Solid-liquid mixture flow through a slim hole annulus with rotating inner cylinder

An experimental study was conducted to study solid-liquid mixture upward hydraulic transport of solid particles in vertical and inclined annuli with rotating inner cylinder. Lift forces acting on a fluidized particle play a central role in many important applications, such as the removal of drill cuttings in horizontal drill holes, sand transport in fractured reservoirs and sediment transport, etc. Annular fluid velocities varied from 0.4 m/s to 1.2 m/s. Effect of annulus inclination and drill pipe rotation on the carrying capacity of drilling fluid, particle rising velocity, and pressure drop in the slim hole annulus have been measured for fully developed flows of water and of aqueous solutions of sodium carboxymethyl cellulose (CMC) and bentonite, respectively. For higher particle feed concentration, the hydraulic pressure drop of mixture flow increases due to the friction between the wall and solids or among solids. This paper was recommended for publication in revised form by Associate Editor Gihun Son Sang-Mok Han received a B.S. degree in Mechanical Engineering from Sung-kyunkwan University in 2001. He then went on to receive his M.S. degrees from Sungkyunkwan University in 2003. He is a candidate for Ph.D. from 2006 to the present at the School of Mechanical Engineering at Sungkyunkwan University in Suwon, Korea. His research interests are in the area of Multi-phase flow and drilling. Nam-Sub Woo received a B.S. degree in Mechanical Engineering from Sungkyunkwan University in 1997. He then went on to receive his M.S. and Ph.D. degrees from Sunkyunkwan University in 1999 and 2007, respectively. Dr. Woo is currently a Senior Researcher at the Fire & Engineering Services Research Center at Korea Institute of Construction and Technology in Goyang, Korea. Dr. Woo’s research interests are in the area of fluid dynamics and plant engineering. Young-Kyu Hwang received a B.S. degree in Mechanical Engineering from Sungkyunkwan University in 1977. He then went on to receive his M.S. from University of Wis-consin at Madison in 1980 and Ph.D. degrees from State Uni-versity of New York at Buffalo in 1984, respectively. Dr. Hwang has served as a Professor, from 1984 to the present at the School of Mechanical Engineering at Sungkyunkwan University in Suwon, Korea. His research interests are in the area of drilling hydraulics, molecular gas flow and hydrodynamic instability.     

Numerical investigation on frictional pressure loss in a perfect square micro channel with roughness and particles

A numerical study is performed to investigate the effect of inner surface roughness and microparticles on adiabatic single phase frictional pressure drop in a perfect square micro channel. With the variation of particles sizes (0.1 to 1 μm) and occupied volume ratio (0.01 to 10%) by particles, the Eulerian multi-phase model is applied to a 100 μm hydraulic diameter perfect square micro channel in laminar flow region. Frictional pressure loss is affected significantly by particle size than occupied volume ratio by particles. The particle properties like density and coefficient of restitution are investigated with various particle materials and the density of particle is found as an influential factor. Roughness effect on pressure drop in the micro channel is investigated with the consideration of roughness height, pitch, and distribution. Additionally, the combination effect by particles and surface roughness are simulated. The pressure loss in microchannel with 2.5% relative roughness surface can be increased more than 20% by the addition of 0.5 μm diameter particles.     

Multichannel wire gas electron multipliers with 1- and 3-mm gaps

The operation of multichannel wire gas electron multipliers (MWGEMs) with gaps between electrodes δ = 1 and 3 mm, when the chamber is filled with commercial neon under a 0.4- and 1.0-atm (abs.) pressure and irradiated with α and β particles, is studied. The following maximal proportional electron multiplication coefficients are obtained: 6 × 10³ (α, irradiation, δ = 3 mm, 1 atm, and 20% streamers), 1.2 × 10⁴ (β⁻, 3 mm, 1 atm, and 50% streamers), 6 × 10³ (α, 3 mm, 0.4 atm, and 20% streamers), and 10⁵ (β⁻, 3 mm, 0.4 atm, and 50% streamers). The maximal proportional electron multiplication coefficients are obtained in the MWGEM and its anode (induction) gap in the sequential electron multiplication mode: 1.08 × 10⁵ (β⁻, 1 mm, 0.4 atm, 50% streamers), 2 × 10⁶ (β⁻, 3 mm, 0.4 atm, 20% streamers), and 1.12 × 10⁵ (α, 3 mm, 0.4 atm, 50% streamers).     

