Ammar Alsairafi | Kuwait University (original) (raw)
Papers by Ammar Alsairafi
this research presents a theoretical investigation on the performance of a vapour compression ref... more this research presents a theoretical investigation on the performance of a vapour compression refrigerating system using different mixtures of Hydrocarbons and Hydrofluorocarbons refrigerants as a refrigerant. Genetic Algorithm method was used to solve a nonlinear constrained optimization problem for the selection of the best blend. The performance of new mixtures of Hydrocarbons and Hydrofluorocarbons refrigerants is compared with the performance of R-134a. The optimal solution of the new blend is has an improvement of 11.9% in the coefficient of performance over the currently used blend of R134a.
Combustion Science and Technology, 2004
ABSTRACT The familiar flames from candles and oil lamps are representative examples of wick-stabi... more ABSTRACT The familiar flames from candles and oil lamps are representative examples of wick-stabilized diffusion flames. The shape and burning characteristics of these flames depend strongly on gravity-induced buoyant flows. To obtain a better understanding of the gravity effect, a diffusion flame model has been formulated and numerically solved. In the computation, gravity is treated as a parameter, spanning from zero to the high blowoff limit. The model includes realistic wick and candle geometry but assumes that the wick surface is coated with liquid fuel. The gas-phase formulation consists of the full Navier–Stokes equations with a one-step finite-rate overall chemical reaction. Gas-phase flame radiation, important in low gravity near the quenching limit, is included by solving the axisymmetric radiation transfer equation using the SN discrete ordinates method. The computed results include flame and flow structures, heat flux distributions, the energy budget, and the overall burning characteristics as a function of gravity and wick diameter.
Desalination, 2004
Recently, large numbers of high capacity TVC/MEB (multi-effect thermal vapor compression combined... more Recently, large numbers of high capacity TVC/MEB (multi-effect thermal vapor compression combined withconventinalmulti effect boiling) desalting units have been built or ordered in the UAE and elsewhere. An in-depth comparison between the predominantly used MSF and the TVC/MEB is conducted in this paper to show the reasons of this trend to used the newly used TVC/MEB units. The TVC/MEB units
Chinese Journal of Chemical Engineering, 2011
This paper reports a study on the role of fluid flow pattern and dynamic pressure on the permeate... more This paper reports a study on the role of fluid flow pattern and dynamic pressure on the permeate flux through a micro filtration membrane in laboratory scale. For this purpose, a dead-end membrane cell equipped with a marine type impeller was used. The impeller was set to rotate in the clockwise and counter clockwise directions with the same angular velocities in order to illustrate the effect of rotation direction on permeate flux. Consequently, permeate fluxes were measured at various impeller rotational speeds. The computational fluid dynamics (CFD) predicted dynamic pressure was related to the fluxes obtained in the experiments. Using the CFD modeling, it is proven that the change in dynamic pressure upon the membrane surface has direct effect on the permeate flux.
International Communications in Heat and Mass Transfer, 2011
This paper reports the experimental and Computational Fluid Dynamics (CFD) modeling studies on he... more This paper reports the experimental and Computational Fluid Dynamics (CFD) modeling studies on heat transfer, friction factor and thermal performance of an air cooled heat exchanger equipped with three types of tube insert including butterfly, classic and jagged twisted tape. In the studied range of Reynolds number the maximum thermal performance factor was obtained by the butterfly insert with an
International Communications in Heat and Mass Transfer, 2010
In the present study a gas/liquid two-phase flow and the simultaneous evaporation and condensatio... more In the present study a gas/liquid two-phase flow and the simultaneous evaporation and condensation phenomena in a thermosyphon was modeled. The volume of fluid (VOF) technique was used to model the interaction between these phases. Experiments in a thermosyphon were carried out at different operating conditions. The CFD predicted temperature profile in the thermosyphon was compared with experimental measurements and a good agreement was observed. It was concluded that CFD is a useful tool to model and explain the complex flow and heat transfer in a thermosyphon.
