Uniform Velocity Distribution Research Articles

A Study on the Flow Characteristics According to the Structure Change of Filtration in a Pressurized Type Filtration System Using Numerical Model

In this study, a prototype was constructed and a field experiment was conducted to develop the water supply system that can purify polluted water quickly and efficiently. As a result of water quality analysis on the filtered water treated by a prototype, it could be used for living water, graywater and drinking water. There is the pressurized type filtration system that plays an important role in the water supply and production system. A filtration filter in the pressurized type filtration system absorbs pollutants and produces clean water. Filtration filter that can filter out contaminants is closely related to flow phenomena. Since it is impossible to observe in the vicinity of the filtration filter, the flow phenomenon is analyzed using CFX model. As the inner structure of the filtration was changed, the flow phenomenon in the filtration filter was examined. After changing the angle of the filter plate inside the filtration from 15º to 20º, the velocity distribution was analyzed. The standard deviation was reduced from 0.0575 to 0.0154. A uniform flow velocity distribution was formed around the filter. As a result, filtration efficiency is expected to increase. Keywords: Water Supply System, Pressurized Type Filtration System, Filtration, Filtration Filter, 3D Numerical Method, CFX

Experimental study on the characteristics of secondary airflow device in a large enclosed space building

Large space building using side wall nozzle air-conditioning system may result in poor ventilation effectiveness for positions out of the reach of primary supply air. A secondary airflow device is proposed to be applied in such system to improve the uniformity of temperature and velocity distribution in the occupied zone under cooling condition. The characteristics of the secondary airflow device, including central-line velocity decay and jet trajectory model were investigated through experiments to provide fundamental data for the system design. The indoor thermal environment parameters were measured and compared between with and without the secondary airflow device system in a large space factory workshop conditioned by side wall air supply nozzles. Experimental results with the secondary airflow device showed that the vertical thermal stratification height slightly changed, with lower air temperature in unoccupied zone and higher temperature in occupied zone comparing to the cases without secondary airflow device. At occupied level, air diffusion performance index (ADPI) significantly improved, while the percentage dissatisfied (PD) due to draught decreased in the occupied zone. Air velocity uniformity at occupied level also significantly increased. The results of this study provide an exemplary reference for the design of the air distribution system in large-space buildings.

Application of nanofluid to improve the thermal performance of horizontal spiral coil utilized in solar ponds: Geometric study

Abstract Today, one of the most common methods for heat extraction from the solar ponds is using spiral piping system. In this study, effects of nanofluid concentrations and different cross-sections of tube on thermal performance of horizontal spiral-coil in laminar fluid flow are investigated numerically. Water-graphene nanoplatelet/platinum hybrid nanofluid with 0.02, 0.06 and 0.10% volume concentration has used as working fluid. Simulations are performed for different mass flow rates between 0.0005 and 0.005 kg/s. Different shapes including rectangle, elliptic, trapezoid and circle are selected as tube cross-sections. Uniform temperature and velocity distributions with several mass flow rates are applied to geometry at inlet and constant wall temperature as boundary conditions. The results show that variations of average Nusselt number in lower mass flow rates is not dependent to the shape of flow cross-section. By increasing the nanoparticles concentration, the highest Nusselt number belongs to tube with elliptical cross-section. Surfaces with angular corners create greater velocity variations in comparison with surfaces with curved corners and this behavior leads to higher pressure loss as well as more pumping power. Also, by increasing mass flow rate, the heat transfer between hot surfaces and cooling fluid is enhanced. The highest and lowest values of outlet temperature are reported for fluid with highest solid nanoparticle volume concentration and distilled water, respectively. Among the considered mass flow rates in φ = 0.06 and 0.10%, mass flow rate of 0.002 kg/s has the highest thermo-fluid efficiency.

A new approach to mitigate intense temperature gradients in ceramic foam solar receivers

Abstract The present study aims to present an approach to mitigate the maximum solid temperature and its gradient inside the porous material in volumetric solar receivers. To this end, a porous receiver with non-uniform air velocity at the inlet is considered in the present study. Comparison of the results with those obtained for a porous receiver with uniform air velocity at the inlet reveals the ability of the new velocity distribution in reducing the maximum solid temperature and its gradient within the solid phase. The temperature distribution is obtained for different porosities and pore diameters in the porous receivers with uniform and non-uniform air velocity distributions at the inlet. It is observed that the proposed distribution of air velocity at the inlet decreases the maximum solid temperature within the porous receiver even for small porosities and pore diameters of porous media.

