R. Bhargava

Numerical study of heat transfer of a third grade viscoelastic fluid in non-Darcy porous media with thermophysical effects

A numerical solution is presented for the natural convective dissipative heat transfer of an incompressible, third grade, non-Newtonian fluid flowing past an infinite porous plate embedded in a Darcy–Forchheimer porous medium. The mathematical model is developed in an (x,y) coordinate system. Using a set of transformations, the momentum equation is rendered one-dimensional and a partly linearized heat conservation equation is derived. The viscoelastic formulation presented by Akyildiz (2001 Int. J. Non-Linear Mechanics 36 349–52) is adopted, which generates lateral mass and viscoelastic terms in the heat conservation equation, as well as in the momentum equation. A number of special cases of the general transformed model are discussed. A finite element method is implemented to solve, with appropriate boundary conditions, the coupled third-order, second degree ordinary differential equation for momentum and the second-order, fourth degree heat conservation equation. We study the influence of the third grade viscoelastic parameter (β3), Darcian parameter (inversely proportional to permeability (kp)), the Forchheimer inertial parameter (b), transpiration velocity (Vo), the transpiration parameter in the heat equation (R) and the thermal conductivity parameter (S) on momentum and heat transfer. Additionally, we study the influence of the Forchheimer inertial parameter (b) on second-order viscoelastic non-Darcy free convection flow and also the effects of the third grade parameter (β3) on Darcian free convection. Velocities increase with rising permeability (Darcian parameter) for both second and third grade viscoelastic free convection regimes and decrease with rising Forchheimer parameter. The effects of the other parameters are described at length. The flow scenario is important in chemical engineering processes.

Supercritical extraction of sunflower oil: A central composite design for extraction variables.

Supercritical carbon dioxide (SC-CO2) extraction of sunflower seed for the production of vegetable oil is investigated and compared to conventional methods. The effects of extracting variables, namely pressure, temperatures, particle size, SC-CO2 flow rate and co-solvent, on SC-CO2 extraction are investigated. The maximum yield for sunflower oil is found to be about 54.37 wt%, and is obtained when SC-CO2 extraction is carried out at 80 °C, 400 bar, 0.75 mm particle and 10 g/min solvent flow with 5% co-solvent. A central composite design is used to develop the model and also to predict the optimum conditions. At optimum conditions obtained based on desirability function, 80.54 °C, 345 bar, 1.00 mm, 10.50 g/min and 7.58% ethanol, SC-CO2 extraction has performed and found that extraction yield dropped by 2.88% from the predicted value. Fatty acid composition of SC-CO2 and hexane extracted oil shows negligible difference and found high source of linoleic acid.

Selection of optimal feed flow sequence for a multiple effect evaporator system

Abstract A nonlinear model is developed for a SEFFFE system employed for concentrating weak black liquor in an Indian Kraft Paper Mill. The system incorporates different operating strategies such as condensate-, feed- and product-flashing, and steam- and feed-splitting. This model is capable of simulating a MEE system by accounting variations in τ, U, Qloss, physico-thermal properties of the liquor, F and operating strategies. The developed model is used to analyze six different F including backward as well as mixed flow sequences. For these F, the effects of variations of input parameters, T0 and F, on output parameters such as SC and SE have been studied to select the optimal F for the complete range of operating parameters. Thus, this model is used as a screening tool for the selection of an optimal F amongst the different F. An advantage of the present model is that a F is represented using an input Boolean matrix and to change the F this input matrix needs to be changed rather than modifying the complete set of model equations for each F. It is found that for the SEFFFE system, backward feed flow sequence is the best as far as SE is concerned.

Finite element modeling of conjugate mixed convection flow of Al2O3–water nanofluid from an inclined slender hollow cylinder

Steady laminar mixed convection flow and heat transfer characteristics of Al2O3–water nanofluid about a vertical slender hollow cylinder are investigated numerically, under the effect of wall conduction. The transformed, non-dimensional, nonlinear governing equations (obtained with the Boussinesq approximation) are solved, using a robust, extensively validated, Galerkin finite element method for spherical-shaped nanoparticles with volume fraction ranging up to 4%, with associated boundary conditions. Nine-node quadrilateral finite elements are employed. Experimental models for thermal conductivity and viscosity incorporating Brownian motion terms have been taken into consideration. The influence of physical parameters, namely wall conduction parameter, Richardson number (buoyancy parameter) and nanoparticle volume fraction, on velocity profile, temperature profile and on Nusselt number is shown graphically. Excellent validation of the present numerical results has been achieved with earlier published results. Both skin friction coefficient and Nusselt number are enhanced with increasing Richardson number. With increasing inclination angle there is a decrease in average Nusselt number. Furthermore, average Nusselt number and interfacial temperature are both reduced with nanoparticle diameter. The flow is accelerated with increasing Richardson number whereas the bulk temperature is found to be suppressed. The study has important applications in thermal enhancement of solar energy systems.

