to convert the petcoke to value-added products. The process offers the refiners a variety of product slates mainly via synthesis gas route. The products include steam, hydrogen, electricity, chemicals (viz. methanol, ammonia, etc.), liquid fuels via Fischer–Tropsch (F-T) synthesis and so on. Petcoke has been identified as a potential feedstock for about 15% of the total planned gasification capacity worldwide. In the present communication, the published literature pertaining to petcoke gasification has been extensively analysed and a state-of-the-art review has been written that includes: (1) the importance of petcoke gasification in the present petroleum refining scenario; (2) petcoke gasification reaction mechanism, kinetics, and typical product profile; (3) parametric sensitivity of the operating variables such as temperature and pressure; (4) various gasifiers for petcoke gasification; (5) modelling efforts on different types of gasifiers and (6) future prospects of petcoke gasification. An attempt has been made to get the afore-mentioned aspects together in a thematic framework so that the information is available at a glance and is expected to be useful as a single point source to the researchers and practicing refiners.

The condensation of pure steam flowing inside a vertical tube has been extensively studied during the last nine decades. Considerable amount of experimental and analytical efforts can be found due to the significance of this subject in practice. In the present work (Part I), experimental investigations have been performed over a range of pressure (0.1

The condensation of pure steam flowing downward inside a vertical tube has been extensively studied. Considerable amount of experimental and analytical efforts can be found due to the significance of this subject in practice. In this work, a critical review of the most important experimental, analytical and computational fluid dynamic (CFD) investigations have been presented. CFD simulations for the geometries of Goodykoontz and Dorsch [Goodykoontz and Dorsch, NASA TN D-3326, 1966; Goodykoontz and Dorsch, NASA TN D-3953, 1967], Kim and No [Kim and No, Int. J. Heat Mass Transf. 2000;43:4031–4042] and the present work have been performed and compared with the experimental data reported in these investigations. CFD predictions of the pressure drop and the heat transfer coefficient (HTC) were in close agreement with the experimental values. A preliminary regime map has been constructed for downward flow steam condensation inside pipes. Finally, all the published semi-empirical correlations for the HTC have been critically analysed and compared with the CFD predictions. An attempt has been made to make specific recommendations. © 2012 Canadian Society for Chemical Engineering

A system for the conversion of kinetic energy of wind into thermal energy has been developed which can replace relatively expensive electro-mechanical equipment. The system consists of a vertical axis wind turbine (VAWT) which is coupled with the shaft of a stirred vessel. In the present work, computational fluid dynamic (CFD) simulations have been performed for the flow generated in a stirred tank with disc turbine (DT). The predicted values of the mean axial, radial and tangential velocities along with the turbulent kinetic energy have been compared with those measured by laser Doppler anemometry (LDA). Good agreement was found between the CFD simulations and experimental results. Such a validated model was employed for the optimisation of drag-based VAWT. An attempt has been made to increase the efficiency of turbine by optimising the shape and the number of blades. For this purpose, the combination of CFD and experiments has been used. The flows generated in a stirred tank and that generated by a wind turbine were simulated using commercial CFD software Fluent 6.2. A comparison has been made between the different configurations of wind turbines. Results show that a provision in blade twist enhances the efficiency of wind turbine. Also, a wind turbine with two blades has higher efficiency than the turbine with three blades. Based on the detailed CFD simulations, it is proposed that two bladed turbine with 30° twist shows maximum efficiency. © 2011 Canadian Society for Chemical Engineering

