地沟油生物柴油在旋流喷嘴中的雾化实验及模拟

对地沟油生物柴油在旋流雾化喷嘴中的内部流场及外部流场进行数值模拟,考察了喷嘴孔径、旋流芯螺距、螺柱槽道横截面积和槽道形状等结构参数对出口雾化速度及索特平均直径的影响,通过实验对模型进行了验证。结果表明,0.7 mm孔径的喷嘴的韦伯数最大,索特平均直径与雾化锥角最优。螺距4 mm的喷嘴雾化特性最优,旋流芯螺距越小,流体在喷嘴内旋流次数越多,阻力损失越大,流体在切向分量上速度越大。梯形槽道的雾化效果最好,相同横截面积下槽道的水力直径越大,雾化效果越好;截面积1 mm2槽道的喷嘴最优,槽道横截面积越小,流体在槽道中的湍流程度越大,流体内部剪切应力越大,液体表面不稳定波急剧增大。     

Flow field in the freeboard of vortexing fluidized bed

A systematic investigation on the flow field in a vortexing fluidized bed cold model was reported. The gas velocity profiles within the freeboard with diameters of 0.19 m and 0.29 m were measured by using a five-hole pitot tube. A new parameter, called vortex number, V_or defined as the ratio of tangential velocity to axial velocity of the swirling gas stream, was proposed for representing the swirl intensity. V_or is found to be increased with secondary air velocity, and decreased with primary air velocity and diameter of secondary air nozzles. It is also found that the profile of swirl flow is significantly affected by the arrangement of the secondary air nozzles. The effects of inserted length of secondary air nozzles and geometric structure of expansion section on the swirl flow are also studied. Based on the experimental data, a correlation is presented to estimate the vortex number. Vortex number is found to be a function of the geometric structure of exhaust tube, diameter of secondary air nozzle and tangential air flow rate.     

中心气流与环形气流作用下颗粒射流的流动与混合特性

采用PIV测速系统和高速摄像仪对同轴气固两相射流进行了实验研究,着重考察了同轴射流结构和旋流对颗粒流动与混合特性的影响。结果表明,环形气流作用下颗粒获得的轴向速度比相同条件下中心气流作用下的颗粒轴向速度大,且气固两相的混合效果更佳,在这两种同轴射流结构下,颗粒的轴向速度仅在靠近喷嘴的横截面上分布较为均匀。而旋流,特别是强旋的引入不仅可以促进远场区颗粒速度的均布,而且能够有效地改善两相混合效果。     

旋流板式气液分离器的放大规律

对旋流板式气液分离器在3种规模、18种旋流板结构下进行了模型实验研究，考察了旋流板结构参数(径向角、仰角和叶片数量)对分离效率和压降的影响，并建立了预测分离器压降的关联式，为旋流板结构参数的确定提供了依据. 工业应用的标定结果表明分离器压降预测式是准确的，它可用于工业气液分离器的放大设计.     

新型气液逆流撞击洗涤喷嘴的优化

针对一种新型气液逆流撞击式洗涤喷嘴,通过冷模实验,采用溶氧法考察了不同结构喷嘴的气液两相传质性能。结合解析率及流型变化,考察了喷嘴出口直径、切向进液口倾角、旋流室收敛段锥角、切向进液口直径、喷口长度5个参数对传质的影响,确定了优选喷嘴的结构尺寸,分析了该优选喷嘴在不同操作条件下(气速、表观液气比和轴切比)的传质效果。结果表明,优选喷嘴在轴切比为0.4~0.6且气速较高时传质效果较好。     

Optimizing swirl in compact uniflow cyclones

This paper presents an experimental examination of the velocity field distribution in the separation chamber of a uniflow cyclone with closed particle outlet to evaluate the swirl characteristics in the vortex finder region based on stereoscopic particle image velocimetry. A cold flow model with a closed particle outlet was used to assess different angles of attack and core size ratios at typical Reynolds numbers for the separation of low loaded gas-solid flows. The focus of the study was on the relationship between swirl strength as well as performance data. At higher angles, the parabolic swirl strength distribution changed to a region with constant high acceleration of the particles in the separation zone. Integral and differential swirl numbers were correlated with the ratio of tangential to radial velocity and to the calculated cut size diameter. At low angles of attack, implying a strong redirection of flow perpendicular toward the main flow direction and small core size ratios, defined by the radial distance between hub and tip, the local differential swirl number can be more than twice as large as in the base configuration. Yet, the integral swirl number hardly changed. The velocity fields showed mean tangential to radial velocity ratios ranging from 0.73 to 6.85 at swirl vane angles of 15 ^° –60 ^° ; core size ratios between 0.125 and 0.625 at vortex finder diameter were measured and calculated cut size diameters between 10 and 90 μm were derived. This data provides the foundation for further validation studies and the development of new design criteria. © 2018 American Institute of Chemical Engineers AIChE J, 65: 766–776, 2019     