Electrohydrodynamic instability of dielectric liquid between concentric circular cylinders subjected to unipolar charge injection

In this paper, we demonstrate instability of dielectric liquid subjected to unipolar charge injection from a pair of cylindrical electrodes at high Scmidt and high Peclet numbers. The transport of charge density in the annulus is governed by the Nernst-Planck equation and the electric potential by the Poisson equation. The fluid flow is governed by the Navier-Stokes equation together with the continuity equation. The base solutions composed of the one-dimensional conduction state are obtained numerically and the temporal growth of their perturbations is determined from the normal-mode instability analysis by using numerical simulations. The critical values of the parameter for the onset of 2D convective motion are obtained and compared well with the results of full-2D calculation. At high injection, the system tends to be more unstable for the inner injection case and more stable for the outer injection case, as the radius of the inner cylinder is decreased; this trend is however reversed at low injection. It turns out that the critical angular wave number obtained from the flatplate case well predicts the one for an annulus for a wide range of the inner cylinder’s radius.     

A study on the optimal design of a cyclone system for vacuum cleaner with the consideration of house dust

Cyclone, a type of particle collector widely used in the field of ambient sampling and industrial particulate control, is the principal type of gas-solids separator that use a centrifugal force. The goal of this study is to transform conventional cyclone into a new type of cyclone that can be used for the household vacuum cleaners. To meet the goal, first, the analysis about local environment and dust is carried out. Second, it must have enough high-efficiency not to reduce suction power due to clogging of exhaust filter unit. Two single cyclones with central-hopper-dust-outlet and side-wall-dust-outlet and a twin cyclone are designed and fabricated to evaluate, and compare, their dust collection efficiencies and pressure drops. The measurements of separation efficiency for dust by using DMT test dust type 08 are carried out. House dust experiment is additionally performed to check the local matters applicability such as tissue papers, fur and hairs. The collection efficiency of the twin cyclone is found to be 3–6% greater than those of two single cyclones with the same body diameter, inlet and inner cylinder diameter. Twin cyclone with a large body diameter, a small inner cylinder diameter, a short inner cylinder, a narrow inlet has high separation efficiency. This result indicates the possibility of achieving higher collection efficiencies with a twin cyclone.     

A comparison of the effect of the electrohydrodynamic technique on the condensation heat transfer of HFC-134a inside smooth and micro-fin tubes

The results of the condensation heat transfer enhancement and pressure drop of HFC-134a by using the electrohydrodynamic (EHD) technique are presented. The test section is a horizontal tube-in-tube heat exchanger where the refrigerant flows in the inner tube and water flows in the annulus. The outer tube is a smooth copper tube havign outer diameter of 21.2 mm. Two types of inner tubes, smooth and micro-fin copper tubes, are tested. The outer diameter and length of both inner tubes is 9.52 mm and 2.5 m, respectively. A stainless steel cylindrical electrode of 1.47 mm in diameter is placed in the center of the tube. Experiments are conducted under conditions providing mass flux of 400 kg/m²s, saturated temperature of 40°C, heat flux of 20 kW/m² and applied voltage of 2.5 kV. The experimental results indicate that the EHD enhancements of the smooth tube are higher than those of the micro-fin tube over the range of average quality. The maximum heat transfer enhancements for smooth and micro-fin tubes are 1.1. times and 1.08 times, respectively. For a smooth tube, the pressure drop induced by EHD is considerably small. However, the application of EHD in a micro-fin tube can lead to 10% increase in the pressure drop.     

Investigation of two-phase flow mixing mechanism of a swirl burner using an electrostatic sensor array system

A novel electrostatic sensor array was designed to measure particle concentration downstream of a swirl burner. The fundamental mechanism and the primary constituent elements of the sensor array were described. The root-mean-square magnitude of the measured electrostatic voltage was determined as an indication of the particle concentration. The accuracy of the electrostatic sensor array was calibrated by the optical fluctuation method. Local particle concentrations at different cross-sections of the measuring chamber were measured to investigate the diffusion characteristic of the pulverized coal particles. Electrostatic sensor array showed its ability in the field measurement in this work. The measurements indicated that the velocity of the inner secondary air had a significant effect on the diffusion of the pulverized coal particles. The particles concentrated in the center of the cross-section after leaving the burner. With the development of the gas–solid two-phase flow, the particles distributed like a ring shape. The radius of the particle ring increased with the increase of the velocity of the inner secondary air. But the effect of the velocity of outer secondary air on the radius of the particle ring is very slight. The maximum radius occurred when the velocity of inner secondary air was 21 m/s, which was favorable for stable combustion.     

