Gas volume fraction and velocity profiles

Upward inclined gas-liquid flows are frequently encountered in the oil industry and data relating to the local gas volume fraction distribution and the local gas velocity distribution is important, for example, in pressure gradient prediction and in modeling oil well ‘blowouts’. In this paper measurements are presented of the local gas volume fraction distribution and the local axial gas velocity distribution which were taken in bubbly air-water flows in an 80 mm diameter pipe which was inclined at angles of 0°, 15° and 30° to the vertical. Qualitative arguments are presented to explain the influence of the liquid superficial velocity on the local gas volume fraction distribution in inclined flow and also to explain the very high axial gas velocities observed towards the upper side of the inclined pipe.     

EFFECTS OF BOND NUMBERS ON INTERNAL FLOW PATTERNS OF AN INCLINED,CLOSED, TWO-PHASE THERMOSYPHON AT NORMAL OPERATING CONDITIONS

A visual study of internal flow patterns inside an inclined, closed, two-phase thermosyphon at normal operating conditions for several Bond numbers has been conducted. This article describes the effects of varying inclination angles and Bond numbers (Bo) onflow patterns, A copper thermosyphon was used. R123 was selected as the working fluid, with a vapor temperature of 30°C and a filling ratio of 50%. Flow phenomena were observed at selected inclination angles of 90° and 30° from the horizontal axis, with aspect ratios of 30 and 5. The selected external diameters were 12.0 and 28.5 mm. Flow phenomena were also recorded with a standard video camera and a still camera, and the corresponding heat transfer rates were also monitored. It was observed that the basic internal flow patterns could be classified according to the aspect ratios and the Bo as follows: At an aspect ratio of 10 and higher, the annular flow at vertical changes to slug flow in inclined positions for all values of Bo. A thin liquid film always exists in the upper part, promoting heat transfer. In this case, the ratio of heat transfer rates at peak position and those of the vertical (Q / Q90) are almost the same for all Bo. At an aspect ratio of less than 10 and a low Bo, bubbly flow at vertical changes to stratified flow at an inclined position, with bubbly flow in the lower part. Vapor slug is sometimes seen. At an aspect ratio of less than 10 and a high Bo, bubbly flow with a coagulation of bubbles at the vertical position changes to stratified flow with bubbly flow in the upper part, without any vapor slugs. Q / Q90 is comparatively higher than at lower Bo. This result may be attributed to two main factors: (1) there was an area undisturbed by bubbles in the lower part; and (2) no upward vapor slug movement was observed.     

常压下液氮窄缝池沸腾实验研究

采用玻璃钢 (FRP)制成的矩形窄缝 ,对三种不同的间隙尺寸 ,分加热面与水平面呈 0°,4 5°,90°,135°,180°五种角度 ,以液氮为工质进行了 15组池沸腾实验。得出结论 :液氮在窄缝中的沸腾传热有明显的强化换热效果 ;加热面所处角度不同 ,在相同热负荷下壁面过热度亦不同 ,滑移汽泡和微液膜蒸发机理在通道中发挥的作用也相应不同。该研究对于有限空间传热强化的机理和实际应用都有一定的参考价值和指导意义。     

3D numerical analysis on mechanisms of flow and heat transfer in a square channel with right triangular wavy surfaces

Numerical investigations on thermo-hydraulic performance and mechanisms of flow and heat transfer in a square channel heat exchanger inserted with right triangular wavy surfaces are examined. The influence of the flow attack angles (30°, 45° and 60°) is investigated for laminar flow (Re = 100–2000). The configurations of the right triangular wavy surfaces are varied as inclined and V-shaped wavy surfaces (the pointing of V-tip with downstream and upstream called “V-downstream” and “V-upstream”, respectively). The insertions of the wavy surfaces in the channel heat exchanger are divided into two types: middle and diagonal insertions. The computational results reveal that the maximum thermal enhancement factor, TEF, is around 2.31 for the 30° V-downstream wavy surface with diagonal insertion at Re = 2000.     