In the first part of the review, published literature regarding the CFD modelling of single-phase turbulent flow in stirred tank reactors with radial flow impellers was critically analysed. A brief overview of different turbulence models (standard k − e model, RNG k − e model, the Reynolds stress model and large eddy simulation) as well as impeller baffle interaction models has been presented in the previous part. This part is concerned with the review of literature regarding CFD simulation of axial flow impellers. Comprehensive simulations have been carried out using various turbulence models and the model predictions (of all the mean velocities, turbulent kinetic energy and its dissipation rate) have been compared with the experimental measurements at various locations in the tank. The strengths and weaknesses of various turbulence models for axial flow impellers is presented. The quantitative comparison of exact and modelled turbulence production, transport and dissipation terms has highlighted the reasons behind the partial success of various modifications of standard k − e model as well as Reynolds stress model. Literature efforts on multiple impeller systems and multiphase systems have been discussed in a separate section. Based on these results, suggestions have been made for the future work in this area. Dans la premiere partie de l'etude, on a procede a une analyse critique de la litterature concernant la modelisation de la dynamique des fluides numerique de l'ecoulement turbulent a une phase dans les reacteurs a cuve agitee dotes de turbines a ecoulement radial. Une vue d'ensemble rapide des differents modeles de turbulence (modele standard k-e, modele RNG k-e, modele aux tensions de Reynolds et simulation des grandes echelles), ainsi que des modeles d'interaction des deflecteurs de turbine, a ete presentee dans la partie precedente. Cette partie se concentre sur l'analyse de la litterature concernant la simulation de DFN de turbines a ecoulement axial. Des simulations completes ont ete effectuees en utilisant plusieurs modeles de turbulence et les predictions des modeles (de toutes les vitesses moyennes, de l'energie cinetique turbulente et de son taux de dissipation) ont ete comparees aux donnees experimentales relevees a differents endroits de la cuve. On a presente les points forts et les points faibles de plusieurs modeles de turbulence concernant les turbines a ecoulement axial. La comparaison quantitative des donnees exactes et modelisees de la production, du transport et de la dissipation de la turbulence a mis en evidence les raisons qui expliquent la reussite partielle de plusieurs modifications apportees au modele standard k-e ainsi qu'au modele aux tensions de Reynolds. Une partie distincte est consacree a la discussion des resultats indiques dans la litterature concernant les systemes a roues multiples et les systemes multiphases. Sur la base de ces resultats, des etudes a venir dans ce domaine ont ete suggerees. © 2011 Canadian Society for Chemical Engineering

A critical review of the published literature regarding the computational fluid dynamics (CFD) modelling of single-phase turbulent flow in stirred tank reactors is presented. In this part of review, CFD simulations of radial flow impellers (mainly disc turbine (DT)) in a fully baffled vessel operating in a turbulent regime have been presented. Simulated results obtained with different impeller modelling approaches (impeller boundary condition, multiple reference frame, computational snap shot and the sliding mesh approaches) and different turbulence models (standard k − e model, RNG k − e model, the Reynolds stress model (RSM) and large eddy simulation) have been compared with the in-house laser Doppler anemometry (LDA) experimental data. In addition, recently proposed modifications to the standard k − e models were also evaluated. The model predictions (of all the mean velocities, turbulent kinetic energy and its dissipation rate) have been compared with the experimental measurements at various locations in the tank. A discussion is presented to highlight strengths and weaknesses of currently used CFD models. A preliminary analysis of sensitivity of modelling assumptions in the k − e models and RSM has been carried out using LES database. The quantitative comparison of exact and modelled turbulence production, transport and dissipation terms has highlighted the reasons behind the partial success of various modifications of standard k − e model as well as RSM. The volume integral of predicted energy dissipation rate is compared with the energy input rate. Based on these results, suggestions have been made for the future work in this area.

