The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform
S B Koganti - One of the best experts on this subject based on the ideXlab platform.
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residence time distribution and flow patterns in the single phase Annular Region of Annular centrifugal extractor
Industrial & Engineering Chemistry Research, 2009Co-Authors: Sandesh S Deshmukh, Mayur J Sathe, J B Joshi, S B KogantiAbstract:Flow between two concentric cylinders with high-speed rotation of the inner cylinder, also termed as turbulent Taylor−Couette flow, is an integral part of Annular centrifugal extractor (ACE). The vortex motion in the Annular Region causes intense mixing, of the two liquids, and their separation occurs in the inner cylinder under centrifugal action. In the present work, a systematic study of residence time distribution (RTD) in the Annular Region of ACE has been carried out experimentally as well as using computational fluid dynamics (CFD). The effects of rotational speed (10 ≤ ω ≤ 40, r/s), aspect ratio of annulus (11 ≤ Γ ≤ 48), width of Annular gap (1.5 ≤ d ≤ 6.5, mm), and the flow ratio of the immiscible fluids (0.73 ≤ FR ≤ 2.4) have been systematically investigated. Effect of flow ratio, Annular gap, and rotational speed has been investigated on the RTD. It was found that the flow in ACE is near to back-mixed behavior because of the presence of counterrotating vortices. The number of vortices depends o...
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Flow Visualization and Three-Dimensional CFD Simulation of the Annular Region of an Annular Centrifugal Extractor
Industrial & Engineering Chemistry Research, 2008Co-Authors: Sandesh S Deshmukh, J B Joshi, S B KogantiAbstract:The single phase flow patterns in the Annular Region of an Annular centrifugal extractor (ACE) have been studied both experimentally and computationally. Experiments were conducted using particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) to understand the flow patterns and velocity profiles in both the presence and the absence of the net flow through the annulus. The data obtained in these experiments have been used for the validation of the computational fluid dynamics (CFD) simulations. Further, complete energy balance has been established. The CFD simulations were performed over a wide range of operating conditions. In contrast with the Taylor Annular Region (having no end effects), the ACE was found to exhibit markedly different cell patterns. The number of cells was found to be strongly dependent on the Taylor number. The effect of the internals such as radial baffles in the annulus, as well as vanes on the bottom plate, on the flow patterns has been investigated. From the simulations it was revealed that the flow patterns in ACE were also dependent on the start-up procedure of the equipment.
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cfd simulation of rtd and mixing in the Annular Region of a taylor couette contactor
Industrial & Engineering Chemistry Research, 2006Co-Authors: Sreepriya Vedantam, J B Joshi, S B KogantiAbstract:Flow between two concentric cylinders, with either or both of them rotating, has potential advantages over the conventional process equipment. This flow, also termed as Taylor-Couette flow, which reveals a variety of flow regimes, is studied using computational fluid dynamics (CFD) simulations. The vortex motion causes mixing in the annulus, which necessitates the understanding of residence time of the fluid in the annulus and the mixing time. A systematic study of residence time distribution (RTD) and the mixing phenomenon in the Annular Region of the Taylor-Couette contactor has been carried out. The RTD predictions have been found to be in good agreement with the established experimental results. Axial dispersion in the Taylor vortex regime and the turbulent regime has been predicted, and it can be said that, with an increase in the radial mixing, the effect of velocity profile on the dispersion parameter significantly reduces at higher rotational speeds. Effect of axial flow, Annular gap width, and rotational speed has been investigated on the axial dispersion. The dispersion number and the dispersion coefficient have been predicted.
Feng Xing - One of the best experts on this subject based on the ideXlab platform.