Flow visualization of relaminarization phenomena in curved pipes and the related measurements

Flow visualization results for secondary flow phenomena at the exit of 90° and 180° bends and helically coiled pipes (1, 2 and 5 turns), (radius of curvatureR _c=381 mm, inside pipe diameterd=37.5 mm, curvature ratiod/2R _c=0.049) and in the downstream straight pipe (l/d=30) are presented to study the stabilizing (relaminarization) effect in curved pipes with fully developed entry turbulent air flow and the destabilizing (re-transition from laminar to turbulent flow) effect in the downstream straight region. The entry Reynolds numbers areRe=2200, 3200, 4300 and 5300). The related measurement results using a hot-film anemometer are presented for developing profiles of the time-mean streamwise velocity distribution and the axial turbulence intensity field in the 180° return bend and in the downstream straight pipe for Reynolds numbersRe=3200, 4300, 6300 and 8200. The time traces showing the output of the hot-film sensor are also presented for developing fluctuating velocity field in the 180° bend and in the downstream straight pipe for the same Reynolds number range. Some aspects of the relaminarization phenomena in curved pipes and the re-transition phenomena from laminar to turbulent flow in the downstream straight pipe are clarified by the present experimental investigation.     

倾斜管内低温两相弹状流特性实验研究——弹状汽泡运动速度

使用高速动态分析仪对低温倾斜上升管内不同位置处弹状汽泡进行了可视化实验研究。对获得的弹状汽泡的运动速度进行了统计分析,研究了弹状汽泡运动速度的变化规律。结果表明:对于两个不同管径的管路,当倾斜角θ(相对水平方向的夹角)为90,°80,°70°时,弹状汽泡上升速度随着长径比(x/D)的增大而增大,与传统的空气-水两相弹状汽泡沿着管路的运动速度的变化趋势不同;当倾斜角60°时,弹状汽泡上升速度随着x/D的增大先增大后减小;当倾斜角θ为45,°40°时,弹状汽泡上升速度随着x/D的增大而减小;所有工况下,随着倾斜角度的减小,弹状汽泡上升速度先增大后减小,在θ=60°处最大,且在管出口处,汽泡的上升速度几乎不变。该文为进一步研究低温液氮沸腾两相弹状流发展过程中弹状汽泡运动速度提供参考依据。     

Blowout limits of inclined nonpremixed turbulent jet flames

The blowout behavior of inclined nonpremixed turbulent jet flames is investigated by varying the jet inclined angle in the range of -90° to 90° The critical jet velocity at blow-out limit is quantified experimentally for various nozzle diameters, different fuels and inclined angles. Numerical simulations are performed to emphasize the flow field difference for the positive and negative inclined angles. Physical modeling is conducted to incorporate the effect of the inclined angle on blow-out behavior. Major findings include: (1) The negatively inclined jet flames show more intense yellow luminosity with larger sooting zones than the positively inclined jet flames; (2) The blowout limit decreases appreciably with the jet inclined angle for the negatively inclined flames, while for the positively inclined jet flames, this decrease is relatively small; (3) Physical analysis of the flow development of inclined jets is conducted, indicating the centerline velocity along the jet trajectory decreases faster for the flame with smaller inclined angle. And the decrease rate is relatively larger for the negatively inclined jet flames; (4) Based on the analysis of the flow development as well as the characteristic velocity with the inclined angle variation, a model based on the Damköhler number (Da) accounting for the effect of jet inclined angle is developed to characterize the blowout limits of inclined jet flames. The proposed model successfully correlates the experimental data. The present findings provide new data and a basic scaling law for the blowout limit of nonpremixed inclined turbulent jet flames, revealing the effect of the relative angle between the jet momentum and buoyancy.     

重力热管弹状流工况的简化分析

对重力热管弹状流工况进行简化分析，定量描述工业热管工作过程中蒸发段内汽泡的喷涌现象，给出液塞在弹状汽泡载带下的提升高度Ｌ５和体积流量与两端压力间的定量关系．     

倾斜度及温度震荡频率对三维多孔介质方腔自然对流换热的影响

对三维多孔介质倾斜方腔内非稳态自然对流换热进行数值研究.腔体右壁面(X=1)保持恒温T₀,左壁面(X=0)基于温度T₀按正弦规律变化,其他所有壁面保持绝热.采用Brinkman扩展达西模型及SIMPLE算法模拟方腔内的流动.方腔沿y轴转动倾角α1的变化范围为0°~90°,沿x轴转动倾角α2的变化范围为0°~45°,无量纲温度震荡频率f的变化范围为5π~90π.详细研究倾角和温度震荡频率对三维方腔自然对流换热的影响.计算结果表明:当倾角α1=46°,α2=45°及温度震荡频率f=45π时,方腔内的换热最强.     