The objective of this study is to collect the data on overall gas hold-up (∈G) for bubble column reactors handling various gas–liquid systems and further develop a unified data-driven model for the estimation of the same. In this work, around 3300 experimental points for ∈G have been collected from 85 open sources spanning the years 1963–2008. The data-driven model for overall gas hold-up has been established using hybrid Genetic Algorithm-Support Vector Regression (GA-SVR)-based methodology. In the present study, GA has been used for nonlinear rescaling of the parameters. These exponentially scaled parameters are subsequently subjected for SVR training. The technique is an extension of conventional SVR technique, showing relatively enhanced results. The proposed hybrid model is based on various prominent design and operating parameters (15 in number) which includes superficial gas velocity, superficial liquid velocity, gas density, molecular weight of gas, sparger type, sparger hole diameter, number of sparger holes, liquid viscosity, liquid density, liquid surface tension, ionic strength of liquid, operating temperature, operating pressure, liquid height, and the column diameter. The estimations made by the SVR-based unified model for ∈G shows an excellent agreement with actual values with estimation accuracy of 98.5% and % AARE of 9.32%. For ease in applicability and ready reference of the practicing engineers, the hybrid GA-SVR-based model in the form of software and the entire database for ∈G has been uploaded on the link http://www.esnips.com/web/UICT-NCL. L'objectif de cette etude est de collecter les donnees de la retenue d'ensemble de gaz (G) pour des reacteurs a colonne a bulles traitant divers systemes gaz-liquide et perfectionner le developpement d'un modele unifie axe sur les donnees pour l'estimation du meme parametre. Dans ce travail, environ 3300 points experimentaux de G ont ete collectes a partir de 85 sources ouvertes recouvrant la periode 1963/2008. Le modele unifie axe sur les donnees pour la retenue d'ensemble de gaz a ete etabli en utilisant une methodologie basee sur un hybride algorithme genetique-regression a soutien vectoriel (GA-SVR). Dans l'etude presente, l'algorithme genetique a ete utilise pour le reechelonnage non lineaire des parametres. Ces parametres echelonnes exponentiellement sont ensuite assujettis a un traitement de regression a soutien vectoriel (SVR). La technique est une extension de la technique SVR conventionnelle, demontrant des resultats relativement ameliores. Le modele hybride propose est base sur divers concepts bien etablis et les parametres operatoires (au nombre de 15), dont la velocite gazeuse superficielle, la velocite liquide superficielle, la densite gazeuse, le poids moleculaire du gaz, le type d'arroseur, le diametre de l'orifice de l'arroseur, le nombre d'orifices d'arrosage, la viscosite du liquide, la densite du liquide, la tension superficielle du liquide, la force ionique du liquide, la temperature operatoire, la pression operatoire, la hauteur de liquide et le diametre de la colonne. Les estimations faites par le modele unifie base sur la regression a soutien vectoriel (SVR) pour G montre une excellente correspondance avec les valeurs reelles, avec une precision d'estimation de 98,5 et un pourcentage AARE de 9,32%. Pour la facilite d'application et le besoin d'avoir des references pretes a l'emploi des ingenieurs, le modele hybride GA-SVR pour G a ete telecharge sous la forme d'un logiciel et la base de donnees totale est disponible a l'adresse http://www.esnips.com/web/UICT-NCL.

A computational analysis using standard k-e model, RSM and LES has been carried out for jet loop reactors (JLR) to investigate the mean and turbulence quantities. These simulations have revealed that the flow in JLR was different from the self-similar round jets. RSM and LES showed better agreement with PIV measurements compared with standard k-e model. The modeled turbulence production and transport in k-e model overpredicted those estimated from LES data. To reduce the limitations, modified k-e models have been evaluated for JLR. Also, a hybrid k-e model has been suggested, which was found to perform better than other modified k-e models. This model was also found to hold for stirred tank reactors (STRs). Mixing time analysis has been carried out for JLR and STR at same power consumption. It has been shown that JLR can be inferior to STR if proper nozzle diameter is not selected.

