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.     

Evaluating the performance of a portable water–mist fire extinguishing system with additives

This study investigates how high‐pressure water–mist system discharge methodologies influence the fire extinction performance for pan pool fires and the corresponding mechanisms of restraining fire. The fire source is a pool‐fire burner. Fine water spray is injected using a portable device. The additive in the water–mist is neither toxic nor corrosive. All the tests are regarded as fuel controlled. The fire test parameters are fuel type, nozzle discharge angle, and additive solution volume. The fuels used are heptane, gasoline, and diesel. Nozzle discharge angles are 30, 45, and 60° with respect to the ground. Additive solution volumes are 0% (pure water), 3, 6, and 10%. Test results indicate that the nozzle discharge angle and additive solution volume in a water–mist fire extinction system play a significant role. Fire extinguishing efficiency is influenced by mist effects and the additive. Furthermore, the water–mist system can reduce radiation and can provide good protection for operators using portable fire extinguishing equipment. Copyright © 2008 John Wiley & Sons, Ltd.     

Simulation of sprinkler—hot layer interaction using a field model

This paper reports a study of the interaction of a sprinkler water spray with the fire-induced hot layer using the field modelling technique. Data obtained in the large test room of the recent Swedish experiments reported by Ingason and Olsson (1992) are used to validate the results. The problem is divided into a gas phase and a liquid phase. For the gas phase, the set of conservation equations for mass, momentum and enthalpy of air flow induced by the fire is solved numerically using the Pressure Implicit Splitting Operator (PISO) algorithm. For the liquid phase, the sprinkler water spray is described by a number of droplets with initial velocity and diameter calculated by empirical expressions for the nozzle at different operating water pressures and flow rates. The trajectory of each droplet is calculated by solving the equation of motions, by including the dragging and heat transfer with the hot layer. The water droplet is assumed to be non-evaporating and only the source terms in the gas momentum and enthalpy equations of the air flow included the interaction effects with water droplets, i.e. the ‘Particle-Source-in-Cell’ method. The predicted results include the gas flow, temperature and smoke concentration field; the shape of the water spray; and some relevant macroscopic parameters such as amount of convective cooling, drag-to-buoyancy ratio, etc. The average smoke layer temperature and the smoke layer interface height are also calculated. The effect of the mean droplet size on those parameters is illustrated. Finally, a comparison of the water density received at floor level in cases with and without the fire is made.     

Physical properties of a sprinkler water spray

This paper reports an experimental study on the physical properties of a sprinkler water spray. The mass flux density, shape of spray pattern, size distribution and velocity of water droplets discharged from two types of 15 mm orifice sprinkler heads were measured. Three operating flow conditions of the sprinkler system, including one specified for the Ordinary Hazard class under the LPC rules for sprinkler design, were set. The sprinkler head was installed above finished floor levels of either 2 m or 2.2 m. The median droplet size was found to be related to the water pressure and the orifice diameter of the sprinkler head as proposed by Dundas. The droplet size distribution function can be fitted by a Rosin–Rammler function.     

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.     

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.     

Influence of Atomizing Parameters on Droplet Properties in a Pulse Combustion Spray Dryer

A pulse combustor employed in a spray-drying system offers a new approach for liquid atomization that yields high-quality powders at low cost. Using a pulse combustion atomizer, there is no need for any form of nozzle dispersion and its atomization mechanism differs from those of conventional atomizers, such as rotary atomizers and pressure and pneumatic nozzles. In this work, based on the analysis of atomization mechanism, experiments of unsteady pulsating atomization were carried out in an experimental system of a Helmholtz-type pulse combustor. An optical analyzer was used for measuring the mean diameter of atomized droplet and droplet distribution. The effects of liquid feed rate, air flow oscillatory frequency, and liquid viscosity on atomized droplet size and size distribution were investigated and analyzed. The results indicate that the uniform droplet size distribution can be obtained under the conditions of a low feed rate, high-frequency pulsating flow, and moderate viscosity. The range of the droplets' Sauter mean diameter (SMD) is between 50 and 80 µm. The pulsating air flow from the pulse combustor can be used to atomize liquid or slurry without a nozzle and the atomizing quality can meet the requirements of spray drying.     

