99 results on '"secondary flow"'
Search Results
2. Numerical Investigation and Optimization of the Flow Characteristics of Bend Pipe with Different Bending Angles.
- Author
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Zhang, Jianyi, Wang, Dongrui, Wang, Weiwei, and Zhu, Zuchao
- Subjects
PIPE bending ,CENTRIFUGAL force ,FLUID flow ,ANGLES ,ENERGY dissipation ,PIPELINES - Abstract
The bend pipe with a circular section, which is widely used in hydropower, chemical industry and other fields, is a common form in pipeline systems. However, secondary flow occurs when the fluid flows through the bend pipe, thereby affecting the stability of the pipeline system. Different bending angles have various effects. Therefore, this paper establishes 3D models of a circular bend pipe with different bending angles. The influence of bending angle on flow field distribution and downstream flow is analyzed numerically. The larger the bending angle is, the more obvious the flow distribution and even the unevenness at the elbow will be, hence resulting in poor stability. The distance required to restore flow uniformity also increases. The pressure energy loss of the bend pipe with different bending angles is investigated. Results show that with the increase in bending angle, the global pressure loss presents a trend of "increase-decrease-increase." The closer the bending angle is to 90°, the greater the influence of centrifugal force is on the flow, and the more obvious the secondary flow phenomenon will be. Aiming at the nonuniformity phenomenon, the structure optimization of a 90° bend pipe with the greatest influence is conducted. The improvement of the flow characteristics of bend pipe with different thick-diameter ratio and length-diameter ratio is compared. The deflector with a certain thickness can enhance the uniformity, safety and useful life of the bend pipe. The sharp-end length can improve the velocity uniformity to a certain extent but has minimal influence on flow characteristics compared with the thick-diameter ratio. This paper aims to study and improve the flow performance of a multi-structure bend pipe to make it suitable for more complex conditions. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
3. Hydrodynamic characteristics of flow over emergent vegetation in a strongly curved channel.
- Author
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Yang, Yu, Lin, Ying-Tien, and Ji, Xiaoyan
- Subjects
- *
CENTRIFUGAL force , *PLANTS - Abstract
The influences of different emergent and rigid vegetation distributions on hydrodynamic characteristics in a 180° curved open channel are experimentally investigated in this study. Experimental results show that the transverse velocity gradient generated at the vegetation and non-vegetation interface is greater for the vegetation presence on the convex bank (inner case) than the vegetation on the concave bank (outer case) with the effect of centrifugal force pointing to the concave bank. The presence of uniform distributed vegetation will weaken the secondary flow, and theoretical analysis is also developed to indicate the influential range of emergent vegetation on secondary flow over a curved channel. In addition, the peak frequency determined from the spectrum at the vegetation and non-vegetation interface along a curved channel is still associated with the Kelvin–Helmholtz (K-H) instability. Both the curved channel and presence of emergent vegetation can reduce the occurrence frequency of turbulent ejection and sweep events. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
4. The effect of primary and secondary flows on the homogenization process in a vertical bladed mixer.
- Author
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Havlica, J., Kozakovic, M., Kramolis, D., Travnickova, T., and Kohout, M.
- Subjects
- *
CENTRIFUGAL force , *DEFORMATION of surfaces , *COMPUTER simulation - Abstract
This article focuses on numerical simulations of the granular mixing process in a vertical cylindrical mixer with two opposed flat blades with a 45° rake angle. Computer simulations were performed by the discrete element method. The blending was examined for the blades' stirrer speeds in the range from 1.9 to 960 rpm and three different initial spatial configurations. The development of the concentration patterns and the evolution of phase interphase between different types of particles have shown that the homogenization process depends not only on the system's dynamics but also on the initial spatial distribution of particles. The dependence on the initial distribution is provided by involving primary and secondary flows in different time-scale in the homogenization process. This ability of the individual flows to engage in the mixing is granted by the mutual synergy between the direction of movements of particles located on the phase interface and the orientation of the phase interface. Because there is a significant difference between the intensity of primary and secondary flows in most cases, an improperly oriented phase interface will significantly slow down the entire rate of the homogenization process. On the other hand, during the mixing process, the phase interface expands and deforms, which gradually also allows the rest of the flows to get involved in the homogenization process. Based on the results, the basic rules have been identified for effective homogenization. As a mixing index, the relative surface of the phase interface was used. By comparing individual homogenization curves, it follows that the critical factor for the homogenization process is the centrifugal force. When it is in balance with other forces, it encourages homogenization. On the contrary, if it becomes the dominant force in the system, it causes a significant deformation of the surface, and its effect on the homogenization process is destructive. [Display omitted] • The effect of primary and secondary flows on the homogenization was analysed. • The homogenization level was determined by the relative size of a phase interface. • The centrifugal force fundamentally affects the efficiency of the mixing process. • The tangential configuration is best mixed due to the engagement of primary flows. • Secondary flows are crucial to homogenize the radial and axial configuration. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
5. Study of the gas-solid flow characteristics of ice particles in helically coiled tubes.
- Author
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He, Wenbo, Wang, Mengke, Chen, Jingchao, Yin, Qilei, and Cao, Pinlu
- Subjects
- *
TWO-phase flow , *PRESSURE drop (Fluid dynamics) , *TUBES , *CENTRIFUGAL force , *GAS flow - Abstract
Efficient drilling operations in polar regions are crucial given their unique climate and surface conditions. To improve drilling efficiency, a novel technology utilizing helically coiled tubes (HCT) for transporting ice particles has been proposed. This study focuses on the gas-solid flow characteristics of ice particles within the HCT employing the Eulerian-Eulerian models of Ansys-Fluent 2022 R2. Numerical simulations were validated against experimental data, showing good agreement with a maximum error of merely 11.27%. Three distinct flow regions perpendicular to the flow direction were observed, influenced by centrifugal force and secondary flow. The inlet gas velocity, tube inner diameter, coil diameter, particle diameter, and penetration rate all affected the ice particle transport ratio (ITR) and the pressure drop in the HCT. Notably, increasing the tube inner diameter from 30 mm to 75 mm led to a remarkable 398.7% rise in the ITR, while particle diameter changes minimally affected ITR. [Display omitted] • The flow behavior of gas-solid two-phase flow in HCT is investigated. • Transportation efficiency of ice particles in HCT is discussed. • Pressure drops of gas-solid two-phase flow in HCT is analyzed. • Effect of HCT parameters and operation conditions on gas-solid flow is determined. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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6. Numerical investigation of flow characteristics and heat transfer performance in curve channel with periodical wave structure.
- Author
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Zhang, L.Y., Lu, Z., Wei, L.C., Yang, X., Yu, X.L., Meng, X.Z., and Jin, L.W.
- Subjects
- *
HEAT transfer , *THERMAL boundary layer , *CENTRIFUGAL force , *STREAMFLOW - Abstract
• Curve channel with periodical wave structure is proposed to enhance heat transfer. • Secondary flow in curve-wave channel generates more vortices disturbing main flow stream. • Thermal boundary layer in curve-wave channel redevelops periodically along main flow direction. • Heat transfer enhanced by curve-wave channel outweighs its pressure penalty. • The optimum wave amplitude can be obtained by evaluating the dimensionless performance factor. Flow and heat transfer in curve channel have been studied extensively due to the presence of the secondary flow induced by the centrifugal force. However, for the curved channel with small curvature, weakened centrifugal force reduces the intensity of secondary flow and heat transfer enhancement is attenuated accordingly. For sake of maintaining high heat transfer efficiency in curve channel with a wide range of curvature, periodical wave structure was introduced into the smooth-curve channel by this study. A three-dimensional model of the curve-wave structure was established and numerical simulation was carried out to explore the flow characteristics and heat transfer performance in the proposed channel. In addition, the effects of the wave amplitude on the channel performance were analyzed. The results showed that the heat transfer of smooth-curve channel can be enhanced remarkably by applying wave structure on the channel wall, and the overall performance factor indicates that the heat transfer argumentation outweighs the pressure loss penalty. It was also found that the heat transfer in the curve-wave channel can be further enhanced by increasing wave amplitude. The most effective heat transfer enhancement can be achieved based on the evaluation of the overall performance factor. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
7. The mechanisms of energy transformation in sharp open-channel bends: Analysis based on experiments in a laboratory flume.
