Uniform Velocity Distribution Research Articles

Numerical and Experimental Study on Enhancing Performance of the Stand Fan

To meet humans’ need of enhancing the quality of life, the high-performance stand fan has become an essential appliance in every family. On the other hand, energy saving can not only solve the problem of environment protection, but also can reduce the cost of energy consumption. However, the aerodynamic performance and flow characteristics of the stand fan are rarely investigated and analyzed in a systematical manner. Therefore, this research intends to investigate the physical mechanism of the flow pattern and identify the design parameters of the stand fan by combining numerical and experimental methods. First of all, both the structure and performance of a commercial 14-inch stand fan are chosen for analysis and are set as the reference for the fan. The stand fan can be divided into the impeller and the protective cover. Clearly, the impeller blades have a great influence on the fan performance, so they are the first design target. In this work, CFD (computational fluid dynamics) software Fluent (version 14.5, ANSYS Inc., Canonsburg, PA, USA, 2012) is used to analyze and observe the corresponding influences on flow fields and aerodynamic performance by changing the design parameters such as the setting, twist, and inclination angles. Then, the protective cover is studied, improved and integrated with the designed impeller to further enhance the performance of the fan. The protective cover is modified by varying the spacing between the blade tip and cover, as well as varying the shape and angle of ribs to improve the fan’s flow field and performance. Finally, the optimal fan mockup is made via CNC (computer numerical control) technology. Also, its acoustics and performance have been measured to validate the accuracy and reliability of the numerical simulation. The testing results show that the optimally designed stand fan is better than the reference fan with a significant 54% increase in max flow rate. In addition, it has more uniform velocity distribution compared with the reference fan to achieve a comfortable feeling for the human body. In summary, this research successfully establishes a reliable and systematic scheme to design the stand fan. Also, the corresponding performance influences caused by those important parameters are analyzed and summarized to serve as the design reference for the stand fan.

Thermal influences in the star-pre-distributor of a spiral mandrel die

Abstract The main criterion in the design of extrusion dies is to ensure a uniform velocity distribution of the plastics melt at the die outlet. In the case of spiral mandrel dies, the flow balance can be influenced negatively by thermal effects which are especially dominant in the pre-distributor. In previous works, it was shown that thermal inhomogeneity in a 2n-pre-distributor leads to an uneven melt distribution at the end of the pre-distributor. In the present study, the temperature influence on the melt distribution in a star-pre-distributor is investigated for three different polyethylenes with the help of flow simulations in Polyflow (Ansys). The simulation model depicts the whole pre-distributor and takes both the shear heating in the melt and the heat conduction in the pre-distributor into account. The simulative analysis shows that the dissipative shear heating leads to an uneven throughput distribution in the star-pre-distributor. In order to compensate this effect, in the next step of the simulations, heating cartridges are applied to the pre-distributor. In this way a significant homogenization of the pre-distribution can be achieved.

Isothermal modeling of aerodynamic structure of the swirling flow in a two-stage burner

The work deals with the experimental study of the aerodynamic structure of a swirling flow in the isothermal model of two-stage vortex combustion chamber. The main attention is focused on the process of flow mixing of two successively connected tangential swirlers of the first and second stages of the working section. Data on flow visualization are presented for two patterns of flow swirling. Time-averaged profiles of the axial and tangential velocity components are obtained with the help of laser-Doppler anemometer. In the case of flow co-swirling between two stages of the working section, instability of a secondary flow in the form of precessing vortex was distinguished. For the regime with counter flow swirling, effective mixing of the swirl flows was found; this was reflected by formation of the flow with uniform distribution of axial velocity over the cross-section.

Optimized design for heavy mound venturi

The venturi scrubber is one of the most efficient gas cleaning devices for removal of contaminating particles in industrial flue-gas purification processes. The velocity of the gas entering the scrubber is one of the key factors influencing its dust-removal efficiency. In this study, the shapes of the heavy mound and tube wall are optimized, allowing the girth area to become linearly adjustable. The resulting uniformity of velocity distribution is verified numerically.

