Numerical Simulation of the Two‐Phase Fluid Field in a Gas‐Around‐Liquid Spray Nozzle

A new gas‐around‐liquid spray nozzle (GLSN) was designed, and the two‐phase flow fluid field in this nozzle was simulated numerically. Flow characteristics under different structural parameters were obtained by changing the L/D ratio of the premixing chamber, incident angle, and inlet pressures. Increasing the L/D ratio and incident angle improved flow characteristics such as atomization flow, outlet velocity, and turbulence intensity. The nozzle performed optimally at an L/D ratio of 0.5 and incident angle of 60°. The atomization flow decreased with higher gas pressure and increased with higher liquid pressure. The outlet velocity mainly depended on the inlet gas pressure, not on the inlet liquid pressure. These results provide an indication for optimum structures and parameters of the GLSN.     

Turbulent flow study of an isothermal diesel spray injected by a common rail system

The flow characteristics of the intermittent spray of a single-hole diesel nozzle (d_o=0.11 mm) having a 1-spring holder, used in the injection system of heavy-duty diesel engines, were experimentally investigated. The hole belongs to a mini-sac 5-hole nozzle where only on hole is drilled. The mean velocity and turbulent characteristics of the diesel spray injected intermittently by a Common-Rail (CR) system into a pressurized vessel at room temperature were measured by using a 1-D PDPA (phase Doppler particle analyzer). The injection duration was a little stretched out (3 ms) to increase the quasi-steady part of the spray. The axial velocity of the droplets was studied in the main parts of the single-hole nozzle spray, i.e. the leading edge; the central part and the trailing edge. Temporal distributions of the mean axial velocity and its rms were constant in the central spray part, and they showed peaks in the leading edge of the spray. The radial distribution of the normalized axial mean velocity was similar to that of the free gas jet within r/r0.5=1.0−1.5 regardless of time, which is consistent with the theoretical velocity distributions suggested by Hinze. However, in the leading edge near the centreline axis, the normalized axial mean velocity displayed higher values. The turbulence intensity of the axial velocity measured along the radial direction was similar to the free gas jet within r/r0.5=0.5 and higher beyond. However, the turbulence intensity in the leading edge was higher than in the leading edge and the central part within r/r0.5=0.7 where it showed values of the 40–60% of the local mean velocity. The factors of skewness and flatness approached to those of the free gas jet in the central part and the trailing edge. In the leading edge, the flatness factor has presented dispersed values, and the skewness factor was always higher than were those of the two other parts of the spray. The gradient of the half-width exhibited a linear decrease with time since the beginning of the injection to reach the value of 0.106 at the end of the injection. The virtual origin value was within 10–13 mm independently of the injection pressure, and the spray cone angle, determined in comparison to the virtual origin, was close to 30°. The axial decrease of the mean axial velocity showed a great similarity with that of the free gas jet in the central spray part. However, the axial decrease of the rms-velocity was faster than that of the free gas jet.     

Airborne Dust Capture and Induced Airflow of Various Spray Nozzle Designs

Water spray characteristics, including droplet size and velocity, airborne dust capture potential, and induced airflow quantity for various spray nozzle designs were evaluated to provide basic information for improving spray applications. Water droplet size and velocity characteristics were initially measured by a Phase Doppler Particle Analyzer (PDPA) for hollow cone, full cone, flat fan, and air atomized spray nozzles at similar operating parameters. Airflow inducement and dust capture experiments were also conducted under the same operating parameters to examine any salient features of the spray nozzle type, droplet characteristics, induced airflow, and airborne dust capture.

Test results indicate that there are trade offs between airflow inducement and dust capture efficiency. A spray nozzle with a wider discharge angle was observed to induce more airflow, but at reduced dust capture efficiencies. Increasing spray nozzle fluid pressure(s) generally reduced water droplet sizes with concurrent increases in droplet velocity, airflow inducement, and airborne dust capture. Placing a three-sided barrier around the spray nozzles normally reduced spray air induction and increased dust capture efficiency. A direct relationship between airborne dust capture efficiency and spray input power normalized per unit of airflow induced was observed. This information can be utilized to improve the performance of water sprays for reducing airborne dust levels.     

