Experimental flow visualization is a valuable tool for analyzing microfluidics and nanofluidics i... more Experimental flow visualization is a valuable tool for analyzing microfluidics and nanofluidics in a wide variety of applications. Since the late 1990s, considerable advances in optical methods and image postprocessing techniques have improved direct optical measurements, resulting in an accurate qualitative and quantitative understanding of transport phenomena in lab-on-a-chip capillaries. In this study, a comparison of different optical measurement techniques is presented. The state-of-the-art development of particle image velocimetry to date, particularly in microscale applications, is reviewed here in detail. This study reviews novel approaches for estimating velocity field measurements with high precision within interrogation windows. Different regularization terms are discussed to demonstrate their capability for particle displacement optimization. The discussion shows how single- and multi-camera optical techniques provide two-dimensional and three-component velocity fields. ...
This paper investigates the effect of the diameter and the volume fraction variation of the centr... more This paper investigates the effect of the diameter and the volume fraction variation of the centre nanoparticles on the heat transfer characteristics of a two-dimensional slot jet. The jet impinges on stationary flat, convex, and concave aluminium plates. A forced convective heat transfer coefficient of water-CuO nanofluid impinges on a smooth plate under a constant heat flux. The finite volume method (FVM) is implemented for nanoparticles with diameters varying from 7 to 60 nanometers, volume fractions changing from 0 to 5%, and the Reynolds numbers ranging from 1800 to 2800. A grid independence study is carried out to find a grid size that predicts the results accurately and further grid refinement changes the results insignificantly. The single-phase model shows a capability to predicts the fluid and heat transfer parameters faster and make it more suitable for numerical simulations compared to the two-phase model. The results indicate a higher heat transfer coefficient of nanofl...
This paper presents exergy analysis of Micro Gas Turbine (MGT) system. It is proposed to use hot ... more This paper presents exergy analysis of Micro Gas Turbine (MGT) system. It is proposed to use hot MGT exhaust gases heat in a heat recovery steam generator to produce steam. Absorption chillers can help to increase the performance of MGT tri generation plants. MGTs are fuelled with natural gas and their waste heat is used to drive absorption chillers and other thermal energy users. Based on a steady-state model of the processes, exergy flow rates are calculated for all components and a detailed exergy analysis is performed. The components with the highest proportion of irreversibility in these systems are identified and compared.
In this paper, the flow characteristics and heat transfer over two equal square cylinders which a... more In this paper, the flow characteristics and heat transfer over two equal square cylinders which are placed in tandem arrangement, are investigated numerically. The simulations are performed for a Reynolds number range varying from 1 to 200 and spacing between the cylinders is five widths of the cylinders. The calculations are carried out on a finite volume code for both steady and unsteady incompressible laminar flow in the two dimensional regime. In this study, the instantaneous and mean streamlines and isotherm patterns for different Reynolds numbers are presented. In addition, the effect of Reynolds number on the flow patterns around the cylinders are in detail presented. In addition, the quantities such as pressure and viscous drag coefficients and pressure coefficients are presented.
Nowadays, many researchers works in fluid dynamics has been concentrated on determine the suitabl... more Nowadays, many researchers works in fluid dynamics has been concentrated on determine the suitable turbulent model for better describing the flow structure and heat transfer characteristics in a specific problem, there are a lot of cases which are necessary about designation of an optimized turbulent model. In the present work, a ribbed roughened square duct has been investigated numerically. A two-dimensionally study has been done to evaluate the flow structure, heat transfer and computational efforts of seven turbulent RANS models, contemporaneously. In the Part 1 of this study turbulence models, which are used in these type of problems has been investigated. In the next, advantages of introduced turbulence models has been present and explained. The results of numerical simulations will be presented in the Part 2.