FINITE ELEMENT STUDY OF TRANSIENT PULSATILE MAGNETO-HEMODYNAMIC NON-NEWTONIAN FLOW AND DRUG DIFFUSION IN A POROUS MEDIUM CHANNEL

A numerical study of pulsatile hydromagnetic flow and mass transfer of a non-Newtonian biofluid through a porous channel containing a non-Darcian porous material is undertaken. An extensively-validated biofluid dynamics variational finite element code, BIOFLOW, is employed to obtain comprehensive computational solutions for the flow regime which is described using a spatially two-dimensional momentum equation and a spatially one-dimensional mass transport equation, under appropriate boundary conditions. The Nakamura-Sawada rheological model is employed which provides a higher yield stress than the Casson model. A non-Newtonian model is justified on the basis that blood exhibits deviation from Newtonian behavior at low shear rates. The conduit considered is rigid with a pulsatile pressure applied via an appropriate pressure gradient term. One hundred two-noded line elements have been employed in the computations. The influence of magnetic field on the flow is studied via the magnetohydrodynamic body force ...

MODELING AND SIMULATION OF MEE SYSTEM USED IN THE SUGAR INDUSTRY

In this work, a generalized steady-state mathematical model has been developed for simulation of the multiple effect evaporator (MEE) system, used in the Indian sugar industry. The developed model is capable of handling exhaust steam (saturated/superheated) inputs in more than one effect, vapor bleeding from desired effects, heat loss from each effect, and variations in boiling point rise as well as specific heat capacity with combination, heat transfer coefficient through external empirical correlations, and condensate flashing. The developed model has been solved by the globally convergent method. The results of present investigations have been validated against the data obtained from the Indian sugar industry with seven effects. The predicted exit liquor concentration, vapor body temperature, and amount of vapor bleed from each effect shows close agreement with the industry data within a maximum error band of ±2%. Further, a correlation has been developed for the prediction of overall heat transfer coefficient (OHTC) of each effect. The developed model can be further used to improve the steam economy of the MEE system by the incorporation of flash vapors from condensate stream.

The Kinetics of Catalytic Oxidation of 1-Butanethiol in a Gas Liquid System

Abstract In the present study the kinetics of liquid phase oxidation of light thiols using reformulated cobalt phthalocyanine based catalyst has been investigated in a semi batch bubble column reactor. 1-Butanethiol is chosen to represent thiols in lighter range of petroleum fractions like liquefied petroleum gas and light straight run naphtha. The study has shown that rate of catalytic oxidation of 1-butanethiol is linear at lower concentrations and of nonlinear nature at higher concentrations. A mechanism based rate expression has been obtained to explain this behavior and its parameters are estimated. The derived rate law is similar to Michaelis-Menten rate equation.

Experimental Modeling and Simulation of Supercritical Fluid Extraction of Moringa oleifera Seed Oil by Carbon Dioxide

Moringa oleifera seed is an important source of high oleic acid in vegetable oil. In the present work, supercritical extraction of Moringa seed oil has been carried out to study the influence of operating temperature, pressure, particle size, carbon dioxide flow rate, and co-solvent addition by performing experiments in the range of 333–373 K, 20–40 MPa, 0.50–1.00 mm, 0.83 × 10−4–2.50 × 10−4 kg/s, and 0–10% ethanol. The extraction data have been successfully modeled by extended Lack’s model and fitting parameters are optimized by the Box global optimization technique. The results showed that pressure has a significant effect followed by temperature, co-solvent, solvent flow rate, and particle size.

Optimization of parameters for supercritical extraction of watermelon seed oil

ABSTRACT The present work shows that watermelon seeds have great potential to producing high linoleic and oleic acid content vegetable oil, which have beneficial effects on human health. In concern with developing new green processes for high-quality yield, the extraction is carried out with supercritical CO2 and compared with conventional extraction technique. Extraction has been conducted within the temperature and pressure range of 60–100ºC and 200–400 bar, respectively. To describe the kinetics, the extended Lack model has been selected and effectively applied to the description of extraction curves. The fitting parameter Z, W, and xk have been optimized by Box optimization technique.