Experimental investigation of the effect of fuel nozzle geometry on the stability of a swirling non-premixed methane flame

An experimental investigation on the stability of a swirling non-premixed methane flame is reported in this paper. Methane gas is supplied through a central nozzle, and combustion (co-flow) air is supplied through an annulus surrounding the nozzle. Two main parameters were varied independently, which are the nozzle geometry and swirl strength; however the exit velocity of the central (fuel nozzle) jet and co-airflow were also varied to provide a wide range of test conditions. Two nozzles were tested: a contracted circular (referred to hereafter as CCN) and a rectangular (referred to hereafter as RN), which have similar equivalent diameter, D_e (defined as the diameter of a round slot having the same exit area as the nozzle geometry). The contracted circular nozzle has a diameter of 4.82 mm, and the rectangular nozzle has a diameter of 4.71 with an aspect ratio of 2:1. The swirl strength of the co-flow was varied by changing the vanes’ angle. The main results obtained from this study show that the rectangular nozzle exhibits higher entrainment and jet spreading rates compared with its CCN counterpart. In addition, the results revealed that increasing the swirl strength creates a flow recirculation zone which is larger with the RN compared with that of the corresponding CCN. These flow features associated with the RN lead to an enhanced mixing which consequently promotes better flame stability compared with its CCN counterpart.     

旋流燃烧室内气体-颗粒两相湍流流动的数值模拟

综合应用代数Reynolds应力模型和流体相脉动速度大小和方向均具有随机性的颗粒相随机轨道模型,对旋流燃烧室内有直流射流与旋转射流相互作用的气-固两相湍流流动进行了数值模拟.得到的气相轴向与切向速度和轴向脉动速度均方根值分布以及颗粒相轴向总质量流通量和轴向与切向速度分布与实验基本相符合,并比对气相湍流采用k-ε模型的相应计算结果有较明显的改进.     

旋风管分离器流场模拟研究

旋风管作为多管式旋风分离器的主要元件,已经成为气固两相分离的重要研究对象,主要用于处理气量较大且对分离效率要求较高的工况。本文采用大涡模拟的方法考察了分离器内切向与轴向速度分布形态的影响。模拟结果表明：在一定程度上加长排气管的插入深度对分离效率的提升是有益的;旋风管筒体太长对分离效率的提高作用不大;增大排气管直径有助于降低降压。     

Nitrogen dilution effect on flame stability in a lifted non-premixed turbulent hydrogen jet with coaxial air

The nitrogen dilution effect on flame stability was experimentally investigated in a lifted non-premixed turbulent hydrogen jet with coaxial air. Hydrogen gas was used as the fuel and coaxial air was injected to initiate flame liftoff. Hydrogen was injected into an axisymmetric inner nozzle (d_F = 3.65 mm) and coaxial air jetted from an axisymmetric outer nozzle (d_A = 14.1 mm). The fuel jet and coaxial air velocities were fixed at u_F = 200 m/s and u_A = 16 m/s, while the mole fraction of the nitrogen diluent gas varied from 0.0 to 0.2 with a 0.1 step. For the analysis of the flame structure and the flame stabilization mechanism, the simultaneous measurement of PIV/OH PLIF was performed. The stabilization point was in the region of the flame base with the most upstream region and was defined as the point where the turbulent flame propagation velocity was found to be balanced with the axial component of the local flow velocity. The turbulent flame propagation velocity increased as the nitrogen mixture fraction decreased. The nitrogen dilution makes the flame structure more premixed. That is, the stabilization mechanism shifts from edge flame propagation based mechanism toward premixed flame propagation based mechanism. We concluded that the turbulent flame propagation velocity was expressed as a function of the turbulent intensity and the axial strain rate, even though the mole fraction of the nitrogen diluent varied.     

旋流数为1.0的强旋湍流两相流动的PDPA实验

采用相位多普勒颗粒测速仪 (PDPA)对旋流数为 1 0的轴向和切向进风的圆柱形旋风筒内强旋湍流气粒两相流动进行了测量研究 ,并与旋流数为 0 47、 1 5和 2 0 8的实验结果进行了对比分析 ,指出了旋流数变化对两相流场及两相湍流特性的影响 .     

分级进风燃烧室内旋流反应流的湍流特性

This paper presents an experimental investigation of the turbulent reacting flow in a swirl combustor with staged air injection. The air injected into the combustor is composed of the primary swirling jet and the secondary non-swirling jet. A three dimension-laser particle dynamic analyzer （PDA） was employed to measure the instantaneous gas velocity. The probability density functions （PDF） for the instantaneous gas axial and tangential velocities at each measuring location, as well as the radial profiles of the root mean square of fluctuating gas axial and tangential velocities and the second-order moment for the fluctuating gas axial and tangential velocities are obtained. The measured results delineate the turbulence properties of the swirling reacting flow under the conditions of staged combustion.     