Flow characteristics in the onset of vortex shedding and heat transfer pattern over a single and ... more Flow characteristics in the onset of vortex shedding and heat transfer pattern over a single and two same-sized square prisms placed in tandem are studied numerically. All simulations are carried out for Reynolds numbers range varying from 1 to 200 and spacing between the prisms in the order of five widths of prism for in tandem configuration. The calculations are done employing a finite volume in-house computer program according to semi-implicit method for pressure linked equations-consistent (SIMPLEC) numerical procedure and nonstaggered mesh in 2-dimensional, steady/unsteady and incompressible flow regimes. The instantaneous and time-averaged streamlines as well as iso-therm pattern for different Reynolds numbers are analysed. Furthermore, the influence of Reynolds number and the onset of vortex shedding on the flow pattern are studied in detail. Three distinct patterns namely fully-attached, trailing-edge separation and leading-edge separation were observed.
international journal of advanced design and manufacturing technology, 2013
Flow structure and heat transfer characteristics around two-equal in-tandem square cylinders in t... more Flow structure and heat transfer characteristics around two-equal in-tandem square cylinders in the two dimensional laminar and turbulent flow regimes are simulated numerically for Reynolds and Prandtl numbers, Re=1-1×10 5 , Pr=0.71, respectively. The investigation is based on an implicit finite volume scheme for integrating the unsteady Navier-Stokes equations and use of standard κ-e model to Reynolds stresses and scalar fluxes terms modelling. In this study, the instantaneous and mean streamlines, vorticity and isotherm patterns for different Reynolds numbers and distance between the cylinders are presented and discussed. In addition, the global quantities such as drag coefficients, RMS lift and drag coefficients, Strouhal number and Nusselt number are determined. An interesting phenomenon has been observed in the flow patterns depending upon the Reynolds number and the distance between the cylinders. A switch over in the nature of the fluctuations of the lift and drag coefficient...
In this paper, the flow around bluff bodies with different cross sections and determination of fo... more In this paper, the flow around bluff bodies with different cross sections and determination of forces acts on them are investigated.This paper presents the results of a numerical study on the flow characteristics and heat transfer over two equal square cylinders in a tandem arrangement. Spacing between the cylinders is 5 widths of the cylinder and the Reynolds number ranges from 1 to 200, Pr=0.71. Both steady and unsteady incompressible laminar flow in the two-dimensional regime are studied. A study of the effects of spatial resolution and blockage on the results is provided. In this paper, the instantaneous and mean streamlines, vorticity and isotherm patterns for different Reynolds numbers are presented and discussed. Also the global quantities such as pressure and viscous drag coefficients, Strouhal number and Nusselt number are determined and discussed for various Reynolds numbers.
in this paper, diffusion of nano particles from a point source in the viscous sub-layer of turbul... more in this paper, diffusion of nano particles from a point source in the viscous sub-layer of turbulent shear flow is considered. the equation of motion of particles including the brownian effects is used and ensembles of 500 particle trajectories are numerically evaluated and statistically analysed. effects of size on particle dispersion and wall deposition processes are studied. the effect of turbulent near a wall is also considered. the results are compared with the exact solution of corresponding eulerian convective diffusion equation in the absence of turbulent fluctuations. the results show that the brownian diffusion play a significant role in the diffusion of nano particles at distances less than 2 wall units from the solid wall. [M. Mahdavimanesh, A. R. Noghrehabadi, M. Behbahaninejad, G. Ahmadi, M. H. Nirooei, A. Etminan . Diffusion of nano particles in viscous sub-layer. Life Sci J 2013;10(8s):105-109] (ISSN:1097-8135). http://www.lifesciencesite.com. 13
Experimental tests in the case of bat performance in some sports like baseball and cricket is cos... more Experimental tests in the case of bat performance in some sports like baseball and cricket is costly and tedious. In this paper a three dimensional modeling of ball and bat is generated and computational finite element method used to predict the performance of baseball bat. This could be useful for bat designers to use from these results achieved by computational soft wares in order to reduce cost and time spending. A finite element modeling is done in software ANSYS/LSDYNA version 971 R.4.2 that is used to explicit dynamic problems. The ball is created by viscoelastic material and using an orthotropic material for baseball bat the ball exit velocity should be then quantified. Performing modal analysis to bat, the region indicated between first and second fundamental modes of vibration and where the ball has maximum exit velocity is compared. The results will be shown graphically in the case of stress exerted to the bat and modal analysis in transient mode, and graphs will show the ...