- Author
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Hu, Chengwei, Yu, Minghui, Wei, Hongyan, and Liu, Changjie
- Subjects
- *
CENTRIFUGAL force , *KINETIC energy - Abstract
Highlights • An term-by-term estimation was made of the key terms in the kinetic energy equation using detailed experimental data. • An term-by-term estimation was made of the key terms in the enstrophy equation equation using detailed experimental data. • Role of secondary flow in the transport and dissipation of kinetic energy. Abstract In sharp open-channel bends, there exists nonlinear interactions between streamwise and cross-stream velocities, which leads to the adjustment of flow energy transport, increases the energy dissipation and eventually influences the development of river bends. However, previous studies have not yet fully understood the mechanisms underlying the transport and dissipation of energy in open-channel bends. In addition, energy dissipation is directly related to the evolution of enstrophy Ω · Ω / 2. However, it has not yet received much attention in the study of the resistance in meandering rivers. To gain an insight into these mechanisms, with the aid of detailed experimental data collected in a sharp open-channel bend, this study quantified the impacts of the key terms in the kinetic energy equation and the enstrophy equation. Results show that the term related to the transport of kinetic energy by cross-stream circulation is at least an order of magnitude larger than the other terms in the kinetic energy equation, which contributes significantly to the redistribution of kinetic energy over the cross section. The term related to the production of turbulent kinetic energy in the kinetic energy equation shows the smallest order of magnitude and thus is almost negligible for the time-averaged flow field. Furthermore, over most of the measured area, the term related to the centrifugal force shows values of at least an order of magnitude larger than the other terms in the enstrophy equation, which means that this term exerts the dominant influence on the energy dissipation. The results also revealed that the transformation process is insensitive to the variations in Froude number. These results are expected to improve the understanding of the complete process of energy transformation, especially the resistance caused by secondary flow in meandering rivers. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
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8. Flow characteristics simulation of spiral coil reactor used in the thermochemical energy storage system
- Author
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Xiaogang Jin, Dongren Liu, Xiang Ling, Dong Zhang, Xiaoyi Chen, and Danyang Song
- Subjects
Centrifugal force ,Environmental Engineering ,Materials science ,Turbulence ,General Chemical Engineering ,General Chemistry ,Mechanics ,Thermal energy storage ,Secondary flow ,Biochemistry ,Energy storage ,Physics::Fluid Dynamics ,Electromagnetic coil ,Drag ,Particle - Abstract
According to environmental and energy issues, renewable energy has been vigorously promoted. Now solar power is widely used in many areas but it is limited by the weather conditions and cannot work continuously. Heat storage is a considerable solution for this problem and thermochemical energy storage is the most promising way because of its great energy density and stability. However, this technology is not mature enough to be applied to the industry. The reactor is an important component in the thermochemical energy storage system where the charging and discharging process happens. In this paper, a spiral coil is proposed and used as a reactor in the thermochemical energy storage system. The advantages of the spiral coil include simple structure, small volume, and so on. To investigate the flow characteristics, the simulation was carried out based on Energy-Minimization Multi-Scale model (EMMS) and Eulerian two-phase model. CaCO3 particles were chosen as the reactants. Particle distribution was shown in the results. The gas initial velocity was set to 2 m·s-1, 3 m·s-1, and 4 m·s-1. When the particles flowed in the coil, gravity, centrifugal force and drag force influenced their flow. With the Reynold numbers increasing, centrifugal and drag force got larger. Accumulation phenomenon existed in the coil and results showed with the gas velocity increasing, accumulation moved from the bottom to the outer wall of the coil. Besides, the accumulation phenomenon was stabilized when φ>720°. Also due to the centrifugal force, a secondary flow formed, which means solid particles moved from the inside wall to the outside wall. This secondary flow could promote turbulence and mixing of particles and gas. In addition, when the particle volume fraction is reduced from 0.2 to 0.1, the accumulation at the bottom of the coil decreases, and the unevenness of the velocity distribution becomes larger.
- Published
- 2022
9. Experimental investigation and prediction of post-dryout heat transfer for steam-water flow in helical coils.
- Author
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Xiao, Yao, Hu, Zhenxiao, Chen, Shuo, and Gu, Hanyang
- Subjects
- *
HEAT transfer coefficient , *HYDRAULICS , *CENTRIFUGAL force , *PRESSURE drop (Fluid dynamics) , *PREDICTION theory , *THERMODYNAMICS - Abstract
Highlights • Measurements of post-dryout heat transfer in helical coils are obtained. • Curvature significantly enhances post-dryout heat transfer in helical coils. • The post-dryout heat transfer coefficient of helical coils decreases in quality. • Heat transfer correlation for post-dryout regime of helical coils is developed. Abstract Post-dryout heat transfer for steam-water flow in helical coils is experimentally investigated. The inner diameters of the helical coils are 12.5 mm and 14.5 mm, and the coil diameters range from 180 mm to 380 mm. The experimental system pressure covers the range 2–8 MP. The results indicate that the centrifugal force induced secondary flow has a great influence on post-dryout heat transfer in helical coils. In the low quality post-dryout region, because of the high redeposition rate induced by secondary flow, the heat transfer coefficient of helical coils is significantly higher than that of straight tubes. As the total droplet mass decreases with increasing quality, the heat transfer performance of helical coils decreases and continuously approaches that of straight tubes. In high quality post-dryout region, the bulk fluid in helical coils is closer to thermodynamic equilibrium state due to the secondary flow, and the heat transfer coefficient may be exceeded by straight tubes. For the effects of flow parameters, the post-dryout heat transfer performance decreases in heat flux and increases in mass flux. For system pressure, due to the change of the dominant heat transfer mechanism, the post-dryout heat transfer decreases in the low quality region but increases in the high quality region with increasing system pressure. Based on a detailed analysis of the effects of various dimensionless parameters, a new correlation containing a quality correction is proposed and provides good prediction accuracy. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
10. An experimental study of centrifugal microfluidic platforms for magnetic-inertial separation of circulating tumor cells using contraction-expansion and zigzag arrays.
- Author
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Momeni, Maede, Shamloo, Amir, Hasani-Gangaraj, Mojtaba, and Dezhkam, Rasool
- Subjects
- *
LEUCOCYTES , *ANGULAR velocity , *CENTRIFUGAL force , *CELL separation , *MICROFLUIDIC devices , *TRANSCRANIAL magnetic stimulation , *KILLER cells - Abstract
• A microfluidic Lab-On-a-Disk device is introduced to separate cancer cells. • Active (magnetophoresis) and passive (inertial) methods are compared. • Geometrical features, including curvature and unit shape, are studied. • Optimum parameters were numerically calculated. • The curved expansion-contraction channel showed the best separation result. Cancer diagnosis has recently been at the forefront of recent medical research, with ongoing efforts to develop devices and technologies for detecting cancer in patients. One promising approach for cancer diagnosis is the detection of Circulating Tumor Cells (CTCs) in blood samples. Separating these rare cells from the diverse background of blood cells and analyzing them can provide valuable insights into the disease's stage and lethality. Here we present the design and fabrication of a centrifugal microfluidic platform on a polymeric disk that utilizes centrifugal forces for cell isolation. The separation units exploit both active and passive methods. In other words, in addition to introducing novel geometry for channels, an external magnetic field is also employed to separate the target cells from the background cells. In order for the external field to function, the CTCs must first be labeled with antibody-conjugated nanoparticles; the separation process should be then performed. Before the experimental tests, a numerical study was done to determine the optimum parameters; the angular velocity and magnetization investigations showed that 2000 rpm and 868,000 (kA/m) are the optimum conditions for the designed device to reach the efficiency of 100% for both White Blood Cells (WBCs) and CTCs. These results indicate that the passive region of the channels primarily contributes to the focusing of the target cells, and showed that the focusing effect is more pronounced in the expansion-contraction geometry compared to the zigzag geometry. Additionally, the results proved that curved channel geometries performed better than straight ones in terms of separation efficiency. However, if the separation relies solely on channel geometry, the majority of cells would be directed towards the non-target chamber, leading to suboptimal results. This is due to the direction of the forces acting on the cells. However, including an external magnetic field improves the direction of the net force and enhances the separation efficiency. Finally, the numerical and experimental results of the study were compared, and the curved expansion-contraction channel is introduced as the best geometry having 100% and ∼92% CTC separation efficiency, respectively. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
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11. Scour at River Bend: A Parametric Study
- Author
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Biswas, Piya and Barbhuiya, A. K.
- Published
- 2020
- Full Text
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12. Numerical study of liquid-liquid two-phase flow through coiled flow inverters: Effect of volume fraction, dean number and orientation.
- Author
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Kushwaha, Naveen, Jain, Nikita, Kumar, Vimal, and Deo Prasad Nigam, Krishna
- Subjects
- *
TWO-phase flow , *ROTATIONAL motion , *CENTRIFUGAL force , *POROSITY , *LIQUID-liquid extraction , *VORTEX motion - Abstract
[Display omitted] • Two-phase liquid–liquid flow and interaction mechanism in coiled flow invertor (CFI) over a wide range of parameters. • Effect of oil-phase fraction, inlet velocity and CFI orientation on liquid–liquid two-phase flow in CFI. • Oil-fraction have little influence on overall vorticity spectrum of the mixture, however a significant effect on the individual phases vorticity. • The change in CFI orientation (horizontal and vertical) enhanced surface area-to-volume ratio by ≈32%. The present study deals with the numerical investigation of void fraction and flow patterns for liquid–liquid (oil–water) two-phase flow through a coiled flow inverter (CFI) with different flow conditions and geometrical orientations (horizontal and vertical). A CFI comprising 90° bends between two consecutive helical coils, and works on complete flow inversion due to directional change in centrifugal force. The velocity and phase distribution profiles for liquid–liquid two-phase flow in CFI are analysed by varying Reynolds and Dean numbers from 637−5033 and 202–1592, respectively. The orientation significantly influences overall friction factor based on mixture at low inlet velocities, while at higher inlet velocity it is nearly similar despite of CFI orientation. The inherent mechanism of vorticity distribution, to predict fluid rotational motion, is also reported for each phase in CFI. The change in CFI orientation resulted into an increase in the surface area(interface)-to-volume ratio of oil by ≈32%. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
13. Precision of parameter estimation in meander models
- Author
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Droste, C., Bhattacharji, S., editor, Friedman, G. M., editor, Neugebauer, H. J., editor, Seilacher, A., editor, Hergarten, Stefan, editor, and Neugebauer, Horst J., editor
- Published
- 1999
- Full Text
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14. Numerical Analysis of Secondary Flow in the Narrow Gap of Magnetic Fluid Shaft Seal Using a Spectral Finite Difference Method.
