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G. H. Sedahmed - One of the best experts on this subject based on the ideXlab platform.
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Mass transfer inside spiral coils under laminar flow and possible applications
Experimental Heat Transfer, 2020Co-Authors: E.-s. Z. El-ashtoukhy, Mohamed Helmy Abdel-aziz, G. H. SedahmedAbstract:Rates of mass transfer in a spiral coil were measured by a technique involving the diffusion-controlled disSolution of copper in acidified dichromate. The variables studied were Solution Velocity, ...
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Intensification of the Rate of Diffusion-controlled Electrochemical and Catalytic Reactions at a Helical Coil by a Fixed Bed Turbulence Promoter
Croatian Society of Chemical Engineers, 2018Co-Authors: M. A. El-naggar, M. S. Mansour, A. H. El-shazly, S. A. Nosier, Y. A. El-taweel, G. H. SedahmedAbstract:Intensifications of the rate of diffusion-controlled electrochemical and catalytic reactions taking place at the outer surface of a helical coil imbedded in an inert fixed bed of cylinders acting as turbulence promoters was studied using the electrochemical technique. The technique involved measuring the limiting current of the cathodic reduction of K3Fe(CN)6 in a large excess of NaOH as a supporting electrolyte. The variables studied were Solution Velocity, packing cylinder diameter, helical coil tube diameter, and physical properties of the Solution. The rate of mass transfer at the outer surface of the coil was found to increase with increasing Solution Velocity and decreasing packing cylinder diameter, helical coil tube diameter was found to have a little effect on the rate of mass transfer. The data were correlated with the dimensionless equation Sh = 7.14*10(-4) *Sc(0.33)*Re(0.52) *(dp/d)(-2.32) Implication of the above equation for the design and operation of the present reactor was pointed out. The potential importance of using the inner surface of the coil as a builtin heat transfer facility for conducting exothermic electrochemical and catalytic reactions requiring rapid cooling was highlighted. The possibility of using multiple imbedded coaxial helical coils of different coil diameter in practical catalytic reactors to increase their rate of production was noted
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Liquid–solid mass transfer behavior of V-corrugated surfaces under two phase flow
Chemical Engineering and Processing, 2013Co-Authors: Mohamed Helmy Abdel-aziz, Inderjit Nirdosh, Ibrahim Hassan, G. H. SedahmedAbstract:Abstract Rates of mass transfer at V-corrugated surfaces in a rectangular duct were measured under two phase flow by the limiting current technique. Variables studied were groove angle and peak to valley height of the corrugated surface, Solution Velocity and superficial gas Velocity. For a given Solution Velocity and superficial gas Velocity the mass transfer coefficient was found to increase with increasing groove angle and decrease with increasing groove peak to valley height. The volumetric mass transfer enhancement ratio compared to the smooth surface ranged from 3.7 to 7.58 depending on the operating conditions. The mass transfer data at the corrugated surface were correlated by the equation: Sh = 1.52 Sc 0.33 Re L 0.285 Re g 0.28 ( d e / P ) 0.375 . For a batch gas sparged reactor with an active corrugated surface the data were correlated by the equation: j = 0.047(Re · Fr)−0.15(de/P)0.6. Implications of the present results for the design and operation of compact continuous two phase and batch gas sparged heat and mass transfer equipments such catalytic reactors, electrochemical reactors, and heat exchangers was noted.
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Mass transfer controlled corrosion of pipelines under two phase (gas—liquid) flow
British Corrosion Journal, 2013Co-Authors: G. H. Sedahmed, I. S. Mansour, G Abd El-latifAbstract:AbstractRates of diffusion controlled corrosion of smooth and rough pipes were studied under single phase liquid flow and two phase (gas–liquid) flow using the diffusion controlled disSolution of copper in acidified FeCl3. The study was carried out using a recirculating batch tubular reactor through which acidified FeCl3 Solution was circulated. The mass transfer coefficient of the disSolution of the copper pipe in the Solution was obtained from FeCl3 concentration–time data. Variables studied were Solution Velocity, gas Velocity, and peak to valley height of the rough pipe. For single phase fully developed flow, the mass transfer coefficients of the smooth uncorroded pipes were correlated for the conditions 3000 < ReL < 18 000 and 1688 < Sc < 1899 by the equation Sh = 0·054ScO·33ReL0·79, where ReL is the liquid Reynolds number, Sc is the Schmidt number, and Sh is the Sherwood number. For single phase flow in rough pipes, the data were correlated for the conditions 5 < e+ < 52·5, 3000 < ReL < 18 000, and ...
