Experimental study of a heavy fuel oil atomization by pressure-swirl injector in the application of entrained flow gasifier

The available SMD(Sauter mean diameter) correlations on pressure-swirl injectors predict droplet sizing very different from each other, especially for heavy fuels. Also there was a lack in the literature for comparing available correlations. So an experimental study was conducted on a heavy fuel oil(HFO) spray, Mazut 380. A pressure swirl injector was designed and fabricated. The experiments for Mazut at 40 °C and 80 °C were compared with the results for water, including spray half cone angle, breakup length and mean droplet diameter,at different injection pressures. Lower spray angle, higher breakup length and larger droplets were observed for lower injection pressures and higher liquid viscosity. SMD was about 75 μm for water and about 87 μm for Mazut at 80 °C. The results for droplet mean diameter were also compared with correlations from previous studies on pressure swirl atomizers. The SMD results show that for water spray, LISA method was in good agreement,also Babu and Ballester correlations were successful when high viscosity fluid was injected.     

旋流压力式喷嘴低压喷淋液滴粒径的实验研究

以自来水为喷淋介质,对旋流压力式喷嘴低压喷淋液滴粒径进行了测试,分析了压力、喷孔直径和喷嘴流量对液滴索特平均直径(d_(SMD))的影响规律,研究了旋流压力式喷嘴液滴尺寸的分布规律。采用跨径(K)和均匀度指数(N)来揭示喷嘴低压喷淋质量。实验结果表明,d_(SMD)较大,超过250μm；d_(SMD)随喷孔直径增大而增大,随压力和喷嘴流量增大而减小；喷淋液滴尺寸分布均匀性较好,K小于0．65,N大于4。实验结果可以为旋流压力式喷嘴设计和改进提供重要的实验依据。     

Dispersion of spray from swirl nozzles

Atomization and dispersion of a liquid in the form of a spray from an atomizing nozzle is associated firstly with the disintegration of a high speed thin liquid sheet into droplets and then with the dynamics of those droplets in the surrounding atmosphere. In the present work a theoretical model has been set up to evaluate the droplet trajectories of an atomized spray from a swirl nozzle as a function of the liquid properties, injection conditions and geometrical dimensions of the nozzle. The theoretical model is based on the analytical solution of the internal hydrodynamics of the nozzle followed by the dynamics of droplets in a stagnant atmosphere. Experiments have been conducted to determine the drop size distributions and the spatial mass flow distribution of the spray. The pertinent governing parameters regarding the spray dispersion are the liquid velocity, viscosity and surface tension of the liquid, the density of the ambient atmosphere and the geometrical dimensions of the nozzle. The theoretical and ex     

Influence of Nozzle Parameters on Spray Pattern and Droplet Characteristics for a Two-Fluid Nozzle

In this study, a two-fluid nozzle, as, e.g., used in fluidized-bed or spray drying applications, is comprehensively characterized regarding the spray pattern and droplet size. To analyze the spray cone, the spray cone angle and the radial mass distribution of the nozzle were measured at varied liquid flow rate, spray air pressure, liquid insert bore diameter, and air cap position. Additionally, droplet size distributions were recorded at different spray settings. In general, the overall spray cone and single droplets are significantly influenced by the spray parameters, especially the spray air pressure, as well as the nozzle geometry.     

喷淋塔液滴粒径分布及比表面积的实验研究

以水和空气为实验介质,通过拍照法获得喷淋塔内液滴粒径分布,考察了不同喷淋量及空塔气速对塔内不同高度处液滴Sauter平均直径(SMD)的影响,并对液滴粒径分布进行了理论分析.结果表明,喷淋塔顶部液滴分布密集,底部稀疏,液滴群在下落过程中,平均粒径减小且趋于均匀化;塔顶处液滴SMD随喷淋量的增加而增大,处在塔中下部的液滴SMD则随喷淋量增大而减小,提高空塔气速,可减小平均粒径;理论分析认为,液滴粒径减小主要是由于发生了碰撞破碎的缘故,而塔内液滴大小不一是碰撞的主要原因;通过量纲1化拟合得到喷淋塔内液滴SMD经验关联式,其计算结果与实验值吻合较好;考虑液滴破碎的喷淋塔比表面积比不考虑破碎的比表面积大70%左右.     