- Author
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Liu, Jun
- Subjects
MAGNETIC fluids ,FLUID flow ,CENTRIFUGAL force ,FINITE difference method ,MATHEMATICAL functions - Abstract
In the article, attention is focused on a secondary flow in the narrow gap of a magnetic fluid shaft seal, and the secondary flow and circumferential speed of the magnetic fluid are numerically evaluated with variation in magnetic fluid plug shape such as angle of the polar head and seal clearance to be varied, using a spectral finite difference method with a new mapped function. Moreover, the maximum pressure drop is calculated in several patterns of equilibrium magnetic fluid plug, and the influence of the centrifugal force is also discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
15. Numerical investigation of flow characteristics and heat transfer performance in curve channel with periodical wave structure
- Author
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L.Y. Zhang, Xiaohu Yang, Zhao Lu, Xiaoling Yu, Lichuan Wei, Xiangzhao Meng, and Liwen Jin
- Subjects
Fluid Flow and Transfer Processes ,Centrifugal force ,Materials science ,020209 energy ,Mechanical Engineering ,Heat transfer enhancement ,Flow (psychology) ,02 engineering and technology ,Mechanics ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Curvature ,Secondary flow ,Heat transfer ,0202 electrical engineering, electronic engineering, information engineering ,0210 nano-technology ,Intensity (heat transfer) ,Communication channel - Abstract
Flow and heat transfer in curve channel have been studied extensively due to the presence of the secondary flow induced by the centrifugal force. However, for the curved channel with small curvature, weakened centrifugal force reduces the intensity of secondary flow and heat transfer enhancement is attenuated accordingly. For sake of maintaining high heat transfer efficiency in curve channel with a wide range of curvature, periodical wave structure was introduced into the smooth-curve channel by this study. A three-dimensional model of the curve-wave structure was established and numerical simulation was carried out to explore the flow characteristics and heat transfer performance in the proposed channel. In addition, the effects of the wave amplitude on the channel performance were analyzed. The results showed that the heat transfer of smooth-curve channel can be enhanced remarkably by applying wave structure on the channel wall, and the overall performance factor indicates that the heat transfer argumentation outweighs the pressure loss penalty. It was also found that the heat transfer in the curve-wave channel can be further enhanced by increasing wave amplitude. The most effective heat transfer enhancement can be achieved based on the evaluation of the overall performance factor.
- Published
- 2019
16. Granular dynamics in a vertical bladed mixer: Secondary flow patterns
- Author
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K. Jirounkova, Jaromir Havlica, P. Petrus, Martin Kohout, Tereza Travnickova, and Petr Stanovsky
- Subjects
Centrifugal force ,Materials science ,General Chemical Engineering ,Flow (psychology) ,Rotational speed ,02 engineering and technology ,Mechanics ,021001 nanoscience & nanotechnology ,Granular material ,Secondary flow ,Discrete element method ,Rake angle ,020401 chemical engineering ,Fictitious force ,0204 chemical engineering ,0210 nano-technology - Abstract
This article deals with numerical simulations and experimental measurements of the granular mixing process in a vertical cylindrical mixer with two opposed flat blades with a 45° rake angle. The computer simulations were conducted via discrete element method. The experimental measurements were recorded by a color high-speed camera. Both approaches describe the mixing process in the same way with significant agreement in observations. Even though the geometry and operating conditions are simple, the dynamics of the system is often very complex and a variety of flow structures can be created. For that reason, the behavior of individual flows patterns was analyzed and discussed. The effect of the centrifugal force on deformation of the free level of the granular material and the formation of empty spaces behind the stirrer blades was described. In addition, the behavior of individual particles in specific regions was characterized. At low rotational speed of the blades, particles tend to move close to the bottom of the vessel behind the stirrer blade towards the shaft. At high values, particles are moving in the exact opposite direction. Described movements near the base of the vessel create secondary flow in the form of recirculation zones. Presence of the secondary flow during the mixing process was also confirmed by the experimental measurements. Based on the acquired knowledge, two competing mechanisms of secondary flow formation were presented: (i) the different contact time of the particles with the blade; (ii) the different magnitude of inertial forces acting on the particles around the stirrer blade.
- Published
- 2019
17. The buoyancy force and flow acceleration effects of supercritical CO2 on the turbulent heat transfer characteristics in heated vertical helically coiled tube
- Author
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Shijie Zhang, Chao Liu, Chaobin Dang, Yadong Zhang, and Xiaoxiao Xu
- Subjects
Fluid Flow and Transfer Processes ,Centrifugal force ,Buoyancy ,Materials science ,020209 energy ,Mechanical Engineering ,Turbulent heat transfer ,02 engineering and technology ,Mechanics ,engineering.material ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Secondary flow ,Supercritical fluid ,Physics::Fluid Dynamics ,Cross section (physics) ,Heat transfer ,0202 electrical engineering, electronic engineering, information engineering ,engineering ,Tube (fluid conveyance) ,0210 nano-technology - Abstract
Numerical simulations are performed to investigate the turbulent heat transfer characteristics of supercritical CO2 in heated vertical helically coiled tube, and primary focus is to analyze the mechanism of buoyancy force and flow acceleration on the heat transfer. The results show similar effect from buoyancy force and centrifugal force, and both forces induce a secondary flow in the cross section that improves the heat transfer efficiency. The buoyancy parameter ϕ2 and flow acceleration parameter q+ are established with reasonably good validation against numerical results. On the basis of the two parameters, the buoyancy factor Fb and the acceleration factor FAc are proposed to quantify buoyancy and flow acceleration effect, respectively. Furthermore, a temperature difference correction factor Ft is introduced to consider variation of thermo-physical properties. A new semi-empirical heat transfer correlation is proposed for supercritical CO2 in function of Fb, FAc and Ft for the vertical helically coiled tube.
- Published
- 2018
18. Numerical Flow Analysis in a Rotating Square Duct and a Rotating Curved-Duct
- Author
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Je Hyun Baekt and Chang Hwan Ko
- Subjects
Rotating channel ,Numerical analysis ,Coriolis force ,Centrifugal force ,Secondary flow ,Laminar. ,Engineering (General). Civil engineering (General) ,TA1-2040 - Abstract
A numerical study is conducted on the fully-developed laminar flow of an incompressible viscous fluid in a square duct rotating about a perpendicular axis to the axial direction of the duct. At the straight duct, the rotation produces vortices due to the Coriolis force. Generally two vortex cells are formed and the axial velocity distribution is distorted by the effect of this Coriolis force. When a convective force is weak, two counter-rotating vortices are shown with a quasi-parabolic axial velocity profile for weak rotation rates. As the rotation rate increases, the axial velocity on the vertical centreline of the duct begins to flatten and the location of vorticity center is moved near to wall by the effect of the Coriolis force. When the convective inertia force is strong, a double-vortex secondary flow appears in the transverse planes of the duct for weak rotation rates but as the speed of rotation increases the secondary flow is shown to split into an asymmetric configuration of four counter-rotating vortices. If the rotation rates are increased further, the secondary flow restabilizes to a slightly asymmetric double-vortex configuration. Also, a numerical study is conducted on the laminar flow of an incompressible viscous fluid in a 90°-bend square duct that rotates about axis parallel to the axial direction of the inlet. At a 90°-bend square duct, the feature of flow by the effect of a Coriolis force and a centrifugal force, namely a secondary flow by the centrifugal force in the curved region and the Coriolis force in the downstream region, is shown since the centrifugal force in curved region and the Coriolis force in downstream region are dominant respectively.
- Published
- 2000
- Full Text
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19. Combined Effects of Centrifugal and Coriolis Instability of the Flow Through a Rotating Curved Duct of Small Curvature.