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Effect of gravity levels on the flow pattern modulation by the phase separation concept
Computers & Fluids, 2015Co-Authors: Dongliang Sun, Jian Xie, Yanning Wang, Feng XingAbstract:Abstract Suspending a mesh cylinder in a tube modulates flow patterns with gas bubbles in the Annular Region to form thin liquid film on the wall. We investigate the effect of gravity levels on the modulated flow patterns. The volume of fluid (VOF) method simulates the slug bubble train flow in bare tube and modulated flow sections. The bubble population density along the flow direction (β) and averaged liquid film thickness (δα) synthesize a parameter β/δa to characterize the enhancement of phase change heat transfer. It is found that at the normal gravity on earth, counter-flow appears with fast upward flow in the Annular Region and downward liquid flow in the core Region. A lower β due to sparsely populated bubbles and thin liquid film form a larger β/δa to enhance the phase change heat transfer. Convective heat transfer in liquid plugs is enhanced by the fast fluid movement in the Annular Region and liquid circulations at three length scales. At the miniature gravity, quasi-co-current flow happens with upward flows in both Annular Region and core Region, except that a liquid layer inside mesh cylinder flows downward. Bubbles are more densely populated than those at the normal gravity. Liquid circulation occurs only at the bubble length scale. At the micro gravity, the two-phases are thoroughly separated with co-current flows in both Annular Region and core Region. Gas flows slowly and the residence time of gas is increased to result in β = 1. Τhe liquid film is ultra-thin. These two factors create a significantly large β/δa to enhance the phase change heat transfer. We demonstrate the effectiveness of the phase separation concept at miniature and micro gravity environment.
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Modulated flow patterns for vertical upflow by the phase separation concept
Experimental Thermal and Fluid Science, 2014Co-Authors: Hongxia Chen, Jian Xie, Feng XingAbstract:Abstract The passive phase separation concept was proposed to create thin liquid film on the wall surface. The inserted mesh cylinder made of a single layer of mesh pore surface divides the tube cross section into an Annular Region near the tube wall and a core Region. Gas bubbles are prevented from entering the core Region and liquids can be sucked towards the core Region. Thus, the two-phases are majorly flowing in two different Regions. The concept is expected to be used for multiphase (boiling/evaporation and condensation) heat transfer enhancement. Air–water two-phase flow experiments were performed with vertical upflows. Miniature bubbles are modulated to flow in the Annular Region. Cap/slug/plug bubbles are modulated to form the elongated-ring-slug bubble in the Annular Region to generate thin liquid films on the wall. For all the cases, the core Region is full of liquid. Due to the large density difference between liquid in the core Region and gas in the Annular Region, pulsating flow is self-sustained in the core Region. The mesh pore surface promotes the mass and momentum exchange between the Annular Region and core Region. For ring-slug bubbles such as longer than 10 cm, miniature bubbles are emitted from the slug bubble front. The proposed concept is being verified by the phase change heat transfer experiment in our laboratory.
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Numerical simulation of the modulated flow pattern for vertical upflows by the phase separation concept
International Journal of Multiphase Flow, 2013Co-Authors: Qicheng Chen, Jian Xie, Dongliang Sun, Zhen Cao, Feng XingAbstract:Abstract The multiphase heat transfer could be enhanced by creating thin liquid film on the wall. The phase separation concept is called due to the separated flow paths of liquid and gas over the tube cross section to yield thin liquid film. Our proposed heat transfer tube consists of an Annular Region close to the wall and a core Region, interfaced by a suspending mesh cylinder in the tube. The heat transfer tube is a multiscale system with micron scale of mesh pores, miniature scale of Annular Region and macroscale of tube diameter and length. Great effort has been made to link from micron scale to macroscale. The Volume of Fluid (VOF) method simulates air/water two-phase flow for vertical upflow. The three-dimensional system was successfully converted to a two-dimensional one by using three equivalent criteria for mesh pores. The non-uniform base grid generation and dynamic grid adaption method capture the bubble interface. The numerical results successfully reproduce our experimental results. The numerical findings identify the following mechanisms for the enhanced heat transfer: (a) counter-current flow exists with upward flow in the Annular Region and downward flow in the core Region; (b) void fractions are exact zero in the core Region and higher in the Annular Region; (c) the liquid film thicknesses are decreased to 1/6–1/3 of those in the bare tube section; (d) the gas–liquid mixture travels much faster in the Annular Region than in the bare tube; (e) three-levels of liquid circulation exists: meter-scale bulk liquid circulation, moderate-scale liquid circulation around a single-elongated-ring-slug-bubble, and microliquid circulation following the ring-slug-bubble tails. These liquid circulations promote the fluid mixing over the whole tube length and within the radial direction. The modulated parameters of void fractions, velocities and liquid film thicknesses in the Annular Region and three-levels of liquid circulation are greatly beneficial for the multiphase heat transfer enhancement.