旋涡压力喷嘴的雾化特性

利用FAM激光粒度测量仪,以水为工质对不同结构旋涡压力喷嘴在不同压力条件下的雾化特性进行了实验研究。建立了描述喷嘴结构、操作压力及喷出速度与液体雾滴平均直径之间关系的数学模型,为进一步优化设计旋涡压力喷嘴提供了依据。     

Anisokinetic Shrouded Nozzle System for Constant Low-Flow Rate Aerosol Sampling from Turbulent Duct Flow

An anisokinetic shrouded nozzle system was designed for sampling particles at a constant low flow rate from a ventilation duct to an aerodynamic particle sizer (APS). Shrouded anisokinetic nozzles are a means for sampling from a moving airstream with higher particle transmission than with unshrouded isokinetic nozzles. This shrouded nozzle sampling system was evaluated in an experimental ventilation duct system. Aspiration and transport efficiency measurements were made for five particle sizes in the range 1–13 μm at each of three duct air speeds in the range 2.2–8.8 m/s. Under these conditions, the shrouded nozzle system showed improved performance compared to buttonhook isokinetic nozzles, especially for larger particles and higher air speeds. Measured transmission efficiencies through the shrouded nozzle sampling system were generally higher and more reliably predictable than those through buttonhook isokinetic nozzles. Model predictions of transport and aspiration efficiencies of the shrouded nozzle system showed good agreement with measurements over the entire range of experimental conditions. The shrouded nozzle sampling system could be used to measure concentrations in ventilation ducts with an APS for particles in the diameter range 1–13 μm.

Copyright 2014 American Association for Aerosol Research     

Water spray cooling of polymers

The cooling process in conventional rotomolding is relatively long due to poor thermal conductivity of plastics. The lack of internal cooling is a major limitation although rapid external cooling is possible. Various internal cooling methodologies have been studied to reduce the cycle time. These include the use of compressed air, cryogenic liquid nitrogen, chilled water coils, and cryogenic liquid carbon dioxide, all of which have limitations. However, this article demonstrates the use of water spray cooling of polymers as a viable and effective method for internal cooling in rotomolding. To this end, hydraulic, pneumatic, and ultrasonic nozzles were applied and evaluated using a specially constructed test rig to assess their efficiency. The effects of nozzle type and different parametric settings on water droplet size, velocity, and mass flow rate were analyzed and their influence on cooling rate, surface quality, and morphology of polymer exposed to spray cooling were characterized. The pneumatic nozzle provided highest average cooling rate while the hydraulic nozzle gave lowest average cooling rate. The ultrasonic nozzle with medium droplet size traveling at low velocity produced satisfactory surface finish. Water spray cooling produced smaller spherulites compared to ambient cooling whilst increasing the cooling rate decreases the percentage crystallinity. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Influence of Atomizing Parameters on Droplet Properties in a Pulse Combustion Spray Dryer

A pulse combustor employed in a spray-drying system offers a new approach for liquid atomization that yields high-quality powders at low cost. Using a pulse combustion atomizer, there is no need for any form of nozzle dispersion and its atomization mechanism differs from those of conventional atomizers, such as rotary atomizers and pressure and pneumatic nozzles. In this work, based on the analysis of atomization mechanism, experiments of unsteady pulsating atomization were carried out in an experimental system of a Helmholtz-type pulse combustor. An optical analyzer was used for measuring the mean diameter of atomized droplet and droplet distribution. The effects of liquid feed rate, air flow oscillatory frequency, and liquid viscosity on atomized droplet size and size distribution were investigated and analyzed. The results indicate that the uniform droplet size distribution can be obtained under the conditions of a low feed rate, high-frequency pulsating flow, and moderate viscosity. The range of the droplets' Sauter mean diameter (SMD) is between 50 and 80 µm. The pulsating air flow from the pulse combustor can be used to atomize liquid or slurry without a nozzle and the atomizing quality can meet the requirements of spray drying.     

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%。     

Bench‐scale studies of poly(vinyl chloride) fires with water mist

Bench‐scale tests to study the effect of water mist on burning solid poly(vinyl chloride) (PVC) were carried out with a cone calorimeter. Water mist was discharged from a small nozzle under two operating pressures, 0.4 and 0.7 MPa. The corresponding water flow rates were 103.5 and 134 mL/min, respectively. The cone angle of the discharged water spray was 90°, and the volume mean diameter of the mist was about 90 μm. The results were useful in understanding the effects of discharging water mist to suppress the diffusion flame from burning PVC. The reignition process also was studied. The testing method was appropriate for studying the interaction between water mist with smaller droplets and the diffusion flame in a confined space. There, the combined effects of oxygen displacement, gas phase, and fuel surface cooling were the key extinguishing mechanisms. The critical water mist application rate on burning PVC under different thermal radiative heat fluxes was able to be determined. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 2520–2527, 2006     

