Kannan A

Effective removal of the trace quantities of hydrogen and its isotopologues is crucial for the proper functioning of the tritium extraction system (TES) in the fuel cycle system of the fusion reactor. Zeolite molecular sieves of Linde Type A (LTA) framework are considered potential adsorbent materials for the cryogenic molecular sieve bed (CMSB) of the TES. However, the adsorption isotherm data of H2, HD, D2, HT, DT, and T2 on LTA 4A zeolites at low pressures (1–1000 Pa) and 77.4 K temperature is scarce in the literature. Grand canonical Monte Carlo (GCMC) simulations were performed to study the hydrogen isotopologues adsorption in the pressure and temperature ranges of operation of the CMSB of TES. The adsorption isotherms show that the equilibrium loading capacity is larger for T2, followed by D2 and H2 at 77.4 K. In the case of heteronuclear isotopologues, the loading capacity is larger for DT, followed by HT and HD under the same conditions of interest. The increase in the equilibrium adsorption capacity with isotopic mass could be attributed to the difference in the zero-point energies of the isotopologues. The effect of Si/Al ratio in the LTA zeolites on the cryosorption of hydrogen isotopes is investigated. The results show that, as the Si/Al ratio decreased, the equilibrium loading of the hydrogen molecules increased. The results obtained from this work are in good agreement with our experimental results and published data in the literature.

Thermal sterilization of canned viscous liquid foods using saturated steam is enabled by natural convective heat transfer. However, the governing equations for two-dimensional convective heat transfer may be only rigorously solved by numerical calculations. On the other hand, if conduction is assumed to be the only mode of heat transfer, the thermal sterilization problem has analytical solutions for simple boundary conditions. However, the conduction model may not be appropriate in describing thermal sterilization of even viscous liquid foods and may cause considerable error in the prediction of the important parameters such as slowest heating zone (SHZ) temperature and lethality. The longer time for sterilization recommended by the conduction model may lead to overprocessing and an unacceptable food product. The objective of this work is to quantify the faster temperature rise in the food can due to natural convection when compared to the temperature rise obtained by only conductive heating. The consequent enhancement in lethalities is also reported. In addition, this work's objective is to investigate how quickly the natural convective heat transfer effects begin to dominate over the solely conduction heating mode. The volume-averaged temperature as well as the SHZ temperature variations with time was calculated for the convection-augmented mode using computational fluid dynamics (CFD) simulations. Lethality values were then calculated based on volume-averaged temperature as well as the SHZ temperature. Food cans of different aspect ratios and food medium thermal conductivities are considered in this analysis. For the food system investigated, the critical Fourier number at which the transition to convection-augmented mode of heat transfer occurred is identified and explained from scaling considerations. In the conduction-dominated mode, it was possible to use analytical solutions to predict the volume-averaged and SHZ temperatures of the liquid food undergoing thermal sterilization. The Nusselt number correlation developed by Kannan and Gourisankar (2008) was used in the lumped parameter transient heat transfer model to predict the volume-averaged temperatures in the convection-dominated region. The volume-averaged temperatures from this approach were found to be in good agreement with the CFD simulation results. The time predicted for the SHZ to reach the minimum sterilization temperature was significantly lower when convective heating was also considered. The volume-averaged temperature and SHZ temperature enabled an estimation of overall sterility levels attained and minimum sterility levels prevalent inside the can, respectively. Even though the volume-averaged temperature increase due to convection was only about 10 K, the resulting accumulated lethality values were higher by an order of magnitude. The increase in SHZ temperatures was much higher in the convection-augmented mode, and consequently greater integrated lethalities were attained. The simple conduction model that is amenable to analytical solution cannot be used to approximate the heat-transfer-related phenomena even for "quick estimation" purposes when convection effects are significant. This precaution is found necessary even for the reasonably high viscous carboxy methyl cellulose system, whose average viscosity values ranged between 13 and 3 Pa s during the course of the sterilization process. © 2009 Springer Science + Business Media, LLC.

The influence of power ultrasound (20 kHz) on the rate of attainment of saturation of sparingly soluble benzoic acid in distilled water and in 24% (w/w) aqueous glycerol was experimentally investigated at 30 °C. The importance of proper temperature control of process vessel contents when it was irradiated with high ultrasonic power level settings was demonstrated. A method was proposed to calculate the volumetric mass transfer coefficient under non-isothermal conditions. © 2009 Elsevier B.V. All rights reserved.