Optimal design and performance analysis of hydraulic ram pump system

Hydraulic ram pump is an automatic water-pumping equipment generally used to pump drinking and irrigation water in mountainous and rural areas having short of power. In the past, it has been analyzed and optimized by fabricating various prototypes and conducting experiments and comparisons. This process is time and labor consuming and detailed flow features cannot be determined except efficiency, discharge, and period. In this paper, a method for the optimal design and performance analysis of hydraulic ram pump system with numerical simulation and physical experiment is presented to shorten the number of prototypes and develop high-performance product. The proposed evaluation indexes include head loss coefficient, drag coefficient, eccentric distance of pressure, and velocity distribution uniformity. Two types of structures, named front-enlargement and back-enlargement, were initially designed. According to the numerical simulation, the latter one has lower head loss coefficient and drag coefficient, larger eccentric distance of pressure and higher velocity distribution uniformity and was adopted in the novel hydraulic ram pump. Then, the design theory and method on adjustable and high-head experimental platform have been developed, so that the delivery head can be easily controlled and regulated in laboratory. Experiments were carried out for the delivery heads of 2.0 m and 2.7 m and comparisons were conducted with other products. The results show that, when the delivery head is less than 50 m, the efficiency of the new product ranges from 50% to 70% while the delivery flow is the largest. Its application in Liangshui River, Beijing, indicates that the novel hydraulic ram pump is a practical tool in fountain sight and for irrigation purpose without external power input.

Investigation of discharge coefficient for wind-driven naturally ventilated dairy barns

It is important to estimate the ventilation rate of animal houses accurately for the purpose of reducing emissions and providing comfortable indoor climate. The orifice equation is widely applied for estimating the airflow rate of naturally ventilated dairy barns. However, to regard openings’ discharge coefficient (Cd) as a constant maybe not true for large openings. To gain basic knowledge of the opening size effects on Cd values, experiments with a scaled model were carried out in a large boundary layer wind tunnel. Seven cases with different sidewall opening ratios, varying from 18.6% to 81.4%, were investigated under 8 m/s wind speed conditions. The airflow rates, Cd values of windward openings and airflow patterns were analysed. It was found that the Cd value was considerably dependent on the opening size and varied from 0.67 to 0.94 when the opening ratio increased from 18.6% to 62.7%. This is due to the assumptions of pure pressure-driven flow and uniform velocity distributions in the opening were not satisfied for large opening cases. Our study suggests that Cd should be regarded as a variable under different opening size conditions when using the orifice equation to determine the airflow rate of large openings.

Experimental and Numerical Investigations of a Dual‐Stage Cyclone Separator

AbstractCyclone separators can be utilized in parallel to increase particle collection efficiency. However, this leads to a maldistribution problem that causes separation performance deterioration. To improve the flow distribution, a dual‐stage multicyclone separator (DSCS) was designed, containing a tangential‐inlet circle pathway cyclone array, an axial‐inlet radiation pathway cyclone array, and a cylindrical outer chamber. Experimental and computational fluid dynamics results revealed the gas‐particle flow distribution through multicyclone arrays. Effects of flow distribution on particle deposition were investigated experimentally. Particle trajectories inside the cyclone separators were also observed. The multicyclone array proved to generate a uniform inlet velocity distribution. The proposed cyclone separator can be considered as an option to accomplish dilute gas‐particle separation.

Reforming the Exhaust Passage of Low-pressure Cylinder for 330MW Steam Turbine

In concern of the velocity distribution of the exhaust passage of 330MW turbine is not uniform, which results in higher the upper temperature difference of the condenser and higher exhaust pressure. It is introduced in this article that based on mathematical simulation, steam-equalizing equipment is augmented at the exhaust area of the condenser which makes the decrease in the steam resistance, much more uniform velocity distribution, and the increase of the heat transfer coefficient. By comparison of the condenser performance test before the amending and after, the result shows that after the amending, the upper temperature difference of the condenser and the exhaust pressure decreases dramatically.