Chemical Engineering and Processing, 2009
This paper reports experimental and Computational Fluid Dynamics (CFD) investigations on the fric... more This paper reports experimental and Computational Fluid Dynamics (CFD) investigations on the friction factor, Nusselt number and thermal-hydraulic performance of a tube equipped with the classic and three modified twisted tape inserts. The results showed that the Nusselt number and performance of the jagged insert were higher than other ones. Maximum increase of 31% and 22% were observed in the calculated Nusselt and performance of the jagged insert as compared with those obtained for the classic one. The higher turbulence intensity of the fluid close to the tube wall has been expressed as the main reason for the experimental observations.
Korean Journal of Chemical Engineering, 2009
This paper reports experimental and computational fluid dynamics (CFD) modeling studies on the pe... more This paper reports experimental and computational fluid dynamics (CFD) modeling studies on the performance of three modified valves operating in a valve tray column. The original and modified valves including vnotched, warped and double-valve are tested experimentally. The experimental rig was a Perspex column having a single valve equipped with a fluctuating plate to measure the quality of gas distribution by using laser sensors. Two-stage nested designs were employed to show the repeatability and consistency of the measurements. In the CFD modeling, the volume of fluid (VOF) method was used to model the gas-liquid two-phase flow inside the column. A good agreement was observed between experimental data and the CFD predictions. The results showed that the double-valve layout provides a better gas distribution, smaller bubbles with greater interface area and lower pressure drop in comparison with the original and the two other modified valves.
Chemical Engineering and Processing, 2010
In this paper a study on the role of wire coils inserted in the oxygen supply channels of a proto... more In this paper a study on the role of wire coils inserted in the oxygen supply channels of a proton exchange membrane fuel cell (PEMFC) is reported. Different power densities have been obtained at different oxygen flow rates with and without insert. The experimental results clearly reveal that inserting a wire coil can increase the generated power density up to 41% in some layouts. The CFD modeling is carried out to explain and to analyze the observed results. The generated circumferential flow close to the gas diffusion layer (GDL) is found to be the main reason for the obtained experimental results.
International Communications in Heat and Mass Transfer, 2010
In the present study, different two-phase flow regimes in horizontal and vertical tubes have been... more In the present study, different two-phase flow regimes in horizontal and vertical tubes have been studied experimentally and theoretically. A 3-D Computational Fluid Dynamics (CFD) modeling was carried out in order to model gas–liquid two-phase flow using volume of fluid (VOF) model. An Electrical Resistance Tomography (ERT) system was used to visualize these flow regimes, which were produced by change
Korean Journal of Chemical Engineering, 2011
This paper reports experimental and computational frluid dynamics (CFD) studies on an impeller ca... more This paper reports experimental and computational frluid dynamics (CFD) studies on an impeller called Visco-jet with the aim of finding the effect of two side diameters ratio of its blade, which has a semi-conical shape, on drawdown process of floating polymericparticles into high viscosity glycerin solution. Nine different geometries were examined experimentally, and there were significant differences in their performance. The results reveal that when diameter of smaller side of semi-cone impeller is half of the other side, mixing was performed in a more efficient way. The CFD-predicted results have been used for explaining the experimental observation. The CFD-predicted hydrodynamics parameters confirm superiority of this geometry compared with the other ones.
Computers & Chemical Engineering, 2010
In the present study, the volume of fluid (VOF) method implemented in the commercial CFD package,... more In the present study, the volume of fluid (VOF) method implemented in the commercial CFD package, FLUENT6. 2 has been used to model the gasliquid flow in a valve tray column. The effect of valve weight has been investigated using three valves having different ...
International Communications in Heat and Mass Transfer, 2009
This paper reports the effect of jet position on the acid dispersion in a neutralization process.... more This paper reports the effect of jet position on the acid dispersion in a neutralization process. Experiments were carried out in a continuous stirred reactor and the effect of jet nozzle position on non-reactive dye dispersion at seven layouts was studied. Consequently, the neutralization reaction mixing was carried out at the best and worst positions. The results reveal that the ways that flow pushes the acid inside the tank are quite different and the neutralization performance can significantly be affected by the jet position. The Computational Fluid Dynamics (CFD) modeling was carried out in order to analyze the experimental observations.
Numerical Heat Transfer Part A-applications, 2010
NOx emission, heat transfer, and high temperature air combustion (HiTAC) in a boiler of Mobin Pet... more NOx emission, heat transfer, and high temperature air combustion (HiTAC) in a boiler of Mobin Petrochemical Complex, Iran was numerically studied. The comparison between the measured values and the CFD predicted results showed good agreement, which implied ...