Conventional processes for the upgradation of residual feedstocks, viz., thermal cracking and catalytic cracking are carried out in the temperature range of 400–520°C. Such high temperatures can in principle be substituted by acoustic cavitation. In the present work, two vacuum residues, namely, Arabian mix vacuum residue (AMVR) and Bombay high vacuum residue (BHVR) and one asphalt, viz., Haldia asphalt (HA) were subjected to acoustic cavitation for different reaction times from 15 min to 120 min at ambient temperature and pressure. An attempt has been made to seek a performance comparison of two devices of acoustic cavitation, namely, ultrasonic bath and ultrasonic horn with regard to their ability to upgrade the petroleum residues to lighter, more value-added products mainly the hydrocarbons boiling in the range of gas oil fraction. Another attempt has been made to study the effect of ultrasound on the upgradation of the residue when it is emulsified in water with the help of different surfactants. For all the cases, a kinetic model has been developed based on the constituents of the residue so as to get an insight into the reaction mechanism. The study revealed that ultrasonic horn is more effective in bringing about the upgradation than ultrasonic bath and that the acoustic cavitation of the aqueous emulsified hydrocarbon mixture could reduce the asphaltenes content to a greater extent than the acoustic cavitation of non-emulsified hydrocarbon mixture. The reduction in asphaltenes content of BHVR was found to be more followed by AMVR followed by HA. The variation in the rate constants was found to be feed specific and the rate constants for the conditions of maximum conversion of asphaltenes to gas oil for AMVR, BHVR and HA were found to be 0.29 × 10−4 s−1, 1.4 × 10−4 s−1 and 0.23 × 10−4 s−1, respectively. Les procedes traditionnels visant a enrichir la concentration des matieres premieres residuelles, c.-a-d. le craquage thermique et le craquage catalytique, se font a des temperatures variant entre 400 et 520°C. Des temperatures aussi elevees peuvent, en principe, etre substituees par la cavitation acoustique. Dans le cadre de cette etude, deux residus sous vide, a savoir le melange arabe de residus sous vide (MARSV) et le residu de vide pousse de Bombay (RVPB) et un asphalte, c.-a-d. l'asphalte Haldia (AH), ont ete soumis a la cavitation acoustique selon differents temps de reaction, variant entre 15 et 120 minutes, a la temperature et la pression ambiantes. Une tentative a ete faite pour chercher a obtenir une comparaison du rendement des deux dispositifs de cavitation acoustique, a savoir un bain a ultrasons et une sonde a ultrasons, en ce qui a trait a leur capacite a enrichir la concentration des residus de petrole de facon a obtenir des produits plus legers a valeur ajoutee accrue, principalement les hydrocarbures en ebullition dans la gamme de fractions gaz-petrole. Une autre tentative a ete faite pour etudier l'effet des ultrasons sur l'enrichissement de la concentration du residu lorsqu'il est en emulsion dans l'eau avec l'aide de differents agents de surface. Dans tous les cas, on a elabore un modele cinetique fonde sur les elements constitutifs du residu de facon a obtenir un apercu du mecanisme de reaction. L'etude a revele que la sonde a ultrasons est plus efficace pour provoquer l'enrichissement de la concentration que le bain a ultrasons et la cavitation acoustique du melange d'hydrocarbures en emulsion aqueuse pouvait reduire le contenu en asphaltenes dans une plus grande mesure que la cavitation acoustique d'un melange d'hydrocarbures non en emulsion. La reduction du contenu en asphaltenes du RVPB s'est averee etre la plus grande, suivie du MARSV et de l'AH. La variation des constantes de vitesse de reduction s'est averee etre propre a la charge et les vitesses de reduction concernant les conditions de la conversion maximale des asphaltenes en gaz-petrole du MARSV, du RVPB et de l'AH se sont averees etre de 0,29 × 10−4 s−1, 1,4 × 10−4 s−1 et 0,23 × 10−4 s−1, respectivement. Mots-cles: ultrason, cavitation, residu de petrole, agent de surface, emulsion, cinetique.

A three-dimensional CFD model has been developed to predict liquid phase velocities in bubble columns. An agreement was observed between the predicted and the experimental data available in the published literature. The validated CFD model has been extended for the simulation of macro-mixing and hence the prediction of mixing time, RTD and dispersion coefficient. Liquid phase mixing time was measured in 0.2 and 0.4 m i.d. columns over a wide range of superficial gas velocity (0.07 to 0.295 m/s) and height-to-diameter ratio (2 to 10). An agreement was observed between the CFD predictions and the experimental values of the mixing time as well as all the experimental data on dispersion coefficient published in the literature.

A one-dimensional steady-state model is developed for the prediction of axial variation of the gas holdup in flotation column froths. Froth is considered as an inverse fluidized bed of bubbles and hence the frictional pressure gradient is obtained based on the energy balance. Pressure gradient can also be obtained from the Ergun equation with adjustable constants. The model correctly captures the effect of superficial gas velocity, superficial liquid velocity and bubble diameter on the variation of the gas holdup along the froth height. The predictions of the model are in agreement with the experimental data from the literature.

In the present work, a computational fluid dynamics study has been carried out to bring out the mixing characteristics of bubble column and external loop airlift reactor. A comparison of mixing time for two reactors has been presented on the basis of the same reactor volume as well as the total power input. The CFD model was validated by simulating flow, both in bubble column and external loop airlift reactor. An agreement was observed between the predicted and the experimental data available in the published literature. The validated CFD model has been extended for the simulation of the mixing time for both the reactors. The CFD predictions of mixing time show good agreement with the experimental values published in literature. A systematic numerical study was then carried out to bring out the mixing characteristics of both the reactors. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd.

