Uniform Velocity Distribution Research Articles

3D CPFD Simulation of Circulating Fluidized Bed Downer and Riser: Comparisons of Flow Structure and Solids Back-Mixing Behavior

The difference of gas-solids flow between a circulating fluidized bed (CFB) downer and riser was compared by computational particle fluid dynamics (CPFD) approach. The comparison was conducted under the same operating conditions. Simulation results demonstrated that the downer showed much more uniform solids holdup and solids velocity distribution compared with the riser. The radial non-uniformity index of the solids holdup in the riser was over 10 times than that in the downer. In addition, small clusters tended to be present in the whole downer, large clusters tended to be present near the wall in riser. It was found that the different cluster behavior is important in determining the different flow behaviors of solids in the downer and riser. While the particle residence time increased evenly along the downward direction in the downer, particles with both shorter and longer residence time were predicted in the whole riser. The nearly vertical cumulative residence time distribution (RTD) curve in the downer further demonstrated that the solids back-mixing in the downer is limited while that in the riser is severe. Solids turbulence in the downer was much weaker compared with the riser, while the large clusters formation near the wall in the riser would hinder solids transportation ability.

Analysis and improvement of material flow during extrusion process using spreading pocket die for large-size, flat-wide, and multi-ribs profile

Spreading extrusion is an advanced technology to produce the solid aluminum profiles with large-size, flat-wide, and thin-walled structures. Currently, little research has been reported on the hot extrusion process through spreading pocket die for manufacturing these kinds of aluminum profiles. It is a challenging task for die engineers to control the billet through die cavity with a uniform velocity. Reasonable structure design for spreading pocket die can eliminate extrusion defects and improve the performance of extrudate. In this paper, virtual tryout of spreading extrusion process for a large-size, flat-wide, and multi-ribs aluminum profile was performed through arbitrary Lagrangian-Eulerian simulation. Firstly, spreading pocket die was designed based on the theory of metal plastic flowing. The uniformity of flow velocity distribution on the cross-section of die exit was evaluated quantitatively through standard deviation calculation. Then, a series of structure modifications for the spreading pocket die was proposed to improve material flow during die cavity based on the simulated results. Thirdly, a synthetical comparison of extrusion formability for the modified and initial spreading pocket dies was carried out, including the metal flow behavior, exit temperature, residual stress of extrudate, and peak extrusion force. Finally, the modified extrusion dies were manufactured, and corresponding extrusion experiment was performed to verify the effectiveness and reliability of numerical simulations. The key design points of spreading pocket die for large-size, flat-wide, and multi-ribs aluminum profile were concluded.

The influence of internal vane on uniform velocity distribution in the cross-flow fan

The influence of internal vane on uniform velocity distribution in the cross-flow fan

Aerodynamic Characteristics of a Hex-Rotor MAV With Three Coaxial Rotors in Hover

In order to study the aerodynamic characteristics of a Hex-rotor micro aerial vehicle (MAV) with different rotor spacing, both experiments and numerical simulations are performed in this paper. First of all, a series of aerodynamic parameters to characterize the hover performance of the Hex-rotor MAV are analyzed theoretically. Secondly, tests on the Hex-rotor MAV with different rotor spacing ratios ( $i=0.5$ , 0.56, 0.63, 0.71, 0.83, 1.00) is presented in detail. The thrust and power of the Hex-rotor MAV are obtained from the self-designed test platform. In the meanwhile, pressure and velocity distribution of the Hex-rotor MAV are obtained by Computational Fluid Dynamics (CFD) simulation. The results show that the aerodynamic performance of the Hex-rotor MAV is varied with the rotor spacing. Specifically, the rotor interference is inclined to improve the aerodynamic performance of the Hex-rotor MAV with the proper rotor spacing. Owing to the increase of rotor spacing, the interactions between rotors are weakening gradually. In addition, the uniformity of velocity distribution, the stability of downwash distribution and the integrity of vortex are the necessary conditions for a larger thrust of the Hex-rotor MAV. Finally, combined with the test and simulation results, it is also found that there is larger thrust characterized with better aerodynamic performance at $i=0.63$ , which is assumed as the best rotor arrangement of the Hex-rotor MAV. Especially for ${{Re}}=1.16\times 10^{5}$ , the thrust increases by 6.09%, and the hover efficiency increases by about 9.17% in general.