Investigation of single phase frictional pressure loss in circular micro tubes

Single phase pressure drops in micro tubes were investigated through an experimental measurement and a numerical simulation. Experimental Po was obtained in circular micro tubes with 87 and 118 μm diameter with distilled water. Experiments were carried out in laminar flow region with varying the Re 15–450 for the 87 μm diameter tubes and 60–1300 for the 118 μm diameter tube. No early transition from laminar to turbulent flow was detected for the experimental range. The computational estimation of pressure drop in the 87 μm diameter tube was performed with the aid of CFD software. Boundary conditions from experiments were used for the numerical simulation. The results of experimental and numerical studies showed a good agreement with the conventional macro theory.     

Measuring solid cuttings transport in Newtonian fluid across horizontal annulus using electrical resistance tomography (ERT)

The in-situ visualization of flow in the opaque pipes and annulus is a major cause of concern for studying hole cleaning issues and multiphase flow patterns in the oil and gas industry. Electrical resistance tomography is one of the latest non-intrusive technologies, which can provide real-time cross-sectional images of multiphase flow patterns in opaque pipes and annulus. Most studies conducted using the ERT system in the area of multi-phase flow is limited to opaque pipes and two-phase systems. Therefore, in this work is the suitability of the ERT technology has been tested to examine the three-phase flow (air-liquid-solid) and solids cuttings transport in a horizontal flow loop annulus system at wide operating conditions. The effect of different eccentricities (0–50%), inner pipe rotation speed (0–120 RPM), liquid flow rates (164–373 kg/min) and air input pressure (0–0.8 bar) on solids concentration in the specified ERT zone was examined using ERT concentration tomograms.     

Tribological characteristics of polycrystalline Magnéli-type titanium dioxides

The results presented in this paper have clarified experimentally, that titania-based Magnéli-phases (Ti₄O₇/Ti₅O₉ and Ti₆O₁₁) with (121)-shear planes exhibit more anti-wear properties than lubricious (low-frictional) properties. The results for dry sliding indicate that the coefficients of friction lie in the range of 0.1–0.6 depending on sliding speed and ambient temperature. The COF decreased with increasing temperature (T= 22–800°C) and increasing sliding speed (υ= 1−6 m/s). The dry sliding wear rate was lowest for the Al₂O₃ at 1 m/s at 800°C with values of 1.7 × 10−8 and 6.4 × 10−8 mm³/N m, comparable to boundary/mixed lubrication, associated with a high dry frictional power loss of 30 W/mm². The running-in wear length and, more important, the wear rate decreased under oscillating sliding tests with increasing relative humidity. The contact pressure for high-/low-wear transition increased under oscillating sliding tests with increasing relative humidity. At room temperature and a relative humidity of 100% the steady-state wear rate under dry oscillating sliding for the couple Al₂O₃/Ti₄O₇–Ti₅O₉ was lower than 2 × 10−7 mm³/N m and therefore inferior to the resolution of the continuous wear measurement sensor. TEM of wear tracks from oscillating sliding revealed at room temperature a work-hardening as mechanism to explain the running-in behavior and the high wear resistance. The hydroxylation of titania surfaces favours the high-/low-wear transition. This revised version was published online in August 2006 with corrections to the Cover Date.     

Experimental investigation on viscoplastic parameters of conditioned sands in earth pressure balance shield tunneling

A device was developed to determine the viscoplastic parameters of conditioned soil, which works on the principle of torsional shear applied to a standard vane with controlled strain rate. Rheological measurements were taken for three sand samples with the same bentonite slurry injection ratio (14.3%), but with different foam injection ratios (19%, 23%, and 27%), by changing the gasbag pressure levels (i.e., 0, 100, 200, 300, and 400 kPa) and vane speeds (i.e., 1/3.4, 1/4.1, 1/5, 1/6.4, 1/9, 1/15, and 1/30 RPM) to determine the effects of confining pressure and foam injection ratio on the viscoplastic parameters. The results show that the values of viscosity coefficient and yield stress for conditioned sands are in the range of 9.1–53.5 kPa·s and 1.5–10.2 kPa, respectively. The viscoplastic parameters increase with the increase of the confining pressure, and decrease with the increase of the foam injection ratio for all tested samples.     