Influence of die geometric structure on flow balance in complex hollow plastic profile extrusion

The unbalanced flow problem often occurs at die exit in the extrusion process of plastic profile, which directly influences the performance of final products. For the lack of corresponding theoretical basis, reasonable extrusion die design is still a difficult task, especially for the complex hollow profile. With the development of computational fluid dynamics theory, numerical method becomes an effective way to investigate the complex material forming problems. In the present study, a design strategy for complex hollow profile extrusion die was proposed based on the principles of flow balance. The mathematical model for three-dimensional non-isothermal polymer melt flow within complex extrusion die runner was developed based on the computational fluid dynamics (CFD) theory. The governing equations were deduced based on the finite volume method, and the pressure-velocity coupling problem was solved by using the Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) algorithm. The Arrhenius equation was employed to involve the temperature dependence of material parameters. The flow characteristics of PVC polymer melts in the extrusion process of complex hollow profile were investigated. The distributions of principal field variables including flow velocity, melt temperature, and pressure drop were obtained. The effects of die geometric parameters on the velocity distribution uniformity were further analyzed, and a design strategy was proposed to achieve the flow balance in complex plastic profile extrusion process.

Research on the performance of low-lift diving tubular pumping system by CFD and Test

Post-diving tubular pump is always used in large-discharge & low-head irrigation or storm drainage pumping station, its impeller and motor share the same shaft. Considering diving tubular pump system's excellent hydraulic performance, compact structure, good noise resistance and low operating cost, it is used in Chinese pump stations. To study the hydraulic performance and pressure fluctuation of inlet and outlet passage in diving tubular pump system, both of steady and unsteady full flow fields are numerically simulated at three flow rate conditions by using CFD commercial software. The asymmetry of the longitudinal structure of inlet passage affects the flow pattern on outlet. Especially at small flow rate condition, structural asymmetry will result in the uneven velocity distribution on the outlet of passage inlet. The axial velocity distribution uniformity increases as the flow rate increases on the inlet of passage inlet, and there is a positive correlation between hydraulic loss in the passage inlet and flow rate's quadratic. The axial velocity distribution uniformity on the outlet of passage inlet is 90% at design flow rate condition. The predicted result shows the same trend with test result, and the range of high efficiency area between predicted result and test result is almost identical. The dominant frequency of pressure pulsation is low frequency in inlet passage at design condition. The dominant frequency is high frequency in inlet passage at small and large flow rate condition. At large flow rate condition, the flow pattern is significantly affected by the rotation of impeller in inlet passage. At off-design condition, the pressure pulsation is strong at outlet passage. At design condition, the dominant frequency is 35.57Hz, which is double rotation frequency.

Flow field design and process stability in electrochemical machining of diamond holes

The metal grille, commonly composed of an amount of diamond holes, has been growingly used as a key structure on stealth aircraft. Electrochemical machining (ECM) promises to be increasingly applied in aircraft manufacturing on the condition that process stability is guaranteed. In this work, a flow field model was designed to improve the process stability. This model is endowed with a variety of flow channel features, together with vibrating feeding modes. The flow field distribution on the bottom surface of the diamond hole was discussed and evaluated as well. The numerical results show that a short arc flow channel could significantly enhance the uniformity of electrolyte velocity distribution and a vibrating feeding of the cathode enables to reduce both fluctuations of the electrolyte velocity and pressure on the bottom surface of the diamond hole. Consequently, the flow field mutations were eliminated. It is verified from the experimental results that a short arc flow channel, when combined with vibrating feeding, is capable of improving machining localization and process stability markedly. What is more, the side gap on the bottom surface of the diamond hole could also be reduced by the abovementioned approach.

Numerical simulation study on air quality in aircraft cabins

Air pollution is one of the main factors that affect the air quality in aircraft cabins, and the use of different air supply modes could influence the distribution of air pollutants in cabins. Based on the traditional ceiling air supply mode used on the B737NG, this study investigated another 3 different kinds of air supply modes for comparison: luggage rack air supply mode, joint mode combining ceiling and luggage rack air supply, and joint mode combining ceiling and individual air supply. Under the above 4 air supply modes, the air velocity, temperature and distribution of air pollutants in a cabin full of passengers were studied using computational fluid dynamics (CFD), and carbon dioxide (CO2) and formaldehyde were selected as 2 kinds of representative air pollutants. The simulation results show that the joint mode combining ceiling and individual air supply can create a more uniform distribution of air velocity and temperature, has a better effect on the removal of CO2 and formaldehyde, and can provide better air quality in cabins than the other 3 modes.