Адаптация математической модели обобщенного теплообмена в топках

Consideration of the scheme of flows of combustion products in furnaces and flow chambers of combus-tion within the framework of the heat transfer paradigm made it possible to determine the ratio of the genera-lized mechanisms of heat transfer – convection and radiation. The transition from uniform distribution of gas flow velocity to uneven distribution in furnaces with a geometrically peculiar fence has been implemented. This made it possible to take into account the use of recirculation gases, dual-light shades, changes in the shape and size of the cross-section of the furnace, and installation of shade surfaces in a furnace. The condi-tions for the correctness of the mathematical model are considered, and the eigenvalues of the boundary value problem under conditions of an asymmetric temperature field and the function of the gas temperature changing along the height of the furnace are obtained. A comparative analysis of the nature of the change in gas temperature with height according to the proposed model with the calculation for a steam boiler with a capacity of 950 t/h according to the standard method showed a satisfactory agreement of the calculated data with an accuracy of +4.87 %.

Investigation of the gas feeder design for a fluidized bed chemical reactor or combustor

In the present work, a model of a gas feeder for the industrial apparatus of the petrochemical or energy industry is constructed. Using the methods of computational fluid dynamics, we calculated the gas motion in the constructed models. Various options for the size and arrangement of the gas feeder elements in the system are considered. The analysis of the calculation results is carried out and the best design options are determined to ensure uniform distribution of the gas velocity to the nozzle of the gas supply system.

FE Analysis of Effect of Variation in Coil length and Coil-tube Relative Positions on Establishment of Magnetic Fields and Distribution of Velocities in Electromagnetic Forming of Muffler Tube

The electromagnetic forming (EMF) process is a high energy rate process that uses magnetic forces to deform the metal workpieces. It also involves high velocities and high strain rates. It is tough to find out these process parameters experimentally, which proposes the need for numerical models. The EMF of muffler tube is a novel technique of manufacturing a single piece of component of the desired shape, which eliminates the disadvantages of conventional manufacturing techniques. This paper presents an FE model to observe the distribution of the magnetic field and velocities that drives the muffler tube. The coil-tube axial position is significant in the EMF process as the magnetic field produced is not uniform along the length of the coil. In the analysis of EMF processes, it is essential to able to estimate the magnetic field generated along the length of the coil. The presented coupled FE model can estimate the magnetic field and impact velocity generated during different coil-tube positions and discharge energies. The developed model is validated with deformation obtained in experimental runs. The simulation results show that to deform the aluminium tube minimum of 3 T magnetic field or a minimum of 87 m/s velocity is required. It is found that the coil having 100 mm length is giving more uniform pressure compare to other lengths. It is also observed that with the use of 100 mm length coil and amongst all coil-tube positions when offset between coil and tube relative position is zero, it develops the uniform distribution of magnetic field and velocities at a required area which results in maximum deformation compared to other positions. The development of such an FEA model helps to eliminate empirical investigation to discover the magnetic field and velocities involved in the process.

Rotary dryer for thermo sensitive products

To achieve the desired drying objectives in thermal sensitive products, such as medicinal plants, the process chosen should happen under minimally controlled conditions, such as, uniformity of temperature and air velocity, minimizing heat loss and with energy viability and efficiency. If possible, the process must occur using equipment with industrial implementation where the evaporation rate can be controlled. The intermittent drying process, which consist of cycles of exposure of the material to heated air (period of effective drying) and tempering (period of no exposure to heated air), is a great option to preserve the product’s quality during the drying process. We propose a new configuration of rotary dryer intended for intermittent drying; observing the configurations of widely applied rotary dryers, the relationship between angular velocity, period and frequency of rotation and laboratory experiments of manufacturing process in intermittent drying. The proposed dryer is efficient for the application of intermittent drying in products with high thermal sensitivity, such as medicinal plants. Making possible uniformity of temperature and air velocity distribution, minimizing heat loss and with energy viability and efficiency, guarantying the product quality.