Effect of a Nonuniform Radial/Axial Tip Clearance on the Flow Field in a Mixed-Flow Pump

The effect of a nonuniform radial/axial tip clearance on the flow field in a mixed-flow pump was studied by numerical simulation of the unsteady flow in the pump with two tip clearance shapes using the standard Reynolds average Navier–Stokes turbulence model, and the equations were solved with the SIMPLEC computational algorithm. The external characteristics, distribution of static pressure, streamline flow of the tip clearance, and vorticity in the impeller are analyzed. The accuracy of numerical simulation was assessed by comparing experimental data with computational results. Although a nonuniform tip clearance leads to a decline in the pump head, which is more pronounced under part-load conditions, the configuration with a nonuniform tip clearance (c = 0.5–1 mm) provides the more uniform velocity and pressure distribution both in the circumferential and axial directions, as the leakage vortex intensity is weakened and its shedding is suppressed. The research results pointed the way for improving the unsteady flow in the mixed-flow pump.

2006A-G3-24 回流水槽の水面近傍流速の均一性改良について(一般講演(G3))

2006A-G3-24 回流水槽の水面近傍流速の均一性改良について(一般講演(G3))

Optical polishing process: Analysis and optimization using response surface methodology (RSM) for large diameter fused silica flat substrates

The skill dependent optical polishing process remains elusive due to unaccounted parameters and uncertainties. Deterministic relations for surface quality of polished optics have been developed in this paper by analysis and optimization of three significant input parameters: abrasive concentration, relative velocity and abrasive size. Average roughness value (Ra), measured on a surface profilometer: Talysurf PGI-120, indicated the response. MALVERN ZETASIZER was used to measure average size of abrasives using Dynamic Light Scattering principle. The parameter values have been computed in standard units for general relevance across different setups, a feature absent in earlier studies. Flat Fused Silica glass samples of 100mm diameter were polished for two hours on a conventional single arm spindle polisher with a polyurethane pad using Ceria slurry. Central Composite Design (CCD) of RSM was used for fitting a second order model. Kinematic analysis established the polishing spindle and sample rotation speeds to be equal for uniform velocity distribution. Relative velocity was the most significant input, followed by concentration. Surface and contour plots resulted in a domain of peak performance. Optimum combination (velocity 1054.8mm/s, abrasive size 8.5nm, concentration 2.45%) identified using desirability approach based on the second order regression model resulted in Ra value as low as 5.7nm, well within permissible error limits from the predicted value.

Investigation of the Blockage Conditions in a Laminated‐Sheet Microchannel Reactor

AbstractThe microchannel reactor is a generally adopted laminated‐sheet structure in which several microchannel sheets with the same or different structures are laminated together and tightened by welding or other connection methods into a single reaction unit. Uniform velocity distribution among the microchannels can improve the heat and mass transfer efficiency. When one or more microchannels are blocked, the uniformity of the velocity distribution is inevitably affected. In this work, the velocity distributions among the microchannels in a single‐sheet and a double‐sheet laminated structure are investigated under different blockage conditions. It is demonstrated in detail that the different blockage conditions in the microchannels and laminated structure display different effects on the velocity value, the shape of the velocity distribution, and the evaluation parameter for uniformity.

Lattice Boltzmann simulation of temperature jump effect on the nanofluid heat transfer in an annulus microchannel

In this study, laminar forced convection heat transfer of water-alumina nanofluid flow inside an annular microchannel in slip flow regime is investigated by lattice Boltzmann method. Uniform velocity and temperature distributions are assumed at the microchannel inlet. Internal wall is insulated and outer wall is heated uniformly with constant heat flux. In both models that are used to express the kinematic viscosity and thermal conductivity of the nanofluid, the effects of nanoparticles size and Brownian motion are considered. A lattice-Boltzmann computer code is developed and the results are compared with the existing analytical solutions in the literature. In this paper, the effect of various parameters such as nanoparticles volume fraction (0–0.05), diameter (10–100 nm), microchannel radius ratio (0.2–0.8), Reynolds number (5, 10 and 50) and the slip factor (0.005–0.1) on the flow and temperature field are studied. Furthermore, variations of slip velocity, temperature jump, friction factor and Nusselt number along the walls are provided. Results indicate that higher slip factor, radius ratio, Re and volume fractions and also smaller particle diameters, increases the Nusselt number. Also slip velocity and temperature jump increases with slip factor. Nanoparticles volume fraction doesn't have significant effect on slip velocity, while increases the temperature jump.