Predictive models for characterizing the atomization process in pyrolysis of methyl ricinoleate

Pyrolysis of methyl ricinoleate(MR) can produce undecylenic acid methyl ester and heptanal which are important chemicals. Atomization feeding favors the heat exchange in the pyrolysis process and hence increases the product yield. Herein, predictive models to characterize the atomization process were developed. The effect of spray distance on Sauter mean diameter(SMD) of atomized MR droplets was examined, with the optimal spray distance to be 40–50 mm. Temperature mainly affected the physical properties of feedstock, with smaller droplet size obtained at increasing temperature. In addition, pressure had significant influence on SMD and higher pressure resulted in smaller atomized droplets. Then, a model for SMD prediction, combining temperature, pressure, spray distance, and structural parameters of nozzle, was developed through dimensionless analysis. The results showed that SMD was a power function of Reynolds number(Re), Ohnesorge number(Oh), and the ratio of spray distance to diameter of swirl chamber in the nozzle(H/dsc), with the exponents of -1.6618,-1.3205 and 0.1038, respectively. The experimental measured SMD was in good agreement with the calculated values, with the error within ±15%. Moreover, the droplet size distribution was studied by establishing the relationship between the standard deviation of droplet size and SMD. This study could provide reference to the regulation and optimization of the atomization process in MR pyrolysis.     

Y型气流式喷嘴的雾化滴径和滴径分布

索特平均滴径(SMD)和滴径分布是描述喷嘴雾化性能的主要指标.根据Y型喷嘴雾化过程的特征,提出了Y型喷嘴的液滴随机分裂模型,得到了SMD的表达式.考察了Y型喷嘴对氯化聚氯乙烯(CPVC)氯化液的雾化过程,利用Mastersizer2000型测粒仪测定了雾化滴径分布.关联了SMD的经验方程,得到了初次雾化平均滴径.采用液滴随机分裂模型模拟计算了雾化滴径分布,计算结果与实验结果吻合,说明模型和平均滴径方程可以用来预测Y型喷嘴的雾化性能.     

Droplet collision processes in an inter-spray impingement system

The main objectives of the present article are in developing and evaluating a new model for the droplet collision, and in discussing the physical feature for the mutual impinging sprays. The new model is originally devised to be capable of predicting the droplet collision-induced breakup accompanied with the formation of satellite droplets. From the well-established conservation equations, the several formulae are newly proposed by consideration of some important regimes such as bounce, coalescence, and stretching and reflexive separation. This formulation makes it possible to predict the number of satellite droplets, and the droplet sizes and velocities. The extensive experiments are conducted for the inter-spray impingement systems under the various conditions to investigate the influence of impinging angle and impingement distance upon the spray characteristics. The droplet sizes and velocities are measured by the phase Doppler particle analyzer system and the distribution of liquid volume fraction is also measured by the self-manufactured patternator. In addition, numerical predictions by the new model and the O’Rourke model are compared with experimental data for the various parameters. It is found that the SMD (Sauter mean diameter) measured in the downstream region after inter-spray impingement are 40% smaller than those for the case of single nozzle. The new model shows vigorous breakup during collision, which is no longer seen in the O’Rourke model.     

Spray and mixing characteristics of liquid jet in a tubular gas–liquid atomization mixer