Numerical investigation of the fluid flow and heat transfer characteristics of tree-shaped microchannel heat sink with variable cross-section

The bionic fractal microchannel heat sink (MHS), which is characterized by a uniform velocity distribution and higher heat transfer efficiency, is an ideal heat sink candidate, while the structure of the variable cross-section has a great impact on the fluid flow and heat transfer performance of the MHS. Considering the coupling effects of the bionic fractal and variable cross-section, a tree-shaped MHS (TMHS) with a variable cross-section is firstly proposed. The flow characteristics, heat transfer characteristics, pressure drop characteristics, and comprehensive performance of TMHSs with cavities and ribs were analyzed numerically using the commercial software Fluent, and compared with the traditional smooth TMHS. The results indicate that the structure of varibale cross-section can further enhance heat transfer performance of the TMHS. The TMHS with ribs (TMHS-R) exhibited the highest heat transfer performance, but also had the highest pressure drop. Finally, the heat transfer index was put forward to consider both heat transfer and pressure drop characteristics, and the results found that the TMHS with cavities (TMHS-C) had the highest comprehensive performance at the range of the calculating Reynolds number.

Hemodynamic of the patent ductus arteriosus in neonates with modified Blalock-Taussig shunts

Background and objectiveStudying the hemodynamic effects of nonclosure of patent ductus arteriosus (PDA) on the modified Blalock-Taussig shunt (MBTS) is beneficial for surgical PDA management. In the present study, the effect of PDA on MBTS was investigated numerically. A series of parameters including energy loss, wall shear stress (WSS), and left/right Pulmonary artery (LPA/RPA) flow ratio were computed from simulations to analyze the hemodynamic effects of PDA on MBTS. MethodsTo ensure the universality of the research conclusions, three typical models, including models with a well-developed RPA, a symmetrically-developed pulmonary artery(PA) and a well-developed LPA, were constructed based on patient-specific pre-surgery clinical data sets. A commercial CFD solver ANSYS-Fluent software was adopted for this study. A pressure-based solver for incompressible Newtonian flows, the K-omega based shear-stress-transport model and a second-order accurate numerical discretization scheme were employed for simulation. ResultsOur results show that MBTS with nonclosure of PDA is accompanied by lower blood velocity, energy loss and WSS values at the MBT shunt; smaller vortex regions; higher oxygen content(Sao2) and PA flow; and more uniform velocity distribution in the LPA and RPA than MBTS with closure of PDA. If the PDA was not closed when performing primary MBTS, a series of hemodynamic changes occurs during PDA closure in postoperative recovery: the energy loss, PA flow and Sao2 decrease, while the oxygen delivery(Do2) and WSS values at the MBT shunt increase. ConclusionNonclosure of PDA could provide a better hemodynamic environment and play an active role in preventing early acute shunt failure. It could be preferred for cases with very low PA overflow risk and may benefit patients with an underdeveloped myocardium due to its lower energy dissipation than PDA closure. However, excessive PA flow induced by nonclosure of PDA may result in a series of complications. Surgeon's decision-making process with respect to PDA management should consider the individual patient to achieve optimal postoperative recovery.

On the modes of cuttings transport in an inclined annular channel

The paper presents the results of the simulation of cuttings transport (solid spherical particles) by water through a long annular axisymmetric inclined channel. At the inlet uniform distribution of particles and fluid velocity was set. Inclination angle varied from 0 to 90 degrees. Modes of stationary and moving dunes and their transition into wave-shaped and stationary sediment were observed. Moving dunes could oscillate laterally and did not form a crest that occupied the entire width of the channel. In this case, dense sediment formed an S-shaped path, moving along the stream. Despite the general downstream movement of the S-shaped track (dune), a downward flow might occur in the low area with high concentration. Five basic flow regimes were identified: constant sediment, moving wave-like sediment, separated stationary dunes, S-shaped sediment and homogeneous flow. The basic flow pattern could be complicated by lateral motion and backward flow in a region of high concentration. A variant of the flow pattern map is suggested.

ANALYSIS OF AERODYNAMIC CHARACTERISTICS IN THE TUNNEL KILN CHANNEL WHEN CHANGING THE GEOMETRIC CHARACTERISTICS OF THE CHANNEL

The article is devoted to the analysis of the influence of tunneling channel height change on its aerodynamic characteristics by modeling the velocity and pressure distribution of air and furnace gases. Three variants of the tunnel geometry were considered: basic, with reduced height in the firing zone and with reduced height along the entire length of the furnace. The simulation results in the dependence of the static pressure along the length of the furnace and the velocity of the furnace gas moving along its height. The analysis of the change in the velocity of the furnace gases in the tunnel has made it possible to say that the most effective in terms of uniformity of velocity distribution is the variant with the reduction of the height of the arch along the entire length of the furnace.Keywords: tunnel kiln, tunnel kiln channel, change of kiln geometry, velocity distribution modeling, static pressure distribution.

