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.     

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.     

Experimental Study of Spray Drying and Atomization with a Two-Fluid Nozzle to Produce Inhalable Particles

A series of 50 experiments was performed to investigate particle size and yield from three laboratory spray dryers with two-fluid nozzles, using an aqueous solution of egg albumin as the feed. First principles theory suggests that the main parameters affecting final particle size should be atomization gas flowrate and velocity, feed solution flowrate, solution concentration, and inlet and outlet gas temperature. The experiments demonstrated that atomization gas velocity at the nozzle correlated better than volumetric gas flowrate to the final particle size obtained. Increasing atomization gas flow gave a decrease in particle size, levelling off at high nozzle gas velocities approaching sonic values. Liquid flowrate had little effect, and hybrid ratios such as the ALM (atomization gas to liquid flow ratio) did not correlate well to measured final particle size for this system. This seems likely to apply to aqueous systems with temperature limitations, where liquid flowrates will be relatively low compared to gas flowrates (both atomization and main gas flow). Particle size generally increased with solution concentration, and in some cases scaled exactly, assuming a constant initial droplet size and final particle density. All experiments were performed below the boiling point and therefore temperature had little effect. Particles of 2–3 microns were obtained at high atomization gas flows, indicating initial droplet sizes of 4–7 microns at most, while lower flowrates gave substantially larger particles and a wider size distribution.     

Monodisperse Droplet Generators as Potential Atomizers for Spray Drying Technology

Spray drying is a widely used unit operation for manufacturing powders of different characteristics. Many technological improvements have been made in the last few decades, and a great amount of research work is still being conducted. Recently, the hybrid spray-drying technique was reported, which combines the ink-jet technology with spray drying in order to produce particles of uniform characteristics.^[1-4¹, ², ³, ^4] The monodisperse droplet generators (MDGs) have certain features that make them attractive for use as atomizers in spray-drying operations. In this article, a comprehensive introduction to a variety of monodisperse droplet generators is provided. The advantages and limitations of these generators are discussed. The fundamental equations for predictions of the average droplet size are summarized. The discussion given in this study is aimed at the development of a hybrid technology that marries a suitable MDG with the existing spray-dryer technique (yet with some modifications) to manufacture the product with uniform characteristics containing micro- to nanosized particles.     

Monodisperse Droplet Generators as Potential Atomizers for Spray Drying Technology

Spray drying is a widely used unit operation for manufacturing powders of different characteristics. Many technological improvements have been made in the last few decades, and a great amount of research work is still being conducted. Recently, the hybrid spray-drying technique was reported, which combines the ink-jet technology with spray drying in order to produce particles of uniform characteristics.^[ 1-4 Patel , K.C. ; Chen , X.D. ; Lin , S.X.Q. Development of a laboratory ink-jet spray dryer . Chemeca 2006 , Auckland , New Zealand , September 17–20, 2006 (CD-Rom) . Patel , K.C. ; Chen , X.D. Drying of aqueous lactose solutions in a single stream dryer (S²D) . Transactions of the IChemE: Food and Bioproduct Processing 2007 , accepted . Patel , K.C. ; Chen , X.D. Production of spherical and uniform-sized particles using a laboratory ink-jet spray dryer . Asia-Pacific Journal of Chemical Engineering 2007 , 2 ( 5 ), 415 – 430 . Patel , K.C. ; Wu , W.D. ; Chen , X.D. Review on generation of monodisperse sprays for manufacturing micro-size uniform particles using a spray drying technology . In Proceedings of Asia-Pacific Drying Conference , Hong Kong , China , August 13–15, 2007 .  ^] The monodisperse droplet generators (MDGs) have certain features that make them attractive for use as atomizers in spray-drying operations. In this article, a comprehensive introduction to a variety of monodisperse droplet generators is provided. The advantages and limitations of these generators are discussed. The fundamental equations for predictions of the average droplet size are summarized. The discussion given in this study is aimed at the development of a hybrid technology that marries a suitable MDG with the existing spray-dryer technique (yet with some modifications) to manufacture the product with uniform characteristics containing micro- to nanosized particles.     