- Author
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Mondal, Rabindra Nath, Islam, Md. Zohurul, and Perven, Rina
- Subjects
CENTRIFUGAL force ,CORIOLIS force ,INCOMPRESSIBLE flow ,CURVATURE ,VISCOUS flow - Abstract
In this paper, a comprehensive numerical study is presented for the fully developed two-dimensional flow of viscous incompressible fluid through a rotating curved rectangular duct of small curvature. Numerical calculations are carried out by using a spectral method, and covering a wide range of the Taylor number 0 ≤ Tr ≤ 2000 for the Dean numbers Dn = 500 and 1000. A temperature difference is applied across the vertical sidewalls for the Grashof number Gr = 100, where the outer wall is heated and the inner wall cooled. The rotation of the duct about the center of curvature is imposed, and the effects of rotation ( Coriolis force ) on the unsteady flow characteristics are investigated. It is found that the unsteady flow undergoes in the scenario ‘ Chaotic → multi-periodic → periodic → steady-state’ , if Tr is increased in the positive direction. Contours of secondary flow patterns and temperature profiles are also obtained at several values of Tr , and it is found that there exist two- and multi-vortex solutions for the unsteady flow if the duct rotation is involved in the present cases. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
20. Numerical modeling of centrifugal microfluidic flow in rectangular channels for Lab-on-a-CD platform applications
- Author
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Viorel Ionescu
- Subjects
Centrifugal force ,Finite volume method ,Materials science ,Microchannel ,Multiphysics ,Fluent ,Fluid dynamics ,Mechanics ,Secondary flow ,Finite element method - Abstract
A rectangular radial microchannel model having the same geometric dimensions as one type of microchannel placed on a PC-controlled centrifugal Disk: length e = 2.1 cm, height h = 65 μm and width Δy = 320 μm was considered here from an experimental work reported in literature. Fluid flow transport through this standard channel was numerically developed with the Finite Element Method (FEM) based Comsol Multiphysics software, simulation performed at rotating speeds ω between 25 and 300 rad/s. Other three rotating microchannel models with different aspect ratios AR have been simulated after by increasing the channel height from 65μm to 160 μm, 200 μm and 240 μm and by maintaining the same width of 320 μm. From the simulations of standard experimental type channel resulted that even at 300 rad/s, transverse Coriolis force was only close to half of centrifugal force, no secondary flow being induced in this case and a diffusion-based mixing is developed for this particular channel geometry. The radially rotating channel model was validated after comparing the FEM results with results from other two commercial finite volume codes (CFX and Fluent) reported in a numerical research study of a microchannel with e = 10 mm and Δy = h = 200 μm.
- Published
- 2020
21. Study the effect of dehumidification in horizontal spirally coiled tube and straight tube.
- Author
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Sivaranjani, R., Venkatesh, Sivanandam, and Sundaram, S.
- Abstract
Effect of dehumidification in the horizontal spirally coiled tube is investigated. The spirally coiled tube is fabricated by bending an 8.00 mm diameter straight tube into a spiral-coil of different turns. The rate of dehumidification increases along the length of the spiral coil. This is because the dehumidification in the curved tube strongly depends on the behavior of the secondary flow. The secondary flow in curved tube is caused by the centrifugal force. This force affects the flow pattern of air in the spiral coil and disturbs the humidity of the system. Moreover the dehumidification results obtained from the spirally coiled tube is proved to be higher than that of the straight tube. [ABSTRACT FROM PUBLISHER]
- Published
- 2012
22. Inertial focusing of non-neutrally buoyant spherical particles in curved microfluidic ducts
- Author
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Yvonne M. Stokes and Brendan Harding
- Subjects
Centrifugal force ,Physics ,0303 health sciences ,Inertial frame of reference ,Mechanical Engineering ,media_common.quotation_subject ,Bend radius ,Mechanics ,Condensed Matter Physics ,Inertia ,Secondary flow ,01 natural sciences ,Centripetal force ,010305 fluids & plasmas ,Physics::Fluid Dynamics ,03 medical and health sciences ,Flow velocity ,Mechanics of Materials ,Drag ,0103 physical sciences ,030304 developmental biology ,media_common - Abstract
We examine the effect of gravity and (rotational) inertia on the inertial focusing of spherical non-neutrally buoyant particles suspended in flow through curved microfluidic ducts. In the neutrally buoyant case, examined in Harding et al. (J. Fluid Mech., vol. 875, 2019, pp. 1–43), the gravitational contribution to the force on the particle is exactly zero and the net effect of centrifugal and centripetal forces (due to the motion around the curved duct) is negligible. Inertial lift force and drag from the secondary fluid flow vortices interact and lead to focusing behaviour which is sensitive to the bend radius of the device and the particle size (each measured relative to the height of the cross-section). In the case of non-neutrally buoyant particles the behaviour becomes more complex with the two additional perturbing forces. The gravitational force, relative to the inertial lift force, scales with the inverse square of the flow velocity, making it a potentially important factor for devices operating at low flow rates with a suspension of non-neutrally buoyant particles. In contrast, the net centripetal/centrifugal force scales with the inverse of the bend radius, similar to the drag force from the secondary flow. We examine how these forces perturb the stable equilibria within the cross-sectional plane to which neutrally buoyant particles ultimately migrate.
- Published
- 2020
23. Three-dimensional gravity-current flow within a subaqueous bend: Spatial evolution and force balance variations.
- Author
-
Wei, Taoyuan, Peakall, Jeff, Parsons, Daniel R., Chen, Zhongyuan, Zhao, Baocheng, and Best, Jim
- Subjects
- *
GRAVITY , *RIVER channels , *WATER currents , *UNDERWATER tunnels , *SPATIO-temporal variation , *CORIOLIS force , *CENTRIFUGAL force - Abstract
The nature of three-dimensional flow in submarine channel bends is poorly understood, largely due to the absence of detailed data from natural channels. Herein, data from density-driven flows in a large reservoir on the Huanghe (Yellow) River are presented showing the spatio-temporal variation of flow around a subaqueous bend. The data demonstrate for the first time that reversed helical flow, relative to that found in river channel bends, can occur from the centrifugal forcing of flow, even when the Coriolis force acts in the opposite direction. The data also suggest that reversed helical flow fields in submarine channels may be more frequent than currently estimated, notably for bends where Coriolis and centrifugal forces combine in the same direction. In addition, this study provides the first field evidence suggesting that sinuous submarine channels can exhibit an asymmetry in helical flow orientation between left and right-turning bends, which will have major implications for the morphodynamics of submarine channels, their resultant patterns of sedimentation and, ultimately, the distribution of depositional units across submarine fan systems. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
24. Numerical investigation of gas-liquid hydrodynamics during trapped-liquid displacement from low sections of high-pressure gas pipelines
- Author
-
Amos Ullmann, Neima Brauner, Mirco Magnini, and E. Hamami Bissor
- Subjects
Centrifugal force ,Materials science ,Turbulence ,Flow (psychology) ,Energy Engineering and Power Technology ,Mechanics ,Geotechnical Engineering and Engineering Geology ,Secondary flow ,Supercritical fluid ,Volumetric flow rate ,Vortex ,Physics::Fluid Dynamics ,Fuel Technology ,Displacement (fluid) - Abstract
Assuring the displacement of trapped liquids from low sections by gas flow is essential for a proper operation of high-pressure natural gas pipelines. Numerical investigation of the associated transient turbulent high-pressure gas-liquid flow can provide understanding of the involved two-phase flow phenomena. To this aim, the numerical tool OpenFOAM has been used for simulating the gas-liquid flow encountered in a pipeline of a long shallow upward inclined section connected to a horizontal section by an elbow. Effects of various system parameters (e.g., gas pressure, liquid properties, up-comer inclination, elbow radius of curvature) on the gas-liquid flow dynamics are studied. Since 3D transient numerical simulations are more challenging, results obtained by 2D and 3D numerical simulations are compared to identify the similarities, sources of discrepancies, and their significance. Quantitative integral flow characteristics and the associated local flow phenomena are examined. 3D simulations verify the main findings of 2D simulations concerning the flow pattern, the associated critical gas velocity for purging the liquid and liquid propagation rate at supercritical gas velocities. The critical gas flow rate required to purge out the accumulated liquid is associated with that required to mobilize the liquid film tail along the up-comer. The main differences between 3D and 2D simulation results were captured near the elbows. The 3D effects, which result from the centrifugal force acting on the gas during its flow through the elbow, affect the downstream axial gas velocity profile and the secondary flow pattern (i.e., Dean vortices). The resulting higher interfacial shear exerted by the gas on the liquid film tail is the source of the deviations between the 3D and 2D simulation results. However, 2D simulations are sufficient for representing the gas-liquid dynamics out of the elbows’ influence region, where their effects on the flow fade out.
- Published
- 2021
25. Numerical investigation of heat transfer and pressure drop in helically coiled tube with spherical corrugation
- Author
-
Xu Peng, Sa Xiang, Dingbiao Wang, Yong Han, and Cancan Zhang
- Subjects
Fluid Flow and Transfer Processes ,Centrifugal force ,Pressure drop ,Materials science ,020209 energy ,Mechanical Engineering ,Thermodynamics ,02 engineering and technology ,Mechanics ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Secondary flow ,Boundary layer ,Heat transfer ,Turbulence kinetic energy ,Heat exchanger ,0202 electrical engineering, electronic engineering, information engineering ,Tube (fluid conveyance) ,0210 nano-technology - Abstract
Heat transfer and pressure drop in helically coiled tube with spherical corrugation are investigated by a three-dimensional numerical simulation. Different geometrical parameters of spherical corrugation in helically coiled-tube heat exchangers are studied to improve the heat transfer rate. Calculated results have been compared to experimental tests and existing empirical formulas to study the validity of the numerical results. The simulation results indicate that the secondary flow induced by the centrifugal force has significant ability to enhance the heat transfer rate, the eddy caused by the corrugation structure destroys the flow boundary layer and increases the turbulence intensity of the flow and strengthens the heat transfer process. With the increase of the corrugation height (H), the augmentation on heat transfer performance is about 1.05–1.7 times as compared to the smooth helically coiled tube, while friction factor sharply increases 1.01–1.24 times. With the increase of the corrugation pitch (P), the enhancement on heat transfer is in the range of 1.37–1.66 times and the friction factor increases 1.18–1.28 times compared to the smooth helically coiled tube. The overall heat transfer performance of helically coiled tube with corrugation is better than that of smooth helical tube under the same condition. The value of performance evaluation criterion (PEC) could be up to 1.56.