Application of Arbitrary Vortex Method in Wind Tunnel Axial Fan Design

The flow axial velocity is assumed equal everywhere in free vortex design method, and the pressure rise of flow pass through fan is assumed also equal at different radial height. But in arbitrary vortex design method, on the assumption that axial velocity along radial is variable, the flow rotational velocity along radial is not must an inverse distribution. Therefore, arbitrary vortex design method could have a more uniform axial velocity at the outlet of fan system by regulating the rotational velocity distribution. In the numerical simulation, the fan of a pilot wind tunnel is used as physical model. By comparison with the experimental data the reliability of the numerical simulation could be verified. Two fan physical models are established which are based on the designs of arbitrary vortex method and free vortex method. The result of numerical simulation indicated that compared to the free vortex method, the arbitrary vortex fan minished the separation on the tip and root of blade, obtained a more well uniform axial velocity distribution at the outlet of fan system. And the efficiency of blade is also increased by arbitrary vortex method.

Air inlet angle influence on the air-side heat transfer and flow friction characteristics of a finned oval tube heat exchanger

In this study, the influence of various air inlet angles on the heat transfer and flow friction characteristics of a 2-row plain finned oval tube heat exchanger is analyzed by experimental and numerical methods. The experimental results show that an air inlet angle 45° provides the best heat transfer performance, and an air inlet angle 90° provides the smallest pressure drop, while an air inlet angle 30° provides the worst heat transfer performance associated with the largest pressure drop. The 3-D numerical simulation results indicate that with the decrease of the air inlet angle, the uniformity of the air velocity distribution in the z-direction of the heat exchanger becomes worse. The heat transfer characteristics at different air inlet angles are analyzed from the prospective of the field synergy principle and the effect of the air velocity distribution uniformity. The overall heat transfer performance is also evaluated by the JF factor under the same air mass flow rate. The results show that the air inlet angle 45° offers the best overall heat transfer performance, next is the air inlet angle 60°, while the air inlet angle 30° has the worst overall heat transfer performance.

Improving Flows in Misaligned Culverts

This study investigated different approaches to optimize flows in misaligned culverts. Structures aligned with the natural stream are always preferred, as misalignments cause a change of direction at the culvert inlet associated with lower performance and sedimentation and erosion problems. This optimal positioning can cause high financial costs and a flow optimization minimizing the associated problems could be a viable alternative. In this study, we used computational fluid dynamics analysis to evaluate the flow in 44 different scenarios with misalignment angles ranging from 0 ∘ –90 ∘ . It was found that smooth transitions towards the narrowest point in the stream (culvert) were possible for any degree of misalignment resulting in improved, uniform velocity distributions and less turbulence. An experimental setup was able to confirm the possible flow improvements. The proposed approach of flow redirection can lower construction costs and gives planners and designers more flexibility as tailored reinforcement and redesign of the stream embankment can be used as an alternative to costly creek alignments.

Influence of confining wall on pressure drop and particle-to-fluid heat transfer in packed beds with small D/d ratios under high Reynolds number

The presence of the confining wall exerts critical influences on packing structure, as well as transport properties of packed beds with small D/d ratios. In the present work, the variations of pressure drop and particle-to-fluid convective heat transfer in the packed beds of strong wall interference were evaluated under the high Reynolds number regime (Rem ∼ 104) by using the CFD simulation combined with the DEM method for random packing generation. The variations upon the D/d ratios were discussed, and the applicability of empirical correlations was examined. It found that the lower D/d ratios, the lower pressure drop and heat transfer performance, and the Carman correlation and the Wakao correlation provided predictions of better accuracy for the two parameters respectively than the other empirical correlations. Then, the discussion was extended to the packing structure and fluid flow distribution. A packed bed with distinct features—the quasi-regular packed bed—was encountered at D/d = 4, in which the packing structure regularity from the wall extents over the entire bed. Accordingly, much uniform flow velocity and temperature distributions were observed in the bed. Finally, some literature results in the range of 1 < D/d < 4 were revisited in conjunction with the present findings to reach a complete picture of the confining wall influence on the packing structure and related transport properties. It suggests that the studies for packed beds in the range of D/d < ∼ 4 should be isolated from the other packed beds of higher D/d ratios and the related analysis should be developed on a case-by-case basis. These findings may provide a new perspective to address the confining wall influence in packed beds with small D/d ratios.

