Khalil Khanafer - Academia.edu (original) (raw)

Papers by Khalil Khanafer

Research paper thumbnail of Original

Unsteady numerical simulation of double diffusive convection heat transfer in a pulsating horizon... more Unsteady numerical simulation of double diffusive convection heat transfer in a pulsating horizontal heating annulus

Research paper thumbnail of Three Dimensional Finite Element Analysis of Thermal Behavior of Supercapacitors

Special Topics & Reviews in Porous Media: An International Journal, 2020

Research paper thumbnail of The effect of the position of the heated thin porous fin on the laminar natural convection heat transfer in a differentially heated cavity

International Communications in Heat and Mass Transfer, 2016

Laminar natural convection heat transfer in a differentially heated cavity with two thin porous f... more Laminar natural convection heat transfer in a differentially heated cavity with two thin porous fins attached to the hot wall and bottom insulated surface was studied numerically for various pertinent parameters. Such parameters include Richardson number, Darcy number, thermal conductivity ratio, and location of the porous fin. The left wall of the cavity is assumed to be uniformly heated while the right wall is kept at a lower temperature. In addition, the horizontal walls of the cavity were considered insulated. Furthermore, the governing transport equations within the porous media were written according to the volume-average theory. The governing equations are solved using a finite element formulation based on the Galerkin method of weighted residuals. The results of this investigation showed that the presence of a horizontal porous fin increases the average Nusselt number when compared with the differentially heated cavity for various Richardson numbers and thermal conductivity ratios. However, a vertical porous fin attached to the bottom insulated surface exhibited a lower average Nusselt number than the no-fin case.

Research paper thumbnail of Nonsimilar Combined Convection Flow over a Vertical Surface Embedded in a Variable Porosity Medium

Journal of Porous Media, 1999

Research paper thumbnail of Natural Convection Due to Solar Radiation from a Vertical Plate Embedded in a Porous Medium with Variable Porosity

Journal of Porous Media, 2001

ABSTRACT

Research paper thumbnail of Effect of Heated Wall Position on Mixed Convection in a Channel with an Open Cavity

Numerical Heat Transfer, Part A: Applications, 2003

Mixed convection in an open cavity with a heated wall bounded by a horizontally insulated plate i... more Mixed convection in an open cavity with a heated wall bounded by a horizontally insulated plate is studied numerically. Three basic heating modes are considered: (a) the heated wall is on the inflow side (assisting flow); (b) the heated wall is on the outflow side (opposing flow); and (c) the heated wall is the horizontal surface of the cavity (heating from below). Mixed convection fluid flow and heat transfer within the cavity is governed by the buoyancy parameter, Richardson number (Ri), and Reynolds number (Re). The results are reported in terms of streamlines, isotherms, wall temperature, and the velocity profiles in the cavity for Ri ¼ 0.1 and 100, Re ¼ 100 and 1000, and the ratio between the channel and cavity heights (H=D) is in the range 0.1-1.5. The present results show that the maximum temperature values decrease as the Reynolds and the Richardson numbers increase. The effect of the H=D ratio is found to play a significant role on streamline and isotherm patterns for different heating configurations. The present investigation shows that the opposing forced flow configuration has the highest thermal performance in terms of both maximum temperature and average Nusselt number.

Research paper thumbnail of Hydromagnetic Natural Convection from an Inclined Porous Square Enclosure with Heat Generation

Numerical Heat Transfer, Part A: Applications, 1998

The problem of unsteady. laminar, two-dimensional hydromagnetic natural conuection heal transfer ... more The problem of unsteady. laminar, two-dimensional hydromagnetic natural conuection heal transfer in an inclined square enclosure filhd with a fluid-salaraled porous medium in the presence of a transverse magnetic field and fluid heal generation effects is studied numerically. The walls of the enclosure are maintained al constant temperatures. The flow in the porous region is modeled using the Brinkman-extended Darcy's "'W to account for the no-slip conditions al the walls. The control volume method is used to solue the governing ba"'nce equations fOT different values of the Darcy number, Hartmann number, and the inclination angle. Favorable comparisons with previously published work are performed. These comparisons confirmed the correctness of the numerical results. The obtained numerical resulJsare presented graphically in terms ofstreamlines and isotherms as weU as velocity and temperature profiles al midsections ofthe awity to illmtrote interesting features of the solution.