Velocity Uniformity of Microchannels in a Laminated‐Sheet Structure Under Parallel and Series Methods

AbstractAn integral microchannel device is generally formed by lamination of multiple microchannel sheets. Uniform velocity distribution among the microchannels in each sheet shows a large influence on the device's performance. The effects of microchannel and manifold structure on the velocity uniformity in each sheet with different structural parameters under parallel and series laminated structures are investigated. For the laminated‐sheet structure where each sheet has the same structural parameters, a more uniform velocity distribution exists as compared to where the structural parameters are different. There exists a direct correlation between the velocity values in each sheet and structural parameters, whereas an inverse correlation is found under series laminated structure.

The properties of dilute debris flow and hyper-concentrated flow in different flow regimes in open channels

Particle Image Velocimetry (PIV) technique was used to test the analogues of hyper-concentrated flow and dilute debris flow in an open flume. Flow fields, velocity profiles and turbulent parameters were obtained under different conditions. Results show that the flow regime depends on coarse grain concentration. Slurry with high fine grain concentration but lacking of coarse grains behaves as a laminar flow. Dilute debris flows containing coarse grains are generally turbulent flows. Streamlines are parallel and velocity values are large in laminar flows. However, in turbulent flows the velocity diminishes in line with the intense mixing of liquid and eddies occurring. The velocity profiles of laminar flow accord with the parabolic distribution law. When the flow is in a transitional regime, velocity profiles deviate slightly from the parabolic law. Turbulent flow has an approximately uniform distribution of velocity and turbulent kinetic energy. The ratio of turbulent kinetic energy to the kinetic energy of time-averaged flow is the internal cause determining the flow regime: laminar flow (k/K 1). Turbulent kinetic energy firstly increases with increasing coarse grain concentration and then decreases owing to the suppression of turbulence by the high concentration of coarse grains. This variation is also influenced by coarse grain size and channel slope. The results contribute to the modeling of debris flow and hyper-concentrated flow.

Large eddy simulation of compound angle hole film cooling with hole length-to-diameter ratio and internal crossflow orientation effects

Compound angle hole film cooling with varying length-to-diameter ratio and internal crossflow orientations is investigated by large eddy simulation (LES). The film density ratio is 1.5, and the blowing ratio ranges from 0.4 to 1.2. The compound angle of 45° and three length-to-diameter ratios (L/D) from 0.5 to 5 are chosen for the simulations. In addition to the vertical inflow through the plenum, internal crossflow orientations that are perpendicular to and parallel to the mainstream flow are investigated. The prediction accuracy is validated by the reported hydrodynamic data and present film effectiveness data measured by pressure sensitive paint (PSP). Results show that compound angle hole film effectiveness generally shows a decreasing trend as length-to-diameter ratio increases, which is contrary to the cylindrical hole. This is associated with the fact that length-to-diameter ratio influences the in-tube flow behavior, formation of Kelvin-Helmholtz (K-H) structures, and development of single asymmetric main vortex (SAMV). The internal crossflow orientation is demonstrated to have a significant effect on the in-tube flow behavior and the film cooling effectiveness. The perpendicular-counter flow and parallel-inline flow cases are found to provide more uniform hole exit velocity distributions than other internal crossflow orientations and vertical inflow case. Also found is that uniform hole exit velocity distribution provides favorable influence on the film effectiveness.

