The flow of “settling” slurries in tubes with internal spiral ribs

The secondary flows created by an internal spiral rib in an otherwise conventional smooth tube are illustrated by reference to the axial, and combined tangential and radial velocity components for a fluid flowing in a 2-inch diameter tube containing a rib with a pitch-to-diameter ratio of 3 The effect of such secondary flows on the transportability of “settling”(suspensions)was investigated by measuring pressure gradients for the flow of two sand/water slurries in a smooth 2-inch tube and in 2-inch diameter tubes with ribs of pitch-to-diameter ratio 5.15, 3.32 and 1.80. Average flow velocities ranged from 0.5 to 8 feet/sec. and delivered concentrations ranged from 5 to 18 per cent by volume While the ribs were found to be a disadvantage at relatively high average mixture velocities because of increased pressure gradients, they were found to be advantageous at relatively low velocities, i.e. velocities less than the critical deposit velocity for flow in the smooth tube, in that the pressure gradients, for a given sand/water slurry with a given delivered concentration and average velocity, were lower in the ribbed tubes than in the smooth tube. Because of this, the power consumption per unit mass of solid transported was reduced by the presence of a rib. The optimum pitch-to-diameter ratio was estimated to be about 5 Pressure gradients measured for one of the slurries with air added as a third phase showed the presence of air to be a definite disadvantage     

New investigation in regime transition from bubbling to turbulent fluidization

The regime transition velocity from bubbling to turbulent fluidization was investigated in a 0.267 m diameter fluidized bed with FCC particles. Different transition velocities and processes are found from the measurements of differential pressure fluctuations and local solids concentration. The measurements of differential pressure fluctuations shows a relatively quicker global regime transition, while the local regime transition obtained from the local solids concentration presents a more gradual process marked by two transition velocities. These transition velocities increase with initial static bed height. For the same initial static bed height, increasing the spacing between two pressure taps leads to lower pressure fluctuations and the appearance of two transition velocities.     

Liquid Holdup in a Pilot‐Scale Turbulent Contact Absorber – An Experimental and Comparative Study

Liquid holdup in a turbulent contact absorber was determined experimentally. Experiments were performed in a 44.7 cm diameter Perspex column. Hollow spherical high‐density polyethylene balls were used as packing. The effect of liquid and gas velocities, static bed height, diameter and density of packing on liquid holdup was investigated for the range of gas velocities greater than minimum fluidization velocities. Also, the effect of gas and liquid distributors on liquid holdup was studied. Correlations for liquid holdup were developed and compared with those in the literature. It was observed that liquid holdup increased with the increase in liquid velocity, packing density, and the decrease in static bed height. Liquid holdup also increased with gas velocity when the gas distributor section was included, while no effect was observed for the bed. Lack of information on the contribution of liquid and gas distributors seems to be the logical explanation for the wide variation in data reported in the literature.     

基于ANSYS的闸阀阻力系数研究

应用有限体积法,借助专用于分析二、三维流体流动场的先进工具——ANSYS软件的FLOT-RAN CFD工具,分析计算了闸阀的内部流场特性。依据流场的压力分布计算了不同开度、进口速度和内径下闸阀的阻力系数。指出阀门的阻力系数不仅与开度、进口速度有关,还与管径相关;不同管径的阀门,在同一开度、进口速度下的阻力系数不同。     

Corner Turning Rib Tests on LX-17

A circularly curved piece of LX-17 of square cross section was detonated at one end with a plane-wave lens. Detonation velocities along the inner and outer edge were measured with pins and a streak camera measured the detonation front curvature on the end face. A steady state “shadow” or inner curve velocity of 7.13 mm/μs was measured for rib radii of 89 mm and 114 mm. Time constants for the change to steady state on the curve were derived. The outer time constant is set by the time for the energy to flow across the explosive, not by the reaction zone length, and this results in a considerable tilt of the front. The tilt causes the leading point of the front to move far inward, close to the inner edge. A simple theory for reaction zone lengths is used first on slabs and then on the rib. Because the tilt directs the front away from the inner edge, the inner edge of the rib can sustain a shadow velocity lower than the failure velocity of the cylinder or slab. The rib has been modeled with Ignition and Growth in DYNA2D, producing a smooth set of detonation velocities that are slightly low. The production beta/program burn package in VHEMP produces a less smooth set of velocities that are too high.     