The velocity distribution of a cutting microchannel plate based on the resistance network method

Velocity distribution has a very important influence on the performance of microchannel devices. In this paper, a cutting microchannel plate was proposed, and the velocity distribution was investigated based on the resistance network method. The results showed that the asymmetric cutting microchannel plate had the most uniform velocity distribution. Finally, the optimal results were further confirmed via ANSYS Fluent simulation and the heat and mass transfer efficiencies were also investigated. Taken together, the present findings provide direct evidence that uniform velocity distribution results in the higher performance of microchannel devices.

Numerical study of fluid behavior on protruding shapes within the inlet part of pressurized membrane module using computational fluid dynamics

This study analyzes the velocity and pressure incurred by protruding shapes installed within the inlet part of a pressurized membrane module during operation to determine the fluid flow distribution. In this paper, to find the flow distribution within a module, it investigates the velocity and pressure values at cross-sectional and outlet planes, and 9 sections classified on outlet plane using computational fluid dynamics. From the Reynolds number (Re), the fluid flow was estimated to be turbulent when the Re exceeded 4,000. In the vertical cross-sectional plane, shape 4 and 6 (round-type protrusion) showed the relatively high velocity of 0.535 m/s and 0.558 m/s, respectively, indicating a uniform flow distribution. From the velocity and pressure at the outlet, shape 4 also displayed a relatively uniform fluid velocity and pressure, indicating that fluid from the inlet rapidly and uniformly reached the outlet, however, from detailed data of velocity, pressure and flowrate obtained from 9 sections at the outlet, shape 6 revealed the low standard deviations for each section. Therefore, shape 6 was deemed to induce the ideal flow, since it maintained a uniform pressure, velocity and flowrate distribution.

Optimized design of a novel filter brick in denitrification deep-bed filter.

Denitrification deep-bed filter has been widely applied in the field of advanced wastewater treatment, yet its efficient operation is highly dependent on the filter bricks-controlled water and air distribution system. Considering the restrictions of existing bricks such as poor hydraulic properties and large non-working area during backwashing, a cuboid novel filter brick with two internal distribution chambers was designed and its hydraulic behaviors under three conditions (air washing, water and air joint backwashing, water washing) were simulated using computational fluid dynamic (CFD) analysis. Results showed that the uniformity of fluid velocity distribution was better than that of the conventional brick under two hydraulic conditions, especially in water and air joint backwashing process with a 10% promotion of water and air distribution uniformity. Furthermore, a 30-day engineering validation test was also carried out to testify the actual performance of the novel filter brick. Better performance was testified in the filters with novel bricks. The present study showed that the novel filter brick had a better uniformity of water and air distribution and smaller dead zone area than those of the conventional brick, implying a good feasibility of application in denitrification deep-bed filter.

Qualitative analysis of coupling effect of fluid velocity distribution in microchannels on the performance of the LED water cooling system

PurposeThe purpose of this paper is to ensure adequate thermal management to remove and dissipate the heat produced by a light-emitting diode (LED) and to guarantee reliable and safe operation.Design/methodology/approachA three-dimensional (3-D) computational fluid dynamics (CFD) model was used to analyze the distribution of fluid velocities among microchannels at four different aspect ratios.FindingsThe results showed that at the same inlet flow rate, the larger the aspect ratio of the microchannels, the better the uniformity of the internal fluid velocity and thus better the heat dissipation performance on the surface of the high-power LED chip. In addition, the thermal performance of a high-power LED water cooling system with four different aspect ratios’ microchannel structures is further studied experimentally. Specifically, the coupling effect between the fluid velocity distribution in the microchannels and the heat dissipation performance of a high-power LED water cooling system is qualitatively analyzed and compared with the simulation results of the fluid velocity distribution. The results fully demonstrated that a larger aspect ratio of the microchannels results in better heat dissipation performance on the surface of the high-power LED chip.Originality/valueOptimizing the structural parameters to facilitate a relatively uniform velocity distribution to improve the water cooling system performance may be a key factor to be considered.