- Published
- 2017
26. The non-isothermal Bödewadt problem applied to an advanced plasma centrifuge
- Author
-
J. V. Whichello, V. D. Borisevich, and E. P. Potanin
- Subjects
Centrifugal force ,Centrifuge ,Materials science ,Gas centrifuge ,Vapor pressure ,Rotor (electric) ,law ,General Physics and Astronomy ,Mechanics ,Plasma ,Secondary flow ,Rotation ,law.invention - Abstract
Several valuable isotopes used in medicine, industry, and science cannot be separated by a gas centrifuge with a driven mechanical rotor due to the lack of a suitable working gas that has a sufficiently high vapor pressure at room temperature. Such isotopes are typically produced by more costly separation processes. An advanced plasma centrifuge (PC) has been proposed that can separate specific isotopes at a lower cost. The PC achieves increased separation performance by the excitation of an axial counterflow in the plasma medium. In this work, we consider the non-isothermal Bodewadt problem for the PC with thermally driven axial circulation created by cooling one end of the PC's separation chamber. Due to the imbalance between the centrifugal force and the radial pressure gradient, we show that a secondary flow appears, which is imposed on the medium's rotation motion. The effect is analogous to the classical Bodewadt problem, where a rotational flow decelerates over a fixed surface.
- Published
- 2021
27. Efficient investigation on fully developed flow in a mildly curved 180° open-channel.
- Author
-
Yuchuan Bai, Xiaolong Song, and Shuxian Gao
- Subjects
- *
CHANNEL flow , *TURBULENT flow , *CENTRIFUGAL force , *SHEARING force , *RENORMALIZATION group , *FINITE volume method - Abstract
Turbulent flow in meandering open channels is one of the most complicated and unpredictable turbulent flows as the interaction of various forces, such as pressure gradient, centrifugal force, and wall shear stresses severely affect the flow pattern. In order to improve significance in engineering application, understanding the overall flow characteristic is the focus. This paper presents the results of numerical and experimental investigations of flow in a 180° mild bend, which is close to criticality with curvature ratio R/B= 3. Considering the characteristic of various models, three-dimensional (3D) re-normalization group (RNG) k-ε model was adopted to simulate the flow efficiently. Governing equations of the flow were solved with a finite-volume method. The pressure-based coupled algorithm was used to compute the pressure. The flow velocities were measured experimentally with Micro acoustic Doppler velocimeter. Good agreement between the numerical results and measurements indicated that RNG k-ε model can successfully predict this flow phenomenon. The flow pattern in this bend is influenced widely by the secondary flow. The variations of velocity components, streamlines, secondary flow, and wall shear stresses are analysed in the study. Some newly discovered phenomenon in this special state are worth noting. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
28. A Review of Flow and Heat Transfer in Rotating Microchannels.
- Author
-
Roy, Pratanu, Anand, N.K., and Banerjee, Debjyoti
- Subjects
HEAT transfer ,MICROCHANNEL flow ,MICROFLUIDIC devices ,ANALYTICAL chemistry ,FLUID dynamics ,CORIOLIS force - Abstract
Abstract: Rotating microchannels are integral part of centrifugally actuated miniaturized microfluidic devices, which have important applications in chemical analysis and biomedical diagnostics. As the field of centrifugal microfluidics continues to evolve, it is becoming imperative to understand the fundamental principles of fluid flow inside microchannels under the influence of centrifugal and Coriolis forces. These forces arise as a consequence of expressing the governing equations in rotating Eulerian reference frame and change the flow pattern significantly from the symmetric parabolic profile of a non-rotating channel. In this paper, we have summarized the recent advances in the area of fluid flow and heat trans er applications in radially rotating microchannels. A review of experimental and numerical studies available in the current literature is performed and issues with the applicability of analytical correlations for conventional macro-sized channels to describe the microscale flow phenomena have been discussed. From this state of the art review, it is evident that further systematic investigations are needed for a clear understanding of the transport mechanism associated with the flow and heat transfer inside rotating microchannels. [Copyright &y& Elsevier]
- Published
- 2013
- Full Text
- View/download PDF
29. Experimental and numerical simulation of flow in a 90°bend
- Author
-
Abhari, M. Naji, Ghodsian, M., Vaghefi, M., and Panahpur, N.
- Subjects
- *
FLUID dynamics , *COMPUTER simulation , *TURBULENCE , *PRESSURE , *CENTRIFUGAL force , *FLOW meters - Abstract
Abstract: The purpose of this study is to simulate flow pattern in a 90°bend experimentally and numerically. The numerical model used in this study is SSIIM 1.1. The model was used to predict the turbulence and the SIMPLE method was used to compute the pressure. For verification of the results of the numerical model the experimental data was used. The flow velocities were measured experimentally with P-EMS velocimeter. The results of the experimental data and the numerical simulation showed that the flow pattern in a channel bend is influenced widely by the secondary flow and centrifugal force. The comparison between the experimental data and the numerical model showed that SSIIM-1.1 is capable to simulate accurately the flow pattern in a 90°bend. The variations of components of velocity, streamlines, bed shear velocity and secondary flow are addressed in the study. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
30. Study of force-dependent and time-dependent transition of secondary flow in a rotating straight channel by the lattice Boltzmann method
- Author
-
Zhang, Jinlong, Liu, Yu, Zhang, Junfeng, and Yang, Jun
- Subjects
- *
TRANSITION flow , *TRANSPORT theory , *ROTATING masses of fluid , *FLUID mechanics , *CENTRIFUGAL force , *CORIOLIS force - Abstract
Abstract: A numerical study using the lattice Boltzmann method has been carried out for flow through a rotating straight channel with a rectangular cross section. With different forces applied, the secondary flow exhibits two-cell states, four-cell states or six-cell states at a range of low rotational Reynolds number, however, within which only the two-cell states have been commonly reported. In addition to the force-dependent flow transition, a time-dependent flow transition of the secondary flow among two-cell states, four-cell states and six-cell states is also discovered during flow development. These newly found flow transitions and their regulations by force application have been analyzed. Based on numbers of case studies, it is found that a dimensionless number, the ratio of the driving pressure gradient to the centrifugal force, regulates such flow transitions. This study not only releases new phenomena of flow transition, but also indicates new applications in flow control, particle separation and heat transfer. [Copyright &y& Elsevier]
- Published
- 2009
- Full Text
- View/download PDF
31. Confined Swirling Flows Of Aqueous Surfactant Solutions Due to a Rotating Disk in a Cylindrical Casing.
- Author
-
Tamano, Shinji, Itoh, Motoyuki, Yoshida, Mitsunori, and Yokota, Kazuhiko
- Subjects
SURFACE active agents ,ORGANIC chemistry ,ROTATIONAL motion (Rigid dynamics) ,ROTATING disks ,CENTRIFUGAL force ,FLUID mechanics ,FLUIDS - Abstract
In this study, confined swirling flows of an aqueous surfactant solution due to a rotating disk in a cylindrical casing were investigated using a sectional flow visualization technique and a two-component laser Doppler velocimetry system. The concentrations of aqueous surfactant solutions (C
14 TASal) are 0.4 wt %, 0.8 wt %, and 1.2 wt %. Rheological properties such as shear viscosity and first normal stress difference of the surfactant solution were measured with a rheometer The patterns of secondary flow were classified using the Reynolds and elasticity numbers. We revealed that the projection formed near the center of the rotating disk moved up and down at a constant frequency for C14 TASal 0.8 wt % and 1.2 wt %, which has not been reported as far as we know. The effects of the Reynolds number elasticity number and aspect ratio on the velocity profiles were clarified. It was also found that the region of rigid body rotation existed at the higher Reynolds number tested for C14 TASal 0.4 wt %. [ABSTRACT FROM AUTHOR]- Published
- 2008
- Full Text
- View/download PDF
32. Slug flow in curved microreactors: Hydrodynamic study
- Author
-
Kumar, Vimal, Vashisth, Subhashini, Hoarau, Yannick, and Nigam, K.D.P.