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Flow pattern modulation in a horizontal tube by the passive phase separation concept
International Journal of Multiphase Flow, 2012Co-Authors: Hongxia Chen, Feng Xing, Jian Xie, Wei Wang, Wei ZhangAbstract:Abstract A passive phase separation concept was proposed to modulate flow pattern in a condenser tube. An empty mesh cylinder is suspended in the condenser tube. The miniature mesh pores prevent gas bubble entering the mesh cylinder but capture liquid into the mesh cylinder, ensuring largest possibility for cold tube wall directly contacted with gas to form the perfect thin liquid film condensation heat transfer. We performed the air–water two-phase flow experiment. It was found that for a relatively higher liquid height in the horizontal tube, all liquid can be captured by the mesh cylinder to form the “gas-floating-liquid” mode. If the liquid height is small in the horizontal tube, partial liquid can be sucked by the mesh cylinder, the contact area between tube wall and gas is increased. When plug flow reaches the mesh cylinder surface, elongated saddle bubbles are formed in the Annular Region to envelop the mesh cylinder surface. When bubbly flow in the horizontal tube approaches the mesh cylinder area, miniature bubbles can merge to form large bubbles in the Annular Region. For the later two cases, all the gas flow rate is flowing in the Annular Region and the inside mesh cylinder is the liquid.
J B Joshi - One of the best experts on this subject based on the ideXlab platform.
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residence time distribution and flow patterns in the single phase Annular Region of Annular centrifugal extractor
Industrial & Engineering Chemistry Research, 2009Co-Authors: Sandesh S Deshmukh, Mayur J Sathe, J B Joshi, S B KogantiAbstract:Flow between two concentric cylinders with high-speed rotation of the inner cylinder, also termed as turbulent Taylor−Couette flow, is an integral part of Annular centrifugal extractor (ACE). The vortex motion in the Annular Region causes intense mixing, of the two liquids, and their separation occurs in the inner cylinder under centrifugal action. In the present work, a systematic study of residence time distribution (RTD) in the Annular Region of ACE has been carried out experimentally as well as using computational fluid dynamics (CFD). The effects of rotational speed (10 ≤ ω ≤ 40, r/s), aspect ratio of annulus (11 ≤ Γ ≤ 48), width of Annular gap (1.5 ≤ d ≤ 6.5, mm), and the flow ratio of the immiscible fluids (0.73 ≤ FR ≤ 2.4) have been systematically investigated. Effect of flow ratio, Annular gap, and rotational speed has been investigated on the RTD. It was found that the flow in ACE is near to back-mixed behavior because of the presence of counterrotating vortices. The number of vortices depends o...
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Flow Visualization and Three-Dimensional CFD Simulation of the Annular Region of an Annular Centrifugal Extractor
Industrial & Engineering Chemistry Research, 2008Co-Authors: Sandesh S Deshmukh, J B Joshi, S B KogantiAbstract:The single phase flow patterns in the Annular Region of an Annular centrifugal extractor (ACE) have been studied both experimentally and computationally. Experiments were conducted using particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) to understand the flow patterns and velocity profiles in both the presence and the absence of the net flow through the annulus. The data obtained in these experiments have been used for the validation of the computational fluid dynamics (CFD) simulations. Further, complete energy balance has been established. The CFD simulations were performed over a wide range of operating conditions. In contrast with the Taylor Annular Region (having no end effects), the ACE was found to exhibit markedly different cell patterns. The number of cells was found to be strongly dependent on the Taylor number. The effect of the internals such as radial baffles in the annulus, as well as vanes on the bottom plate, on the flow patterns has been investigated. From the simulations it was revealed that the flow patterns in ACE were also dependent on the start-up procedure of the equipment.
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cfd simulation of rtd and mixing in the Annular Region of a taylor couette contactor
Industrial & Engineering Chemistry Research, 2006Co-Authors: Sreepriya Vedantam, J B Joshi, S B KogantiAbstract:Flow between two concentric cylinders, with either or both of them rotating, has potential advantages over the conventional process equipment. This flow, also termed as Taylor-Couette flow, which reveals a variety of flow regimes, is studied using computational fluid dynamics (CFD) simulations. The vortex motion causes mixing in the annulus, which necessitates the understanding of residence time of the fluid in the annulus and the mixing time. A systematic study of residence time distribution (RTD) and the mixing phenomenon in the Annular Region of the Taylor-Couette contactor has been carried out. The RTD predictions have been found to be in good agreement with the established experimental results. Axial dispersion in the Taylor vortex regime and the turbulent regime has been predicted, and it can be said that, with an increase in the radial mixing, the effect of velocity profile on the dispersion parameter significantly reduces at higher rotational speeds. Effect of axial flow, Annular gap width, and rotational speed has been investigated on the axial dispersion. The dispersion number and the dispersion coefficient have been predicted.
