Ashraf Balabel

Bio: Ashraf Balabel is an academic researcher from Taif University. The author has contributed to research in topics: Turbulence & Control volume. The author has an hindex of 10, co-authored 48 publications receiving 326 citations. Previous affiliations of Ashraf Balabel include Menoufia University & University College of Engineering.

On the performance of linear and nonlinear k–ε turbulence models in various jet flow applications

Abstract: In this paper, a thorough numerical investigation of the performance of several linear and nonlinear k – e turbulence model variants in various jet flow applications is carried out. Three k – e based turbulence models are considered, namely the standard k – e model, the υ 2 – f model, and the nonlinear k – e model. The selected turbulence models are applied for the prediction of simple as well as complex jet flow applications to underpin knowledge about the accuracy obtained from the two-equation turbulence models. The numerical code developed by the present authors solves the unsteady RANS equations by using the control volume approach on a non-staggered grid system. Three jet flow applications are selected, namely a turbulent free jet, a turbulent jet impinging on a flat plate, and a turbulent wall jet. In order to validate the numerical results obtained and to investigate the performance of the different turbulence models considered, different experimental measurements from the literature are used. The present work is primarily motivated by the desire to provide a rational way for deciding how complex the turbulence model is required to be for a given application and to find out how the accuracy changes with model complexity. Due to the superior predictive performance of modern turbulence models in a wide range of complex industrial and engineering applications, it was believed that a ‘universal’ turbulence model might exist. In general, that is not true. Simple flows can be analysed using standard two-equation models. The present numerical investigation showed that the linear turbulence model could give good results in simple (non-impinging) jet flows. However, in complicated flows, such as impinging jet problems or wall jet flows, a more elaborate level of modeling is required. In such contexts, nonlinear models are appropriate for predicting the turbulent viscosity structure, namely the inhomogeneous near-wall flow region and the anisotropic Reynolds stresses, which is a vital part of turbulent jet flow prediction.

Experimental Investigation of the Operating Parameters Affecting Hydrogen Production Process through Alkaline Water Electrolysis

Abstract: Alkaline water electrolysis is considered to be a basic technique for hydrogen production. Many researchers have investigated the alkaline water electrolysis in order to promote electrochemical reaction. In the present paper, the effects of voltage, electrolyte concentration and space between the pair of electrodes on the amount of hydrogen produced and consequently on the overall electrolysis efficiency are experimentally investigated. The experimental measurements are carried out by the present authors at the fluid mechanics laboratory of Menoufiya University. The alkaline water electrolysis of different potassium hydroxide aqueous solutions is conducted under atmospheric pressure using stainless steel electrodes. The experimental results showed that the performance of water electrolysis unit is highly affected by the voltage input and the gap between the electrodes. Higher rates of produced hydrogen can be obtained at smaller space between the electrodes and also at higher voltage input. Higher system efficiency was also gained at smaller gap distances between the pair of electrodes.

Optimum Operating Conditions for Alkaline Water Electrolysis Coupled with Solar PV Energy System

Abstract: This paper investigates theoretically and experimentally the optimum operating conditions for alkaline water electrolysis coupled with a solar photovoltaic (PV) source for hydrogen generation with emphasis on the electrolyzer efficiency under different operating conditions. The PV generator is simulated using Matlab/Simulink to obtain its characteristics under different operating conditions with solar irradiance and temperature variations. A wide range of operating parameters, which include input voltage, temperature, concentration of the electrolyte, and distance between the electrodes, are considered, and their effects on the efficiency of hydrogen production process are explored. A group of performance curves for the solar-hydrogen energy system (SHES) under a wide range of operating conditions are obtained through a number of individual experimental measurements. The optimum operating conditions, which correspond to the maximum electrolyzer efficiency, are determined for the proposed SHES. The effects of the ambient temperature and the electrolyte temperature on the performance of the solar PV energy system and the hydrogen production process are also investigated.

Boundary Layer Theory

Abstract: The boundary layer equations for plane, incompressible, and steady flow are $$\matrix{ {u{{\partial u} \over {\partial x}} + v{{\partial u} \over {\partial y}} = - {1 \over \varrho }{{\partial p} \over {\partial x}} + v{{{\partial ^2}u} \over {\partial {y^2}}},} \cr {0 = {{\partial p} \over {\partial y}},} \cr {{{\partial u} \over {\partial x}} + {{\partial v} \over {\partial y}} = 0.} \cr }$$

Atomization and Sprays

Abstract: Preface 1.General Considerations 2.Basic Processes in Atomization 3.Drop Size Distributions of Sprays 4.Atomizers 5.Flow in Atomizers 6.Atomizer Performance 7.External Spray Charcteristics 8.Drop Evaporation 9.Drop Sizing Methods Index

Teaching for quality learning at university

Abstract: by J. Biggs and C. Tang, Maidenhead, England, Open University Press, 2007, 360 pp., £29.99, ISBN-13: 978-0-335-22126-4

Computational Fluid Mechanics And Heat Transfer

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Alkaline Water Electrolysis Powered by Renewable Energy: A Review

Abstract: Alkaline water electrolysis is a key technology for large-scale hydrogen production powered by renewable energy. As conventional electrolyzers are designed for operation at fixed process conditions, the implementation of fluctuating and highly intermittent renewable energy is challenging. This contribution shows the recent state of system descriptions for alkaline water electrolysis and renewable energies, such as solar and wind power. Each component of a hydrogen energy system needs to be optimized to increase the operation time and system efficiency. Only in this way can hydrogen produced by electrolysis processes be competitive with the conventional path based on fossil energy sources. Conventional alkaline water electrolyzers show a limited part-load range due to an increased gas impurity at low power availability. As explosive mixtures of hydrogen and oxygen must be prevented, a safety shutdown is performed when reaching specific gas contamination. Furthermore, the cell voltage should be optimized to maintain a high efficiency. While photovoltaic panels can be directly coupled to alkaline water electrolyzers, wind turbines require suitable converters with additional losses. By combining alkaline water electrolysis with hydrogen storage tanks and fuel cells, power grid stabilization can be performed. As a consequence, the conventional spinning reserve can be reduced, which additionally lowers the carbon dioxide emissions.