- Subjects
- *
HYDRODYNAMICS , *SURFACE tension , *MICROREACTORS , *FINITE differences , *CRYOBIOLOGY , *CENTRIFUGAL force , *NUMERICAL analysis , *VISCOSITY - Abstract
The need for eco-friendly and energy saving processes which are substantially compact and give higher efficiency has led to the concept of process intensification (PI). Curved microchannel is such innovative device, which has potential for the intensification of processes currently carried out in conventional straight or T-type microchannels. Curved microchannels utilize the benefits of centrifugal force to its advantage. The present study deals with the numerical simulation of the Taylor flow in curved microchannels, particularly on gas and liquid slugs with varying curvature ratios (i.e., coil to tube , 10, 20 and 30). The three-dimensional, unsteady slug flow development in the curved microchannel was carried out using control volume finite difference method (CVFDM). The gas and liquid slug lengths at various operating and fluid conditions were obtained. The slug flow development for different inlet conditions and geometries (premixed feed, T-type and Y-type inlets) was also studied in the curved microchannels. It was found that for low curvature ratio , the phenomenon of flow reversal and slug freezing takes place due to centrifugal and buoyancy forces. For the similar process conditions, with an increase in curvature ratio to 5 and 10, the phenomenon of flow reversal and slug freezing observed was very minor. The non-uniformity in the slug formation was observed for low curvature ratio as compared to the higher curvature ratios. Further the influence of surface tension, viscosity and wall adhesion was studied on slug flow development in the curved microchannels. From the results it was observed that the surface tension, viscosity and wall adhesion have significant influence on slug flow development in curved microchannels. [Copyright &y& Elsevier]
- Published
- 2007
- Full Text
- View/download PDF
33. Continuous Reactive Precipitation in a Coiled Flow Inverter: Inert Particle Tracking, Modular Design, and Production of Uniform CaCO3 Particles
- Author
-
Norbert Kockmann, Safa Kutup Kurt, Krishna D.P. Nigam, and Mohd Akhtar
- Subjects
Centrifugal force ,Materials science ,General Chemical Engineering ,Taylor–Couette flow ,Multiphase flow ,Flow (psychology) ,Mixing (process engineering) ,02 engineering and technology ,General Chemistry ,Mechanics ,021001 nanoscience & nanotechnology ,Secondary flow ,Slug flow ,Industrial and Manufacturing Engineering ,020401 chemical engineering ,Particle ,0204 chemical engineering ,0210 nano-technology - Abstract
A multiphase flow profile inside a helically coiled tubular device (HCTD) was observed by using a high-speed camera. Gas–liquid slug flow observations revealed that the Taylor vortices are influenced by secondary flow due to the centrifugal force acting perpendicular to the flow direction. Hence, mixing inside the liquid slug is enhanced by the combination of Dean and Taylor vortices in HCTD. The modular design of a specific type of HCTD, that is, the coiled flow inverter (CFI) is elucidated by the representation of a new design space diagram. Continuous precipitation of calcium carbonate (CaCO3) was investigated for modular CFI made of polyvinyl chloride (PVC) tubes (di = 3.2 mm) with slug flow patterns. CaCO3 was continuously precipitated along CFI with a conversion of ca. 90%. CFI provided a narrower particle size distribution with median particle diameters around 28 μm and more uniform morphology in comparison to a batch reactor.
- Published
- 2017
34. Fluid flow and convective heat transfer in a rotating helical square duct
- Author
-
Chen, Yitung, Chen, Huajun, Zhang, Benzhao, and Hsieh, Hsuan-Tsung
- Subjects
- *
HEAT transfer , *CENTRIFUGAL force , *CORIOLIS force , *NUSSELT number - Abstract
Abstract: A numerical study is performed to examine the characteristics of fluid flow and convective heat transfer in a helical square duct rotating at a constant angular velocity about the center of curvature. Due to the combined effects of rotation (the Coriolis force), torsion and curvature (the centrifugal force), the flow behaviors become very complicated. A wide range of parameters is covered in this work. The variations of flow structure and temperature distribution with the force ratio F (the ratio of the Coriolis force to the centrifugal force) and the torsion are examined in details. The effects of rotation and torsion on the friction factor and Nusselt number are also studied at length. And also multiple solutions for a rotating toroidal square duct have been obtained. Certain hitherto unknown flow patterns are found. The present work shows both the nature of flow behaviors and the characteristics of heat transfer in a rotating helical square duct. [Copyright &y& Elsevier]
- Published
- 2006
- Full Text
- View/download PDF
35. Heat transfer performance of aviation kerosene RP-3 flowing in a vertical helical tube at supercritical pressure
- Author
-
Yanchen Fu, Jie Wen, Haoran Huang, Guoqiang Xu, and Kun Zhu
- Subjects
Centrifugal force ,Materials science ,Convective heat transfer ,020209 energy ,Heat transfer enhancement ,Energy Engineering and Power Technology ,Thermodynamics ,02 engineering and technology ,Heat transfer coefficient ,Mechanics ,Secondary flow ,Nusselt number ,Industrial and Manufacturing Engineering ,Supercritical fluid ,020401 chemical engineering ,Heat transfer ,0202 electrical engineering, electronic engineering, information engineering ,0204 chemical engineering - Abstract
Convective heat transfer characteristics of aviation kerosene RP-3 at supercritical pressure (P = 5 MPa) in vertical helical tube were experimentally studied. The helical tube has 1.82 mm equivalent inner diameter, 20 mm helical diameter and 10 mm pitch. Circumferential temperatures were detected at both upward and downward flow experiments and the results indicated that: The secondary flow induced by centrifugal force moves outward of the cross section and inside temperature is larger than the outside. Thus, the outside heat transfer coefficient (HTC) is averagely 31.5% larger than that of the inside. Furthermore, heat transfer enhancement leading by centrifugal secondary flow is the key factor when the Richardson ratio is larger than 10. At last, two correlations of Nusselt number are developed to predict heat transfer of aviation kerosene RP-3 in helical tube based on experimental data at supercritical pressure.
- Published
- 2017
36. Theoretical Analysis on the Secondary Flow in a Rotating Helical Pipe With an Elliptical Cross Section.
- Author
-
Yitung Chen, Huajun Chen, Jinsuo Zhang, and Hsuan-Tsung Hsieh
- Subjects
FLUID dynamics ,NAVIER-Stokes equations ,CENTRIFUGAL force ,TORSION ,FLUID mechanics - Abstract
In the present study, the flow in a rotating helical pipe with an elliptical cross section is considered. The axes of the elliptical cross section are in arbitrary, directions. Using the perturbation method, the Navier-Stokes equations in a rotating helical coordinate system are solved. The combined effects of rotation, torsion, and geometry on the characteristics of secondary flow and fluid particle trajectory are discussed. Some new and interesting conclusions are obtained, such as how the number of secondary flow cells and the secondary flow intensity depends on the ratio of the Coroilis force to the centrifugal force. The results show that the increase of torsion has the tendency to transfer the structure of secondary flow into a saddle flow and that the incline angle a increases or decreases the secondary flow intensity depending on the resultant force between the Corilois force and centrifugal force. [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
37. An analytical approach to explain the generation of secondary circulation in spiral concentrators
- Author
-
Venugopal Rayasam and Pankaj Jain
- Subjects
Centrifugal force ,Body force ,Engineering ,business.industry ,General Chemical Engineering ,Work (physics) ,Secondary circulation ,02 engineering and technology ,Mechanics ,Secondary flow ,020501 mining & metallurgy ,Classical mechanics ,020401 chemical engineering ,0205 materials engineering ,Drag ,0204 chemical engineering ,Spiral (railway) ,business ,Conservative force - Abstract
The spiral concentrator has been extensively used in the industry for decades. Gaps, however, appear to remain in understanding and explaining its unique flow pattern. Spiral is marked by the existence of high shear rate. Gravity, drag, frictional force between particles and trough, centrifugal force and lift force act in a particular manner to generate a unique flow pattern called secondary circulation. The present work attempts to explain how geometrical features and different forces help in generation of secondary circulation in pure fluid. A new concept of force balance from classical solid mechanics has been introduced to explain the generation of secondary flow and behavior of particles on the spiral trough. A modified form of Bagnold force equation has been presented along with simulation results.
- Published
- 2017
38. Nanofluids heat transfer and flow analysis in vertical spirally coiled tubes using Eulerian two-phase turbulent model
- Author
-
T. Nualboonrueng, T. Arisariyawong, and Paisarn Naphon
- Subjects
Fluid Flow and Transfer Processes ,Centrifugal force ,Pressure drop ,Materials science ,Turbulence ,020209 energy ,Heat transfer enhancement ,Thermodynamics ,02 engineering and technology ,Mechanics ,Condensed Matter Physics ,Secondary flow ,01 natural sciences ,010305 fluids & plasmas ,Physics::Fluid Dynamics ,Nanofluid ,0103 physical sciences ,Heat transfer ,0202 electrical engineering, electronic engineering, information engineering ,Fluid dynamics - Abstract
A computation fluid dynamics study has been performed to analyze the nanofluids heat transfer and flow characteristics in the spirally coiled tubes. Eulerian two-phase turbulent model is applied to simulate the heat transfer and flow characteristics in the vertical spirally coiled tube. The spirally coiled tubes are fabricated by bending a 8.50 mm inner diameter straight copper tube into a spiral-coil with two different curvature ratios of 0.035, 0.060. The predicted results are verified with the present measured data. Reasonable agreement is obtained from the comparison between the measured data and the predicted results. In addition, due to the centrifugal force, the induced secondary flow has significant effect on the heat transfer enhancement as flowing through the spirally coiled tube. Effects of curvature, nanofluids concentration and hot water temperature on the nanofluids heat transfer characteristics and pressure drop are considered.