Turbulent heat transfer and flow structure inside straight, divergent and convergent ducts with s... more Turbulent heat transfer and flow structure inside straight, divergent and convergent ducts with square ribs has been investigated for Reynolds number varying from 7000 to 100000 numerically. The simulations have been employed using the one and two turbulent models in particular Re-normalization group (RNG) as the most efficient model. The impact of divergence or convergence on thermal efficiency of ducts during cooling process is explored in two and three dimensional flow regimes. Results reveal that divergent channel transfers higher amount of heat in comparison to other kinds of channels. Furthermore, divergent channel records less pressure loss and higher thermal efficiency where fully developed flow can be seen just through the straight duct. Computational data show a good agreement with experimental results available in the literature.
Computational Fluid Dynamics (CFD) has been widely employed by investigators to simulate Taylor f... more Computational Fluid Dynamics (CFD) has been widely employed by investigators to simulate Taylor flow in microchannels. High-resolution images captured by numerical techniques reveal significant details of an ultra-thin liquid film around the gas bubble. The interface between the liquid and the gas phases is a decisive factor in order to determine the flow pattern, the gas bubble profile, the bubble length–separation distance, the slug length, and so forth. Since the thickness of the liquid film is on the order of 10-15 μm for low capillary number flows, the mesh generation requires careful modeling to capture it and transport phenomena, such as momentum and heat. The present study is to develop a model of a transient Taylor flow in a two-dimensional microchannel using commercial ANSYS Fluent software. The Volume of Fluid (VoF) method was employed to simulate the interface between two phases, i.e., air and water. A comprehensive grid study was carried out to identify a sufficiently f...
Taylor flow is a strategy-aimed flow to transfer conventional single-phase into a more efficient ... more Taylor flow is a strategy-aimed flow to transfer conventional single-phase into a more efficient two-phase flow resulting in an enhanced momentum/heat/mass transfer rate, as well as a multitude of other advantages. To date, Taylor flow has focused on the processes involving gas–liquid and liquid–liquid two-phase systems in microchannels over a wide range of applications in biomedical, pharmaceutical, industrial, and commercial sectors. Appropriately micro-structured design is, therefore, a key consideration for equipment dealing with transport phenomena. This review paper highlights the hydrodynamic aspects of gas–liquid and liquid–liquid two-phase flows in microchannels. It covers state-of-the-art experimental and numerical methods in the literature for analyzing and simulating slug flows in circular and non-circular microchannels. The review’s main objective is to identify the considerable opportunity for further development of microflows and provide suggestions for researchers in...
This paper presents a CFD-based simulation method for air/water and water/dodecane Taylor flows t... more This paper presents a CFD-based simulation method for air/water and water/dodecane Taylor flows through an axisymmetric microchannel with a circular cross-sectional area. A systematic analysis is conducted by exploring the effects of different superficial velocities and apparent viscosities on the hydrodynamics of a slug flow regime. A concentric junction is employed to make bubbles of air in a continuous flow of water and slugs of water in a continuous flow of dodecane oil. A time-history study is conducted to predict the air-bubble and water-slug evolution processes, in particular at the moment of slug breakup. The results show that the larger apparent viscosity ratio of phases involved in the liquid-liquid flow generates a more stable interface. However, the liquid slug length is less and film thickness is slightly larger in liquid-liquid compared to gas-liquid flow. Furthermore, variations in gas and liquid holdups are correlated by the superficial velocity ratio. The numerical ...