同时实现多角度非垂轴面均匀照明的衍射光学器件

本文利用长焦深器件设计思路,提出了通过设计衍射光学器件相位分布使得在三个垂轴面上满足均匀照明要求来间接实现非垂轴面均匀照明的设计方法,并完成了同时实现多种角度非垂轴面均匀照明的衍射光学器件设计.基于爬山法和模拟退火法相结合的混合算法,设计了器件的相位分布,在30°、45°、55°非垂轴面上光斑不均匀性分别为5.91%、4.00%、3.38%.该方法可推广至二维情形,实现任意曲面均匀照明的要求.     

Experimental investigation of flame length of buoyancy-controlled jet flames from inclined rectangular nozzles

In this paper, the buoyancy-controlled jet flames from the inclined rectangular nozzles with different aspect ratios have been investigated. The length-to-width aspect ratios of nozzles are 1, 2.25, 4, 9, and 16 with the same cross-sectional area. The inclined angles of the nozzle to the horizontal direction are 0°, 30°, 60°, and 90°. The value of flame length changes at the same inclined angle for different aspect ratios. A correlation has been developed to calculate the flame length of jet flame for different inclined nozzle and aspect ratios with an arbitrary angle.     

Experimental Characterization of Sub-Millimetric Fluidic Actuators: Application to Boundary Layer Separation Control

Abstract

Sub-millimetric synthetic, continuous, and pulsed-jet actuators under identical conditions of generation are experimentally compared. Particle image velocimetry and hot-wire anemometry were used for measuring the velocity field. In the second part of the article, the interaction of these three types of actuators with a transverse external flow is characterized using the same experimental techniques. The studied plate is bended downstream from the actuator. Two angles are studied—0° and 28°. The efficiency of the fluidic action on the reattachment of the boundary layer is shown to be strongly dependant on the type of the jet.     

倾斜管内低温两相弹状流特性实验研究——液弹运动速度

使用高速动态分析仪对低温倾斜上升管内不同位置处弹状汽泡进行了可视化实验研究。对获得的液弹的运动速度进行了统计分析,研究了液弹运动速度的变化规律。结果表明:对于两个不同管径的管路,当倾斜角θ(相对水平方向的夹角)发生变化时,液弹的运动速度随着管径的不同呈现出不同的变化规律;随着倾斜角度的减小,液弹上升速度先增大后减小,在θ=60°和70°处达到最大值,且在管出口处,液弹的上升速度几乎不变。为进一步研究低温液氮沸腾两相弹状流发展过程中弹状汽泡运动速度提供参考依据。     

Be9(d,p),(d,t),(d,a)反应研究

本文在E_d=0.1—2.5MeV能量范围内,研究了Be⁹(d,p₀)Be¹⁰(0),Be⁹(d,p₁)Be¹⁰(3.368MeV),Be⁹(d,t₀)Be⁸(0),Be⁹(d,α₀)Li⁷(0)及Be⁹(d,α₁)Li⁷(0.478MeV)诸反应。在E_d=0.150,0.220,0.401,0.706,1.005,1.301,1.484,1.750,2.000,2.250和2.500MeV共十一个能量上分别测量了这五群出射粒子在θ_L=10—155°区间的角分布。在θ_L=135°,E_d=0.1—2.5MeV,在θ_L=95°,E_d=0.1—2.2MeV,和在θ_L=112.5°,E_d=0.5—2.5MeV测量了Be⁹(d,p₀)Be¹⁰的激发函数。在θ_L=135°和112.5°,E_d=1.2MeV,用较厚靶(100—300μg/cm²)测量了Be⁹(d,p₀)Be¹⁰(0)反应的截面绝对值,结果为σ_(p0)(θ_L=135°)=1.60mb/sr,σ_(p0)(θ_L=112.5°)=1.55mb/sr。这样就得到了在此能区内,这五群出射粒子的截面情况。对所得结果进行了一些讨论。     

Experimental investigation of subcooled flow boiling of a 50/50 ethylene glycol/water mixture in finned rectangular aluminum channels

Subcooled flow boiling heat transfer experiments were performed with a 50/50 ethylene glycol/water mixture in a finned aluminum channel. The channel represented a hybrid electric vehicle power electronic cold plate receiving a 50/50 mixture from the radiator at 105°C and 2 atmospheres. Experiments used a range of mixture flow rates and both top- and bottom-heating situations. Boiling curves were generated, and subcooled flow boiling heat transfer coefficients were determined including the test channel fin effects. Subcooled flow boiling heat transfer coefficients showed a 25–30% increase compared to single-phase convection.     