- Published
- 2017
39. Fluid flow and mixed convection heat transfer in a rotating curved pipe
- Author
-
Chen, Huajun and Zhang, Benzhao
- Subjects
- *
FLUID dynamics , *CENTRIFUGAL force , *HYDRODYNAMICS - Abstract
When a temperature-induced variation of fluid density occurs in a rotating curved pipe, the Coriolis force, the centrifugal-type buoyancy force and the centrifugal force will contribute to the generation of the secondary flow. The interaction of these body forces complicates the characteristics of flow and heat transfer. A numerical study is performed to examine the combined effects of rotation (Coriolis force), curvature (centrifugal force) and heating/cooling (centrifugal-type buoyancy force), and solutions are obtained for a wide range of parameters. The combined effects of these comparable order of magnitude forces on the flow structure, temperature distribution, friction factor and Nusselt number are examined in detail. Present works show the natures of the flow and heat transfer in rotating curved pipes. [Copyright &y& Elsevier]
- Published
- 2003
- Full Text
- View/download PDF
40. Numerical Analysis of Secondary Flow in the Narrow Gap of Magnetic Fluid Shaft Seal Using a Spectral Finite Difference Method
- Author
-
Jun Liu
- Subjects
Centrifugal force ,Materials science ,Mechanical Engineering ,Numerical analysis ,Drop (liquid) ,Analytical chemistry ,Finite difference method ,02 engineering and technology ,Surfaces and Interfaces ,Mechanics ,equipment and supplies ,Secondary flow ,01 natural sciences ,Seal (mechanical) ,010305 fluids & plasmas ,Surfaces, Coatings and Films ,Physics::Fluid Dynamics ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,0103 physical sciences ,Head (vessel) ,Polar ,human activities - Abstract
In the article, attention is focused on a secondary flow in the narrow gap of a magnetic fluid shaft seal, and the secondary flow and circumferential speed of the magnetic fluid are numerically evaluated with variation in magnetic fluid plug shape such as angle of the polar head and seal clearance to be varied, using a spectral finite difference method with a new mapped function. Moreover, the maximum pressure drop is calculated in several patterns of equilibrium magnetic fluid plug, and the influence of the centrifugal force is also discussed.
- Published
- 2016
41. Liquid flow in a simplex swirl nozzle
- Author
-
Ghobad Amini
- Subjects
Fluid Flow and Transfer Processes ,Centrifugal force ,Materials science ,Mechanical Engineering ,Flow (psychology) ,Nozzle ,General Physics and Astronomy ,02 engineering and technology ,Mechanics ,Secondary flow ,01 natural sciences ,Discharge coefficient ,010305 fluids & plasmas ,Physics::Fluid Dynamics ,Boundary layer ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Inviscid flow ,0103 physical sciences ,Body orifice - Abstract
Pressure-swirl nozzles are widely used in applications such as combustion, painting, air-conditioning, and fire suppression. Understanding the effects of nozzle geometry and inlet flow conditions on liquid film thickness, discharge coefficient and spray angle is very important in nozzle design. The nozzle-internal flow is two-phase with a secondary flow which makes its detailed analysis rather complex. In the current work, the flow field inside a pressure-swirl nozzle is studied theoretically. Using the integral momentum method, the growth of the boundary layer from the nozzle entry to the orifice exit is investigated and the velocity through the boundary layer and the main body of the swirling liquid is calculated. A numerical modeling and a series of experiments have also been performed to validate the theoretical results. The effect of various geometrical parameters is studied and results are compared for viscous and inviscid cases. In addition, the condition in which the centrifugal force of the swirling flow overcomes the viscous force and induces an air core is predicted. The theoretical analysis discussed in this paper provides better criteria for the design and the performance analysis of nozzles.
- Published
- 2016
42. Swirling performance of flow-driven rotating mixing vane toward critical heat flux enhancement
- Author
-
In Cheol Bang, Seok Bin Seo, Hyo Heo, Han Seo, and Seong Dae Park
- Subjects
Fluid Flow and Transfer Processes ,Centrifugal force ,Pressure drop ,Materials science ,Particle image velocimetry ,Critical heat flux ,Turbulence ,Mechanical Engineering ,Enhanced heat transfer ,Heat transfer ,Mechanics ,Condensed Matter Physics ,Secondary flow - Abstract
This paper presents experimental swirl generation measurements using a flow-driven rotating vane for heat transfer and critical heat flux enhancement in subchannels. In nuclear power plants, there are swirl generators, which are located on the top of the structural grids in the fuel assemblies. The mixing vanes are fixed on the spacer grids, thus there would be a limit for enhancing heat transfer performance because of the fixed positions. An innovative swirl generator, called moving rotational vane, was used to enhance heat transfer performance as well as critical heat flux by maximizing centrifugal force due to the swirl flow on the spacer grid. The experiments were conducted in vertical and horizontal flow experimental facilities using three types of vanes: (1) spacer grid (SG), (2) fixed split vane (FSV), and (3) moving rotational vane (MRV). Particle image velocimetry was applied to visualize the flow characteristics along the test sections; averaged velocity fields, averaged velocity vector components u and v, lateral and longitudinal flow distributions, turbulence intensities, and swirl ratio were analyzed. Computational fluid dynamics analysis was performed to show the effect of swirl generation and an air bubble injection experiment was conducted to show the effect of using the MRV. The pressure drop observed from the experiment using the SG, FSV, and MRV was 0.85, 1.97 and 2.59 kPa, respectively. On the other hand, in the CFD analysis, the pressure drop of the SG, FSV, and MRV was 1.86, 1.95, and 2.01 kPa at the same measurement length of the experiment, respectively. Swirl ratio was analyzed for the FSV and MRV. The swirl ratio of the MRV showed higher value compared to the FSV including conventional fixed split vanes. The analysis showed that the MRV induced the most powerful swirl generation. The MRV could provide secondary flow structures such as mixing and turbulence; thus, enhanced heat transfer as well as critical heat flux performance could be expected.
- Published
- 2015
43. Numerical analysis of quasi-steady flow characteristics in large diameter pipes with low liquid loading under high pressure
- Author
-
Jin Youhai, Dalei Zhang, Guan Xiaorui, Yingliang Zhao, and Jianjun Wang
- Subjects
Centrifugal force ,endocrine system ,Gravity (chemistry) ,Materials science ,business.industry ,Flow (psychology) ,technology, industry, and agriculture ,Energy Engineering and Power Technology ,Structural engineering ,Mechanics ,Computational fluid dynamics ,Geotechnical Engineering and Engineering Geology ,Secondary flow ,complex mixtures ,eye diseases ,Vortex ,Physics::Fluid Dynamics ,Fuel Technology ,Streamlines, streaklines, and pathlines ,Thin film ,business - Abstract
Computational fluid dynamics (CFD) modeling was carried out to study wavy thin film flow and droplet transport in high-pressure natural gas pipelines with low liquid loading. The interactions between droplets and thin film were considered. The results of the CFD analysis showed periodic fluctuation in the axial film distribution in the straight pipe. In the bend, gas streamlines originated from the inside of the bend. As the gas velocity was increased, more droplets were stripped, while the stripped droplets were deposited further away. Liquid film peak formation and droplet motion were attributed to the actions of centrifugal force and gravity in the bend. Secondary flow enhanced the transport of droplets to the upper side of the pipe and supplemented the upper film. The droplet fraction distribution changed periodically with time. The accumulation of droplets on the film has a periodic characteristic. Dense droplets tended to accumulate in regions of low vortices. The results of the CFD simulation were in good agreement with previous experimental data and theoretical analyses reported in the literature.
- Published
- 2015
44. Performance Study of a Circumferential Overlap Trisection Helical Baffle Heat Exchanger at the Shell Side
- Author
-
Ruibing Cao, Yaping Chen, Cong Dong, and Jiafeng Wu
- Subjects
Fluid Flow and Transfer Processes ,Centrifugal force ,Materials science ,business.industry ,Mechanical Engineering ,Shell (structure) ,Baffle ,Mechanics ,Condensed Matter Physics ,Secondary flow ,Vortex ,Optics ,Heat exchanger ,Heat transfer ,business ,Spiral - Abstract
Using the three-dimensional (3D) modeling software Gambit, a mathematical model of a circumferential overlap trisection helical baffle shell-and-tube heat exchanger (cothSTHX) was developed with 34 tubes and three pulling rods with an equilateral triangle tube layout and a baffle incline angle of 20°. The numerical simulation of flow and thermal performances was performed with the analysis software Fluent. The temperature, pressure, and velocity nephograms are shown for different slices, including spiral, concentric hexagon longitudinal, meridian, eccentric longitudinal, and transverse slices. The nephograms of temperature, pressure, and velocity with superimposed velocity vectors vividly display the important parameters of the cothSTHX. The “Dean vortex secondary flow” is a key mechanism to enhance the heat transfer in heat exchangers, which is clearly depicted to show that the spiral fluid flows outward under the centrifugal force, then flows back to the axis under the radial differential pressure, form...