Performance evaluation of different air distribution systems in an aircraft cabin mockup

The purpose of this study was to evaluate the performance of different ventilation systems in an aircraft cabin mockup. The related experimental research was conducted to obtain the local mean age of air, temperature and velocity distribution under different air distribution systems by using trace gas, thermocouples, and an ultrasonic anemometer measurement system. The results showed that in a comprehensive comparison of mixing ventilation and displacement ventilation, displacement ventilation has high ventilation efficiency. The velocity nonuniformity indices (VNUI), temperature nonuniformity indices (TNUI), and heat removal efficiency (HRE) of different ventilation systems in the cabin were compared and analyzed. A cabin airflow evaluation system is proposed. Compared to the mixing air supply, the displacement ventilation has high heat removal efficiency, but it aggravates nonuniformity. Using a plurality of air inlets can improve the uniformity of air temperature and velocity distribution. Side wall air supply is necessary to improve the ventilation performance of single-aisle cabin.

Oxygen mass transfer and shear stress effects on Pseudomonas putida BCRC 14365 growth to improve bioreactor design and performance.

In this work, the experimental evidence is presented for two basic issues including oxygen mass transfer and shear analysis on the microorganism containing medium on the most prominent sections of the bioreactor. Computational fluid dynamics (CFD) methodology reproduces shear rate values for specific impeller designs using the commercial code (Fluent 6.2). CFD calculates volumetric mass transfer coefficient based on the Higbie's penetration theory. Four types of impeller are used. The spherical probe is used to measure flow hydrodynamic parameters to obtain shear rate by electro-diffusion (ED) method. The obtained results are validated experimentally and it is shown that a fully axial pattern impeller represents more enhanced results than partially axial and radial. In this regard, experimental results for volumetric oxygen mass transfer coefficient (k l a) confirm CFD predictions by acceptable deviations of 2.65, 8.90, and 9.20 for 0.15, 0.2, and 0.3 VVM, respectively. These results collaboratively indicate that LIGHTNIN-C 200 type operates more efficiently by reflecting the flow to the bottom corner stagnation areas with the minimum tolerable shear and the most velocity distribution uniformity. Furthermore, the values of k l a improve by aeration rate. Conversely, increasing the rotational speed of impeller creates difficulties for cell growth due to the generated harsh shear condition. CFD provide a better understanding of how operational and geometrical variables may be manipulated to achieve a moderate shear rate and acceptable level of mass transfer.

Design and simulation of a novel bipolar plate based on lung-shaped bio-inspired flow pattern for PEM fuel cell

Finding the optimal flow pattern in bipolar plates of a proton exchange membrane is a crucial step for enhancing the performance of the device. This design plays a critical role in fluid mass transport through microporous layers, charge transfer through conductive media, management of the liquid water produced in microchannels, and microporous layers and heat management in fuel cells. This article investigates different types of common flow patterns in bipolar plates while considering a uniform pressure and velocity distribution as well as a uniform distribution of reactants through all the surfaces of the catalyst layer as the design criteria so that there would be a consistent electron production by the catalyst layer. Then, by identifying the important parameters in achieving the best performance of a fuel cell, a microfluidic flow pattern is inspired from the lungs in the human body, and an innovative bipolar plate is suggested, which was not proposed before. Afterwards, numerical simulations were carried out using computational fluid dynamics methods, and the mentioned bipolar plate called lung-shaped bipolar plate was modeled. Simulations in this research showed that the lung-shaped microfluidic flow pattern is an appropriate flow pattern to gain maximum power and energy density. In other words, the best polarization curve and power density curve are obtained by using the lung-shaped bipolar plate in a proton exchange membrane fuel cell compared with previously suggested patterns. Copyright © 2017 John Wiley & Sons, Ltd.

Large Eddy Simulation Investigation of an Industrial Cyclone Separator Fitted with a Pressure Recovery Deswirler

AbstractA cyclone fitted with a deswirler of original design has been investigated by means of large eddy simulation. Installation of the deswirler reduces significantly the positive static pressure near the wall as well as the negative static pressure in the central region. It also decreases the maximum tangential velocities in the main separation zone. The deswirler enables a substantial reduction of the backward flow at the gas outlet and a more uniform distribution of the axial velocities at the gas outlet. It also considerably reduces pressure losses in the vortex finder lowering the cyclone pressure drop by almost about one third but it deteriorates the collection efficiency of particles with diameters of less than 8 µm, thus increasing the cut size.