Research paper thumbnail of Double-Diffusive Mixed Convection in a Lid-Driven Enclosure Filled with a Fluid-Saturated Porous Medium

Numerical Heat Transfer, Part A: Applications, 2002

This article presents a numerical study of mixed-convection heat and mass transport in a liddrive... more This article presents a numerical study of mixed-convection heat and mass transport in a liddriven square enclosure lled with a non-Darcian uid-saturated porous medium. The two vertical walls of the enclosure are insulated, while the horizontal walls are kept at constant but different temperatures and concentrations with the top surface moving at a constant speed. The transport equations are solved numerically using the nite-volume approach along with the alternating direct implicit (ADI) procedure. Comparisons with previously published work are performed and found to be in excellent agreement. The results of the present investigation indicate that the buoyancy ratio, Darcy number, Lewis number, and Richardson number have profound effects on the double-diffusive phenomenon.

Research paper thumbnail of Water diffusion in biomedical systems as related to magnetic resonance imaging

Magnetic Resonance Imaging, 2003

Water diffusion within the brain is studied numerically for various clinical conditions. The nume... more Water diffusion within the brain is studied numerically for various clinical conditions. The numerical procedure used in this work is based on the Galerkin weighted residual method of finite-element formulation. A wide range of pertinent parameters such as Lewis number, cell volume, and the buoyancy ratio are considered in the present study. Comparisons with previously published work show excellent agreement. The results show that the diffusion coefficient, cell volume, and the buoyancy ratio play significant roles on the characterization of the mass and heat transfer mechanisms within the cell. Concentration maps are developed for various clinical conditions. Pertinent results for the streamlines, isotherms and the mass and heat transfer rates in terms of the average Sherwood and Nusselt numbers are presented and discussed for different parametric values. Experimental tests are also conducted to produce an 8 Tesla image which is compared with our numerical simulation. The present study provides essential maps for brain disorders classified based on several pertinent clinical attributes.

Research paper thumbnail of Computational modeling of cerebral diffusion-application to stroke imaging

Magnetic Resonance Imaging, 2003

Water diffusion within the structure of a brain extracellular space is analyzed numerically for v... more Water diffusion within the structure of a brain extracellular space is analyzed numerically for various diffusion parameters of brain tissue namely extracellular space porosity and tortuosity. An algorithm for predicting diffusion pattern of water molecules within human brain considering the mechanics of water diffusion within porous media is developed. The extracellular space is modeled as a homogeneous porous medium with uniform porosity and permeability. Discretization of the fluid flow, heat transfer and mass transport equations is achieved using a finite element scheme based on the Galerkin method of weighted residuals. Concentration maps are developed in this study for various clinical conditions. The effect of the space porosity and the turtousity on the heat and mass transport within the extracellular space are found to be significant. The results presented in this work play an important role in producing more effective imaging techniques for brain injury based on the apparent diffusion coefficient.

Research paper thumbnail of The Role of Porous Media in Modeling Fluid Flow Within Hollow Fiber Membranes of the Total Artificial Lung

Journal of Porous Media, 2012

A numerical study was conducted to analyze fluid flow within hollow fiber membranes of the artifi... more A numerical study was conducted to analyze fluid flow within hollow fiber membranes of the artificial lungs. The hollow fiber bundle was approximated using a porous media model. In addition, the transport equations were solved using the finite-element formulation based on the Galerkin method of weighted residuals. Comparisons with previously published work on the basis of special cases were performed and found to be in excellent agreement. A Newtonian viscous fluid model for the blood was used. Different flow models for porous media, such as the Brinkman-extended Darcy model, Darcy's law model, and the generalized flow model, were considered. Results were obtained in terms of streamlines, velocity vectors, and pressure distribution for various Reynolds numbers and Darcy numbers. The results from this investigation showed that the pressure drop across the artificial lung device increased with an increase in the Reynolds number. In addition, the pressure drop was found to increase significantly for small Darcy numbers.

Research paper thumbnail of Spatial optimization of an array of aligned microcantilever based sensors

Journal of Micromechanics and Microengineering, 2004

The present work establishes the optimized spatial arrangement for an array of aligned microcanti... more The present work establishes the optimized spatial arrangement for an array of aligned microcantilever sensors placed inside a fluidic cell. The results of the present investigation show that the optimum spacing distance between the microcantilevers decreases as the fluidic cell height decreases. An increase in the flow Reynolds number is found to increase the optimum spacing distance. However, this increase is not noticeable at relatively small Reynolds numbers where the flow exhibits creep characteristics. Hydromagnetic effects are found to decrease the optimum spacing distance. The results of the present investigation show that the location of the microcantilevers from the wall of the fluidic cell also plays a significant role on the optimum distance between the microcantilevers. Finally, a correlation for the optimum spacing distance between the microcantilevers is obtained for various pertinent parameters. This correlation can be used to determine the minimum size of biochips that will produce similar flow conditions on each microcantilever, resulting in independent microcantilever detections for different analytes.