Experimental flow visualization is a valuable tool for analyzing microfluidics and nanofluidics i... more Experimental flow visualization is a valuable tool for analyzing microfluidics and nanofluidics in a wide variety of applications. Since the late 1990s, considerable advances in optical methods and image postprocessing techniques have improved direct optical measurements, resulting in an accurate qualitative and quantitative understanding of transport phenomena in lab-on-a-chip capillaries. In this study, a comparison of different optical measurement techniques is presented. The state-of-the-art development of particle image velocimetry to date, particularly in microscale applications, is reviewed here in detail. This study reviews novel approaches for estimating velocity field measurements with high precision within interrogation windows. Different regularization terms are discussed to demonstrate their capability for particle displacement optimization. The discussion shows how single- and multi-camera optical techniques provide two-dimensional and three-component velocity fields. ...
This paper investigates the effect of the diameter and the volume fraction variation of the centr... more This paper investigates the effect of the diameter and the volume fraction variation of the centre nanoparticles on the heat transfer characteristics of a two-dimensional slot jet. The jet impinges on stationary flat, convex, and concave aluminium plates. A forced convective heat transfer coefficient of water-CuO nanofluid impinges on a smooth plate under a constant heat flux. The finite volume method (FVM) is implemented for nanoparticles with diameters varying from 7 to 60 nanometers, volume fractions changing from 0 to 5%, and the Reynolds numbers ranging from 1800 to 2800. A grid independence study is carried out to find a grid size that predicts the results accurately and further grid refinement changes the results insignificantly. The single-phase model shows a capability to predicts the fluid and heat transfer parameters faster and make it more suitable for numerical simulations compared to the two-phase model. The results indicate a higher heat transfer coefficient of nanofl...
This paper presents exergy analysis of Micro Gas Turbine (MGT) system. It is proposed to use hot ... more This paper presents exergy analysis of Micro Gas Turbine (MGT) system. It is proposed to use hot MGT exhaust gases heat in a heat recovery steam generator to produce steam. Absorption chillers can help to increase the performance of MGT tri generation plants. MGTs are fuelled with natural gas and their waste heat is used to drive absorption chillers and other thermal energy users. Based on a steady-state model of the processes, exergy flow rates are calculated for all components and a detailed exergy analysis is performed. The components with the highest proportion of irreversibility in these systems are identified and compared.
In this paper, the flow characteristics and heat transfer over two equal square cylinders which a... more In this paper, the flow characteristics and heat transfer over two equal square cylinders which are placed in tandem arrangement, are investigated numerically. The simulations are performed for a Reynolds number range varying from 1 to 200 and spacing between the cylinders is five widths of the cylinders. The calculations are carried out on a finite volume code for both steady and unsteady incompressible laminar flow in the two dimensional regime. In this study, the instantaneous and mean streamlines and isotherm patterns for different Reynolds numbers are presented. In addition, the effect of Reynolds number on the flow patterns around the cylinders are in detail presented. In addition, the quantities such as pressure and viscous drag coefficients and pressure coefficients are presented.
Nowadays, many researchers works in fluid dynamics has been concentrated on determine the suitabl... more Nowadays, many researchers works in fluid dynamics has been concentrated on determine the suitable turbulent model for better describing the flow structure and heat transfer characteristics in a specific problem, there are a lot of cases which are necessary about designation of an optimized turbulent model. In the present work, a ribbed roughened square duct has been investigated numerically. A two-dimensionally study has been done to evaluate the flow structure, heat transfer and computational efforts of seven turbulent RANS models, contemporaneously. In the Part 1 of this study turbulence models, which are used in these type of problems has been investigated. In the next, advantages of introduced turbulence models has been present and explained. The results of numerical simulations will be presented in the Part 2.