Comparison of the thermal behaviors and pollutant emissions of pelletized bamboo combustion in a fluidized bed combustor at different secondary gas injection modes

Staged combustion significantly affects the complete combustion of biomass and reduces pollutant emissions. This study primarily aimed to compare the thermal behaviors and pollutant emissions of different secondary gas injection modes in a pilot-scale fluidized bed combustor (FBC). Pelletized thorny bamboo was used as the fuel, and silica sand was used as the bed material. Flue gas recirculation (FGR) was employed. The experimental results demonstrate that the secondary gas injection modes in the FBC affected the combustion characteristics. The temperature of pelletized bamboo combustion with tangential injection mode (T mode) was lower than that of centripetal injection mode (C mode); however, T mode produced lower CO and NOx emissions than C mode because of the well-swirling effect. The secondary gas velocity and airflow distribution uniformity in the secondary gas layers jointly affect combustion, while T mode with four nozzles or C mode with two nozzles is optimal to reduce emissions. Furthermore, increasing the elevation of secondary air further reduces NOx emissions in C mode but does not significantly affect emissions in T mode.

Dispersion of indoor air pollutants emitted at near-floor levels in rooms with floor heating and mixing ventilation

The usage of floor heating is increasing in low-energy buildings as it enables efficient applications of low-exergy level heat sources as well as provides a uniform distribution of air temperature and low air velocities in heated spaces. The aim of this study was to analyse the effects of floor heating on the dispersion of gaseous pollutants emitted at the floor level, considering that carpets and flooring materials can be sources of such pollution. Mixing ventilation with high-level wall grille air supply and in-ceiling four-way air supply was tested numerically and experimentally in the full-scale chamber at the air change rate of 2 h−1. Three positions of a heated dummy in relation to the pollution source, cold surface and air supply diffusers were analysed. Both experiments and CFD predictions revealed the overall positive effect of floor heating on ventilation effectiveness and personal exposure. Floor heating increased pollutant removal effectiveness by 5% and reduced personal exposure by 22% on average.

Meridional shape design and the internal flow investigation of centrifugal impeller

This paper describes an inverse design method for calculating the shape of meridional plane of centrifugal impeller. This design method permits the shroud and hub contours to be indirectly calculated by medial axis contour and constraint equations. The design process is computationally inexpensive and can conveniently modify the shroud and hub shapes as the design’s demand. Based on this design method, new constraint equations are used for a new shape design of meridional plane that lead to a uniform velocity distribution in the inlet of impeller. Numerical simulations are employed to investigate the fluid flows of centrifugal fan. After validation of the numerical strategy, the pressure and velocity distributions in centrifugal fan are illustrated. The numerical results show that the inlet performance is improved and the velocity distribution is more uniform. Furthermore, in order to understand the flow mechanism inside the centrifugal fan, the secondary flow in the blade passage and velocity distribution at the shroud and hub have been carried out a detailed investigation and study.

Extrusion Process Parameters Optimization for the Aluminum Profile Extrusion of an Upper Beam on the Train Based on Response Surface Methodology

Extrusion process parameters play key roles in aluminum profile extrusion processes. In this literature, by using Box-Behnken experimental design to arrange the simulations using the ALE software HypereXtrude, Response Surface Methodology (RSM) were applied to study the simulation results and discuss the effects of five process parameters, namely billet diameter, billet preheat temperature, die temperature, container temperature, and ram speed, on the outlet velocity distribution uniformity of the profile named an Upper beam on the Train. The interactions between the five parameters also were investigated. Additionally, a second order response surface model between the extrusion process parameters and the evaluation criterion of outlet velocity uniformity was established. An optimization of the process parameters with the purpose to find the most uniform outlet velocity distribution was carried out based on the response surface model. The results show that the three parameters, namely billet diameter, ram speed and die temperature, have significant impact on the outlet velocity uniformity. And there are obvious interactions between these three parameters. After the subsequent optimizations, a more uniform outlet velocity distribution was obtained, and the final acceptable profiles were produced.

Simulation of air velocity in a vertical perforated air distributor

Perforated pipes are utilized to divide a fluid flow into several smaller streams. Uniform flow distribution requirement is of great concern in engineering applications because it has significant influence on the performance of fluidic devices. For industrial applications, it is crucial to provide a uniform velocity distribution through orifices. In this research, flow distribution patterns of a closed-end multiple outlet pipe standing vertically for air delivery in the horizontal direction was simulated. Computational Fluid Dynamics (CFD), a tool of research for enhancing and understanding design was used as the simulator and the drawing software SolidWorks was used for geometry setup. The main purpose of this work is to establish the influence of size of orifices, intervals between outlets, and the length of tube in order to attain uniformity of exit flows through a multi outlet perforated tube. However, due to the gravitational effect, the compactness of paddy increases gradually from top to bottom of dryer, uniform flow pattern was aimed for top orifices and larger flow for bottom orifices.

