Zied Driss

Effects of baffle length on turbulent flows generated in stirred vessels

The aim of this paper is to study the effect of baffles length on the turbulent flows in stirred tanks. The hydrodynamic behaviour induced by a Rushton turbine (RT6) is numerically predicted by solving the Navier-Stokes equations in conjunction with the Renormalization Group (RNG) of the k-ɛ turbulence model. These equations are solved by a control volume discretization method. The numerical results from the application of the computational fluid dynamics (CFD) code Fluent with the multi-reference frame (MRF) model are presented in the vertical and horizontal planes in the impeller stream region. Our studies were carried out on three different systems. The most effective system was selected based on its calculated power consumption figure. All numerical results showed good agreement with experimental data.

CFD simulation of the laminar flow in stirred tanks generated by double helical ribbons and double helical screw ribbons impellers

In this paper, the mixing performance of double helical ribbons and double helical screw ribbons impellers mounted on stirred tanks is numerical investigated. The computer simulations are conducted within a specific computational fluid dynamic (CFD) code, based on resolution of the Naviers-Stokes equations in the laminar flow with a finite volume discretization. The field velocity and the viscous dissipation rate are presented in different vessel planes. The global characteristics and the power consumption of these impellers are also studied. The numerical results showed that the velocity field is more active with the double helical screw ribbons impeller. In this case, the effectiveness of the viscous dissipation and the pumping flow has been obviously noted. Also, the pumping and the energy efficiency reach the highest values at the same Reynolds number. The good agreement between the numerical results and the experimental data quietly confirmed the analysed method.

A computational and an experimental study on the effect of the chimney height on the thermal characteristics of a solar chimney power plant

The aim of this paper is to highlight the impact of the chimney height on the local characteristics of the air flow within a solar chimney power plant. The solar chimney power plant prototype was numerically and experimentally investigated. The experimental prototype of the solar chimney power plant was built in the National School of Engineers of Sfax, University of Sfax, Tunisia in the North Africa. The prototype is characterized by a collector diameter equal to D = 2750 mm, a collector height equal to h = 50 mm, a chimney height equal to H = 3000 mm, and a chimney diameter equal to d = 160 mm. The air flow has been simulated using the commercial software Ansys Fluent 17.0 and the computational findings have been validated using our experimental results. Computational fluid dynamics findings confirm that the chimney height is very influential on the local characteristics of the solar chimney power plant.

Estimation of solar radiation on horizontal and inclined surfaces in Sfax, TUNISIA

This paper has been made to estimate the solar radiation on horizontal and inclined surfaces in Sfax, Tunisia. The model developed in this communication can be used to estimate the hourly global, diffuse and direct solar radiations for horizontal surfaces and the total daily solar radiation on inclined and vertical surfaces in the region of Sfax. Moreover, the method presented here can be used to evaluate the energy production in Sfax of photovoltaic projects like water pumping solar, on-grid applications and off-grid applications. The estimation method of the hourly and daily solar radiations used the Liu and Jordon model. In addition, the values of monthly of average daily solar radiation on a horizontal surface are taken from NASA, Surface meteorology and Solar Energy. The mounting position of solar panel is assumed to be facing towards the south of Sfax. The present results are comparable with results of the PVGIS (Photovoltaic Geographical Information System).

Hydromechanics Characterization of The Turbulent Flow Generated by Anchor Impellers

Abstract Hydromechanics of a stirred tank generated by a classical anchor and an anchor blade are numerically simulated. The numerical results gives good prediction of the hydrodynamics such as the velocity field, the turbulent kinetic energy and its dissipation rate. These results are obtained by the computational fluid dynamics (CFD) code. The mechanical deformation of these anchors is calculated by the computational structural dynamics (CSD) code. The deformed shape of the anchor blade has been found in turbulent flow. However, the anchor blade has not been affected by this flow. Predictions of the numerical results have been compared with literature data and a satisfactory agreement has been found.