Research paper thumbnail of The effect of radiation on free convection flow of fluid with variable viscosity from a porous vertical plate

International Journal of Thermal Sciences, 2001

The effect of thermal radiation on the natural convection flow along a uniformly heated vertical ... more The effect of thermal radiation on the natural convection flow along a uniformly heated vertical porous plate with variable viscosity and uniform suction velocity was investigated numerically. The fluid considered in this study is of an optically dense viscous incompressible fluid of temperature-dependent viscosity. The laminar boundary layer equations governing the flow are shown to be nonsimilar. The governing equations are analyzed using a variety of methods: (i) a series solution for small values of ξ (a scaled streamwise coordinate depending on the transpiration); (ii) an asymptotic solution for large values of ξ ; and (iii) a full numerical solution using the Keller box method. The solutions are expressed in terms of the local shear stress and the local heat transfer rate. The working fluid is taken to have Prandtl number Pr = 1, and the effects of varying the viscosity variation parameter, γ , the radiation parameter, R d , and the surface temperature parameter, θ w , are discussed.  2001 Éditions scientifiques et médicales Elsevier SAS radiation / free convection / variable viscosity / porous vertical plate

Research paper thumbnail of Natural convection from an inclined plate embedded in a variable porosity porous medium due to solar radiation

International Journal of Thermal Sciences, 2002

Natural convection boundary-layer flow of an absorbing and electrically-conducting fluid over a s... more Natural convection boundary-layer flow of an absorbing and electrically-conducting fluid over a semi-infinite, ideally transparent, inclined flat plate embedded in a porous medium with variable porosity due to solar radiation is considered. The governing equations are derived using the usual boundary-layer and Boussinesq approximations and accounting for the presence of an applied magnetic field and an applied incident radiation flux. To account for the heat loss from the plate surface, a convective-type boundary condition is employed there. These equations and boundary conditions are non-dimensionalized and transformed using a non-similarity transformation. The resulting non-linear partial differential equations are then solved numerically subject to the transformed boundary conditions by an implicit iterative finite-difference scheme. Graphical results for the velocity and temperature fields as well as the boundary friction and Nusselt number are presented and discussed for various parametric conditions.  2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.

Research paper thumbnail of Buoyancy-driven flow and heat transfer in open-ended enclosures: elimination of the extended boundaries

International Journal of Heat and Mass Transfer, 2000

The present study is focused on obtaining an accurate representation of eective boundary conditio... more The present study is focused on obtaining an accurate representation of eective boundary conditions at the open side of two-and three-dimensional open-ended structures. Implementation of this representation reduces the more complicated open-ended boundary conditions to a closed-ended domain and results in substantial savings in CPU and memory usage. The numerical procedure used in this work is based on the Galerkin weighted residual method of ®nite-element formulation. Comparisons between the present investigation using the correlations for the proposed closed-ended model and the results for the extended computational domain attest to the successful implementation of the proposed model. The results presented in this work constitute an innovative way to describe correctly the boundary conditions at the open side of an open-ended boundary.

Research paper thumbnail of Mixed convection heat transfer in two-dimensional open-ended enclosures

International Journal of Heat and Mass Transfer, 2002

Mixed convection heat transfer in open-ended enclosures has been studied numerically for three di... more Mixed convection heat transfer in open-ended enclosures has been studied numerically for three different flow angles of attack. Discretization of the governing equations is achieved using a finite element scheme based on the Galerkin method of weighted residuals. Comparisons with previously published work on special cases of the problem are performed and the results show excellent agreement. A wide range of pertinent parameters such as Grashof number, Reynolds number, and the aspect ratio are considered in the present study. The obtained results show that thermal insulation of the cavity can be achieved through the use of high horizontal velocity flow. Various results for the streamlines, isotherms and the heat transfer rates in terms of the average Nusselt number are presented and discussed for different parametric values.