Comparison of hydraulics and particle removal efficiencies in a mixed cell raceway and Burrows pond rearing system

We compared the hydrodynamics of replicate experimental mixed cell and replicate standard Burrows pond rearing systems at the Dworshak National Fish Hatchery, ID, in an effort to identify methods for improved solids removal. We measured and compared the hydraulic residence time, particle removal efficiency, and measures of velocity using several tools. Computational fluid dynamics was used first to characterize hydraulics in the proposed retrofit that included removal of the traditional Burrows pond dividing wall and establishment of four counter rotating cells with appropriate drains and inlet water jets. Hydraulic residence time was subsequently established in the four full scale test tanks using measures of conductivity of a salt tracer introduced into the systems both with and without fish present. Vertical and horizontal velocities were also measured with acoustic Doppler velocimetry in transects across each of the rearing systems. Finally, we introduced ABS sinking beads that simulated fish solids then followed the kinetics of their removal via the drains to establish relative purge rates. The mixed cell raceway provided higher mean velocities and a more uniform velocity distribution than did the Burrows pond. Vectors revealed well-defined, counter-rotating cells in the mixed cell raceway, and were likely contributing factors in achieving a relatively high particle removal efficiency-88.6% versus 8.0% during the test period. We speculate retrofits of rearing ponds to mixed cell systems will improve both the rearing environments for the fish and solids removal, improving the efficiency and bio-security of fish culture. We recommend further testing in hatchery production trials to evaluate fish physiology and growth.

Study of aerodynamic performances of different wind tunnel configurations and air inlet velocities, using computational fluid dynamics (CFD)

Livestock and agricultural activities contribute significantly to atmospheric ammonia emission in Europe. The volatilization process depends on many factors, especially wind speed and rainfall. The most important methods to evaluate ammonia volatilization are the wind tunnel and micrometeorological methods. The tunnels are more flexible and simple to use in every situation. Few studies have been carried out to determine, which conditions are established inside the chamber and how they influence the ammonia volatilization and measurement.The aim of this research was to investigate the effects of the wind tunnel configuration and flow inlet velocity, by means of CFD simulations and wind speed measurements, in order to achieve a better aerodynamic performance. The SST k–ω model used for simulations was first validated in order to prove the consistency of the model itself. Several configurations were simulated and compared. In particular, in order to overcome the asymmetric flow conditions that occurred in all wind tunnel configurations, four flow distribution devices were proposed and simulated. The best setup was chosen with the purpose of reaching both the best uniform velocity distribution (to ensure homogeneous volatilization from the emitting surface) and easy transport for field applications. It consists of an emission chamber 40cm wide, 25cm high and 80cm long, situated between a divergent diffuser and a convergent duct, respectively 50cm and 25cm long. Moreover, structures similar to honeycombs, namely guiding channels, were introduced in the divergent diffuser, because they showed the best aerodynamic performance. These 20 channels, located in the divergent diffuser, prevent flow from separating, by means of the reduction of the expansion angle, obtaining the desired flow conditions inside the wind tunnel. Finally, it was verified that CFD confirmed its usefulness as a decision-support instrument to design and simulate possible solutions, reducing design time.

Design of an outdoor stacked – tubular reactor for biological hydrogen production

Photofermentation is one alternative to produce hydrogen sustainably. The photobioreactor design is of crucial importance for an economically feasible operation, and an optimal design should provide uniform velocity and light distribution, low pressure drop, low gas permeability and efficient gas–liquid separation. A glass, stacked tubular bioreactor aimed at satisfying these criteria has been designed for outdoor photofermentative hydrogen production by purple non sulfur bacteria. The design consists of 4 stacked U-tubes (tube diameter 3 cm) and 2 vertical manifolds. The hydrodynamics of the 3-dimensional model of this reactor was solved via COMSOL Multiphysics 4.1. The effects of tube length (1.4, 2.0, 3.8 m), tube pitch (8, 10.5, 13 cm) and volumetric flow rate (25–250 L/h) on the flow distribution were investigated. The glass stacked tubular reactor design results in less ground area and longer life time. This design has been constructed and operated with using Rhodobacter capsulatus YO3 hup− and molasses as the carbon source under outdoor conditions.