Immobilization of His-tagged recombinant xylanase from Penicillium occitanis on Nickel-chelate Eupergit C for increasing digestibility of poultry feed

Recombinant xylanase 2 from Penicillium occitanis expressed with an His-tag in Pichia pastoris, termed PoXyn2, was immobilized on nickel-chelate Eupergit C by covalent coupling reaction with a high immobilization yield up to 93.49%. Characterization of the immobilized PoXyn2 was further evaluated. The optimum pH was not affected by immobilization, but the immobilized PoXyn2 exhibited more acidic and large optimum pH range (pH 2.0–4.0) than that of the free PoXyn2 (pH 3.0). The free PoXyn2 had an optimum temperature of 50 °C, whereas that of the immobilized enzyme was shifted to 65 °C. Immobilization increased both pH stability and thermostability when compared with the free enzyme. Thermodynamically, increase in enthalpy and free energy change after covalent immobilization could be credited to the enhanced stability. Immobilized xylanase could be reused for 10 consecutive cycles retaining 60% of its initial activity. It was found to be effective in releasing reducing sugar from poultry feed. Immobilization on Eupergit C is important due to its mechanical resistance at high pH and temperature. Hence, considerable stability and reusability of bound enzyme may be advantageous for its industrial application.

Intake Manifold Shape Influence on the Unsteady In-Cylinder Flow: Application on LPG Bi-fuel Engine

The flow in the internal combustion (IC) engine intake manifold determines the flow in the cylinder prior and during the combustion. Consequently, intake-air manifolds have a major effect on engine’s performances and emission pollutants. In order to achieve the best volumetric and thermal efficiency, the design of intake manifolds presents a very important objective for engines manufacturers. In this paper, the flow characteristics of air-fuel mixture flowing in various designs of manifold of IVECO 6 cylinder heavy-duty engine are studied. This engine operates with bi-fuel LPG (liquefied petroleum gas)-gasoline technology. The proposed paper aims to present a three dimensional unsteady CFD (Computational Fluid Dynamics) analysis of the flow inside the two manifold shapes. The mass flow rate of the in-cylinder charge, the velocity and the turbulent kinetic energy are investigated in order to develop a thorough understanding of the in-cylinder flow and identify the optimal manifold. The cyclic dynamic in-cylinder flow results show that the second intake manifold shape present the optimal configuration for engine charging. The comparison between simulation results and those from the literature showed a good concordance.

PIV Study of the Down-Pitched Blade Turbine Hydrodynamic Structure

The aim of this study is to investigate the blade inclination effect in the flow generated by three different down-pitched blade turbines in a stirred tank. Particle image velocimetry (PIV) technique is used to predict the velocity fields and the turbulent characteristics. This technique consist on a 532 nm Nd:YAG laser, a CCD camera and a mini-synchronizer. In this study, it has been noted that the velocity increases with increasing the blade inclination.

Effect of the number of turbine blades on the air flow within a solar chimney power plant

Solar chimney power plants generate thermal heat and electrical power using the radiation from sun. These systems are characterized by their high costs. In fact, it is required to optimize the components of the solar system such as the collector, the chimney, the absorber, and the turbine. This paper focuses on the effect of the number of turbine blades on the air flow within a small prototype of a solar chimney power plant. Four configurations with different turbine blades are proposed to study the effect of the turbine blades number on the thermal characteristics of a solar chimney power plant. For each configuration, the distribution of the magnitude velocity, the air temperature, the pressure, the turbulent kinetic energy, and the turbulent viscosity are presented and discussed. This paper is identified to be of interest for engineers and designers for increasing the power output of a solar chimney power plant.

Numerical Simulation of the Overlap Effect on the Turbulent Flow Around a Savonius Wind Rotor

This study aimed to investigate the effect of the overlap on the aerodynamic characteristics of the flow around a Savonius wind rotor. A numerical simulation was developed using a commercial CFD code. The considered numerical model is based on the resolution of the Navier–Stokes equations in conjunction with the k-e turbulence model. These equations were solved by a finite volume discretization method. We were particularly interested in visualizing the velocity field, the mean velocity, the static pressure, the dynamic pressure, the turbulent kinetic energy, the dissipation rate of the turbulent kinetic energy, and the turbulent viscosity. The comparison of the numerical results with previous results shows a good agreement.