Prediction of Droplet Velocities and Rain Out in Horizontal Isothermal Free Jet Flows of Air and Viscous Liquid in Stagnant Ambient Air

Two‐dimensional phase Doppler anemometer measurements of droplet size and velocity conducted under several nozzle conditions and a systematic variation of the air mass flow quality and liquid phase viscosity show that the air entrainment process is enhanced when keeping all test conditions constant except for increasing the Newtonian liquid viscosity above of that of water. A two‐zone entrainment model based on a variable two‐phase entrainment coefficient is proposed with the normalized axial distance allowing for a change in the jet angle. Thus, the jet perimeter is lower and the breakup length is longer in the case of air/relatively higher viscosity liquid phase. It provides the most accurate reproduction of the experimental droplet velocity in comparison with that of other models in the literature and, hence, is recommended for the prediction of the droplet velocity in the case of two‐phase air/liquid phase free jet flow in stagnant ambient air. A model for predicting the droplet rain out, considering the droplet trajectories in the free jet flow, allows also for an adequate reproduction of the experimental data.     

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     

固定床熔渣气化高速射流区气固运动行为研究

为研究固定床熔渣气化炉中气化剂喷嘴安装角度、喷嘴口径、气化剂射流速度与高速射流区深度的关系,利用模化原理对工业级气化炉高速射流区建立50 cm二维冷态模型,采用精密皮托管测量颗粒床层中的气体速度分布,并采用无量纲分析方法,对试验数据进行处理。结果表明:射流穿透深度与喷嘴口径的二次方大致成正比关系;射流深度随喷嘴安装角度的增大呈现先增加后减小的趋势,使得射流深度最大的安装角度为17°~20°;射流深度随射流气速增加呈增大趋势,并拟合出气化剂喷嘴安装角度、射流速度、喷嘴口径与射流区深度的无量纲关系式。     

Bubble/droplet formation and mass transfer during gas–liquid–liquid segmented flow with soluble gas in a microchannel

Microchannels have great potential in intensification of gas–liquid–liquid reactions involving reacting gases, such as hydrogenation. This work uses CO₂–octane–water system to model the hydrodynamics and mass transfer of such systems in a microchannel with double T‐junctions. Segmented flows are generated with three inlet sequences and the size laws of dispersed phases are obtained. Three generation mechanisms of dispersed gas bubbles/water droplets are identified: squeezing by the oil phase, cutting by the droplet/bubble, cutting by the water–oil/gas–oil interface. Based on the gas dissolution rate, the mass transfer coefficients are calculated. It is found that water droplet can significantly enhance the transfer of CO₂ into the oil phase initially. When bubble‐droplet cluster are formed downstream the microchannel, droplet will retard the mass transfer. Other characteristics such as phase hold‐up, bubble velocity and bubble dissolution rate are also discussed. The information is beneficial for microreactor design when applying three‐phase reactions. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1727–1739, 2017     

Effect of cross flow on the spray characteristics of an industrial feed nozzle

The spray characteristics of a scaled-down version of an industrial feed nozzle are studied in the presence of a cross flow. Aerated liquid nitrogen is injected through the nozzle to generate the spray. The aeration rate is low and held constant, while two different liquid flow rates are used to produce the spray. A nonuniform wind profile is chosen to represent the cross flow condition. The droplet diameter and velocity measurements are acquired using a phase-Doppler particle analyzer. The results of the present study indicate that the spray momentum flux determines the extent of the jet bending. The droplets are accelerated significantly in the initial jet region as a result of flashing. However, further downstream of the nozzle, the vaporization of the droplets is considered to be negligible. The size-velocity correlation changes significantly for the case where the spray is shifted due to the cross flow.     

EFFECT OF CROSS FLOW ON THE SPRAY CHARACTERISTICS OF AN INDUSTRIAL FEED NOZZLE

The spray characteristics of a scaled-down version of an industrial feed nozzle are studied in the presence of a cross flow. Aerated liquid nitrogen is injected through the nozzle to generate the spray. The aeration rate is low and held constant, while two different liquid flow rates are used to produce the spray. A nonuniform wind profile is chosen to represent the cross flow condition. The droplet diameter and velocity measurements are acquired using a phase-Doppler particle analyzer. The results of the present study indicate that the spray momentum flux determines the extent of the jet bending. The droplets are accelerated significantly in the initial jet region as a result of flashing. However, further downstream of the nozzle, the vaporization of the droplets is considered to be negligible. The size-velocity correlation changes significantly for the case where the spray is shifted due to the cross flow.     