离轴三反射望远镜遮光罩设计与杂光分析

分析了离轴三反射望远镜的杂散光特性,给出了遮光罩设计的基本原则并进行了初步的设计.根据系统所要探测到的极限星等,通过计算得到了望远镜光学系统的点源透射比所必需满足的条件;在Tracepro杂光分析软件中建模,在方位角为0°、45°、90°、135°和180°时分别对0.1°～80°之间共15个离轴角度进行了光线追迹,通过计算得到了系统的PST曲线.结果表明,系统PST整体上是下降的且在离轴角30°以后接近指标要求,但在方位角0°和180°时,PST曲线在个别角度有突增的现象,通过光线追迹数据,得到了主要的杂光传输路径,提出了对遮光罩的修改方案并对其进行了修改.最后对改进后的系统重新进行了仿真分析.仿真结果表明,系统的杂光抑制能力达到了指标要求.     

A Predictive Model for the Initial Droplet Size and Velocity Distributions in Sprays and Comparison with Experiments

The distribution of sizes and velocities of droplets initially formed in sprays is an important piece of information needed in the spray modelling, because it defines the initial condition of the spray droplets in the predictive calculations of the downstream two‐phase flow fields. A predictive model for the initial droplet size and velocity distributions in sprays is formulated in this study. The present model incorporates both the deterministic and the stochastic aspect of spray formation process. The deterministic aspect takes into account of the unstable wave motion before the liquid bulk breakup through the linear and nonlinear instability analysis, which provides information for the liquid bulk breakup length, the mass‐mean diameter and a prior distribution for the droplet sizes corresponding to the unstable wave growth of various wavelengths. The stochastic aspect deals with the final stage of droplet formation after the liquid bulk breakup by statistical means through the maximum entropy principle based on Bayesian entropy. The two sub‐models are coupled together by the various source terms signifying the liquid‐gas interaction, the mass mean diameter and the prior distribution based on the instability analysis. The initial droplet size and velocity distributions are measured experimentally by phase‐Doppler interferometry for sprays generated by a planar research nozzle and a practical gas turbine airblast nozzle. For the two nozzles, the liquid bulk sheet is formed before its breakup in a coflowing air stream. It is found that the model predictions are in satisfactory agreement with the experimental data for all the cases measured. Hence the present model may be applied to a variety of practical sprays to specify the initial conditions for the spray droplets formed in practical spray systems.     

Hydrophobization of epoxy nanocomposite surface with 1H,1H,2H,2H-perfluorooctyltrichlorosilane for superhydrophobic properties

Nature inspires the design of synthetic materials with superhydrophobic properties, which can be used for applications ranging from self-cleaning surfaces to microfluidic devices. Their water repellent properties are due to hierarchical (micrometer- and nanometre-scale) surface morphological structures, either made of hydrophobic substances or hydrophobized by appropriate surface treatment. In this work, the efficiency of two surface treatment procedures, with a hydrophobic fluoropolymer, synthesized and deposited from 1H,1H,2H,2H-perfluorooctyltrichlorosilane (PFOTS) is investigated. The procedures involved reactions from the gas and liquid phases of the PFOTS/hexane solutions. The hierarchical structure is created in an epoxy nanocomposite surface, by filling the resin with alumina nanoparticles and micron-sized glass beads and subsequent sandblasting with corundum microparticles. The chemical structure of the deposited fluoropolymer was examined using XPS spectroscopy. The topography of the modified surfaces was characterized using scanning electron microscopy (SEM), and atomic force microscopy (AFM). The hydrophobic properties of the modified surfaces were investigated by water contact and sliding angles measurements. The surfaces exhibited water contact angles of above 150° for both modification procedures, however only the gas phase modification provided the non-sticking behaviour of water droplets (sliding angle of 3°). The discrepancy is attributed to extra surface roughness provided by the latter procedure.