Korean Journal of Chemical Engineering, 2011
This paper reports a numerical study on the possibility of using high temperature air combustion ... more This paper reports a numerical study on the possibility of using high temperature air combustion (HiTAC) technique in the heat recovery steam generator (HRSG) boiler of the Fajr Petrochemical Complex, Iran. For this purpose a theoretical fuel nozzle which operates in HiTAC mode of combustion has been installed and modeled using the computational fluid dynamics (CFD) technique. By aim of establishing an efficient heat transfer rate to the boiler’s tubes, the proper nozzle location and an optimum mass flow rate of fuel have been found. The results show that by using this modification it is possible to increase the steam temperature up to 37 percent.
Korean Journal of Chemical Engineering, 2010
Experimental and computational fluid dynamic (CFD) modeling studies have been performed on mixing... more Experimental and computational fluid dynamic (CFD) modeling studies have been performed on mixing characteristics of a new modified helical ribbon impeller in a viscous medium. A novel arrangement for the multiple reference frame (MRF) technique was proposed and the modeling results were compared with those of conventional MRF selecting method. Calculations were performed to study the effects of several parameters: axial flow number, axial circulation time, impeller clearance, and power consumption. The higher performance of the modified impeller has been proven in terms of axial flow number and axial circulation time. The results showed that significant improvement in mixing performance can be obtained at a higher impeller clearance with the modified impeller employed. In addition, the power consumption by the new impeller has been compared with that of the classic one. The CFD-predicted flow patterns generated by the impellers were used to explain the higher performance of the modified impeller. In addition, the results reveal that the CFD-predicted particle volume fractions at various axial distances from the tank bottom are reasonably in agreement with the experimental observations.
International Communications in Heat and Mass Transfer, 2011
The influence of the fuel temperature on NOx formation was investigated numerically. For this pur... more The influence of the fuel temperature on NOx formation was investigated numerically. For this purpose CFD modeling of NOx emission in an experimental furnace equipped with high temperature air combustion (HiTAC) system was studied. The comparison between the predicted results and measured values have shown good agreement, which implies that the adopted combustion and NOx formation models are suitable for predicting the characteristics of the flow, combustion, heat transfer, and NOx emissions in the HiTAC chamber. Moreover the predicted results show that increase of the fuel temperature results in a higher fluid velocity, better fuel jet mixing with the combustion air, smaller flame and lower NOx emission.
International Communications in Heat and Mass Transfer, 2009
A large number of experiments in a 2 cm diameter and 6 m length tube were carried out in order to... more A large number of experiments in a 2 cm diameter and 6 m length tube were carried out in order to study the two-phase flow regimes and pressure drops in it. The two-phase flow in the experimental tube was modeled using commercial CFD code, Fluent 6.2. An Artificial Neural Network (ANN) with three inputs including gas and liquid velocities and tube slope was designed and trained to predict average pressure drop across the tube. The comparison between CFD and ANN predictions of pressure drops with experimental measurements shows that the CFD results are more accurate than the ANN evaluations for new conditions.
Chemical Engineering and Processing, 2009
This paper reports Computational Fluid Dynamics (CFD) and experimental studies on microfiltration... more This paper reports Computational Fluid Dynamics (CFD) and experimental studies on microfiltration fouling of a Blue Indigo solution. A hydrophilic Polyvinylidene Fluoride (PVDF) membrane was used and experiments were carried out at three cross-flow velocities of 0.5, 1 and 1.3 m s −1 . The fouled membranes were analyzed using simple photographs and precise Scanning Electron Microscope (SEM) micrographs. A 3-D CFD modelling was carried out using the commercial CFD code, FLUENT6.2. The predicted shear stress distributions upon the membrane were used to explain the observed fouling. In addition, the particles deposition pattern upon the membrane surface was predicted using discrete phase modelling.