For the design and optimization of a tubular gas–liquid atomization mixer,the atomization and mixing characteristics of liquid jet breakup in the limited tube space is a key problem.In this study,the primary breakup process of liquid jet column was analyzed by high-speed camera,then the droplet size and velocity distribution of atomized droplets were measured by Phase-Doppler anemometry (PDA).The hydrodynamic characteristics of gas flow in tubular gas–liquid atomization mixer were analyzed by computational fluid dynamics (CFD) numerical simulation.The results indicate that the liquid flow rate has little effect on the atomization droplet size and atomization pressure drop,and the gas flow rate is the main influence parameter.Under all experimental gas flow conditions,the liquid jet column undergoes a primary breakup process,forming larger liquid blocks and droplets.When the gas flow rate (Q_g) is less than 127 m~3·h~(-1),the secondary breakup of large liquid blocks and droplets does not occur in venturi throat region.The Sauter mean diameter (SMD) of droplets measured at the outlet is more than 140μm,and the distribution is uneven.When Q_g127 m~3·h~(-1),the large liquid blocks and droplets have secondary breakup process at the throat region.The SMD of droplets measured at the outlet is less than 140μm,and the distribution is uniform.When 127Q_g162 m~3·h~(-1),the secondary breakup mode of droplets is bag breakup or pouch breakup.When 181Q_g216 m~3·h~(-1),the secondary breakup mode of droplets is shear breakup or catastrophic breakup.In order to ensure efficient atomization and mixing,the throat gas velocity of the tubular atomization mixer should be designed to be about 51 m·s~(-1)under the lowest operating flow rate.The pressure drop of the tubular atomization mixer increases linearly with the square of gas velocity,and the resistance coefficient is about 2.55 in single-phase flow condition and 2.73 in gas–liquid atomization condition.     

转炉一次除尘新OG系统高效喷淋塔喷嘴雾化特性的模拟

利用离散相模型对转炉一次除尘新OG系统高效喷淋塔内喷嘴的雾化特性进行模拟,分析了喷射角度、喷射压力、喷射流量及喷嘴水平间距等因素对雾化场索太尔平均直径(SMD)和蒸发效率的影响. 结果表明,在一定范围内随喷射角度增加,液滴在雾化场中的覆盖面增大,液滴驻留时间变长,蒸发效率增加,雾化场SMD减小,喷射角度大于60o时,SMD值减小缓慢. 随喷射压力增大,液滴蒸发效率增加,雾化场SMD减小,压力大于1.0 MPa时对SMD的影响较小. 随喷射流量增加,液滴蒸发效率减小,雾化场SMD增加,流量小于0.15 kg/s时,SMD增加幅度偏小. 两喷嘴水平间距越大,液滴分布面积越大,但对雾化场SMD影响较小. 在一定条件下,喷嘴间距约为800 mm时,截面速度分布较均匀.     

Effects of co- and counter-swirl on the droplet characteristics in a spray flame

This paper reports measurements of droplet characteristics and flow field in a spray flame with inner and outer swirling air streams. The spatial distribution of droplet characteristics produced by the burner's airblast atomizer was measured using dual-phase Doppler anemometry (PDA). The spray flame was operated near the lean blow-out limit at two flow conditions: co-swirling (flow rotation in the same direction) and counter-swirling (flow rotation in opposite directions). In both cases, the flame exhibited a U-shaped form and was marked by a large central recirculation zone. Based on the measurements of the droplet velocity components, differences between both configurations appeared for the counter-rotational setup mainly in the near burner region, where the decrease of total swirl causes deeper penetration of the droplets from the inner duct into the combustion chamber, resulting in a much more homogeneous distribution than the other one. The droplet size in terms of the Sauter mean diameter (SMD) shows little variation in the change of the direction swirl condition. Application of counter-swirl results in more turbulent droplet motion.     

An atomization model for splash plate nozzles

A model for the atomization and spray formation by splash plate nozzles is presented. This model is based on the liquid sheet formation theory due to an oblique impingement of a liquid jet on a solid surface. The continuous liquid sheet formed by the jet impingement is replaced with a set of dispersed droplets. The initial droplet sizes and velocities are determined based on theoretically predicted liquid sheet thickness and velocity. A Lagrangian spray code is used to model the spray dynamics and droplet size distribution further downstream of the nozzle. Results of this model are confirmed by the experimental data on the droplet size distribution across the spray. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Numerical simulation of heavy fuel oil atomization using a pulsed pressure-swirl injector