Research paper thumbnail of Mixed convection flow in a lid-driven enclosure filled with a fluid-saturated porous medium

International Journal of Heat and Mass Transfer, 1999

Volume averaged equations governing unsteady\ laminar\ mixed convection~ow in an enclosure _lled ... more Volume averaged equations governing unsteady\ laminar\ mixed convection~ow in an enclosure _lled with a Darciañ uid!saturated uniform porous medium in the presence of internal heat generation is formulated[ The two vertical walls of the enclosure are insulated while the horizontal walls are kept at constant temperatures with the top surface is moving at a constant speed[ The developed equations are nondimensionalized and then solved numerically subject to appropriate initial and boundary conditions by the _nite!volume approach along with the alternating direct implicit "ADI# procedure[ Comparisons with previously published work are performed and found to be in excellent agreement[ A parametric study is conducted and a set of graphical results is presented and discussed to elucidate interesting features of the solution[ Þ 0888 Elsevier Science Ltd[ All rights reserved[ Key words] Mixed convection^Heat generation^Porous medium Nomenclature a i\j coe.cient of _nite di}erence equation at point "i\ j# in a grid b right!hand side of _nite di}erence equation c p~u id speci_c heat ðJ kg −0 K −0 Ł Da Darcy number\ k:H 1 Da −0 inverse Darcy number "0:Da# g gravitational acceleration ðm s −1 Ł Gr Grashof number\ gbDTH 2 :n 1 H enclosure length ðmŁ K e e}ective thermal conductivity of the porous medium ðW m −0 K −0 Ł M grids number in x!direction N grids number in y!direction Nu average Nusselt number\ Nu Ð 0 9 ð"1u:1Y#−Pr Re VŁ dX P~uid pressure ðPaŁ Pr Prandtl number\ n:a e q1 volumetric heat generation Re Reynolds number\ U 9 H:n e

Research paper thumbnail of A critical synthesis of thermophysical characteristics of nanofluids

International Journal of Heat and Mass Transfer, 2011

A critical synthesis of the variants within the thermophysical properties of nanofluids is presen... more A critical synthesis of the variants within the thermophysical properties of nanofluids is presented in this work. The experimental results for the effective thermal conductivity and viscosity reported by several authors are in disagreement. Theoretical and experimental studies are essential to clarify the discrepancies in the results and in proper understanding of heat transfer enhancement characteristics of nanofluids. At room temperature, it is illustrated that the results of the effective thermal conductivity and viscosity of nanofluids can be estimated using the classical equations at low volume fractions. However, the classical models fail to estimate the effective thermal conductivity and viscosity of nanofluids at various temperatures. This study shows that it is not clear which analytical model should be used to describe the thermal conductivity of nanofluids. Additional theoretical and experimental research studies are required to clarify the mechanisms responsible for heat transfer enhancement in nanofluids. Correlations for effective thermal conductivity and viscosity are synthesized and developed in this study in terms of pertinent physical parameters based on the reported experimental data.

Research paper thumbnail of Mixed convection within a porous heat generating horizontal annulus

International Journal of Heat and Mass Transfer, 2003

A numerical investigation of mixed convection in a horizontal annulus filled with a uniform fluid... more A numerical investigation of mixed convection in a horizontal annulus filled with a uniform fluid-saturated porous medium in the presence of internal heat generation is carried out. The inner cylinder is heated while the outer cylinder is cooled. The forced flow is induced by the cold outer cylinder rotating at a constant angular velocity. The flow field is modeled using a generalized form of the momentum equation that accounts for the presence of porous medium viscous, Darcian and inertial effects. Discretization of the governing equations is achieved using a finite element scheme based on the Galerkin method of weighted residuals. Comparisons with previous works are performed and the results show excellent agreement. The effects of pertinent parameters such as the internal Rayleigh number, the Darcy number, the annulus gap, and the Richardson number on the flow and heat transfer characteristics are considered in the present study. The obtained results depict that the Richardson number plays a significant role on the heat transfer characterization within the annulus. The present results show that an increase in Reynolds number has a significant effect on the flow patterns within the annulus with respect to two-eddy, one-eddy and no-eddy flows. Categorization of the flow regimes according to the number of eddies is established on the RaRe plane for various Rayleigh numbers.

Research paper thumbnail of Buoyancy-driven heat transfer enhancement in a two-dimensional enclosure utilizing nanofluids

International Journal of Heat and Mass Transfer, 2003

Heat transfer enhancement in a two-dimensional enclosure utilizing nanofluids is investigated for... more Heat transfer enhancement in a two-dimensional enclosure utilizing nanofluids is investigated for various pertinent parameters. A model is developed to analyze heat transfer performance of nanofluids inside an enclosure taking into account the solid particle dispersion. The transport equations are solved numerically using the finite-volume approach along with the alternating direct implicit procedure. Comparisons with previously published work on the basis of special cases are performed and found to be in excellent agreement. The effect of suspended ultrafine metallic nanoparticles on the fluid flow and heat transfer processes within the enclosure is analyzed and effective thermal conductivity enhancement maps are developed for various controlling parameters. In addition, an analysis of variants based on the thermophysical properties of nanofluid is developed and presented. It is shown that the variances within different models have substantial effects on the results. Finally, a heat transfer correlation of the average Nusselt number for various Grashof numbers and volume fractions is presented.