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。     

Liquid‐like wave structure on granular film from granular jet impact

Results in the literature show that a granular film appears from a dense granular jet impacting on a circular target under certain conditions (Cheng X, Varas G, Citron D, Jaeger HM, Nagel SR, Phys Rev Lett. 2007; 99(18):188001). In current study, granular jet impacts are experimentally studied using a high‐speed camera, and interesting liquid‐like wave structures on the granular film are observed with increasing granular jet velocities or decreasing solid fractions of granular jets. Effects of the particle diameter, the granular jet velocity, and the solid fraction of granular jet on the wave structures are investigated. The dynamic characteristics of granular wave such as the wave frequency and velocity are demonstrated and compared with the liquid jet impact. Results reveal that increasing pushing pressure enhances the gas‐particle interaction inside the nozzle, which causes the granular jet instability and further gives rise to the granular wave at lower solid fractions and higher granular jet velocities. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3276–3285, 2017     

A study of liquid droplet disintegration for the development of nanostructured coatings

Thermal spray coatings produced from a liquid feedstock are receiving an increasing level of interest due to the advanced, nanostructured coatings which are obtainable by these processes. In this article, a high‐velocity oxy‐fuel (HVOF) thermal spray system is computationally investigated to make a scientific assessment of the liquid droplet behavior on injection. An existing liquid‐fuelled HVOF thermal spray gun is simulated using the computational fluid dynamic approach. The steady‐state gas‐phase dynamics are initialized by the introduction of liquid kerosene and oxygen which react within the combustion chamber producing a realistic compressible, turbulent jet. Discrete‐phase water droplets are injected at the powder injection port. On injection, the water droplets breakup and vaporize, while being entrained through the acceleration barrel of the HVOF system. The results obtained give an insight to the mechanism which control the water droplet sizes and disintegration process, and serve as a fundamental reference for future development of liquid feedstock devices. © 2012 American Institute of Chemical Engineers AIChE J, 2012     

Bivariate population balance model of ethanol‐fueled spray combustors

We present a bivariate population balance‐based formulation of the performance of well‐mixed adiabatic combustors fed by ethanol (EtOH)‐containing sprays of prescribed droplet size distribution (DSD) and composition. Our historically interesting example is the fuel‐cooled V‐2 chemical rocket—using 75 wt % EtOH + H₂O solution, and oxidizer O₂(L). Of special interest are the predicted combustion “intensity” (GW/m³) and efficiency (EtOH fraction vaporized) at each ratio of combustor mean residence time to feed‐droplet characteristic vaporization time. Our formulation exploits a quasi‐steady, gas‐diffusion‐controlled individual droplet evaporation rate law, and the method‐of‐characteristics to solve the associated first‐order population balance partial differential equation governing the joint distribution function n(m₁, m₂) of the fuel spray exiting such a chamber, where m₁ = EtOH mass/droplet, and m₂ = H₂O mass/droplet. Besides the combustor efficiency and intensity, this bivariate distribution function enables predictions of corresponding unconditional DSD, and the joint distribution function(diam., droplet temperature)—perhaps measurable. Our numerically exact formulation/results also provide valuable test cases for convenient approximate methods (bivariate moment and spectral/weighted residual) to predict these “correlated” bivariate distribution functions in more complex situations. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

Simulation and analysis of group-hole nozzle sprays using a gas jet superposition model

A gas jet superposition model has been recently developed for computing group-hole nozzle sprays in computational fluid dynamics (CFD) simulations. The objectives of this study are: (1) to perform a systematic validation of the comprehensive spray model for group-hole nozzles using a broad range of experimental data; (2) to analyze the dynamics and physical insight of group-hole nozzle sprays based on the simulation results; and (3) to further clarify the impact of included-angle on spray/mixture properties of group-hole nozzle sprays. An updated version of the KIVA-3V Release 2 code, which employs the Lagrangian-Drop Eulerian-Fluid (LDEF) methodology for numerical calculation of two-phase flows, was used in the simulations. Diverging group-hole nozzles with various included-angles were considered. The test conditions included non-evaporating and evaporating ambient conditions, free sprays and sprays impinging on a flat wall. Detailed comparisons were made between the experiments and computations in terms of spray/mixture characteristics. The results show that numerical parameter dependencies are significantly reduced with the new models, and good levels of agreement are obtained in terms of spray structure, liquid/vapor penetration, overall SMD and cumulative vaporized fuel mass. Both experimental measurements and simulations reveal the importance of included-angle in group-hole nozzle sprays. In particular, some important features of group-hole nozzle spray are captured in the computations by the present models: compared to the equivalent single-hole nozzle, smaller local droplet size can be achieved in the near nozzle field, indicating an enhanced fuel primary atomization; the ambient gas entrainment rate is increased during the injection period, implying the better mixing; the spray axis deflection is identified in the case of group-hole nozzles with smaller angles, which is caused by a negative relative pressure region that exists between the sprays; in addition, the asymmetric structure of wall-impinging group-hole nozzle spray is well predicted by the present models through applying the gas jet superposition model in the entire computational domain.     