Numerical Prediction of Acoustic Sounds Occurring by the Flow Around a Circular Cylinder

Acoustic sounds generated by uniform flow around a two-dimensional circular cylinder at Re=150 are simulated by applying the finite difference lattice Boltzmann method. A third-order-accurate up-wind scheme is used for the spartial derivatives. A second-order-accurate RungeKutta scheme is also used for time marching. Very small acoustic pressure fluctuation, with same frequency as that of Karman vortex street, is compared with pressure fluctuation around a circular cylinder. The propagation velocity of acoustic sound shows that acoustic approaching the upstream, due to the Doppler effect in uniform flow, slowly propagates. For the downstream, on the other hand, it quickly propagates. It is also apparent that the size of sound pressure is proportional to the central distance τ^-1/2 of the circular cylinder.     

Experimental study on the vortex flow in a concentric annulus with a rotating inner cylinder

This experimental study concerns the characteristics of vortex flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one is rotating. Pressure losses and skin friction coefficients have been measured for fully developed flows of water and of 0.4% aqueous solution of sodium carboxymethyl cellulose (CMC), respectively, when the inner cylinder rotates at the speed of 0-600 rpm. Also, the visualization of vortex flows has been performed to observe the unstable waves. The results of present study reveal the relation of the bulk flow Reynolds number Re and Rossby number Ro with respect to the skin friction coefficients. In somehow, they show the existence of flow instability mechanism. The effect of rotation on the skin friction coefficient is significantly dependent on the flow regime. The change of skin friction coefficient corresponding to the variation of rotating speed is large for the laminar flow regime, whereas it becomes smaller as Re increases for the transitional flow regime and, then, it gradually approach to zero for the turbulent flow regime. Consequently, the critical (bulk flow) Reynolds number Re_c decreases as the rotational speed increases. Thus, the rotation of the inner cylinder promotes the onset of transition due to the excitation of Taylor vortices.     

Tribological behaviors and mechanisms of Ti<Subscript>3</Subscript>AlC<Subscript>2</Subscript>

Tribological behaviors and the relevant mechanism of a highly pure polycrystalline bulk Ti₃AlC₂ sliding dryly against a low carbon steel disk were investigated. The tribological tests were carried out using a block-on-disk type high-speed friction tester, at the sliding speeds of 20–60 m/s under a normal pressure of 0.8 MPa. The results showed that the friction coefficient is as low as 0.1∼0.14 and the wear rate of Ti₃AlC₂ is only (2.3–2.5) × 10⁻⁶ mm³/Nm in the sliding speed range of 20–60 m/s. Such unusual friction and wear properties were confirmed to be dependant dominantly upon the presence of a frictional oxide film consisting of amorphous Ti, Al, and Fe oxides on the friction surfaces. The oxide film is in a fused state during the sliding friction at a fused temperature of 238–324 °C, so it takes a significant self-lubricating effect.     

Eulerian simulation of subcooled boiling flow in straight and curved annuli

In this study, two types of water flow, turbulent single-phase flow and low-pressure subcooled boiling flow, in straight and curved horizontal annuli are investigated numerically. The control volume technique is used for discretizing governing equations, the SIMPLEC algorithm for pressure-velocity coupling, and the shear stress transport k-ω model for turbulent flow. A three-dimensional two-fluid model is used for the subcooled boiling flow, the results of which are compared with those of the single-phase flow. The available water boiling experiment results at low pressure are used to validate the numerical results and were found to have good agreement. The inner cylinder surface temperature of the curved annulus in almost all angles is less than that of the straight annulus in both single-phase and subcooled boiling flow. The maxmum and minimum temperatures in the curved annulus occur at defferent points compared to straight annulus ones due to effects of the centrifugal force.     