Sandesh S Deshmukh - One of the best experts on this subject based on the ideXlab platform.
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residence time distribution and flow patterns in the single phase Annular Region of Annular centrifugal extractor
Industrial & Engineering Chemistry Research, 2009Co-Authors: Sandesh S Deshmukh, Mayur J Sathe, J B Joshi, S B KogantiAbstract:Flow between two concentric cylinders with high-speed rotation of the inner cylinder, also termed as turbulent Taylor−Couette flow, is an integral part of Annular centrifugal extractor (ACE). The vortex motion in the Annular Region causes intense mixing, of the two liquids, and their separation occurs in the inner cylinder under centrifugal action. In the present work, a systematic study of residence time distribution (RTD) in the Annular Region of ACE has been carried out experimentally as well as using computational fluid dynamics (CFD). The effects of rotational speed (10 ≤ ω ≤ 40, r/s), aspect ratio of annulus (11 ≤ Γ ≤ 48), width of Annular gap (1.5 ≤ d ≤ 6.5, mm), and the flow ratio of the immiscible fluids (0.73 ≤ FR ≤ 2.4) have been systematically investigated. Effect of flow ratio, Annular gap, and rotational speed has been investigated on the RTD. It was found that the flow in ACE is near to back-mixed behavior because of the presence of counterrotating vortices. The number of vortices depends o...
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Flow Visualization and Three-Dimensional CFD Simulation of the Annular Region of an Annular Centrifugal Extractor
Industrial & Engineering Chemistry Research, 2008Co-Authors: Sandesh S Deshmukh, J B Joshi, S B KogantiAbstract:The single phase flow patterns in the Annular Region of an Annular centrifugal extractor (ACE) have been studied both experimentally and computationally. Experiments were conducted using particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) to understand the flow patterns and velocity profiles in both the presence and the absence of the net flow through the annulus. The data obtained in these experiments have been used for the validation of the computational fluid dynamics (CFD) simulations. Further, complete energy balance has been established. The CFD simulations were performed over a wide range of operating conditions. In contrast with the Taylor Annular Region (having no end effects), the ACE was found to exhibit markedly different cell patterns. The number of cells was found to be strongly dependent on the Taylor number. The effect of the internals such as radial baffles in the annulus, as well as vanes on the bottom plate, on the flow patterns has been investigated. From the simulations it was revealed that the flow patterns in ACE were also dependent on the start-up procedure of the equipment.
Jian Xie - One of the best experts on this subject based on the ideXlab platform.
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Effect of gravity levels on the flow pattern modulation by the phase separation concept
Computers & Fluids, 2015Co-Authors: Dongliang Sun, Jian Xie, Yanning Wang, Feng XingAbstract:Abstract Suspending a mesh cylinder in a tube modulates flow patterns with gas bubbles in the Annular Region to form thin liquid film on the wall. We investigate the effect of gravity levels on the modulated flow patterns. The volume of fluid (VOF) method simulates the slug bubble train flow in bare tube and modulated flow sections. The bubble population density along the flow direction (β) and averaged liquid film thickness (δα) synthesize a parameter β/δa to characterize the enhancement of phase change heat transfer. It is found that at the normal gravity on earth, counter-flow appears with fast upward flow in the Annular Region and downward liquid flow in the core Region. A lower β due to sparsely populated bubbles and thin liquid film form a larger β/δa to enhance the phase change heat transfer. Convective heat transfer in liquid plugs is enhanced by the fast fluid movement in the Annular Region and liquid circulations at three length scales. At the miniature gravity, quasi-co-current flow happens with upward flows in both Annular Region and core Region, except that a liquid layer inside mesh cylinder flows downward. Bubbles are more densely populated than those at the normal gravity. Liquid circulation occurs only at the bubble length scale. At the micro gravity, the two-phases are thoroughly separated with co-current flows in both Annular Region and core Region. Gas flows slowly and the residence time of gas is increased to result in β = 1. Τhe liquid film is ultra-thin. These two factors create a significantly large β/δa to enhance the phase change heat transfer. We demonstrate the effectiveness of the phase separation concept at miniature and micro gravity environment.