喷嘴雾化特性及脱硫废水蒸发数值模拟

利用相位多普勒粒度分析仪（PDA）实验台测量了双流体喷嘴出口速度与粒径分布,利用得到的速度与粒径数据对江苏某生物质电厂进行小水量脱硫废水蒸发的数值模拟,着重研究了液滴粒径以及烟气中水蒸气的体积分数对液滴蒸发过程的影响。PDA实验结果表明,该双流体喷嘴在特定气液比条件下出口粒径均小于100μm。应用离散相模型与随机轨道模型,利用Rosin-Rammler分布模拟喷雾液滴分布范围（0～100μm）。模拟结果表明,粒径低于100μm的液滴能够完全蒸发,液滴粒径越小,完全蒸发时间越短,液滴经历的平稳吸热时间越短。随着粒径的增加,液滴完全蒸发时间增幅变大。随着烟气中水蒸气体积分数增加,液滴蒸发速率变缓,液滴开始蒸发的时间延长,且体积分数越大,出口未蒸发完全的液滴直径越大,但出口液滴粒径增大的幅度在减小。     

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     

FLUID SHEET THICKNESS AND VELOCITY AT THE TIP OF A BLACK LIQUOR SPLASHPLATE NOZZLE

The fluid sheet thickness and velocity at the tip of a spray nozzle have previously been identified as being important to the ultimate droplet size distribution. In this investigation both the fluid sheet thickness and the velocity of the top surface just beyond the rim of a splashplate nozzle have been measured as functions of nozzle exit velocity and fluid viscosity. Measurements were made on two Babcock & Wilcox Co. splashplate nozzles, a 12-49 and a 15-52, specifically designed for black liquor, a by-product of wood pulping. Comparisons of the ratio of the sheet velocity to the nozzle velocity are shown to be very similar to previous data for the ratio of droplet velocity to nozzle velocity. Likewise, the dependence of the sheet thickness on nozzle exit velocity closely matches the previously measured dependence of the ultimate median droplet size on nozzle exit velocity. Both of these results are consistent with current theories of droplet formation mechanisms. Analysis of continuity and viscous drag on the splashplate are used to develop correlation equations for the data     

Mass transfer and hydrodynamic characteristics in a co‐current downflow contacting column

Hydrodynamic and mass transfer characteristics of water–air system in a co‐current downflow contacting column (CDCC) were studied for various nozzle diameters at different superficial gas velocities and liquid re‐circulation rates. Gas hold‐up and liquid‐side mass transfer coefficient increased with increasing superficial gas velocity and liquid flow rate but decreased with increasing nozzle diameter. It is shown that correlations developed, which are based on liquid kinetic power per liquid volume present in the column, and superficial gas velocity explains gas hold‐up and the mass transfer coefficient within an error 20% for all gas and liquid flow rates and nozzle diameters used. The constants of correlations for gas hold‐up and mass transfer coefficient were found to be considerably different from other gas–liquid contacting systems. © 2003 Society of Chemical Industry     

Chemical hydrodynamics of a downward microbubble flow for intensification of gas‐fed bioreactors

Bioreactors are of interest for value‐upgrading of stranded or waste industrial gases. Reactor intensification requires development of low cost bioreactors with fast gas–liquid mass transfer rate. Here we assess published reactor technology in comparison with a novel downward bubble flow created by a micro‐jet array. Compared to known technology, the advanced design achieves higher volumetric gas transfer efficiency (k_La per power density) and can operate at higher k_La. We measure the effect of four reactor heights (height‐to‐diameter ratios of 12, 9, 6, and 3) on the gas transfer coefficient k_L, total interfacial area a, liquid residence time distribution, energy consumption, and turbulent hydrodynamics. Leading models for predicting k_L and a are appraised with experimental data. The results show k_L is governed by “entrance effects” due to Higbie penetration dominate at short distances below the micro‐jet array, while turbulence dominates at intermediate distances, and finally terminal rise velocity dominates at large distances. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1399–1411, 2018