- Published
- 2015
45. Density-gradient-assisted centrifugal microfluidics: an approach to continuous-mode particle separation
- Author
-
Yuzuru Takamura, Takayuki Oguro, and Yoshiaki Ukita
- Subjects
Centrifugal force ,Density gradient ,Chemistry ,010401 analytical chemistry ,Microfluidics ,Biomedical Engineering ,Analytical chemistry ,Centrifugal micro-fluidic biochip ,Centrifugation ,02 engineering and technology ,Mechanics ,Equipment Design ,021001 nanoscience & nanotechnology ,Secondary flow ,01 natural sciences ,0104 chemical sciences ,Volumetric flow rate ,Lab-On-A-Chip Devices ,Particle ,Particle Size ,0210 nano-technology ,Molecular Biology ,Spinning - Abstract
Centrifugal microfluidics has been recognized as a promising pumping method in microfluidics because of its simplicity, easiness of automation, and parallel processing. However, the patterning of stripe flow in centrifugal microfluidics is challenging because a fluid is significantly affected by the Coriolis force, which produces an intrinsic secondary flow. This paper reports a technical and design strategy for centrifugal microfluidics called “density-gradient-assisted centrifugal microfluidics.” The flow behavior is observed with the presence of a density gradient and without a density gradient in two concentrically traveling phase flows. As a result, clear stripe flow pattern is observed with a density difference of 0.05 g/cm3 between water and a percoll solution at a flow rate of 11.8 μl/s (7 ml/10 min) and spinning speed of 3000 rpm. In contrast, without a density gradient, it is necessary to reduce the flow rate and spinning speed to 0.1 μl/s and 1000 rpm, respectively. This paper also presents the use of a density gradient to assist in focusing resin (polystyrene) particles on the boundary of a stripe flow pattern that consists of water and percoll with different densities. Moreover, the density-based separation and sorting of particles in a mixed particle suspension is demonstrated. Polystyrene is selectively focused on the boundary, but silica particles are separated from the focused trajectory due to a difference in density. The separated particles are continuously sorted into different reservoirs with polystyrene and silica separation efficiencies of 96.5% and 98.5%, respectively. The pumping, stripe flow pattern formation, particle concentration, and sorting are simultaneously realized by applying a density gradient and centrifugal force. Therefore, this principle can realize a very simple technique for label-free particle separation by just spinning a disk device and can be applied in other applications by the use of the density-gradient assistance.
- Published
- 2017
46. Experimental and Numerical Study on Velocity Fields and Water Surface Profile in a Strongly-Curved 90° Open Channel Bend
- Author
-
Ali Akbar Akhtari, Akbar A. Javadi, Azadeh Gholami, Yasser Minatour, and Hossein Bonakdari
- Subjects
Centrifugal force ,Engineering ,Finite volume method ,General Computer Science ,Turbulence ,business.industry ,Mechanics ,Secondary flow ,Open-channel flow ,Physics::Fluid Dynamics ,Transverse plane ,Modeling and Simulation ,Free surface ,Volume of fluid method ,business ,Simulation - Abstract
The flow pattern changes at open channel bend as the result of the presence of centrifugal force. Parameters such as water surface level, the transverse and depth velocity distribution, secondary flow and separation zones deeply depend on bend angel and radius, while many researchers are interested in flow patterns at bends. This paper presents an experimental and numerical study of the flow patterns in a strongly-curved 90° open channel bend. The numerical modelling was carried out using the finite volume method. In this numerical study, the k – e (RNG) model was used to predict the turbulence, and the volume of fluid (VOF) method was used to simulate the water free surface. The numerical results were verified against data from a program of experiments conducted in this study. A comparison between the experimental data and the results of the numerical model showed that the k – e (RNG) and VOF methods are capable of simulating the flow pattern in the strongly-curved bends. The results showed that ...
- Published
- 2014
47. Particle inertial focusing and its mechanism in a serpentine microchannel
- Author
-
Ming Li, Nam-Trung Nguyen, Weihua Li, Jun Zhang, and Gursel Alici
- Subjects
Physics ,Centrifugal force ,Inertial frame of reference ,Microchannel ,Flow (psychology) ,Nanotechnology ,Mechanics ,Condensed Matter Physics ,Secondary flow ,Electronic, Optical and Magnetic Materials ,Physics::Fluid Dynamics ,Cross section (physics) ,Drag ,Materials Chemistry ,Particle - Abstract
Particle inertial focusing in a curved channel promises a big potential for lab-on-a-chip applications. This focusing concept is usually based on the balance of inertial lift force and the drag of secondary flow. This paper proposes a new focusing concept independent of inertial lift force, relying solely on secondary flow drag and particle centrifugal force. Firstly, a focusing mechanism in a serpentine channel is introduced, and some design considerations are described in order to make the proposed focusing concept valid. Then, numerical modelling based on the proposed focusing mechanism is conducted, and the numerical results agree well with the experimental ones, which verify the rationality of proposed mechanism. Thirdly, the effects of flow condition and particle size on the focusing performance are studied. The effect of particle centrifugal force on particle focusing in a serpentine microchannel is carefully evaluated. Finally, the speed of focussed particles at the outlet is measured by a micro-PIV, which further certifies the focusing positions of particles within the cross section. Our study provides insights into the role of centrifugal force on inertial focusing. This paper demonstrates for the first time that a single focusing streak can be achieved in a symmetric serpentine channel. The simple serpentine microchannel can easily be implemented in a single-layer microfluidic device. No sheath flow or external force field is needed allowing a simple operation in a more complex lab-on-a-chip system.
- Published
- 2013
48. Control of secondary flow in concentrically traveling flow on centrifugal microfluidics
- Author
-
Yoshiaki Ukita and Yuzuru Takamura
- Subjects
Centrifugal force ,Microchannel ,Materials science ,Analytical chemistry ,Rotational speed ,Laminar flow ,Mechanics ,Condensed Matter Physics ,Secondary flow ,Flow measurement ,Electronic, Optical and Magnetic Materials ,Volumetric flow rate ,Physics::Fluid Dynamics ,Flow (mathematics) ,Materials Chemistry - Abstract
This paper reports a fundamental study of the stripe laminar flow pattern on a centrifugal microfluidic device with the goal of realizing a sedimentation-based, continuous mode particle separation technique. Microfluidic channels were designed with a concentrically integrated microchannel, and the patterning of the flow in the channel was investigated. A significant secondary flow was observed as a preliminary result. We conclude that the origin of this secondary flow was not the Dean force, because it was observed in a straight microchannel, but was not observed in curved channel during the spinning of the system at rest. The transition of the pattern was investigated using a simulation and experiment, and the flow pattern’s dependence on the rotational speed was determined, which suggested that the origin of the secondary flow was the Coriolis force. The significance of the secondary flow was controlled by adjusting the rotational speed of the disk, and the flow rate and laminar flow patterns were controlled by the stripe flow pattern.
- Published
- 2013
49. Numerical simulation of flow and heat transfer in radially rotating microchannels
- Author
-
N. K. Anand, Debjyoti Banerjee, and Pratanu Roy
- Subjects
Centrifugal force ,Microchannel ,Chemistry ,Centrifugal micro-fluidic biochip ,Reynolds number ,Mechanics ,Condensed Matter Physics ,Secondary flow ,Electronic, Optical and Magnetic Materials ,Physics::Fluid Dynamics ,symbols.namesake ,Classical mechanics ,Heat transfer ,Materials Chemistry ,Fluid dynamics ,Compressibility ,symbols - Abstract
Investigation of fluid flow and heat transfer in rotating microchannels is important for centrifugal microfluidics, which has emerged as an advanced technique in biomedical applications and chemical separations. The centrifugal force and Coriolis force, arising as a consequence of the microchannel rotation, change the flow pattern significantly from the symmetric profile of a non-rotating channel. Successful design of microfluidic devices in centrifugal microfluidics depends on effectively regulating these forces in rotating microchannels. In this work, we have numerically investigated the flow and heat transfer in rotating rectangular microchannel with continuum assumption. A pressure-based finite-volume technique with a staggered grid was applied to solve the steady incompressible Navier–Stokes and energy equations. It was observed that the effect of Coriolis force was determined by the value of the non-dimensional rotational Reynolds number (Reω). By comparing the root mean square deviation of the axial velocity profiles with the approximate analytical results of purely centrifugal flow for different aspect ratios (AR = width/height), a critical rotational Reynolds number (Reω,cr) was computed. Above this value of (Reω,cr), the effect of secondary flow becomes dominant. For aspect ratios of 0.25, 0.5, 1.0, 2.0, 4.0 and 9.09, this critical rotational Reynolds number (Reω,cr) was found to be 14.0, 5.5, 3.8, 4.7, 6.5 and 10.0, respectively.
- Published
- 2013
50. CFD analysis of the two-phase bubbly flow characteristics in helically coiled rectangular and circular tube heat exchangers
- Author
-
Alamin Hussain and Andrew Fsadni
- Subjects
Flow visualization ,Centrifugal force ,Engineering ,H990 ,business.industry ,Physics ,QC1-999 ,Flow (psychology) ,Mechanical engineering ,02 engineering and technology ,Computational fluid dynamics ,Secondary flow ,01 natural sciences ,010305 fluids & plasmas ,Physics::Fluid Dynamics ,020401 chemical engineering ,0103 physical sciences ,Heat exchanger ,Micro heat exchanger ,Tube (fluid conveyance) ,0204 chemical engineering ,business - Abstract
Due to their ease of manufacture, high heat transfer efficiency and compact design, helically coiled heat exchangers are increasingly being adopted in a number of industries. The higher heat transfer efficiency over straight pipes is due to the secondary flow that develops as a result of the centrifugal force. In spite of the widespread use of helically coiled heat exchangers, and the presence of bubbly two-phase flow in a number of systems, very few studies have investigated the resultant flow characteristics. This paper will therefore present the results of CFD simulations for the two-phase bubbly flow in helically coiled heat exchangers as a function of the volumetric void fraction and the tube cross-section design. The CFD results are compared to the scarce flow visualisation experimental results available in the open literature.
- Published
- 2016
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