World petroleum residue processing capacity has reached about 725 million metric tons per annum (MMTPA). The high demand for transportation fuels and the ever-rising heavy nature of crude oil have resulted in a renewed interest in the bottom-of-the-barrel processing using various conversion processes. Delayed coking, known for processing virtually any refinery stream (which not only poses a serious threat to environment, but also involves a disposal cost) has garnered tremendous importance in the current refining scenario. Needle coke obtained from delayed coking process is a highly sought-after product, which is used in electric arc furnaces (in the form of graphite electrodes) in steel making applications. In the present communication, the published literature has been extensively analyzed and a state-of-the-art review has been written that includes: (1) importance and place of delayed coking as a residue upgrading process in the current refining scenario; (2) coking mechanism and kinetics; (3) design aspects; (4) feedstocks suitable for the production of needle coke; (5) characteristics of needle coke; (6) factors affecting needle coke quality and quantity; and (7) future market for needle coke. An attempt has been made to get the above-mentioned aspects together in a coherent theme so that the information is available at a glance and could be of significant use for researchers and practising refiners.

A population balance model is developed for the prediction of the average gas holdup and axial gas holdup profile in the bubble columns operating in the homogeneous regime. The model takes into account the effect of bubble expansion along the column height and thus it is applicable to tall columns such as flotation columns in the mineral processing industries. The model captures the effect of superficial gas and liquid velocities, bubble rise velocity, operating pressure, and column height on the gas holdup. In the case of flotation columns, because of the presence of surfactants in the liquid phase, froth is observed at the top of the column. Typically, froth shows the axial profile of gas holdup and the mean bubble size, indicating that the coalescence is an important phenomenon to describe the dynamics of the froth. A probabilistic perspective is developed to address the bubble coalescence process occurring in the froth and the bubble transition probability for coalescence is obtained from experimental data in the literature.

A CFD analysis has been carried out to elucidate the characteristic features of axial mixing in gas-liquid dispersed upflow when the flow changes between two extremes: from bubble column, with very low/no liquid velocity, to pipe flow with very high liquid velocity. The CFD model was validated by simulating flow both in multiphase and in single phase. An agreement was observed between the predictions and the experimental data available in the published literature. The validated CFD model has been extended for the simulation of the axial dispersion coefficient for both multiphase and single phase. CFD predictions of the axial dispersion coefficient show good agreement with experimental values published in the literature. A systematic numerical study was done by varying the superficial liquid velocity, from a very low value to a very high value, to understand its effect on axial dispersion.

A new method is developed for the determination of bubble size distributions from experimental laser Doppler anemometry (LDA) data through simultaneous measurement of only two orthogonal velocity components and the intermittent time gaps arising out of bubbles passing through the measurement point. An experimentally verifiable assumption of axisymmetry allowed the calculation of the three-dimensional velocity distributions from the two-dimensional measurement through the elegant use of a mathematical transform called Abel's transform. In conjunction with the use of probability theory, it allows calculation of the chord length distribution. The bubble size distribution is obtained by an inversion procedure, which facilitates the transformation of chord lengths to bubble sizes. The inversion procedure is successfully tested with Monte Carlo simulations, in which bubbles of prescribed size distribution were generated for obtaining synthetic data on subtended chord lengths at any given point in the column. It is unambiguously demonstrated that assumptions that do not account for correlation between bubble size and direction of motion can yield highly erroneous size distributions from chord length data. The procedure was then used on experimental chord length distributions obtained using LDA to estimate local bubble size distributions in our bubble column. It is particularly interesting to observe that the mean bubble size estimated from the calculated bubble size distributions were consistent with an estimation based on slip velocity information in accord with the Zuber-Findlay drift flux model.

The absorption of NO X gases in water and alkalies /NaOH, NH 4 OH, Ca(OH) 2 )] provides commercially important products nitric acid and salts (nitrates and nitrites), respectively. This complex phenomena of mass transfer with chemical reactions is described quantitatively in terms of /H(kD)] J values for J = N 2 O 3 , N 2 O 4 . However, the reported value of H(kD) for N 2 O 3 absorption in strong alkaline solution was 50 times its value in water. For the intermediate case of NO X absorption in weak alkali Ca(OH) 2 , it was necessary to have a mathematical model which incorporated the HNO 2 decomposition, as well as neutralization by alkali. This led to a unified model for NO X absorption, which can be used for predicting point rates of NO X absorption as well as selectivity, for various gas compositions and liquid-phase pH. Parametric sensitivity has been reported. A comparison of the model predictions with data from patent on Ca(NO 2 ) 2 manufacture has been made to test the model validity.

In chemical process industry, a variety of equipment is used for carrying out different unit operations and unit processes. The design procedures for this equipment have been largely empirical due to the complexity of fluid mechanics. In view of this, a stepwise procedure has been suggested based on experimental fluid dynamics (EFD) and computational fluid dynamics (CFD). One application of EFD and CFD is presented for the prediction of the heat transfer coefficient in the single-phase turbulent pipe flow. The present capabilities of CFD for the design of different process equipment have been outlined.