CFD Evaluation of Droplet Drying Models in a Spray Dryer Fitted with a Rotary Atomizer

Computational fluid dynamics (CFD) modeling of spray dryers requires a simple but sufficiently realistic drying model. This work evaluates two such models that are currently in discussion; reaction engineering approach (REA) and characteristic drying curve (CDC). Two versions of the CDC, linear and convex, drop in drying rate were included. Simulation results were compared to the overall outlet conditions obtained from our pilot-scale experiments. The REA and CDC with a linear drop in drying rate predicted the outlet conditions reasonably well. This is contrary to the kinetics determined previously. Analysis shows that the models exhibit different responses to changes in the initial feed moisture content. Utilizing different models did not result in significantly different particle trajectories. This is due to the low relaxation time of the particles. Despite the slight differences in the drying curves, both models predicted similar particle rigidity depositing the wall. For the first time in a CFD simulation, the REA model was extended to calculate the particle surface moisture, which showed promising results for wet particles. Room for improvement was identified when applying this concept for relatively dry particles.     

湿法脱硫雾化喷嘴特性实验研究

利用FAM激光颗粒测量仪,以水为工质对撞击流燃煤烟气湿法脱硫装置中采用的旋涡压力喷嘴的雾化特性进行了实验研究,测量了不同压力下液体雾化粒子的平均粒径和粒径分布,讨论了压力对雾化特性的影响,得出了压力和喷片结构尺寸对雾化特性的影响规律。     

Research Note: Effects of Ozonated Water Spray Droplet Size and Distance on the Dissolved Ozone Concentration at the Spray Target

Dissolved ozone concentration (DOC) of ozonated water (OW) sprayed from four different distances using three different droplet sizes (expressed in terms of Sauter mean diameter; small, medium, large) was measured at the spray target to obtain fundamental data for improving disease control efficacy when spraying OW onto plants. DOC in the OW at the spray target decreased with decreasing droplet size. DOC was also greatly reduced at the typical spray distances of 0.50 to 0.75 m to less than one-seventh of the initial DOC (2.2 mg/L^?1) in the sprayer reservoir, and DOC one-third lower than the initial DOC was observed even at the shortest spray distance of 0.05 m for all three nozzle sizes used. Based on the results of these experiments, disease control efficacy by spraying OW can be improved by minimizing the spray distance and using a nozzle that produces a larger spray droplet size, within the range such that adhesion efficiency of OW to the leaf surface is not greatly reduced.     

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.     

湿法脱硫用喷嘴的研究与进展

阐述了脱硫用喷嘴国内外的研究现状,重点介绍了湿法脱硫装置中最常用喷嘴的结构特点、材料要求、雾化特性、雾化机理以及塔内布置。指出了脱硫用喷嘴研究目前存在的问题及发展趋势。     

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.     

The Influence of the Spray Drying Process on Product Properties

Abstract

Uniform and repeatable product characteristics are critical in the performance and acceptance of consumer products, and the spray drying process can have a major influence on achieving these characteristics. This article shares experiences in the Spray Drying of powdered detergent granules in Procter & Gamble. It looks at the influence of both process operation and process equipment design on product characteristics. Procter & Gamble (P&G) is a major global producer of consumer products in the areas of fabric and home care; personal and beauty care; health care; and snacks and beverages. Whilst different drying operations, and product quality measuring tools are mentioned by Genskow (Genskow, L.R.¹ Considerations in Drying Consumer Products, Proceedings of 6th International Drying Symposium, Versailles, September, 1988; Keynote lecture, 39–46.) as being involved in all of the categories of Company production, I will concentrate on the counter-current Spray Drying process and controls, used in the manufacture of most of the detergent granules business of P&G. This area is the oldest and largest of the Company's core business activities. Innovative technology development is critical in continuing to satisfy the consumer need for performance and value. Use of modeling in the spray drying process is helping the Company to move faster in delivering these advanced technologies. And, through better understanding of the process, it is possible to minimize capital expenditure, and improve trouble-shooting ability across the global production facilities.     