It is known that increasing the injection pressure reduces the breakup length and the droplet size. Adding pulses, on the other hand, helps to atomize the liquid into finer droplets, similar to air-assisted injectors but without altering the air-to-fuel concentration.To further reduce the droplet size and breakup length, a novel injector type, called ‘‘Pulsed Pressure-Swirl"(PPS), is introduced in this work, which is a combination of pressure-swirl and ultrasonic pulsed injectors. A pressure-swirl atomizer was designed and fabricated specifically for Mazut HFO(Heavy Fuel Oil). The droplet formation process and droplet size distribution have been studied experimentally(by shadowgraphy high speed imaging) and numerically(with the open-source Volume-of-Fluid code Gerris).Changing liquid injection pressure effect on the spray angle and film thickness has been quantified.These simulations have been used to study the primary breakup process and quantify the droplet size distributions, using different injection pulse frequencies and pressures.The numerical results have revealed that the new injector concept successfully produces finer droplets and results in a decrease in the breakup length, especially when applying high pulse frequencies, with no significant changes in the spray angle.     

压力旋流喷嘴雾化滴径分布的模型预测和实验

利用激光片光荧光诱导技术（PLIF）测得不同液体流量下的压力旋流喷嘴雾化滴径分布,用平均粒径约束的三参数最大熵模型对雾化滴径分布进行预测。将理论预测分布与实验结果进行拟合,得到广义伽玛参数α随着液体流量变化的一般表达式。用拟合模型对粒径分布的特点和规律进行总结,结果表明：拟合模型能很好地预测粒径的数量分布,且不受小液滴的影响;随着液体流量的增加,液滴粒径分布范围逐渐变窄,峰值液滴粒径呈线性减小趋势,峰值液滴百分数呈线性增加趋势。     

Mean Droplet Size and Local Velocity in Horizontal Isothermal Free Jets of Air and Water,respectively, Viscous Liquid in Quiescent Ambient Air

Measurements using two‐dimensional Phase Doppler Anemometry as well as high speed cinematography in free jets at several nozzle exit pressures and mass flow rates, show that the Sauter mean droplet diameter decreases with increasing air and liquid‐phase mass flow ratio due to the increase of the air stream impact on the liquid phase. This leads to substantial liquid fragmentation, respectively primary droplet breakup, and hence, satellite droplet formation with small sizes. This trend is also significant in the case of a liquid viscosity higher than that of water. The increased liquid viscosity stabilizes the droplet formation and breakup by reducing the rate of surface perturbations and consequently droplet distortions, ultimately also leading, in total, to the formation of smaller droplets. The droplet velocity decreases with the nozzle downstream distance, basically due to the continual air entrainment and due to the collisions between the droplets. The droplet collisions may induce further liquid fragmentation and, hence, formation of a number of relatively smaller droplets respectively secondary breakup, or may induce agglomeration to comparatively larger liquid fragments that may rain out of the free jet.     

基于图像法的环雾状流液滴参数测量与分析

环雾状流广泛存在于石油化工领域,其内部流场测量具有重要意义。本文结合光学图像法和高速摄影技术对撞针式喷嘴的雾化特性进行了测量分析,以此为基础对基于雾化混合的环雾状流中夹带液滴特性开展了实验研究。利用高速摄影技术对喷雾进行可视化,采用单帧单曝光法对液滴尺寸和速度信息进行提取。研究发现,液滴速度随轴向距离增大呈衰减趋势,且相同轴向距离（约在径向位置10mm处）条件下,速度达到峰值;液滴索泰尔平均直径（SMD）随喷嘴孔径d₀的增大而增大,并与液相质量流量m_l和喷嘴上下游压差?p均呈负相关;另外,在环雾状流环境中,相同气压条件下液滴SMD随气相体积流量Q_g增大而减小,而相同气相体积流量条件下SMD随气压p_g增大而增大。基于实验测量结果,以气相韦伯数We_g和液相雷诺数Re_l为主影响参数,引入相间滑移和压力系数建立了基于量纲分析的环雾状流液滴SMD预测模型,平均绝对百分比误差MAPE为11.4672%。     