Research paper thumbnail of Original

Unsteady numerical simulation of double diffusive convection heat transfer in a pulsating horizon... more Unsteady numerical simulation of double diffusive convection heat transfer in a pulsating horizontal heating annulus

Research paper thumbnail of Three Dimensional Finite Element Analysis of Thermal Behavior of Supercapacitors

Special Topics & Reviews in Porous Media: An International Journal, 2020

Research paper thumbnail of The effect of the position of the heated thin porous fin on the laminar natural convection heat transfer in a differentially heated cavity

International Communications in Heat and Mass Transfer, 2016

Laminar natural convection heat transfer in a differentially heated cavity with two thin porous f... more Laminar natural convection heat transfer in a differentially heated cavity with two thin porous fins attached to the hot wall and bottom insulated surface was studied numerically for various pertinent parameters. Such parameters include Richardson number, Darcy number, thermal conductivity ratio, and location of the porous fin. The left wall of the cavity is assumed to be uniformly heated while the right wall is kept at a lower temperature. In addition, the horizontal walls of the cavity were considered insulated. Furthermore, the governing transport equations within the porous media were written according to the volume-average theory. The governing equations are solved using a finite element formulation based on the Galerkin method of weighted residuals. The results of this investigation showed that the presence of a horizontal porous fin increases the average Nusselt number when compared with the differentially heated cavity for various Richardson numbers and thermal conductivity ratios. However, a vertical porous fin attached to the bottom insulated surface exhibited a lower average Nusselt number than the no-fin case.

Research paper thumbnail of Nonsimilar Combined Convection Flow over a Vertical Surface Embedded in a Variable Porosity Medium

Journal of Porous Media, 1999

Research paper thumbnail of Natural Convection Due to Solar Radiation from a Vertical Plate Embedded in a Porous Medium with Variable Porosity

Journal of Porous Media, 2001

ABSTRACT

Research paper thumbnail of Effect of Heated Wall Position on Mixed Convection in a Channel with an Open Cavity

Numerical Heat Transfer, Part A: Applications, 2003

Mixed convection in an open cavity with a heated wall bounded by a horizontally insulated plate i... more Mixed convection in an open cavity with a heated wall bounded by a horizontally insulated plate is studied numerically. Three basic heating modes are considered: (a) the heated wall is on the inflow side (assisting flow); (b) the heated wall is on the outflow side (opposing flow); and (c) the heated wall is the horizontal surface of the cavity (heating from below). Mixed convection fluid flow and heat transfer within the cavity is governed by the buoyancy parameter, Richardson number (Ri), and Reynolds number (Re). The results are reported in terms of streamlines, isotherms, wall temperature, and the velocity profiles in the cavity for Ri ¼ 0.1 and 100, Re ¼ 100 and 1000, and the ratio between the channel and cavity heights (H=D) is in the range 0.1-1.5. The present results show that the maximum temperature values decrease as the Reynolds and the Richardson numbers increase. The effect of the H=D ratio is found to play a significant role on streamline and isotherm patterns for different heating configurations. The present investigation shows that the opposing forced flow configuration has the highest thermal performance in terms of both maximum temperature and average Nusselt number.

Research paper thumbnail of Hydromagnetic Natural Convection from an Inclined Porous Square Enclosure with Heat Generation

Numerical Heat Transfer, Part A: Applications, 1998

The problem of unsteady. laminar, two-dimensional hydromagnetic natural conuection heal transfer ... more The problem of unsteady. laminar, two-dimensional hydromagnetic natural conuection heal transfer in an inclined square enclosure filhd with a fluid-salaraled porous medium in the presence of a transverse magnetic field and fluid heal generation effects is studied numerically. The walls of the enclosure are maintained al constant temperatures. The flow in the porous region is modeled using the Brinkman-extended Darcy's "'W to account for the no-slip conditions al the walls. The control volume method is used to solue the governing ba"'nce equations fOT different values of the Darcy number, Hartmann number, and the inclination angle. Favorable comparisons with previously published work are performed. These comparisons confirmed the correctness of the numerical results. The obtained numerical resulJsare presented graphically in terms ofstreamlines and isotherms as weU as velocity and temperature profiles al midsections ofthe awity to illmtrote interesting features of the solution.