Flow characteristics in the onset of vortex shedding and heat transfer pattern over a single and ... more Flow characteristics in the onset of vortex shedding and heat transfer pattern over a single and two same-sized square prisms placed in tandem are studied numerically. All simulations are carried out for Reynolds numbers range varying from 1 to 200 and spacing between the prisms in the order of five widths of prism for in tandem configuration. The calculations are done employing a finite volume in-house computer program according to semi-implicit method for pressure linked equations-consistent (SIMPLEC) numerical procedure and nonstaggered mesh in 2-dimensional, steady/unsteady and incompressible flow regimes. The instantaneous and time-averaged streamlines as well as iso-therm pattern for different Reynolds numbers are analysed. Furthermore, the influence of Reynolds number and the onset of vortex shedding on the flow pattern are studied in detail. Three distinct patterns namely fully-attached, trailing-edge separation and leading-edge separation were observed.
international journal of advanced design and manufacturing technology, 2013
Flow structure and heat transfer characteristics around two-equal in-tandem square cylinders in t... more Flow structure and heat transfer characteristics around two-equal in-tandem square cylinders in the two dimensional laminar and turbulent flow regimes are simulated numerically for Reynolds and Prandtl numbers, Re=1-1×10 5 , Pr=0.71, respectively. The investigation is based on an implicit finite volume scheme for integrating the unsteady Navier-Stokes equations and use of standard κ-e model to Reynolds stresses and scalar fluxes terms modelling. In this study, the instantaneous and mean streamlines, vorticity and isotherm patterns for different Reynolds numbers and distance between the cylinders are presented and discussed. In addition, the global quantities such as drag coefficients, RMS lift and drag coefficients, Strouhal number and Nusselt number are determined. An interesting phenomenon has been observed in the flow patterns depending upon the Reynolds number and the distance between the cylinders. A switch over in the nature of the fluctuations of the lift and drag coefficient...
In this paper, the flow around bluff bodies with different cross sections and determination of fo... more In this paper, the flow around bluff bodies with different cross sections and determination of forces acts on them are investigated.This paper presents the results of a numerical study on the flow characteristics and heat transfer over two equal square cylinders in a tandem arrangement. Spacing between the cylinders is 5 widths of the cylinder and the Reynolds number ranges from 1 to 200, Pr=0.71. Both steady and unsteady incompressible laminar flow in the two-dimensional regime are studied. A study of the effects of spatial resolution and blockage on the results is provided. In this paper, the instantaneous and mean streamlines, vorticity and isotherm patterns for different Reynolds numbers are presented and discussed. Also the global quantities such as pressure and viscous drag coefficients, Strouhal number and Nusselt number are determined and discussed for various Reynolds numbers.
in this paper, diffusion of nano particles from a point source in the viscous sub-layer of turbul... more in this paper, diffusion of nano particles from a point source in the viscous sub-layer of turbulent shear flow is considered. the equation of motion of particles including the brownian effects is used and ensembles of 500 particle trajectories are numerically evaluated and statistically analysed. effects of size on particle dispersion and wall deposition processes are studied. the effect of turbulent near a wall is also considered. the results are compared with the exact solution of corresponding eulerian convective diffusion equation in the absence of turbulent fluctuations. the results show that the brownian diffusion play a significant role in the diffusion of nano particles at distances less than 2 wall units from the solid wall. [M. Mahdavimanesh, A. R. Noghrehabadi, M. Behbahaninejad, G. Ahmadi, M. H. Nirooei, A. Etminan . Diffusion of nano particles in viscous sub-layer. Life Sci J 2013;10(8s):105-109] (ISSN:1097-8135). http://www.lifesciencesite.com. 13
Experimental tests in the case of bat performance in some sports like baseball and cricket is cos... more Experimental tests in the case of bat performance in some sports like baseball and cricket is costly and tedious. In this paper a three dimensional modeling of ball and bat is generated and computational finite element method used to predict the performance of baseball bat. This could be useful for bat designers to use from these results achieved by computational soft wares in order to reduce cost and time spending. A finite element modeling is done in software ANSYS/LSDYNA version 971 R.4.2 that is used to explicit dynamic problems. The ball is created by viscoelastic material and using an orthotropic material for baseball bat the ball exit velocity should be then quantified. Performing modal analysis to bat, the region indicated between first and second fundamental modes of vibration and where the ball has maximum exit velocity is compared. The results will be shown graphically in the case of stress exerted to the bat and modal analysis in transient mode, and graphs will show the ...