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Mass-transfer-controlled impingement corrosion at the jet inlet zone of an annulus under turbulent flow
Industrial & Engineering Chemistry Research, 2006Co-Authors: R.r. Zahran, O E Abdelwahab, G. H. Sedahmed, W. M. El-sarrafAbstract:Diffusion-controlled impingement corrosion of the lower part of the inner cylinder of an annulus caused by a perpendicular inlet jet was studied using the diffusion-controlled disSolution of copper in acidified dichromate technique. Variables studied were Solution Velocity, physical properties of the Solution, diameter of the perpendicular feed nozzle, and the effect of drag-reducing polymers. For blank Solution, the rate of mass-transfer-controlled impingement corrosion was correlated by the equation Sh = 2.74Sc 0.33 Re 0.46 (d n /d) -0.4 . Drag-reducing polymers were found to decrease the rate of mass-transfer-controlled impingement corrosion by an amount ranging from 29.9 to 68.9% depending on electrolyte concentration, polymer concentration, and feed nozzle diameter. The importance of the present results to the design of annular equipment was noted.
Gomaa H. Sedahmed - One of the best experts on this subject based on the ideXlab platform.
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Liquid/Solid Mass Transfer in Fixed Beds
Chemical Engineering & Technology, 2004Co-Authors: M. M. Zaki, Inderjit Nirdosh, Gomaa H. Sedahmed, Malcolm H. I. BairdAbstract:The liquid/solid mass transfer behavior of a fixed bed of cylinders was studied using the diffusion-controlled disSolution of copper in acidified potassium dichromate. Variables studied were Solution Velocity and cylinder diameter. For a steady flow, the data were correlated for the conditions 25 < Re < 600 and Sc = 990 by the equation Sh = 2.65 Sc 0.33 Re 0.5 . A comparison between the present data and previously obtained data for a fixed bed of Raschig rings has revealed that cylinder packing produces higher rates of mass transfer than Raschig rings.
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Mass transfer in smooth and rough annular ducts under developing flow conditions
Journal of Applied Electrochemistry, 1997Co-Authors: Ahmed Mobarak, Hassan A. Farag, Gomaa H. SedahmedAbstract:Rates of solid–liquid mass transfer were measured at the inner surface of an annular duct by the electrochemical technique under developing flow conditions. Variables studied were physical properties of the Solution, Velocity, length of the annulus, inlet port diameter and surface roughness. Inlet port diameter was found to have no effect on the rate of mass transfer. For smooth annuli the laminar flow data fit the equation: Sh = 1.029Sc0.33Re0.55(L/d)-0.472 The turbulent flow data fit the equation: Sh = 0.095Sc0.33Re0.85(L/d)-0.472 Surface roughness in the form of V-threads normal to the flow was found to have a negligible effect on the rate of mass transfer in the laminar flow region while in the turbulent region the data fit the equation: Sh = 0.167Sc0.33Re(L/d)-0.472(e/d)0.33 Under the present conditions, where the dimensionless roughness height e+ lies between 0.5 and 22, the rate of mass transfer was found to increase by an amount ranging from 10% to 200% depending on e+.
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Mass transfer in smooth and rough annular ducts under developing flow conditions
Journal of Applied Electrochemistry, 1997Co-Authors: Ahmed Mobarak, Hassan A. Farag, Gomaa H. SedahmedAbstract:Rates of solid–liquid mass transfer were measured at the inner surface of an annular duct by the electrochemical technique under developing flow conditions. Variables studied were physical properties of the Solution, Velocity, length of the annulus, inlet port diameter and surface roughness. Inlet port diameter was found to have no effect on the rate of mass transfer. For smooth annuli the laminar flow data fit the equation:
Yoshinobu Tanaka - One of the best experts on this subject based on the ideXlab platform.
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Limiting Current Density
Ion Exchange Membranes, 2015Co-Authors: Yoshinobu TanakaAbstract:When an electric current passes through an ion exchange membrane, salt concentration on the desalting surface of the membrane decreases because of concentration polarization and reduces to zero at the limiting current density. In this circumstance, there are no more salt ions available to carry the electric current; as a result, the voltage drop across the boundary layer increases drastically and causes higher energy consumption and the generation of water dissociation. The limiting current density of an ion exchange membrane i lim is measured using the current–voltage relationship. The mechanism of i lim can be understood from the Nernst diffusion model and analyzed with chemical engineering techniques. When the current density reaches i lim at the outlet of a desalting cell at its lowest linear Velocity and electrolyte concentration, the average current density applied to an electrodialyzer is defined as limiting current density ( I / S ) lim . The Solution Velocity distribution in an electrodialyzer strongly influences ( I / S ) lim .