Research paper thumbnail of Double-Diffusive Mixed Convection in a Lid-Driven Enclosure Filled with a Fluid-Saturated Porous Medium

Numerical Heat Transfer, Part A: Applications, 2002

This article presents a numerical study of mixed-convection heat and mass transport in a liddrive... more This article presents a numerical study of mixed-convection heat and mass transport in a liddriven square enclosure lled with a non-Darcian uid-saturated porous medium. The two vertical walls of the enclosure are insulated, while the horizontal walls are kept at constant but different temperatures and concentrations with the top surface moving at a constant speed. The transport equations are solved numerically using the nite-volume approach along with the alternating direct implicit (ADI) procedure. Comparisons with previously published work are performed and found to be in excellent agreement. The results of the present investigation indicate that the buoyancy ratio, Darcy number, Lewis number, and Richardson number have profound effects on the double-diffusive phenomenon.

Research paper thumbnail of Water diffusion in biomedical systems as related to magnetic resonance imaging

Magnetic Resonance Imaging, 2003

Water diffusion within the brain is studied numerically for various clinical conditions. The nume... more Water diffusion within the brain is studied numerically for various clinical conditions. The numerical procedure used in this work is based on the Galerkin weighted residual method of finite-element formulation. A wide range of pertinent parameters such as Lewis number, cell volume, and the buoyancy ratio are considered in the present study. Comparisons with previously published work show excellent agreement. The results show that the diffusion coefficient, cell volume, and the buoyancy ratio play significant roles on the characterization of the mass and heat transfer mechanisms within the cell. Concentration maps are developed for various clinical conditions. Pertinent results for the streamlines, isotherms and the mass and heat transfer rates in terms of the average Sherwood and Nusselt numbers are presented and discussed for different parametric values. Experimental tests are also conducted to produce an 8 Tesla image which is compared with our numerical simulation. The present study provides essential maps for brain disorders classified based on several pertinent clinical attributes.

Research paper thumbnail of Computational modeling of cerebral diffusion-application to stroke imaging

Magnetic Resonance Imaging, 2003

Water diffusion within the structure of a brain extracellular space is analyzed numerically for v... more Water diffusion within the structure of a brain extracellular space is analyzed numerically for various diffusion parameters of brain tissue namely extracellular space porosity and tortuosity. An algorithm for predicting diffusion pattern of water molecules within human brain considering the mechanics of water diffusion within porous media is developed. The extracellular space is modeled as a homogeneous porous medium with uniform porosity and permeability. Discretization of the fluid flow, heat transfer and mass transport equations is achieved using a finite element scheme based on the Galerkin method of weighted residuals. Concentration maps are developed in this study for various clinical conditions. The effect of the space porosity and the turtousity on the heat and mass transport within the extracellular space are found to be significant. The results presented in this work play an important role in producing more effective imaging techniques for brain injury based on the apparent diffusion coefficient.

Research paper thumbnail of The Role of Porous Media in Modeling Fluid Flow Within Hollow Fiber Membranes of the Total Artificial Lung

Journal of Porous Media, 2012

A numerical study was conducted to analyze fluid flow within hollow fiber membranes of the artifi... more A numerical study was conducted to analyze fluid flow within hollow fiber membranes of the artificial lungs. The hollow fiber bundle was approximated using a porous media model. In addition, the transport equations were solved using the finite-element formulation based on the Galerkin method of weighted residuals. Comparisons with previously published work on the basis of special cases were performed and found to be in excellent agreement. A Newtonian viscous fluid model for the blood was used. Different flow models for porous media, such as the Brinkman-extended Darcy model, Darcy's law model, and the generalized flow model, were considered. Results were obtained in terms of streamlines, velocity vectors, and pressure distribution for various Reynolds numbers and Darcy numbers. The results from this investigation showed that the pressure drop across the artificial lung device increased with an increase in the Reynolds number. In addition, the pressure drop was found to increase significantly for small Darcy numbers.

Research paper thumbnail of Spatial optimization of an array of aligned microcantilever based sensors

Journal of Micromechanics and Microengineering, 2004

The present work establishes the optimized spatial arrangement for an array of aligned microcanti... more The present work establishes the optimized spatial arrangement for an array of aligned microcantilever sensors placed inside a fluidic cell. The results of the present investigation show that the optimum spacing distance between the microcantilevers decreases as the fluidic cell height decreases. An increase in the flow Reynolds number is found to increase the optimum spacing distance. However, this increase is not noticeable at relatively small Reynolds numbers where the flow exhibits creep characteristics. Hydromagnetic effects are found to decrease the optimum spacing distance. The results of the present investigation show that the location of the microcantilevers from the wall of the fluidic cell also plays a significant role on the optimum distance between the microcantilevers. Finally, a correlation for the optimum spacing distance between the microcantilevers is obtained for various pertinent parameters. This correlation can be used to determine the minimum size of biochips that will produce similar flow conditions on each microcantilever, resulting in independent microcantilever detections for different analytes.