The thermal efficiency of currently employed cooking methods ranges between 10 and 25%. Cooking accounts for ∼40% of total energy consumed in developing world indicating toward huge scope for improvement. To develop the cooking methods of better efficiency, bringing down the energy consumption, it is necessary to understand the kinetics of cooking. As rice is a staple food for nearly 50% of the world's population, an attempt is made to scientifically explore the kinetics of rice cooking process. It is a well-known fact that presoaking of the rice reduces the cooking time and thus reduces energy consumption, to support this numerically, different parametric measurements such as moisture absorption, change in dimensions (length and width) of rice grain while cooking, are utilized for estimating the cooking kinetics. In addition, the technique of image analysis was also used for easy and quick estimation of the extent of cooking. Experiments were performed with both un-soaked and presoaked rice at three different temperatures (80, 90, and 97 °C) to evaluate the kinetics of rice cooking process. The activation energies for cooking of un-soaked and presoaked rice were found to be ∼ 75 kJ/mol and ∼ 70 kJ/mol, respectively, which is in good agreement with the values reported in literature. Regime of operation for cooking of rice is found to be diffusion controlled based on swelling particle model. Practical applications Around 40 % of the total energy consumed in the developing world (population more than 496 billion) goes in cooking processes (Joshi et al., 2012). This huge energy consumption can be attributed to the inefficiencies related to cooking methods and/or devices. There is an urgent need to employ an energy efficient engineering solution for preparing hygienic, nutritious meals, which also has advantages of energy efficiency, ease of operation and efficient resource utilization. In order to design any efficient cooking device, kinetics of cooking for particular food material must be studied. Shinde et al. (2016), Joshi et al. (2012) have designed the energy efficient batch and continuous cookers. Presented work utilizes simple method for determining kinetics of rice cooking, which can be easily extended to obtain kinetics of any other food material.

Cooking methods used currently are about 10–15% thermally efficient. To develop better efficient methods of cooking, it is desirable to understand the kinetics of cooking. Experiments were performed with both unsoaked and presoaked split-peas (commonly known as Dhal in India) at three different temperatures (90 °C, 94 °C, and 98 °C). It has been found that Dhal does not cook at 90 °C even after 120 min of cooking time. Pre-soaking of Dhal does not found to reduce the time required for cooking. In the present work, the rate of water absorption and hardness of cooked Dhal grains were measured. Both the measurements were used for the estimation of cooking kinetics. The rate constants for cooking of unsoaked and presoaked Dhal were found to be ∼ 4 × 10−4 s−1 at 94 °C and ∼8 × 10−4 s−1 at 98 °C. Regime of operation for cooking of Dhal is found to be diffusion controlled based on swelling particle model of (Singhal et al., 2012). Practical applications About 40 % of the total energy consumed in the developing World (population more than 4 billion) is used for cooking. In developing countries, where 70 % of the population resides in rural areas, open pan cooking method (efficiency ∼15%) is still the most widely used. Pressure cooker development has improved the thermal efficiency to some extent. There is an urgent need to employ an energy efficient engineering solution for preparing hygienic, nutritious meals, which also has advantages of energy efficiency, ease of operation and efficient resource utilization. In order to design any efficient cooking device, kinetics of cooking for particular food material must be studied. Shinde et al., (2016), Joshi et al., (2012) have designed the energy efficient batch and continuous cookers. Presented work utilizes simple method for determining kinetics of spilt peas, which can be easily extended to obtain kinetics of any other food material.

Weeping through perforated plates occurs when the pressure drop of the gas/vapor passing through it is insufficient to support the liquid. The critical weep velocities (VO, crit) were measured for the plates having hole diameter range of 1 to 6mm. The thickness to hole diameter ratio (t/dO ) and the pitch to hole diameter ratio (P/dO) were varied in the range of 1 to 6 and 3.9 to 25.8, respectively. It was found that the VO, crit, crit is a strong function of plate parameters and the clear liquid height. A mathematical model for "No weep" condition was developed under the following two extreme conditions: (i) holes are partially open, (ii) holes are completely active. The results obtained from the experimentation and the mathematical correlation were put into a coherent form. The weeping criterion in terms of the Froude number was correlated with the plate parameters and the clear liquid height.