Effect of air injection method on the performance of an air lift pump

Air lift pump performance was investigated experimentally for different submergence ratios (the ratio between the immersed length of the riser and its total length) using different air injection footpiece designs. For this purpose an air lift pump with a riser 200 cm long and 2.54 cm in diameter, was designed and tested. Nine different air injection footpiece designs were used at four submergence ratios with different air injection pressures (from 0.2 to 0.4 bar). An area of 10 mm² was chosen and divided into nine injection hole arrangements (1, 2, 3, 4, 6, 15, 25, 34 and 48 holes) to cover the whole experimental range. Four submergence ratios were used for this work: 0.75, 0.7, 0.6 and 0.5. The experimental results showed a marked effect on the pump performance when operated with different types of injectors at different submergence ratios. The results indicated that the disk with three holes (D3) gives the highest efficiency at nearly all submergence ratios. Moreover, it is found that there is a suitable disk design for maximum water flow rate at every submergence ratio. Further, the highest efficiency resulted at the largest used submergence ratio, namely 0.75. The pump capacity and efficiency were found to be functions of air flow rate, lift ratio, and injection pressure.     

Performance of a small air-lift pump

Pumping of liquids using two-phase flow has been examined experimentally in small air-lift pumps with 12—19 mm bore plexiglass tubes. An air injection system was devised to create and maintain ‘perfect’ slug flow in the vertical riser tube. An equation has been derived, based on momentum conservation considerations, which correlates well with the measurements obtained. Slip variation, or liuid holdup, between the two phases and the formation of the ‘entrance’ section part of the pump (suction pipe) were taken into consideration. Unlike its predecessors, this equation predicts the reversal in the pump performance curve observed experimentally.     

Effect of local pipe bends on pump performance of a small air-lift system in transporting solid particles

The pump performance of a small air-lift system in transporting solid particles is investigated experimentally. Three types of riser pipe were used to examine the effect of local bends of riser pipes on the flow characteristics of a three-phase air–water–solid particles mixture. Two of them were locally S-shaped either below or above a gas injector. The other was vertically straight. Alumina particles of 3 or 5 mm diameter were used as solid particles. It is indicated that the pump performance is appreciably reduced when the pipe bend is above the gas injector. The critical condition under which solid particles are vertically lifted is discussed from a practical viewpoint. In addition, the particle motion in the region of a pipe bend is investigated by photographic observations.     

The effect of radial diffusion on the performance of a liquid-liquid displacement process

The effect of radial diffusion on the performance of a liquid-liquid displacement process is considered in fluid flow between porous parallel plates and through a porous tube, as examples of a two-zone problem in unsteady-state mass transfer. The double Laplace transformation is applied to the system equations. In obtaining the inversion of the Laplace transformed equations the first inversion (with respect to the transformed dimensionless axial distance) is performed by use of the residue method, and then the second inversion (with respect to the transformed dimensionless time) is performed by use of the numerical Laplace transform technique advanced by Bellman et al. A numerical example is shown and discussed.     

The effect of size on the performance of a fluidized bed cooling tower

Application of the principles of the fluidization is made for cooling towers. The performance on a smaller size Fluidized Bed Cooling Tower (FBCT) is found to be encouraging. Hence a larger size FBCT is designed and the performance is found to be equally good. The pressure drop encountered in FBCT is comparable to that of conventional cooling towers. The packing height in FBCT reduces considerably because of fluidization. A table is provided to show that the throughput of the FBCT is greater than that of conventional cooling towers.

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Der Einfluß der Größe auf die Leistung eines Wirbelschicht-Kühlturms

Zusammenfassung Das Prinzip der Fluidisierung wird für Kühltürme eingesetzt. Die Leistung eines Wirbelschicht-Kühlturms mit geringer Größe ist als ermutigend angesehen worden. Deshalb wurde ein größerer Wirbelschicht-Kühlturm entwickelt, dessen Leistung ebenso gut eingestuft wurde. Der Druckverlust, der in einem Wirbelschicht-Kühlturm auftritt, ist mit dem Druckverlust in einem konventionellen Kühlturm vergleichbar. Die Packungshöhe in einem Wirbelschicht-Kühlturm verringert sich aufgrund der Fluidisierung wesentlich. In einer Tabelle wird gezeigt, daß die Durchflußleistung eines Wirbelschicht-Kühlturms erheblich größer ist, als bei konventionellen Kühltürmen.