Insights into the hydrodynamics in the annular pipe of industrial-scale top-blown smelting furnace

The coaxial jet consisting of swirl jet and axial jet plays a critical role in the industrial processes but is rarely investigated; therefore, it is numerically explored by means of the computational fluid dynamics (CFD) approach in the present work. The force on the swirler, axial and tangential velocity at the annular pipe outlet, and the spatial distribution of swirl number (SN) are selected to evaluate the effect of geometrical parameters on the swirling performance. The results clarify that the velocity and their azimuthal components in the transverse cross-section can be categorized into six segments based on high/low velocity values. The coaxial jets form a weak swirl with high axial, certain tangential, and low radial velocities. x- and y-vorticity vary within −200 to 200 s⁻¹. Coaxial jet mixing decays the SN. Based on the multi-objective matrix analysis, swirler height has the largest effect on swirl performance followed by diameter, angle, and number based on analysis. Optimal parameters are 130° vane angle, 240 mm diameter, 10 vanes, and 250 mm height of the swirler.     

Pressure Drop in Liquid‐liquid Two Phase Horizontal Flow: Experiment and Prediction

The present study is aimed at an investigation of the pressure drop characteristics during the simultaneous flow of a kerosene‐water mixture through a horizontal pipe of 0.025 m diameter. Measurements of pressure gradient were made for different combinations of phase superficial velocities ranging from 0.03–2 m/s such that the regimes encountered were smooth stratified, wavy stratified, three layer flow, plug flow and oil dispersed in water, and water flow patterns. A model was developed, which considered the energy minimization and pressure equalization of both phases.     

Hydrodynamics and liquid phase axial mixing in orifice pipe reactor

Two phase flow in a horizontal pipe, with orifice plates placed at regular intervals as obstructions, was studied for the effect of phase velocities on flow patterns, fractional phase hold-ups, pressure drop and liquid phase axial dispersion. Radioactive technetium-99m (as an aqueous solution of sodium pertechnatate) was used as tracer. A pulse injection technique with two point measurements was employed. Three different orifice diameters were used (8 mm, 16 mm, and 20 mm) in a pipe diameter of 32 mm. The orifice spacing was 500 mm in all cases. Superficial gas (air) velocity was varied over a range from 0.02 m/s to 1.0 m/s and superficial liquid (water) velocity from 0.03 m/s to 0.85 m/s. Different flow patterns under different flow conditions were identified and a generalised flow map is presented. Variations in hold-ups and pressure drop with flow patterns have been explained. Rational correlations have been developed for fractional phase hold-ups and pressure drop. A preliminary comparison of two phase gas-liquid flow in a horizontal pipe with orifice obstructions (to be called orifice pipe reactor), as a gas-liquid contacting device, is made with a conventional bubble column reactor. Recommendations have been made for future work.     

Generalized master curve for threshold superficial velocities in particle-fluid systems

This paper presents our previous analyses of pickup gas velocity from a layer of particles in pipes and big wind tunnels, pickup liquid velocity, boundary saltation and minimum pressure velocities, and a new analysis of the minimum fluidization velocity and the terminal velocity. All these threshold velocities are defined as simple relations between the Reynolds and Archimedes numbers as modified by various effects. The Reynolds number is modified by taking into account the pipe diameter while the Archimedes number is modified by taking into account various properties that affect each threshold mechanism. Since all threshold velocities could be defined successfully by the same non-dimensional groups it was possible, at the first time, to present a Generalized Master Curve, which provides an overview of all the threshold velocities. This overview enabled, for example, to find quantitatively the relationships between all the threshold velocities to the terminal velocity and to compare the pickup and saltation velocities.     

环形通道内置螺旋线圈过冷流动沸腾传热特性

研究了置有螺旋线圈的内管加热环形通道中水的过冷流动沸腾传热特性。环形通道由铜制加热棒外套石英玻璃管构成,不同螺旋节距和线丝直径构成的5种螺旋线圈用于实验。对每种置入螺旋线圈管和光滑管分别进行了不同质量流速和热负荷下的16组实验,分析了线丝直径和线圈节距对传热系数的影响规律及机理。结果表明,螺旋线圈存在能使流体发生旋转分离,且使汽化核心密度增大,从而有效强化过冷沸腾换热;传热系数随着线圈节距的减小、线丝直径的增加,即节径比(P/e)减小而增大,当P/e最小为1.5时强化效果最好;最佳强化换热性能较光滑管的高出109%。将实验数据与4个经验关系式的预测值进行了比较,并给出了不同工况下各实验管的强化系数对比。     