空气助力改善气化炉激冷室喷嘴特性的实验研究

设计了4种不同结构的用于气化炉激冷室内喷雾激冷的压力雾化喷嘴,采用马尔文激光粒度分析仪和数码单反照相机分别测量了不同压差、不同水流量等工况参数下的液滴粒径(SMD)D32分布和雾化角变化规律,并对4种喷嘴进行了优化选型。研究结果表明:雾滴粒径随压力的增加而减小,随水流量的减小而减小,空气助力可以明显改善液滴的雾化质量;雾化角随压差的增大先增大后趋于平缓;当压差增大到0.4 MPa时,雾滴粒径、雾化角等参数的变化渐趋平缓。通过比较气化炉激冷室中4种压力式雾化喷嘴的测量结果,1-2号内混式空气雾化喷嘴在4组喷嘴中具有最好的雾化效果,当气压为0.8 MPa,水流量为20 L/h时,SMD极小值为16,因此优选出喷嘴1-2作为气化炉激冷室冷模实验的定型喷嘴。     

Spray Characteristics of Two‐phase Feed Nozzles

The present study focuses on understanding the spray characteristics of a turbulent gas‐liquid jet (Re_liq = 24,000). Air and water are used as the test fluids. The angles of injection of the two phases upstream of the nozzle are varied (θ = 20°, 45° and 90°) and the effect of carrier gas on the droplet characteristics is are also investigated. The droplet size and velocity are non‐intrusively measured using a Phase‐Doppler Particle Analyzer (PDPA). In some respects, the characteristics of the present two‐phase jet are similar to those noticed in previous studies, while revealing some important differences. The centreline mean droplet velocities (15 ～ 20 m/s) increase in the initial region of the jet, attain a maximum and then decrease at larger distances from the nozzle exit. Most of the entrainment occurs at the tip of the nozzle and the jet expansion rate decreases significantly at distances where the spray velocity profiles become self‐similar. A Lorentz‐type fit has been used to model the normalized radial velocity profiles. The results indicate that the test configuration with θ = 45° may be beneficial for the scenario discussed.     

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.     

Comparison of the impact of flow pulsations on the performance of various liquid–gas injectors in a gas–solid fluidised bed

This article shows that spray nozzles pulsations can greatly improve the distribution of the sprayed liquid on fluidised bed particles, as characterised by a Nozzle Performance Index (NPI). Appropriate pulsations increased the NPI by nearly 100% under several operating conditions. This article compares four pulsating, gas atomised nozzles under various operating conditions. The performance of each nozzle was evaluated by measuring the electric conductance of a bed of silica sand particles fluidised by air, subsequent to liquid injection. Three sets of experiments were conducted to investigate the effect of operating conditions on the performance of the four gas atomised nozzles. The first set determined the effect of the liquid flowrate, the second set measured the effect of a restriction orifice on the atomisation gas line and the third set studied the effect of the atomisation air to liquid ratio. Artificial nozzle spray pulsations were found to have similar beneficial effects with the different types of gas‐atomised nozzles. © 2011 Canadian Society for Chemical Engineering     

超音速和亚音速喷嘴对可调式喷射器性能的影响

以探针轴向移动的可调式喷射器为研究对象,对超音速和亚音速两种喷嘴配置的喷射器性能进行了实验和模拟研究。结果显示：喷嘴出口驱动流流动特性与喷射器性能有着密切关系,且是导致两种喷嘴配置的喷射器性能调节差异性的主要原因。对于超音速喷嘴,喷嘴出口驱动流状态随探针位置发生改变,而亚音速喷嘴无此变化特性。通过探针调节喷射器性能过程中,当超音速喷嘴出口驱动流为理想膨胀时,系统处于最优运行状态;而当驱动流为过膨胀时,将产生压缩激波,系统性能降低,且低于亚音速喷嘴。进而,提出了两种配置喷嘴的选择方案。     

涂装线喷漆室排风管路的自动消防装置

设计了一种用于涂装线喷漆室排风管路的自动消防装置,主要包括排风组件和自动喷淋系统。详细介绍了它的结构。该装置在监测到排风管道内的火势时,能通过阀门自动将排风管道与外界空气隔绝,同时启动喷淋系统。该装置结构简单,设计合理,使用方便。     

A numerical study of two-phase transonic steam flow through convergence-divergence nozzles with different rates of expansion

During transonic flow of steam in divergence nozzles, flow first supercools and then nucleates to become two-phase droplet flow. This phenomenon especially occurs in the last stages of steam turbines and affects performance. In this research, a numerical scheme for two-phase flow in nozzle passages is developed. An Eulerian-Eulerian reference frame is used for both phases. The shear stress transport turbulence model is used to model the Reynolds stresses appearing in the averaged Navier-Stokes equations. The homogeneous nucleation model is applied for the mass transfer in the transonic conditions. In this paper three nozzles with different rate of expansion are employed to be under study. Overall pressure ratio (static to total pressure) and droplet size are compared with the experimental data and good agreements are observed.