Development of mixing time correlation for a double jet mixer

BACKGROUND: Jet mixing is one of the simplest methods to achieve mixing. There have been a number of experimental studies concerned with jet mixing; some of these studies report empirical correlations. The existing correlations are not useful where there are significant deviations from the idealized conditions. Most correlations reported in the literature deal with liquid flow with single or multiple jets, whereas the effect of radial angle on mixing time was not studied. This present study investigates the effect of operating parameters on experimental mixing time in a double jet mixer. Nozzle configuration for jet1 was fixed based on earlier studies (2/3rd position, nozzle angle 45° and nozzle diameter 10 mm). Mixing times were estimated for different jet2 configurations of jet angle (30°, 45° and 60°), radial angles (60°, 120°, 180°), jet diameter (5 mm and 3 mm) and located at different tank heights (2/3rd and 1/3rd from the bottom of the tank). RESULTS: A mixing time correlation was developed in terms of all the parameters using dimensional analysis. The constants and powers of the parameters involved in the correlation developed were estimated using a least square method to calculate the straight line that best fitted the mixing time data obtained during the experiments. The effects of change in angle of inclination of jet2 (θ₂), radial angle of jet2 with respect to jet1 (Φ₂) and diameter of jet2 (d₂) on mixing time were analyzed and compared with the experimental mixing time. CONCLUSION: The correlation developed based on the dimensional analysis and least square method predicts the mixing time for a double jet mixing tank. Copyright © 2009 Society of Chemical Industry     

不同旋流数下湍流气粒两相流动特性的PDPA实验研究

利用相位多普勒仪 (PDPA)系统研究了不同旋流数下突扩旋风筒内气粒两相湍流特性的变化规律 .在相同的进口形状和总风量的条件下 ,分别测量了旋流数为 0、 0 .5和 1.0时气相和颗粒相的轴向、切向的平均速度和脉动速度 .结果表明 :旋流数的变化对轴向速度的分布和切向速度的似固核 -位涡结构 ,以及两相脉动速度和两相湍流各向异性都有比较明显的规律性影响 ;总体上 ,旋流对两相湍流起抑制作用 ,但随旋流数的增大 ,两相湍流脉动及其各向异性都有先减弱 ,后来又有所增大的趋势     

A novel approach for determining the flow patterns in centrifuges by means of Laser-Doppler-Anemometry

The flow pattern in process machinery has a significant impact on the product quality, because it influences the residence time, the mixing of components and the stability of chemical reactions. Hence the determination of the residence time and the measurement of the flow patterns have been the emphasis of many studies. The work presented shows a novel approach for the determination of the tangential and axial velocity profiles in a tubular bowl centrifuge. For the first time, flow velocities inside a fast rotating centrifuge have been measured using Laser-Doppler-Anemometry. The rotor of the centrifuge is made of carbon fibre reinforced plastic with an inner diameter of 100 mm and a length of 200 mm. The maximum rotational speed is 20,000 rpm, creating the multiple of 22,400 times the earth gravitational force. No failure of the material was detected at any process parameters. The centrifuge is operated with two different setups. One setup employs an assembly of two coaxial cylinders, in which the void between them is entirely filled with water. In the second arrangement, only the outer rotor is assembled and the centrifuge is operated like an overflow centrifuge. The Laser-Doppler measurements of the axial fluid velocity are confirmed by determining the residence time distribution at various parameters. The results obtained show an effective tangential acceleration; the liquid exhibits a rigid body rotation for rotational speeds up to 8000 rpm for throughputs between 0.5 and 1.8 l/min. The axial flow pattern depend on the volume flux and the rotational speed. The cross-section through which the liquid flows was in most cases between 60% and 100% of the overall area. The influence of the inlet subsides towards the outlet with an inlet zone of 15% of the length of the rotor. No boundary layer flow was detected in the overflow setup, which is due to the plunged inlet and the effective tangential acceleration of the incoming liquid.     