-
Modulated flow patterns for vertical upflow by the phase separation concept
Experimental Thermal and Fluid Science, 2014Co-Authors: Hongxia Chen, Jian Xie, Feng XingAbstract:Abstract The passive phase separation concept was proposed to create thin liquid film on the wall surface. The inserted mesh cylinder made of a single layer of mesh pore surface divides the tube cross section into an Annular Region near the tube wall and a core Region. Gas bubbles are prevented from entering the core Region and liquids can be sucked towards the core Region. Thus, the two-phases are majorly flowing in two different Regions. The concept is expected to be used for multiphase (boiling/evaporation and condensation) heat transfer enhancement. Air–water two-phase flow experiments were performed with vertical upflows. Miniature bubbles are modulated to flow in the Annular Region. Cap/slug/plug bubbles are modulated to form the elongated-ring-slug bubble in the Annular Region to generate thin liquid films on the wall. For all the cases, the core Region is full of liquid. Due to the large density difference between liquid in the core Region and gas in the Annular Region, pulsating flow is self-sustained in the core Region. The mesh pore surface promotes the mass and momentum exchange between the Annular Region and core Region. For ring-slug bubbles such as longer than 10 cm, miniature bubbles are emitted from the slug bubble front. The proposed concept is being verified by the phase change heat transfer experiment in our laboratory.
-
Numerical simulation of the modulated flow pattern for vertical upflows by the phase separation concept
International Journal of Multiphase Flow, 2013Co-Authors: Qicheng Chen, Jian Xie, Dongliang Sun, Zhen Cao, Feng XingAbstract:Abstract The multiphase heat transfer could be enhanced by creating thin liquid film on the wall. The phase separation concept is called due to the separated flow paths of liquid and gas over the tube cross section to yield thin liquid film. Our proposed heat transfer tube consists of an Annular Region close to the wall and a core Region, interfaced by a suspending mesh cylinder in the tube. The heat transfer tube is a multiscale system with micron scale of mesh pores, miniature scale of Annular Region and macroscale of tube diameter and length. Great effort has been made to link from micron scale to macroscale. The Volume of Fluid (VOF) method simulates air/water two-phase flow for vertical upflow. The three-dimensional system was successfully converted to a two-dimensional one by using three equivalent criteria for mesh pores. The non-uniform base grid generation and dynamic grid adaption method capture the bubble interface. The numerical results successfully reproduce our experimental results. The numerical findings identify the following mechanisms for the enhanced heat transfer: (a) counter-current flow exists with upward flow in the Annular Region and downward flow in the core Region; (b) void fractions are exact zero in the core Region and higher in the Annular Region; (c) the liquid film thicknesses are decreased to 1/6–1/3 of those in the bare tube section; (d) the gas–liquid mixture travels much faster in the Annular Region than in the bare tube; (e) three-levels of liquid circulation exists: meter-scale bulk liquid circulation, moderate-scale liquid circulation around a single-elongated-ring-slug-bubble, and microliquid circulation following the ring-slug-bubble tails. These liquid circulations promote the fluid mixing over the whole tube length and within the radial direction. The modulated parameters of void fractions, velocities and liquid film thicknesses in the Annular Region and three-levels of liquid circulation are greatly beneficial for the multiphase heat transfer enhancement.
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Flow pattern modulation in a horizontal tube by the passive phase separation concept
International Journal of Multiphase Flow, 2012Co-Authors: Hongxia Chen, Feng Xing, Jian Xie, Wei Wang, Wei ZhangAbstract:Abstract A passive phase separation concept was proposed to modulate flow pattern in a condenser tube. An empty mesh cylinder is suspended in the condenser tube. The miniature mesh pores prevent gas bubble entering the mesh cylinder but capture liquid into the mesh cylinder, ensuring largest possibility for cold tube wall directly contacted with gas to form the perfect thin liquid film condensation heat transfer. We performed the air–water two-phase flow experiment. It was found that for a relatively higher liquid height in the horizontal tube, all liquid can be captured by the mesh cylinder to form the “gas-floating-liquid” mode. If the liquid height is small in the horizontal tube, partial liquid can be sucked by the mesh cylinder, the contact area between tube wall and gas is increased. When plug flow reaches the mesh cylinder surface, elongated saddle bubbles are formed in the Annular Region to envelop the mesh cylinder surface. When bubbly flow in the horizontal tube approaches the mesh cylinder area, miniature bubbles can merge to form large bubbles in the Annular Region. For the later two cases, all the gas flow rate is flowing in the Annular Region and the inside mesh cylinder is the liquid.