水平和倾斜管内气液分层流界面稳定性

A viscous Kelvin-Helmholtz criterion of the interfacial wave instability is proposed in this paper based on the linear stability analysis of a transient one-dimensional two-fluid model. In thismodel, the pressure is evaluated using the local momentum balance rather than the hydrostatic approximation. The criterion predicts well the stability limit of stratified flow in horizontal and nearly horizontal pipes. The experimental and theoretical investigation on the effect of pipe inclination on the interfacial instability are carded out. It is found that the critical liquid height at the onset of interfacial wave instability is insensitive to the pipe inclination. However, the pipe inclination significantly affects critical superficial liquid velocity and wave velocity especially lor low gas velocities.     

Effect of air distributor on the fluidization characteristics in conical gas fluidized beds

The effect of an air distributor on the fluidization characteristics of 1 mm glass beads has been determined in a conical gas fluidized bed (0.1 m-inlet diameter and 0.6 m in height) with an apex angle of 20‡. To determine the effect of distributor geometry, five different perforated distributors were employed (the opening fraction of 0.009–0.037, different hole size, and number). The differential bed pressure drop increases with increasing gas velocity, and it goes from zero to a maximum value with increasing or decreasing gas velocity. From the differential bed pressure drop profiles with the distributors having different opening fractions, demarcation velocities of the minimum and maximum velocities of the partial fluidization, full fluidization, partial defluidization and the full defluidization are determined. Also, bubble frequencies in the conical gas fluidized beds were measured by an optical probe. In the conical bed, the gas velocity at which the maximum bed pressure drop attained increases with increasing the opening fraction of distributors.     

Effect of Helical Surface Disc Turbulators on Heat Transfer and Friction Factor Characteristics in the Annuli of a Double‐Pipe Heat Exchanger

The heat transfer and pressure drop characteristics in annuli of a double‐pipe heat exchanger (DPHE) using helical surface disc turbulators (HSDTs) are experimentally investigated. The effect of a helical surface disc turbulator is studied for three pitch ratios, three diameter ratios, and varying Reynolds numbers. Water flows in the inner tube and air through the annulus. The tests are conducted for air with uniform wall temperature condition. The heat exchanger with the least pitch ratio and least diameter ratio was found to exhibit the highest Nusselt number and pressure drop. The thermal performance factor turned out to be greater than unity for all cases. Correlations were developed for Nusselt number, friction factor, and thermal performance.     

Experimental test of a model for laminar slurry flow with sedimentation

The ability of a flow-sedimentation model to simulate the flow of a slowly-settling suspension being transported in the laminar regime through a pipeline with a constant overall pressure drop imposed on it was assessed using experimental scaled-down pipeline data. Comparison of predicted volumetric flow rate versus time profiles to those observed suggested that the blockage process took place in two steps. Initially, a sediment grew on the lower pipe wall and the flow gradually lessened, as was modelled. As the flow slowed down, ultimately a plug, which enclosed the full cross-section of the pipe, formed and lead to the rapid blockage of the pipe. It was envisioned that the granular properties of the concentrated suspension became dominant during the final blockage process. A deposit velocity criterion was also developed from the flow-sedimentation model and was used to generate a deposit velocity versus pipe diameter plot. Results from the plot indicate that the laminar pipeline flow of a slowly-settling suspension is possible in small diameter pipes.     

Theoretical and experimental studies of confined vortex flow

A study of the air flow characteristics is reported for a vortex chamber 122 cm in diameter consisting of an upper cylindrical section 61 cm high and of a lower conical section 108 cm high. Measurements were made with a five-channel pressure probe of the radial profiles of tangential and axial velocities, with varying inlet air velocity and axial distance from the top of the chamber. Measurements of the static pressure profiles were made simultaneously. Finally, the angle of flow of the air entering through the single tangential inlet could be adjusted, and its effects on the flow recorded. From these results and from a theoretical analysis, generalized expressions for the tangential velocity profiles were obtained for the two regions of flow, forced-vortex and quasi-free vortex, which prevail in a confined vortex chamber, as a function of the entrance air velocity and of the radius at the point considered only. The angle of entering air was found to have no effect on the tangential velocity and only a minor effect on the static pressure distribution. The outlet diameter of the chamber was found to have a large effect on the profile of the axial velocities, reflecting the influence of the chamber static pressure on the later.     