Research paper thumbnail of The effect of radiation on free convection flow of fluid with variable viscosity from a porous vertical plate

International Journal of Thermal Sciences, 2001

The effect of thermal radiation on the natural convection flow along a uniformly heated vertical ... more The effect of thermal radiation on the natural convection flow along a uniformly heated vertical porous plate with variable viscosity and uniform suction velocity was investigated numerically. The fluid considered in this study is of an optically dense viscous incompressible fluid of temperature-dependent viscosity. The laminar boundary layer equations governing the flow are shown to be nonsimilar. The governing equations are analyzed using a variety of methods: (i) a series solution for small values of ξ (a scaled streamwise coordinate depending on the transpiration); (ii) an asymptotic solution for large values of ξ ; and (iii) a full numerical solution using the Keller box method. The solutions are expressed in terms of the local shear stress and the local heat transfer rate. The working fluid is taken to have Prandtl number Pr = 1, and the effects of varying the viscosity variation parameter, γ , the radiation parameter, R d , and the surface temperature parameter, θ w , are discussed.  2001 Éditions scientifiques et médicales Elsevier SAS radiation / free convection / variable viscosity / porous vertical plate

Research paper thumbnail of Natural convection from an inclined plate embedded in a variable porosity porous medium due to solar radiation

International Journal of Thermal Sciences, 2002

Natural convection boundary-layer flow of an absorbing and electrically-conducting fluid over a s... more Natural convection boundary-layer flow of an absorbing and electrically-conducting fluid over a semi-infinite, ideally transparent, inclined flat plate embedded in a porous medium with variable porosity due to solar radiation is considered. The governing equations are derived using the usual boundary-layer and Boussinesq approximations and accounting for the presence of an applied magnetic field and an applied incident radiation flux. To account for the heat loss from the plate surface, a convective-type boundary condition is employed there. These equations and boundary conditions are non-dimensionalized and transformed using a non-similarity transformation. The resulting non-linear partial differential equations are then solved numerically subject to the transformed boundary conditions by an implicit iterative finite-difference scheme. Graphical results for the velocity and temperature fields as well as the boundary friction and Nusselt number are presented and discussed for various parametric conditions.  2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.

Research paper thumbnail of Buoyancy-driven flow and heat transfer in open-ended enclosures: elimination of the extended boundaries

International Journal of Heat and Mass Transfer, 2000

The present study is focused on obtaining an accurate representation of eective boundary conditio... more The present study is focused on obtaining an accurate representation of eective boundary conditions at the open side of two-and three-dimensional open-ended structures. Implementation of this representation reduces the more complicated open-ended boundary conditions to a closed-ended domain and results in substantial savings in CPU and memory usage. The numerical procedure used in this work is based on the Galerkin weighted residual method of ®nite-element formulation. Comparisons between the present investigation using the correlations for the proposed closed-ended model and the results for the extended computational domain attest to the successful implementation of the proposed model. The results presented in this work constitute an innovative way to describe correctly the boundary conditions at the open side of an open-ended boundary.

Research paper thumbnail of Mixed convection heat transfer in two-dimensional open-ended enclosures

International Journal of Heat and Mass Transfer, 2002

Mixed convection heat transfer in open-ended enclosures has been studied numerically for three di... more Mixed convection heat transfer in open-ended enclosures has been studied numerically for three different flow angles of attack. Discretization of the governing equations is achieved using a finite element scheme based on the Galerkin method of weighted residuals. Comparisons with previously published work on special cases of the problem are performed and the results show excellent agreement. A wide range of pertinent parameters such as Grashof number, Reynolds number, and the aspect ratio are considered in the present study. The obtained results show that thermal insulation of the cavity can be achieved through the use of high horizontal velocity flow. Various results for the streamlines, isotherms and the heat transfer rates in terms of the average Nusselt number are presented and discussed for different parametric values.

Research paper thumbnail of Mixed convection flow in a lid-driven enclosure filled with a fluid-saturated porous medium