Scale-up of high power density redox flow batteries by introducing interdigitated flow fields

Lab-scale redox flow batteries (RFBs) employing thinner electrodes have achieved outstandingly high power densities. When these high-performance thinner electrodes are scaled up to larger sizes required for kW-scale stacks, adding interdigitated flow fields is a simple solution in maintaining low pressure drops. A 3-D model of a half-battery with an active area of 900cm2 was developed to explore the design rules of flow fields. Optimizing the number and size of channels is essentially striking a balance between the pressure drop and the electrolyte velocity in the electrode, which have important effects on the pumping loss and mass transport loss respectively. In addition to the magnitude of the average velocity, the uniformity of velocity distribution should also be paid attention to in designing flow fields, which is determined by the ratio of flow resistance in the electrode to that in the channels. Acceptably thicker channels are recommended to improve uniformity of velocity distribution.

Achieving quasi-adiabatic thermal environment to maximize resolution power in very high-pressure liquid chromatography: Theory, models, and experiments

A cylindrical vacuum chamber (inner diameter 5cm) housing a narrow-bore 2.1mm×100mm column packed with 1.8μm HSS-T3 fully porous particles was built in order to isolate thermally the chromatographic column from the external air environment. Consistent with statistical physics and the mean free path of air molecules, the experimental results show that natural air convection and conduction are fully eliminated for housing air pressures smaller than 10−4Torr. Heat radiation is minimized by wrapping up the column with low-emissivity aluminum-tape (emissivity coefficient ϵ=0.03 vs. 0.28 for polished stainless steel 316). Overall, the heat flux at the column wall is reduced by 96% with respect to standard still-air ovens. From a practical viewpoint, the efficiency of the column run at a flow rate of 0.6mL/min at a constant 13,000psi pressure drop (the viscous heat power is around 9W/m) is improved by up to 35% irrespective of the analyte retention. Models of heat and mass transfer reveal that (1) the amplitude of the radial temperature gradient is significantly reduced from 0.30 to 0.01K and (2) the observed improvement in resolution power stems from a more uniform distribution of the flow velocity across the column diameter. The eddy dispersion term in the van Deemter equation is reduced by 0.8±0.1 reduced plate height unit, a significant gain in column performance.

Numerical Analysis of Compact Heat Exchanger for Flow Distribution

Background/Objectives: The common assumption made in basic heat exchanger design is that the fluid to be distributed uniformly at the inlet of the exchanger on each fluid side and throughout the core. But in actual practice it doesn’t happen. Thus the main objective of this paper is to reduce the non uniformity in the flow of fluid in compact heat exchanger form the header tube to the lateral tube. Methods/Statistical Analysis: In this work, the flow mal-distribution of heat exchanger at different cross-sectional headers like circular, rectangular, square and triangular header with various flow rates ranging from Re 1000 to 20000 is analyzed. Numerical models and boundary conditions used in the analyses are validated against experimental data. Following the validated procedure, three-dimensional CFD analyses are carried out to study the effect of geometrical variation of headers on flow distribution. For each geometrical variation, analysis is continued till the trend of behavior of flow distribution is completely understood. The results are analyzed to reach the optimum configuration with each variation. Findings: For all the four types of header cross section and for various inlet mass flow rates, the triangular header produces more uniform distribution. With low pressure drop in triangular cross section, the velocity distribution is uniform. Because of uniform velocity distribution in the header the flow maldistribution is minimum in heat exchanger with triangular cross sectional header. Triangular header shows 77%, 45%, and 70% less flow maldistribution when compared to circular, square and rectangular headers respectively. Application/Improvements: Development in the field of renewable energy had made a great revolution in the usage of solar flat plate water heater in each and every home. Implement of this triangular shaped header cross in the core tube of flat plate collector, would increase the efficiency of solar flat plate water heater, which would ultimately improve its usage among the people. Keywords: CFD, Fluent, Flow Maldistribution, Heat Exchanger

DEM simulation of particle descending velocity distribution in the reduction shaft furnace

Reduction shaft furnace is a promising alternative to blast furnace ironmaking. The particle descending velocity distribution has a great influence on the shaft furnace, which directly affects the production index and further the shaft furnace normal smelting. Therefore, a three-dimensional model (3D) is established based on the discrete element method (DEM) and computation fluid dynamic (CFD). The effect of the gas flow in the shaft furnace, the height, the diameter and the bosh angle of the shaft furnace on the particle descending velocity distribution during discharging process is investigated by the model and analyzed based on the granular dynamic theory and Janssen theory. The results show that the particle velocity reduces along the radius. The effect of the gas flow on the velocity distribution is insignificant. In order to obtain a uniform velocity distribution, it is better to increase the height, or the diameter, or to decrease the bosh angle. An improved model is proposed for the uniform velocity distribution at last.