Turbulent heat transfer and flow structure inside straight, divergent and convergent ducts with s... more Turbulent heat transfer and flow structure inside straight, divergent and convergent ducts with square ribs has been investigated for Reynolds number varying from 7000 to 100000 numerically. The simulations have been employed using the one and two turbulent models in particular Re-normalization group (RNG) as the most efficient model. The impact of divergence or convergence on thermal efficiency of ducts during cooling process is explored in two and three dimensional flow regimes. Results reveal that divergent channel transfers higher amount of heat in comparison to other kinds of channels. Furthermore, divergent channel records less pressure loss and higher thermal efficiency where fully developed flow can be seen just through the straight duct. Computational data show a good agreement with experimental results available in the literature.
Computational Fluid Dynamics (CFD) has been widely employed by investigators to simulate Taylor f... more Computational Fluid Dynamics (CFD) has been widely employed by investigators to simulate Taylor flow in microchannels. High-resolution images captured by numerical techniques reveal significant details of an ultra-thin liquid film around the gas bubble. The interface between the liquid and the gas phases is a decisive factor in order to determine the flow pattern, the gas bubble profile, the bubble length–separation distance, the slug length, and so forth. Since the thickness of the liquid film is on the order of 10-15 μm for low capillary number flows, the mesh generation requires careful modeling to capture it and transport phenomena, such as momentum and heat. The present study is to develop a model of a transient Taylor flow in a two-dimensional microchannel using commercial ANSYS Fluent software. The Volume of Fluid (VoF) method was employed to simulate the interface between two phases, i.e., air and water. A comprehensive grid study was carried out to identify a sufficiently f...
Taylor flow is a strategy-aimed flow to transfer conventional single-phase into a more efficient ... more Taylor flow is a strategy-aimed flow to transfer conventional single-phase into a more efficient two-phase flow resulting in an enhanced momentum/heat/mass transfer rate, as well as a multitude of other advantages. To date, Taylor flow has focused on the processes involving gas–liquid and liquid–liquid two-phase systems in microchannels over a wide range of applications in biomedical, pharmaceutical, industrial, and commercial sectors. Appropriately micro-structured design is, therefore, a key consideration for equipment dealing with transport phenomena. This review paper highlights the hydrodynamic aspects of gas–liquid and liquid–liquid two-phase flows in microchannels. It covers state-of-the-art experimental and numerical methods in the literature for analyzing and simulating slug flows in circular and non-circular microchannels. The review’s main objective is to identify the considerable opportunity for further development of microflows and provide suggestions for researchers in...
This paper presents a CFD-based simulation method for air/water and water/dodecane Taylor flows t... more This paper presents a CFD-based simulation method for air/water and water/dodecane Taylor flows through an axisymmetric microchannel with a circular cross-sectional area. A systematic analysis is conducted by exploring the effects of different superficial velocities and apparent viscosities on the hydrodynamics of a slug flow regime. A concentric junction is employed to make bubbles of air in a continuous flow of water and slugs of water in a continuous flow of dodecane oil. A time-history study is conducted to predict the air-bubble and water-slug evolution processes, in particular at the moment of slug breakup. The results show that the larger apparent viscosity ratio of phases involved in the liquid-liquid flow generates a more stable interface. However, the liquid slug length is less and film thickness is slightly larger in liquid-liquid compared to gas-liquid flow. Furthermore, variations in gas and liquid holdups are correlated by the superficial velocity ratio. The numerical ...
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