Solid-liquid separation in suspension atomization

The aim of this paper is to define the conditions controlling the fragmentation process within the atomization of a suspension. Correlations for the droplet diameter of a suspension spray generated by a twin-fluid nozzle have been derived. Two separate regimes in suspension atomization have been identified with respect to the solid particle size. The atomized droplets from suspensions containing relatively fine solid particles are suspension droplets (containing liquid and solid particles). In this case a correlation for the drop size distribution in the spray of a twin-fluid nozzle has been deduced. Droplet size measurements in the suspension spray with varying solid particle sizes showed that when the suspended solid particle size exceeds a critical value, solid particles and liquid will be more and more separated. This effect is indicated by a bimodal size distribution in the suspension spray. It is shown that complete solid-liquid separation in the suspension spray may be achieved, where the pure liquid drops are significantly smaller than the separated solid particles. The critical process conditions where the solid-liquid separation process is found will be derived. Depending on the operating conditions of the atomizer, the resulting pure liquid droplet size is equal or less than the hydraulic diameter.     

Numerical simulation of cone‐jet formation in electrohydrodynamic atomization

Electrohydrodynamic atomization (EHDA) process has received more research attention in recent years due to its potential to generate monodisperse droplets of low electric conductivity. It is reported that the EHDA process can be fine‐tuned by adjusting the electrical field strength by an additional ring electrode near the nozzle tip to control both the spray mode and the droplet size. In the present study, a computational fluid dynamic (CFD)‐based front tracking/finite volume method has been used to investigate numerically the effect of the secondary electric field source and the ring electrode on the EHDA process. The full Navier–Stokes equations are solved for both the liquid phase and the ambient air near the nozzle tip, and the liquid–air interface is monitored using a front tracking approach. At the interface, both the surface tension and the electrical stress due to surface charging and the applied electric field are taken into account. Because of the large dimension difference between the Taylor cone and the liquid jet, the simulations involve two drastically different length scales for describing the dynamic of the entire process. To accurately include the effect of the ring electrode, the electrical field distribution is first calculated over a domain large enough to enclose all key components of the EHDA process. Subsequently, the calculated electrical field in the large domain is integrated with the detailed CFD analysis on a small domain near the region of the nozzle tip. The formations of the Taylor cone, liquid jet, and droplets are successfully simulated and compared with experimental results with reasonable agreement. The numerical simulation method proposed in this article can be used as a platform for the investigation, analysis, and optimization of electrohydrodynamic atomization process. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Experimental investigation and model improvement on the atomization performance of single-hole Y-jet nozzle with high liquid flow rate

Y-jet nozzle, as an efficient multi-hole internal-mixing twin-fluid atomizer, has been widely used for liquid fuel spray in many industrial processes. However, single-hole Y-jet nozzle with high liquid flow rate is indispensable in some confined situations due to a small spray cone angle. In this paper, the atomization performance of single-hole Y-jet nozzles with high liquid mass flow rates ranging from 400 to 1500 kg/h for practical semidry flue gas desulfurization processes was investigated by the laser particle size analyzer, and the effects of spray water pressure, atomizing air pressure and air to liquid mass flow ratio on the liquid mass flow rate and the droplet size distribution were analyzed. Moreover, the secondary atomization model was modified on the basis of previous random atomization model of Y-jet nozzle. The predicted results agreed well with the experimental ones, and the improved atomization model of Y-jet nozzle was well validated to design the nozzle geometry and to predict the droplet size distributions for single-hole Y-jet nozzle with high liquid mass flow rate.     

双流体喷嘴雾化特性实验

双流体雾化降温冷却技术是将气体和液体在喷嘴内部直接混合,在高压射流作用下直接雾化,雾化的小液滴气化时带走热量,从而降低工作区域温度。喷雾冷却降温系统广泛应用于养殖、高精度建筑及机械切削加工中刀具的冷却等。影响喷雾降温冷却的关键因素是雾滴粒径和雾滴运动速度。雾滴粒径越小,其总表面积越大,易于蒸发、气化,从而产生良好的降温效果;而雾滴运动速度加快则可以进一步加快工作区域的换热过程。文章利用相位多普勒粒子动态分析仪(PDA)对4种不同喷孔直径的喷嘴进行了较为详细的实验研究,获得了影响雾滴粒径和雾滴运动速度的重要因素,得到了双流体雾化喷嘴工作的最佳压力与孔径组合,为喷雾冷却降温的研究奠定了基础。