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Nomenclature L water flow rate, kg per hour/m² - K overall enthalpy transfer coefficient, kg per hour/m² - V active tower volume, m³/m² plan area - T _i cold water temp. deg. C - i _i enthalpy of the air at the interface, Kcal/kg - G airflow rate, kg per hour/m² - a area of water interface, m²/m³ - H _st static height of packing - T ₂ hot water temp. deg. C - i _g enthalpy of air, Kcal/kg     

Experimental stress analysis in the design of a liquid-hydrogen pump rotor

A design optimization of the cross section of a high-speed rotor to pump liquid hydrogen was accomplished by means of photoelastic evaluations and model tests. The photoelastic models were rotated in the field of a polariscope with stroboscopic light synchronized to this rotation to evaluate the stresses. Differential radial growths were measured from model tests.     

Buffeting lift forces and local air–water flow aspects around a rigid cylinder

A new experimental programme is conducted in order to relate the characteristics of two-phase flow around a rigid cylinder with the resulting lift forces. The local characteristics of air–water flow measured in the vicinity of the cylinder provide a useful source of information about the effects of flow on the excitation mechanisms. In particular, a selection of relevant parameters has been identified which, with the help of a standard dimensional analysis, may explain the energetic contents of buffeting forces. Among the parameters effective in reducing the data are the flow regime, bubble frequency and gravity forces. In addition, in the range of bubbly regimes, the magnitude of the random forces is found to be related to the local fluctuations of void fraction. Finally, a new formulation is proposed to collapse the dimensionless spectra of the buffeting lift forces in a single characteristic curve. This analysis shows a marked improvement over the collapse of data in comparison with previous normalized models.     

The effect of a small isolated roughness element on the forces on a sphere in uniform flow

The effect of an isolated roughness element on the forces on a sphere was examined for a Reynolds number range of 5 × 10⁴ < Re < 5 × 10⁵ using a novel sting-mounted sphere apparatus. The roughness element was a circular cylinder, and its width and height was varied to be 1, 2, and 4% of the sphere diameter. At subcritical Re, a lateral force is produced in the direction of the roughness, while at supercritical Re, the force is in the opposite direction. This is caused by asymmetric boundary layer separation, as shown using particle image velocimetry. At supercritical Re, a roughness element that is only 1% the sphere diameter produces a lift to drag ratio of almost one. It was found that the isolated roughness element has the largest effect on the lateral forces when it is located between a streamwise angle of about 40° and 80°. In addition to the mean forces, the unsteady forces were also measured. It was found that at subcritical Re, vortex shedding is aligned to the plane of the roughness element. In addition, the probability distribution of the forces was nearly Gaussian for subcritical Re, but for supercritical Re, the skewness and kurtosis deviate from Gaussian, and the details are dependent on the roughness size. A simple model developed for the vortical structure formed behind the roughness element can be extended to explain aspects of nominally smooth sphere flow, in which external disturbances perturb the sphere boundary layer in an azimuthally local sense. These results also form the basis of comparison for an investigation into the effectiveness of a moving isolated roughness element for manipulating sphere flow.     

定常升阻力普适理论的特色和升力的物理来源

现代空气动力学诞生一百多年来,己经发展出众多关于升力和阻力的理论.但是,其远场合力理论一直停留在低速不可压流.虽经几代人的努力,但仍未能把它精确地推广到黏性可压缩流.这种状况直到最近才得以突破.本文作者及其合作者依据对远场线化Navier-Stokes方程解析解的研究,获得了经典不可压二维定常流的Kutta-Jouko...     

高升阻比乘波构型优化设计

在M∞ =6, 30km高空条件下,以升阻比为目标函数,进行了锥形流乘波体的黏性优化设计,讨论 了影响乘波体升阻比的因素,并对优化结果进行了数值验证. 结果表明：对于升阻比最大的 黏性优化乘波体,存在最优圆锥角使得源自该基本流场的乘波体升阻比最大;摩阻和波阻处 于同一量级;体积率、细长比和展长比都随着基本流场圆锥角的增大而增大.     