Theoretical and experimental studies of confined vortex flow

A study of the air flow characteristics is reported for a vortex chamber 122 cm in diameter consisting of an upper cylindrical section 61 cm high and of a lower conical section 108 cm high. Measurements were made with a five-channel pressure probe of the radial profiles of tangential and axial velocities, with varying inlet air velocity and axial distance from the top of the chamber. Measurements of the static pressure profiles were made simultaneously. Finally, the angle of flow of the air entering through the single tangential inlet could be adjusted, and its effects on the flow recorded. From these results and from a theoretical analysis, generalized expressions for the tangential velocity profiles were obtained for the two regions of flow, forced-vortex and quasi-free vortex, which prevail in a confined vortex chamber, as a function of the entrance air velocity and of the radius at the point considered only. The angle of entering air was found to have no effect on the tangential velocity and only a minor effect on the static pressure distribution. The outlet diameter of the chamber was found to have a large effect on the profile of the axial velocities, reflecting the influence of the chamber static pressure on the latter.     

Axial pressure profile in circulating fluidized beds

Design and operation of a circulating fluidized bed requires the knowledge of fluid mechanics. According to heat and mass transfer as well as chemical reactions, the effect of the set superficial gas velocity on the axial pressure profile is of particular interest. The axial pressure profile was measured for a variety of solids, as a function of the superficial gas velocity, in a cylindrical circulating fluidized bed with an inner diameter of 0.19 m and an overall height of 11.5 m. Depending on the solids content and superficial gas velocity, two or one sections can be observed in the plant where the pressure gradient is constant. A pressure profile with one pressure gradient exists only at high gas velocities, so long as the acceleration pressure drop immediately above the gas distributor is negligible. Comparison of measured pressure drops in circulating fluidized beds with those measured in vertical pneumatic conveying led to a state diagram for vertical gas-solid flows. The operation behaviour of different types of circulating fluidized bed plants can be explained with the aid of this diagram.     

缩放管内湍流对流换热(Ⅰ)场协同控制机理

通过对缩放管管内湍流对流换热的模拟研究,考察了热边界层厚度、湍流强度及时均速度与时均温度梯度之间夹角的变化规律,得出了影响对流换热强度的场协同作用沿流动方向的分布规律.通过讨论两种不同结构尺寸缩放管的换热情况,发现流体在收缩段可获得较好的场协同作用,增强换热能力,而在扩张段场协同作用的效果减弱.     

Experimental study of kerosene–water two‐phase flow in a vertical pipe using hot‐film and dual optical probes

The local parameters for kerosene–water upward flow are measured in a vertical pipe of 77.8 mm inner diameter at 4200 mm from the inlet (L/D = 54) using hot‐film and dual optical probes. The effect of superficial water velocity and volumetric quality on radial distribution of two‐phase flow parameters is investigated. The results show the following: (i) the profiles of volume fraction and drop frequency are very similar, and increasing superficial water velocity at low volumetric qualities (<18.6%) change the profile from a convex shape with peak at the pipe centreline to uniform then to concave shape with peak near the wall; (ii) the profiles of drop cut chord change from a parabolic shape with peak at centreline for low superficial water velocities to a flat shape at higher superficial water velocity, and the area‐averaged drop diameter decreases with higher superficial water velocities for all volumetric qualities; (iii) velocity profiles for both phases have shapes similar to single phase flow, flatter at higher values of superficial water velocity and volumetric quality and centreline peaked at low superficial water velocities and volumetric qualities; (iv) the slip velocity decreases with radial distance having a peak at centreline and zero values near the wall; (v) introducing kerosene drops into single phase water flow results in a sharp increase in turbulent intensity, particularly at low water velocity, and the difference between the single phase and two‐phase flow turbulence intensities decreases with higher superficial water velocities and (vi) the results show that interfacial area concentration increased with higher volumetric quality and higher number of bubbles thereby increases the contact area between the two phases. © 2012 Canadian Society for Chemical Engineering     

新型旋风分离器气相流场测试实验研究

针对高温高压的特殊情况提出了一种新型的旋风分离器,并用三维动态粒子分析仪PDA对不同结构参数和操作条件下的气相流场进行了测试,得出该旋风分离器内气相流场的整体特性———流场的切向速度分布在分离空间具有明显的对称性,任一截面上的分布分成内外2层旋流,外旋流是准自由涡,内旋流是准强制涡;同时分析了入口角度、排气管直径、高径比和入口气速等因素对其切向速度的影响规律,在此基础上依据实验数据关联出了计算内旋流直径和速度分布指数的公式。