International Journal of Heat and Mass Transfer, 1999

Volume averaged equations governing unsteady\ laminar\ mixed convection~ow in an enclosure _lled ... more Volume averaged equations governing unsteady\ laminar\ mixed convection~ow in an enclosure _lled with a Darciañ uid!saturated uniform porous medium in the presence of internal heat generation is formulated[ The two vertical walls of the enclosure are insulated while the horizontal walls are kept at constant temperatures with the top surface is moving at a constant speed[ The developed equations are nondimensionalized and then solved numerically subject to appropriate initial and boundary conditions by the _nite!volume approach along with the alternating direct implicit "ADI# procedure[ Comparisons with previously published work are performed and found to be in excellent agreement[ A parametric study is conducted and a set of graphical results is presented and discussed to elucidate interesting features of the solution[ Þ 0888 Elsevier Science Ltd[ All rights reserved[ Key words] Mixed convection^Heat generation^Porous medium Nomenclature a i\j coe.cient of _nite di}erence equation at point "i\ j# in a grid b right!hand side of _nite di}erence equation c p~u id speci_c heat ðJ kg −0 K −0 Ł Da Darcy number\ k:H 1 Da −0 inverse Darcy number "0:Da# g gravitational acceleration ðm s −1 Ł Gr Grashof number\ gbDTH 2 :n 1 H enclosure length ðmŁ K e e}ective thermal conductivity of the porous medium ðW m −0 K −0 Ł M grids number in x!direction N grids number in y!direction Nu average Nusselt number\ Nu Ð 0 9 ð"1u:1Y#−Pr Re VŁ dX P~uid pressure ðPaŁ Pr Prandtl number\ n:a e q1 volumetric heat generation Re Reynolds number\ U 9 H:n e

Research paper thumbnail of A critical synthesis of thermophysical characteristics of nanofluids

International Journal of Heat and Mass Transfer, 2011

A critical synthesis of the variants within the thermophysical properties of nanofluids is presen... more A critical synthesis of the variants within the thermophysical properties of nanofluids is presented in this work. The experimental results for the effective thermal conductivity and viscosity reported by several authors are in disagreement. Theoretical and experimental studies are essential to clarify the discrepancies in the results and in proper understanding of heat transfer enhancement characteristics of nanofluids. At room temperature, it is illustrated that the results of the effective thermal conductivity and viscosity of nanofluids can be estimated using the classical equations at low volume fractions. However, the classical models fail to estimate the effective thermal conductivity and viscosity of nanofluids at various temperatures. This study shows that it is not clear which analytical model should be used to describe the thermal conductivity of nanofluids. Additional theoretical and experimental research studies are required to clarify the mechanisms responsible for heat transfer enhancement in nanofluids. Correlations for effective thermal conductivity and viscosity are synthesized and developed in this study in terms of pertinent physical parameters based on the reported experimental data.

Research paper thumbnail of Mixed convection within a porous heat generating horizontal annulus

International Journal of Heat and Mass Transfer, 2003

A numerical investigation of mixed convection in a horizontal annulus filled with a uniform fluid... more A numerical investigation of mixed convection in a horizontal annulus filled with a uniform fluid-saturated porous medium in the presence of internal heat generation is carried out. The inner cylinder is heated while the outer cylinder is cooled. The forced flow is induced by the cold outer cylinder rotating at a constant angular velocity. The flow field is modeled using a generalized form of the momentum equation that accounts for the presence of porous medium viscous, Darcian and inertial effects. Discretization of the governing equations is achieved using a finite element scheme based on the Galerkin method of weighted residuals. Comparisons with previous works are performed and the results show excellent agreement. The effects of pertinent parameters such as the internal Rayleigh number, the Darcy number, the annulus gap, and the Richardson number on the flow and heat transfer characteristics are considered in the present study. The obtained results depict that the Richardson number plays a significant role on the heat transfer characterization within the annulus. The present results show that an increase in Reynolds number has a significant effect on the flow patterns within the annulus with respect to two-eddy, one-eddy and no-eddy flows. Categorization of the flow regimes according to the number of eddies is established on the RaRe plane for various Rayleigh numbers.

Research paper thumbnail of Buoyancy-driven heat transfer enhancement in a two-dimensional enclosure utilizing nanofluids

International Journal of Heat and Mass Transfer, 2003

Heat transfer enhancement in a two-dimensional enclosure utilizing nanofluids is investigated for... more Heat transfer enhancement in a two-dimensional enclosure utilizing nanofluids is investigated for various pertinent parameters. A model is developed to analyze heat transfer performance of nanofluids inside an enclosure taking into account the solid particle dispersion. The transport equations are solved numerically using the finite-volume approach along with the alternating direct implicit procedure. Comparisons with previously published work on the basis of special cases are performed and found to be in excellent agreement. The effect of suspended ultrafine metallic nanoparticles on the fluid flow and heat transfer processes within the enclosure is analyzed and effective thermal conductivity enhancement maps are developed for various controlling parameters. In addition, an analysis of variants based on the thermophysical properties of nanofluid is developed and presented. It is shown that the variances within different models have substantial effects on the results. Finally, a heat transfer correlation of the average Nusselt number for various Grashof numbers and volume fractions is presented.