基于Workbench的缩套式超高压缸体优化设计

某设备的缩套式超高压缸体存在内壁始终为应力最大位置,且缸体应力分布相当不均匀的问题。为满足缸体最大等效应力小于缸体材料的屈服极限,以内外缸体内壁剪应力相等为约束条件,结合过盈配合及设计要求,利用响应面法对缩套式超高压缸体进行优化设计。结果表明,缸体的过盈量从优化前的0.30 mm减小到优化后的0.2662 mm,降低了内外缸安装套合时的工作难度;内缸内壁到外缸内壁的等效应力的变化率从优化前的0.787 MPa/mm降为0.0568 MPa/mm,缸体的应力分布不均匀性较优化前有了较大的改观。     

旋风分离器内颗粒浓度分布特性的数值分析

采用改进的雷诺应力模型和分散的颗粒随机轨道模型,并利用单元内颗粒源法对旋风分离器内的颗粒浓度分布进行数值模拟,与试验结果对比表明两者吻合较好,有较高的预报精度。数值模拟结果表明,旋风分离器外壁的颗粒浓度呈螺旋带状分布,且螺旋灰带以一定的频率上下窜动,在环形空间和灰斗的顶板下方存在顶灰环,且顶灰环不均匀,具有显著的非对称性;在分离空间下部排尘口附近有明显的颗粒返混,范围在排尘口上方约1.5 D (筒体直径)以内,排尘口上方的强旋流动对颗粒有显著的二次分离作用。讨论粒径(3～23 μm)、工作温度(20～ 1 000 ℃)、入口含尘浓度(0.03～10 kg/m3)和进气速度(12～30 m/s)对颗粒浓度分布特性的影响规律。     

Two-phase flow heat transfer of R-134a in microtubes

The characteristics of the two-phase flow heat transfer of R-134a in microtubes with inner diameters of 430 μm and 792 μm were experimentally investigated. The effect of the heat flux on the heat transfer coefficient for microtubes was significant before the transition quality. The boiling number expressed the interrelation between the heat flux and the mass about the heat transfer coefficients. The smaller microtube had greater heat transfer coefficients; the average heat transfer coefficient for the tube A (D _i = 430 μm) was 47.0% greater than that for the tube B (D _i = 792 μm) at G = 370 kg/m²·s and q″ = 20 kW·m². A new correlation for the evaporative heat transfer coefficients in microtubes was developed by considering the following factors: the laminar flow heat transfer coefficient of liquid-phase flow, the enhancement factor of the convective heat transfer, and the nucleate boiling correction factor. The correlation developed in present study predicted the experimental heat transfer coefficients within an absolute average deviation of 8.4%.     

Experimental research on cyclone performance at high temperature

To predict the influence of operating temperatures on cyclone performance, an experimental investigation was conducted on particle separation in a reverse flow, tangential volute-inlet cyclone separator with a diameter of 300 mm and with air heated up to 973 K. The test powder silica has a mass median diameter of 10 um, while inlet velocity range was 12–36 m/s. Both the separation efficiency and pressure drop of the cyclone were measured as a function of the inlet velocity and operating temperature. At the same inlet velocity, both the separation efficiency and pressure drop decrease with increasing temperature. In addition, optimum inlet velocity, at which the cyclone has its highest separation efficiency, tends to increase with a rise in temperature. An analysis on our own data and published results has shown that the fractional efficiency of a cyclone is a definite function of dimensionless numbers such as the Stokes number, the Reynolds number, the Froude number, dimensionless cyclone inlet area, and dimensionless outlet diameter. A nondimensional experimental correlation of the cyclone performance, including the influence of temperature, was obtained on the basis of our own previous work. The prediction of the influence of temperature on separation efficiencies and pressure drops is in fairly good agreement with experimental results. __________ Translated from Journal of China University of Petroleum, 2006, 30(3): 97–100, 105 [译自: 中国石油大学学报 (自然科学版)]     

离心压缩机内固粒运动规律与冲蚀磨损的数值模拟

针对离心压缩机叶轮的冲蚀磨损问题,利用FLUENT中离散相模型、质量冲蚀率模型,对压缩机内部不同粒径的固体颗粒的运行轨迹、运动速度、偏聚浓度及造成的叶片冲蚀率的分布进行了数值模拟。结果表明:粒径为5~20μm的绝大部分的固体颗粒流经大叶片压力面附近流道;固体颗粒在运动到叶片前缘过程中速度迅速升高,在压力面腹侧会有所减小,后缘处重新升高;大叶片后缘根部固体颗粒浓度高、运行速度快,冲蚀磨损严重,且固体颗粒直径越大对大叶片压力面造成的冲蚀磨损越严重。