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A computer simulation of feed and bleed ion exchange membrane electrodialysis for desalination of saline water.
Desalination, 2010Co-Authors: Yoshinobu TanakaAbstract:A computer simulation program is developed to predict desalinating performance of a feed and bleed electrodialysis process, inputting membrane characteristics, electrodialyzer specifications and electrodialytic conditions. Computing results enable to discuss the phenomena such as influence of cell voltage on current density, ionic fluxes, Solution fluxes, current efficiency, ohmic potential and membrane potential, and further the influence of cell voltage and electrolyte concentration on the output of desalted Solutions, energy consumption and water recovery. Excepting limiting current density, the performance of an electrodialyzer is scarcely influenced by the standard deviation of the normal distribution of the Solution Velocity ratio in desalting cells. Energy consumption in a feed and bleed process is larger than that in a batch process for higher feed concentration, and it is less than that in a reverse osmosis process at feed concentration less than one thousand and hundred-odd mg/l.
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a computer simulation of batch ion exchange membrane electrodialysis for desalination of saline water
Desalination, 2009Co-Authors: Yoshinobu TanakaAbstract:Abstract A computer simulation program including the principle of ① mass transport, ② current density distribution, ③ energy consumption and ④ limiting current density is developed for predicting desalinating performance of a continuous (one-pass flow) electrodialysis process. In this simulation the following parameters are inputted; ① membrane characteristics such as overall transport number, overall solute permeability, overall electro-osmotic permeability, overall hydraulic permeability, direct current electric resistance etc. ② electrodialyzer specifications such as flow-pass thickness, flow-pass width and flow-pass length of a desalting cell etc. and ③ electrodialytic conditions such as current density, electrolyte concentration in a feeding Solution, linear Velocity in desalting cells, standard deviation of normal distribution of Solution Velocity ratio etc. In a practical-scale electrodialyzer, electrolyte concentration in a desalting cell is decreased along a flow-pass and it gives rise to electrolyte concentration distribution. It causes electric resistance distribution and current density distribution. Solution velocities in desalting cells vary between the cells, and give rise to Solution Velocity distribution. In this simulation, these distributions are taken into account assuming that the frequency distribution of Solution Velocity ratio is equated by the normal distribution. Further, the influences of electrodialyzer specifications and elctrodialysis conditions described above on the performances of an electrodialyzer (desalting ratio, current efficiency, electrolyte concentration at the outlets of desalting cells, cell voltage, energy consumption, electrolyte concentration distribution, current density distribution, and limiting current density) are predicted. The simulation model is developed on the basis of the experiments and its reasonability is supported by the performance of electrodialyzers operating in salt-manufacturing plants.
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Chapter 11 Limiting Current Density
Membrane Science and Technology, 2007Co-Authors: Yoshinobu TanakaAbstract:Publisher Summary This chapter discusses the limiting current density. When an electric current is passed through an ion exchange membrane, salt concentration on a desalting surface of the membrane is decreased due to concentration polarization, and reduced to zero at the limiting current density. The chapter derives the limiting current density equation introduced from the Nernst–Planck equation. The chapter discusses the dependence of limiting current density on electrolyte concentration and Solution Velocity of a Solution. Concentration polarization occurs in a boundary layer formed on the desalting surface of an ion exchange membrane. The limiting current density is influenced by the Solution flow in a desalting cell and ionic transport in the boundary layer. Limiting current density of an electrodialyzer is influenced by the distribution of Solution flow in desalting cells. The chapter explains limiting current density of an electrodialyzer based on the limiting current density equation.
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limiting current density of an ion exchange membrane and of an electrodialyzer
Journal of Membrane Science, 2005Co-Authors: Yoshinobu TanakaAbstract:Abstract The limiting current density of an ion-exchange membrane was measured using a small-scale electrodialysis apparatus and was expressed by the function of NaCl concentration and linear Velocity of a Solution in a desalting cell. The limiting current density under a flowing Solution in a desalting cell was understandable based on the Nernst-diffusion model assuming that the thickness of a boundary layer is equivalent to that of a diffusion layer, and expressed by the function of NaCl concentration and linear Velocity of a Solution in a desalting cell. A spacer is usually considered to function as turbulence promoter. However, it seems block the main stream of laminar flow in a desalting cell, generate dead spaces between the spacer and a membrane and decrease the limiting current density. In order to increase the limiting current density, the Solution Velocity and the Reynolds number must be increased and create turbulent flow. In an ion-exchange membrane electrodialyzer, Solution velocities in desalting cells are not uniform between the cells incorporated in a stack. This event produces electrolyte concentration distribution between the cells and current density distribution in an electrodialyzer. When an electric current reaches the limiting current density of an ion-exchange membrane at the outlet of a desalting cell in which Velocity and electrolyte concentration are the least, the average current density applied to an electrodialyzer is defined as the limiting current density of the electrodialyzer. In this study, the Solution Velocity distribution was measured using a practical and a semi-practical electrodialyzer. Further, we computed the relationship between the standard deviation of normal distribution of linear velocities in desalting cells and electrolyte concentration at the outlet of the desalting cell in which Velocity and electrolyte concentration are the least. Based on the above computation and the evaluation of the limiting current of an ion-exchange membrane, the limiting current density of an electrodialyzer was determined.