Numerical Heat Transfer Part A-applications, 2011
CFD modeling of NOx emission via N2O-intermediate mechanism was developed to predict the NOx form... more CFD modeling of NOx emission via N2O-intermediate mechanism was developed to predict the NOx formation in an experimental furnace equipped with high temperature air combustion (HiTAC) system. The good agreement between the predicted and measured ...
this research presents a theoretical investigation on the performance of a vapour compression ref... more this research presents a theoretical investigation on the performance of a vapour compression refrigerating system using different mixtures of Hydrocarbons and Hydrofluorocarbons refrigerants as a refrigerant. Genetic Algorithm method was used to solve a nonlinear constrained optimization problem for the selection of the best blend. The performance of new mixtures of Hydrocarbons and Hydrofluorocarbons refrigerants is compared with the performance of R-134a. The optimal solution of the new blend is has an improvement of 11.9% in the coefficient of performance over the currently used blend of R134a.
Combustion Science and Technology, 2004
ABSTRACT The familiar flames from candles and oil lamps are representative examples of wick-stabi... more ABSTRACT The familiar flames from candles and oil lamps are representative examples of wick-stabilized diffusion flames. The shape and burning characteristics of these flames depend strongly on gravity-induced buoyant flows. To obtain a better understanding of the gravity effect, a diffusion flame model has been formulated and numerically solved. In the computation, gravity is treated as a parameter, spanning from zero to the high blowoff limit. The model includes realistic wick and candle geometry but assumes that the wick surface is coated with liquid fuel. The gas-phase formulation consists of the full Navier–Stokes equations with a one-step finite-rate overall chemical reaction. Gas-phase flame radiation, important in low gravity near the quenching limit, is included by solving the axisymmetric radiation transfer equation using the SN discrete ordinates method. The computed results include flame and flow structures, heat flux distributions, the energy budget, and the overall burning characteristics as a function of gravity and wick diameter.
Desalination, 2004
Recently, large numbers of high capacity TVC/MEB (multi-effect thermal vapor compression combined... more Recently, large numbers of high capacity TVC/MEB (multi-effect thermal vapor compression combined withconventinalmulti effect boiling) desalting units have been built or ordered in the UAE and elsewhere. An in-depth comparison between the predominantly used MSF and the TVC/MEB is conducted in this paper to show the reasons of this trend to used the newly used TVC/MEB units. The TVC/MEB units
Chinese Journal of Chemical Engineering, 2011
This paper reports a study on the role of fluid flow pattern and dynamic pressure on the permeate... more This paper reports a study on the role of fluid flow pattern and dynamic pressure on the permeate flux through a micro filtration membrane in laboratory scale. For this purpose, a dead-end membrane cell equipped with a marine type impeller was used. The impeller was set to rotate in the clockwise and counter clockwise directions with the same angular velocities in order to illustrate the effect of rotation direction on permeate flux. Consequently, permeate fluxes were measured at various impeller rotational speeds. The computational fluid dynamics (CFD) predicted dynamic pressure was related to the fluxes obtained in the experiments. Using the CFD modeling, it is proven that the change in dynamic pressure upon the membrane surface has direct effect on the permeate flux.
International Communications in Heat and Mass Transfer, 2011
This paper reports the experimental and Computational Fluid Dynamics (CFD) modeling studies on he... more This paper reports the experimental and Computational Fluid Dynamics (CFD) modeling studies on heat transfer, friction factor and thermal performance of an air cooled heat exchanger equipped with three types of tube insert including butterfly, classic and jagged twisted tape. In the studied range of Reynolds number the maximum thermal performance factor was obtained by the butterfly insert with an
International Communications in Heat and Mass Transfer, 2010
In the present study a gas/liquid two-phase flow and the simultaneous evaporation and condensatio... more In the present study a gas/liquid two-phase flow and the simultaneous evaporation and condensation phenomena in a thermosyphon was modeled. The volume of fluid (VOF) technique was used to model the interaction between these phases. Experiments in a thermosyphon were carried out at different operating conditions. The CFD predicted temperature profile in the thermosyphon was compared with experimental measurements and a good agreement was observed. It was concluded that CFD is a useful tool to model and explain the complex flow and heat transfer in a thermosyphon.
Chemical Engineering and Processing, 2009
This paper reports experimental and Computational Fluid Dynamics (CFD) investigations on the fric... more This paper reports experimental and Computational Fluid Dynamics (CFD) investigations on the friction factor, Nusselt number and thermal-hydraulic performance of a tube equipped with the classic and three modified twisted tape inserts. The results showed that the Nusselt number and performance of the jagged insert were higher than other ones. Maximum increase of 31% and 22% were observed in the calculated Nusselt and performance of the jagged insert as compared with those obtained for the classic one. The higher turbulence intensity of the fluid close to the tube wall has been expressed as the main reason for the experimental observations.