Alginate is a naturally occurring linear polysaccharide that is extracted from brown algae. This is generally produced as water-soluble Na alginate which in turn is transformed into water-insoluble Ca-Alginate beads. These beads are potential adsorbents for the removal of heavy metal ions from water through ion exchange with calcium ions present in the Ca-Alginate matrix. To investigate the feasibility of ion exchange of various heavy metal ions, Density Functional Theory (DFT) calculations were carried out using the Gaussian-16 simulation package. The heavy transition metal ions with + 2 valence in the 4th, 5th, and 6th periods of d-block were considered for the study as most of the heavy metals (e.g., Cu, Cr, Ni, Co, Mn, etc.) are present in this block and significantly contribute to water pollution. The widely accepted egg-box molecular model representation of alginate structures is used for computation purposes. For computation purposes, one monomer attached from top and bottom to the metal center is considered. The computations were carried out in both vapor and aqueous solvent phases and the trends of binding energy were found to be invariant. The binding energies of the alginate complexes formed with Ni, Pd, and Pt metal ions of the 4th, 5th, and 6th series were the highest amongst all the metals considered in this work.

Enhancing natural convective heat transfer in canned food sterilization is explored through modifications to container geometry and its orientation. A conical geometry, of equal volume and height as that of the cylinder, pointing either vertically up or down was considered. The non-Newtonian fluid, 0.85% w/w sodium carboxy-methyl cellulose (CMC), was taken as the test food material and its laminar flow behavior was investigated using computational fluid dynamics (CFD). The movement of the slowest heating zone (SHZ) temperature was tracked and compared for the three geometries. The SHZ temperature was observed to attain the final sterilization fluid temperature of 100 °C fastest for an upright conical geometry followed by the cylinder and the downward pointing cone. There is scope for enhancing the thermal sterilization process through geometry modifications but without mechanical agitation or rotation. Further, the geometry modification if non-uniform must be complemented by its suitable orientation. © 2005 Elsevier Ltd. All rights reserved.

The effect of cylinder inclination on thermal buoyancy induced flows and internal natural convective heat transfer is explored using CFD simulations. The cylinder's top and bottom surfaces were maintained at different temperatures while the curved surface was adiabatic. The aspect ratio (length/diameter) of the cylinder was unity and the Prandtl number of the fluid was fixed at 0.71. The Rayleigh number of the confined fluid was varied from 103 to 3.1 × 104 by changing the specified end wall temperatures. The critical Rayleigh number was estimated to be 3800 for the vertical cylinder. Relaxing the convergence criterion caused false hysteresis in the converged results for the vertical cylinder. Typical natural convective fluid flow and temperature patterns obtained under laminar flow conditions are illustrated for various inclinations ranging from 0° to 180°. Flow visualization studies revealed complex three-dimensional patterns. Different thermal-hydrodynamic regimes were identified and were classified in terms of Rayleigh number and angle of inclination. Empirical correlations for the Nusselt number and maximum velocities in the domain as a function of the inclination angle and Rayleigh number are developed. © 2008 Elsevier Ltd. All rights reserved.

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.

The effect of power ultrasound (20 kHz) on the dissolution rates of a spinning disk made from sparingly soluble benzoic acid was investigated. Ultrasound was found to intensify the dissolution rates especially at lower rotational speeds of the spinning disk. The ultrasonic intensification was found to decrease with increase in the rotational speed of the spinning disk. Empirical correlation was developed for the Sherwood number in the presence of ultrasound and mechanical rotation of the disk. From this, the intensification factor was derived in terms of ultrasonic power input and Reynolds number corresponding to the spinning disk. The intensification factor obtained in the current spinning disk configuration was compared with that obtained for the rotating cylinder configuration studied by Kannan and Pathan [Kannan, A.; Pathan, S. K. Enhancement of Solid Dissolution Process. Chem. Eng. J.2004, 102, 45.]. © 2011 American Chemical Society.

Catalyst loading is an important parameter that needs to be optimized in the operation of photocatalytic slurry reactors. In this study on photocatalytic degradation of phenol, the optimum catalyst loading was found to depend mainly on the dissolved oxygen (DO) concentration in the aqueous solution, especially at higher irradiation intensities. The estimated Langmuir-Hinshelwood (L-H) kinetics constants were found to vary with light intensity and dissolved oxygen concentration. The intermediate products of photocatalytic oxidation were identified. © 2008 Springer.

Valve trays are becoming popular in the chemical process industries owing to their flexibility to handle a wide range of vapor throughputs. Using the rigorous rate based model, the importance of the non-equilibrium approach is demonstrated for a typical extractive distillation process in a Glitsch V-1 valve tray column. Simulation results based on an in-house developed code indicated that the rate based model predictions for a valve tray column operation showed significant differences relative to the equilibrium model. Even small errors in product purities translated into non-optimal feed stage locations and inaccurate number of stages required. The counter-intuitive effect of high reflux ratio on separation is explained.