高速煤粉燃烧器内燃烧特性数值模拟及结构优化

高速煤粉燃烧器火焰喷射速度高达60~200 m/s,炉膛内火焰较长,对流换热比例提高,使得炉膛内温度分布均匀,没有传统低速煤粉燃烧器火焰短,炉膛内局部过热和结焦等缺点。笔者以14 MW高速煤粉燃烧器为研究对象,采用数值模拟的方法,研究旋流强度、二次风温度等关键参数对燃烧器内煤粉燃烧的影响,针对燃烧器内煤粉燃烧特点进行结构优化设计。对旋流强度研究结果表明,当旋流强度S=2.2、2.8、3.2及3.7时,燃烧器内回流区形状变化不大,从一次风喷口开始到旋流叶片位置结束,回流区环绕一次风管;最大回流量在一次风喷口附近,距离一次风喷口越远,回流量越小;旋流强度对一次风喷口附近最大回流量影响不大,喷口附近最大回流量均在0.45 kg/s左右,当距喷口超过一定距离(L/H<0.35)时,旋流强度对回流量的影响开始变得明显,表现为旋流强度越大,回流区末端回流量越大,回流区末端回流量最大为0.30 kg/s,最小为0.17 kg/s。研究燃烧器喷口处燃烧状态表明,喷口处火焰旋流强度为0.10~0.28,与入口旋流强度正相关,火焰喷射速度150 m/s,为中等旋流强度的高速旋流火焰;喷口中心区可燃性组分富集,缺氧,燃料和氧气分层分布。当旋流强度提高,喷口中心区可燃性组分浓度降低,CO浓度从11%降低到10%,H2浓度从1.65%降低到1.40%,焦炭浓度从0. 14%降低到0. 11%,喷口边缘O2浓度从13%降低到10%。旋流强度S=3.2和S=3.7时可燃组分和氧气浓度分布变化较小,说明旋流强度提高对燃烧的影响减弱。考察0、100和200℃下二次风温度对燃烧的影响,结果表明,当二次风温度提高,煤粉在燃烧器内的反应时间有所降低,从0.15 s降低到0.11 s,但燃烧器内的煤粉碳转化率提高20%,达到65%。对燃烧器结构进行优化,加入中心风,对比中心风直流和旋流与不加中心风3种状态,结果表明,加入旋流中心风和直流中心风后喷口中心区半径r≤75 mm范围内可燃组分浓度降低,采用直流时由于气流刚性较强,喷口中心区氧气浓度升高,采用旋流中心风对中心区氧浓度影响弱,对可燃组分浓度降低效果优于直流中心风。     

MODELING OF LATERAL JETS INJECTED INTO SWIRLING CROSSFLOW

A numerical prediction procedure for the computation of turbulent swirling flows is being used to predict the nonreacting flowfield inside a can combustor with lateral jet injection. The three-dimensional code utilizes a finite-difference explicit time marching scheme in cylindrical coordinates. Turbulence is simulated by means of the two-equation k-ε model. Predictions of the time-averaged flowfield of a deflected turbulent jet in a cylindrically confined nonswirling and swirling crossfiow are presented. The effect of jet-to-crossflow velocity ratios of 2, 4, and 6 in a crossflow with swirl strengths (swirler vane angle) of 0°, 45°, and 70° are investigated. Second-order upwind differencing scheme is utilized for the advection terms in the momentum equation to minimize numerical diffusion error. The predicted velocity profiles exhibit good agreement with experiments.     

管内周期性自旋流强化传热的结构优化

在圆管内间隔插入多个旋流片的流道中,流体流动呈现周期性自旋流.用数值模拟方法对空气湍流情况的传热和流阻性能受相邻旋流片间距L_p、旋流角β和旋转角α3个因素的影响进行了分析,并得出旋流片的优化结构,而且实验验证了数值模拟预测的正确性.结果表明：α越大,传热性能越好,阻力越大;L_p越小,传热性能越好,阻力越大;β越大,传热性能越好,而阻力损失因受到摩擦阻力和形体阻力的综合影响而呈现非单调变化.旋流片的最佳结构参数为：旋流角β为20.3°,旋转角α为180°,相邻旋流片间距L_p为33d.与α相比,β对传热和流阻性能的影响更显著.     

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。     

LATERAL JET INJECTION INTO ISOTHERMAL COMBUSTOR FLOWFIELDS

Primary and dilution lateral jet injections into a typical isothermal combustor are investigated using a fully three-dimensional turbulent computer simulation. Predictions of the time-mean flowfield of a deflected turbulent jet in a cylindrically confined swirling crossflow are presented. The effect of jet-to-crossflow velocity ratios of 2, 4, and 6 in a crossflow with swirl strengths of swirler vane angle of 0, 45, and 70 degrees were investigated. Predictions are compared with smoke and neutrally-buoyant helium-filled soap bubbles flow visualization of the deflected jet. Single and multi lateral jets are also considered in the investigation. The predicted results exhibit good agreement with the trajectory and spread pattern of the jet obtained using flow visualization techniques. The three-dimensional prediction technique utilizes a finite-difference explicit time marching scheme in cylindrical coordinates. Turbulence is simulated by means of the standard two-equation κ-ε turbulence model.