Korean Journal of Chemical Engineering, 2009
This paper reports experimental and computational fluid dynamics (CFD) modeling studies on the pe... more This paper reports experimental and computational fluid dynamics (CFD) modeling studies on the performance of three modified valves operating in a valve tray column. The original and modified valves including vnotched, warped and double-valve are tested experimentally. The experimental rig was a Perspex column having a single valve equipped with a fluctuating plate to measure the quality of gas distribution by using laser sensors. Two-stage nested designs were employed to show the repeatability and consistency of the measurements. In the CFD modeling, the volume of fluid (VOF) method was used to model the gas-liquid two-phase flow inside the column. A good agreement was observed between experimental data and the CFD predictions. The results showed that the double-valve layout provides a better gas distribution, smaller bubbles with greater interface area and lower pressure drop in comparison with the original and the two other modified valves.
Chemical Engineering and Processing, 2010
In this paper a study on the role of wire coils inserted in the oxygen supply channels of a proto... more In this paper a study on the role of wire coils inserted in the oxygen supply channels of a proton exchange membrane fuel cell (PEMFC) is reported. Different power densities have been obtained at different oxygen flow rates with and without insert. The experimental results clearly reveal that inserting a wire coil can increase the generated power density up to 41% in some layouts. The CFD modeling is carried out to explain and to analyze the observed results. The generated circumferential flow close to the gas diffusion layer (GDL) is found to be the main reason for the obtained experimental results.
International Communications in Heat and Mass Transfer, 2010
In the present study, different two-phase flow regimes in horizontal and vertical tubes have been... more In the present study, different two-phase flow regimes in horizontal and vertical tubes have been studied experimentally and theoretically. A 3-D Computational Fluid Dynamics (CFD) modeling was carried out in order to model gas–liquid two-phase flow using volume of fluid (VOF) model. An Electrical Resistance Tomography (ERT) system was used to visualize these flow regimes, which were produced by change
Korean Journal of Chemical Engineering, 2011
This paper reports experimental and computational frluid dynamics (CFD) studies on an impeller ca... more This paper reports experimental and computational frluid dynamics (CFD) studies on an impeller called Visco-jet with the aim of finding the effect of two side diameters ratio of its blade, which has a semi-conical shape, on drawdown process of floating polymericparticles into high viscosity glycerin solution. Nine different geometries were examined experimentally, and there were significant differences in their performance. The results reveal that when diameter of smaller side of semi-cone impeller is half of the other side, mixing was performed in a more efficient way. The CFD-predicted results have been used for explaining the experimental observation. The CFD-predicted hydrodynamics parameters confirm superiority of this geometry compared with the other ones.
Computers & Chemical Engineering, 2010
In the present study, the volume of fluid (VOF) method implemented in the commercial CFD package,... more In the present study, the volume of fluid (VOF) method implemented in the commercial CFD package, FLUENT6. 2 has been used to model the gasliquid flow in a valve tray column. The effect of valve weight has been investigated using three valves having different ...
International Communications in Heat and Mass Transfer, 2009
This paper reports the effect of jet position on the acid dispersion in a neutralization process.... more This paper reports the effect of jet position on the acid dispersion in a neutralization process. Experiments were carried out in a continuous stirred reactor and the effect of jet nozzle position on non-reactive dye dispersion at seven layouts was studied. Consequently, the neutralization reaction mixing was carried out at the best and worst positions. The results reveal that the ways that flow pushes the acid inside the tank are quite different and the neutralization performance can significantly be affected by the jet position. The Computational Fluid Dynamics (CFD) modeling was carried out in order to analyze the experimental observations.
Numerical Heat Transfer Part A-applications, 2010
NOx emission, heat transfer, and high temperature air combustion (HiTAC) in a boiler of Mobin Pet... more NOx emission, heat transfer, and high temperature air combustion (HiTAC) in a boiler of Mobin Petrochemical Complex, Iran was numerically studied. The comparison between the measured values and the CFD predicted results showed good agreement, which implied ...