Ahmed Mobarak - One of the best experts on this subject based on the ideXlab platform.
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Mass transfer in smooth and rough annular ducts under developing flow conditions
Journal of Applied Electrochemistry, 1997Co-Authors: Ahmed Mobarak, Hassan A. Farag, Gomaa H. SedahmedAbstract:Rates of solid–liquid mass transfer were measured at the inner surface of an annular duct by the electrochemical technique under developing flow conditions. Variables studied were physical properties of the Solution, Velocity, length of the annulus, inlet port diameter and surface roughness. Inlet port diameter was found to have no effect on the rate of mass transfer. For smooth annuli the laminar flow data fit the equation: Sh = 1.029Sc0.33Re0.55(L/d)-0.472 The turbulent flow data fit the equation: Sh = 0.095Sc0.33Re0.85(L/d)-0.472 Surface roughness in the form of V-threads normal to the flow was found to have a negligible effect on the rate of mass transfer in the laminar flow region while in the turbulent region the data fit the equation: Sh = 0.167Sc0.33Re(L/d)-0.472(e/d)0.33 Under the present conditions, where the dimensionless roughness height e+ lies between 0.5 and 22, the rate of mass transfer was found to increase by an amount ranging from 10% to 200% depending on e+.
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Mass transfer in smooth and rough annular ducts under developing flow conditions
Journal of Applied Electrochemistry, 1997Co-Authors: Ahmed Mobarak, Hassan A. Farag, Gomaa H. SedahmedAbstract:Rates of solid–liquid mass transfer were measured at the inner surface of an annular duct by the electrochemical technique under developing flow conditions. Variables studied were physical properties of the Solution, Velocity, length of the annulus, inlet port diameter and surface roughness. Inlet port diameter was found to have no effect on the rate of mass transfer. For smooth annuli the laminar flow data fit the equation:
M. M. Zaki - One of the best experts on this subject based on the ideXlab platform.
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Liquid/Solid Mass Transfer in Fixed Beds
Chemical Engineering & Technology, 2004Co-Authors: M. M. Zaki, Inderjit Nirdosh, Gomaa H. Sedahmed, Malcolm H. I. BairdAbstract:The liquid/solid mass transfer behavior of a fixed bed of cylinders was studied using the diffusion-controlled disSolution of copper in acidified potassium dichromate. Variables studied were Solution Velocity and cylinder diameter. For a steady flow, the data were correlated for the conditions 25 < Re < 600 and Sc = 990 by the equation Sh = 2.65 Sc 0.33 Re 0.5 . A comparison between the present data and previously obtained data for a fixed bed of Raschig rings has revealed that cylinder packing produces higher rates of mass transfer than Raschig rings.
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effect of surface roughness induced by woven metallic screens wrapped on the inner surface of an annulus on the rate of turbulent flow mass transfer
Industrial & Engineering Chemistry Research, 1996Co-Authors: M. M. Zaki, Inderjit Nirdosh, G. H. SedahmedAbstract:Rates of mass transfer were measured at the inner surface of an annulus wrapped with a woven metallic screen under developing flow conditions using an electrochemical technique which involved measuring the limiting current of the cathodic reduction of potassium ferricyanide. Variables studied were screen characteristics, Solution Velocity, and physical properties of the Solution. Mass-transfer rates based on the projected area of the annulus were found to increase by a factor ranging from 1.2 to 3 depending mainly on Re. The degree of mass-transfer enhancement was found to decrease with an increase in Re. Rates of mass transfer based on the true active area of the annulus and the screen were found to be smaller than the values at the smooth surface, the higher the Re the higher being the percentage decrease in the rate of mass transfer compared to the values at the smooth annulus. Practical implications of the present work in the design and operation of catalytic and electrochemical reactors used to conduct diffusion-controlled reactions have been highlighted.