The effect of material properties on the performance of a new geometry PEM fuel cell

In this paper a computational dynamics model for duct-shaped geometry proton exchange membrane (PEM) fuel cell was used to investigate the effect of changing gas diffusion layer and membrane properties on the performances, current density and gas concentration. The proposed model is a full cell model, which includes all the parts of the PEM fuel cell, flow channels, gas diffusion electrodes, catalyst layers and the membrane. Coupled transport and electrochemical kinetics equations are solved in a single domain; therefore no interfacial boundary condition is required at the internal boundaries between cell components. This computational fluid dynamics code is used as the direct problem solver, which is used to simulate the 2-dimensional mass, momentum and species transport phenomena as well as the electron- and proton-transfer process taking place in a PEMFC that cannot be investigated experimentally. The results show that by increasing the thickness and decreasing the porosity of GDL the performance of the cell enhances that it is different with planner PEM fuel cell. Also the results show that by increasing the thermal conductivity of the GDL and membrane, the overall cell performance increases.     

The effect of velocity on rigid wheel performance

A simulation model to predict the effect of velocity on rigid-wheel performance for off-road terrain was examined. The soil–wheel simulation model is based on determining the forces acting on a wheel in steady state conditions. The stress distribution at the interface was analyzed from the instantaneous equilibrium between wheel and soil elements. The soil was presented by its reaction to penetration and shear. The simulation model describes the effect of wheel velocity on the soil–wheel interaction performances such as: wheel sinkage, wheel slip, net tractive ratio, gross traction ratio, tractive efficiency and motion resistance ratio. Simulation results from several soil-wheel configurations corroborate that the effect of velocity should be considered. It was found that wheel performance such as net tractive ratio and tractive efficiency, increases with increasing velocity. Both, relative wheel sinkage and relative free rolling wheel force ratio, decrease as velocity increases. The suggested model improves the performance prediction of off-road operating vehicles and can be used for applications such as controlling and improving off-road vehicle performance.     

The compressible discharge of air through small thick plate orifices

Summary The choking of nozzles at pressure ratios below the critical has long been understood. Knife edge orifices however do not appear to choke. This can be explained and the variation of discharge coefficient with pressure ratio may be calculated. The present paper is an experimental investigation into the discharge through thick plate orifices when the pressure ratio is in the vicinity of its critical value. A comparison is made with the results of other workers and an attempt is made to explain the discharge characteristics of thick plate orifices.Notation C discharge coefficient - D orifice diameter - P absolute static pressure - T thickness of orifice plate Suffixes c critical pressure - d downstream conditions - i incompressible flow conditions - u upstream conditions     

A dispersion force approach to modelling the effect of lift forces on fibre dispersion

Wood fibres suspended in air were studied whilst flowing through a throttle. Measurements of volume fraction and velocity were compared with results from a two-fluid model simulation. Results from earlier work have shown that the lift forces acting on the individual fibres are of importance for the dispersion of volume fraction. Since the orientation of the individual fibres cannot be determined, a dispersion force was utilised to model the dispersing effect of the lift forces. The addition of a lift dispersion model significantly improved the agreement between measurement and model data.     

The effect of inlet conditions on the air side hydraulic resistance and flow maldistribution in industrial air heaters

Experimental system hydraulic resistance measurements on a scale air heater unit have highlighted the excessive hydraulic resistance of typical industry configurations. Both poor header inlet conditions and large header expansion angles are shown to contribute to system hydraulic resistance magnitudes 20-100% higher than suitable benchmark cases. Typical centrifugal fan system efficiencies well under 80% multiply the system resistance effects resulting in larger fan power penalties. Velocity profile measurements taken upstream and downstream of the test heat exchanger under flow maldistribution conditions provide insight into the flow maldistribution spreading caused by the heat exchanger resistance. The anisotropic resistance of the plate fin-and-tube heat exchanger is shown to result in resistance induced flow dispersion being concentrated in the axis parallel to the plate fins.