Korean Journal of Chemical Engineering, 2011
This paper reports a numerical study on the possibility of using high temperature air combustion ... more This paper reports a numerical study on the possibility of using high temperature air combustion (HiTAC) technique in the heat recovery steam generator (HRSG) boiler of the Fajr Petrochemical Complex, Iran. For this purpose a theoretical fuel nozzle which operates in HiTAC mode of combustion has been installed and modeled using the computational fluid dynamics (CFD) technique. By aim of establishing an efficient heat transfer rate to the boiler’s tubes, the proper nozzle location and an optimum mass flow rate of fuel have been found. The results show that by using this modification it is possible to increase the steam temperature up to 37 percent.
Korean Journal of Chemical Engineering, 2010
Experimental and computational fluid dynamic (CFD) modeling studies have been performed on mixing... more Experimental and computational fluid dynamic (CFD) modeling studies have been performed on mixing characteristics of a new modified helical ribbon impeller in a viscous medium. A novel arrangement for the multiple reference frame (MRF) technique was proposed and the modeling results were compared with those of conventional MRF selecting method. Calculations were performed to study the effects of several parameters: axial flow number, axial circulation time, impeller clearance, and power consumption. The higher performance of the modified impeller has been proven in terms of axial flow number and axial circulation time. The results showed that significant improvement in mixing performance can be obtained at a higher impeller clearance with the modified impeller employed. In addition, the power consumption by the new impeller has been compared with that of the classic one. The CFD-predicted flow patterns generated by the impellers were used to explain the higher performance of the modified impeller. In addition, the results reveal that the CFD-predicted particle volume fractions at various axial distances from the tank bottom are reasonably in agreement with the experimental observations.
International Communications in Heat and Mass Transfer, 2011
The influence of the fuel temperature on NOx formation was investigated numerically. For this pur... more The influence of the fuel temperature on NOx formation was investigated numerically. For this purpose CFD modeling of NOx emission in an experimental furnace equipped with high temperature air combustion (HiTAC) system was studied. The comparison between the predicted results and measured values have shown good agreement, which implies that the adopted combustion and NOx formation models are suitable for predicting the characteristics of the flow, combustion, heat transfer, and NOx emissions in the HiTAC chamber. Moreover the predicted results show that increase of the fuel temperature results in a higher fluid velocity, better fuel jet mixing with the combustion air, smaller flame and lower NOx emission.
International Communications in Heat and Mass Transfer, 2009
A large number of experiments in a 2 cm diameter and 6 m length tube were carried out in order to... more A large number of experiments in a 2 cm diameter and 6 m length tube were carried out in order to study the two-phase flow regimes and pressure drops in it. The two-phase flow in the experimental tube was modeled using commercial CFD code, Fluent 6.2. An Artificial Neural Network (ANN) with three inputs including gas and liquid velocities and tube slope was designed and trained to predict average pressure drop across the tube. The comparison between CFD and ANN predictions of pressure drops with experimental measurements shows that the CFD results are more accurate than the ANN evaluations for new conditions.
Chemical Engineering and Processing, 2009
This paper reports Computational Fluid Dynamics (CFD) and experimental studies on microfiltration... more This paper reports Computational Fluid Dynamics (CFD) and experimental studies on microfiltration fouling of a Blue Indigo solution. A hydrophilic Polyvinylidene Fluoride (PVDF) membrane was used and experiments were carried out at three cross-flow velocities of 0.5, 1 and 1.3 m s −1 . The fouled membranes were analyzed using simple photographs and precise Scanning Electron Microscope (SEM) micrographs. A 3-D CFD modelling was carried out using the commercial CFD code, FLUENT6.2. The predicted shear stress distributions upon the membrane were used to explain the observed fouling. In addition, the particles deposition pattern upon the membrane surface was predicted using discrete phase modelling.
Numerical Heat Transfer Part A-applications, 2011
CFD modeling of NOx emission via N2O-intermediate mechanism was developed to predict the NOx form... more CFD modeling of NOx emission via N2O-intermediate mechanism was developed to predict the NOx formation in an experimental furnace equipped with high temperature air combustion (HiTAC) system. The good agreement between the predicted and measured ...