The Influence of the Spray Drying Process on Product Properties

Uniform and repeatable product characteristics are critical in the performance and acceptance of consumer products, and the spray drying process can have a major influence on achieving these characteristics. This article shares experiences in the Spray Drying of powdered detergent granules in Procter & Gamble. It looks at the influence of both process operation and process equipment design on product characteristics. Procter & Gamble (P&G) is a major global producer of consumer products in the areas of fabric and home care; personal and beauty care; health care; and snacks and beverages. Whilst different drying operations, and product quality measuring tools are mentioned by Genskow (Genskow, L.R.¹ Considerations in Drying Consumer Products, Proceedings of 6th International Drying Symposium, Versailles, September, 1988; Keynote lecture, 39-46.) as being involved in all of the categories of Company production, I will concentrate on the counter-current Spray Drying process and controls, used in the manufacture of most of the detergent granules business of P&G. This area is the oldest and largest of the Company's core business activities. Innovative technology development is critical in continuing to satisfy the consumer need for performance and value. Use of modeling in the spray drying process is helping the Company to move faster in delivering these advanced technologies. And, through better understanding of the process, it is possible to minimize capital expenditure, and improve trouble-shooting ability across the global production facilities.     

Challenges of Simulating Droplet Coalescence within a Spray

This article reports various challenges that have been encountered in the process of developing validated Lagrangian and Eulerian models for simulating particle agglomeration within a spray dryer. These have included the challenges of accurately measuring droplet coalescence rates within a spray, and modeling properly the gas-droplet and droplet-droplet turbulence interactions. We have demonstrated the relative versatility and ease of implementation of the Lagrangian model compared with the Eulerian model, and the accuracy of both models for predicting turbulent dispersion of droplets and the turbulent flow-field within a simple jet system. The Lagrangian and Eulerian droplet coalescence predictions are consistent with each other, which implies that the numerical aspects of each simulation are handled properly, suggesting that either approach can be used with confidence for future spray modeling. However, it is clear that considerable research must be done in the area of particle turbulence modeling and accurate measurement of particle agglomeration rates before any Computational Fluid Dynamics tool can be employed to accurately predict particle agglomeration within a spray dryer.     

Challenges of Simulating Droplet Coalescence within a Spray

Abstract

This article reports various challenges that have been encountered in the process of developing validated Lagrangian and Eulerian models for simulating particle agglomeration within a spray dryer. These have included the challenges of accurately measuring droplet coalescence rates within a spray, and modeling properly the gas–droplet and droplet-droplet turbulence interactions. We have demonstrated the relative versatility and ease of implementation of the Lagrangian model compared with the Eulerian model, and the accuracy of both models for predicting turbulent dispersion of droplets and the turbulent flow-field within a simple jet system. The Lagrangian and Eulerian droplet coalescence predictions are consistent with each other, which implies that the numerical aspects of each simulation are handled properly, suggesting that either approach can be used with confidence for future spray modeling. However, it is clear that considerable research must be done in the area of particle turbulence modeling and accurate measurement of particle agglomeration rates before any Computational Fluid Dynamics tool can be employed to accurately predict particle agglomeration within a spray dryer.     

The Effect of Rotary Disk Atomizer RPM on Particle Size Distribution in a Semi-Industrial Spray Dryer

Spray drying is the most commonly used method in industry to produce powders on a large scale. One of the major problems in spray drying is control of the product particle size distribution since it is very important for most industries; e.g., catalyst, chemicals, foods, pharmaceuticals, ceramics, etc. The objective of this work is to study the effect of the atomizer rotational speed on the product size distribution. In order to obtain the typical particle size distribution of the required product, a specially designed atomizer disk is used in the study. The particle size distributions under atomizer rotating speeds in the 9,000–10,000 rpm range were measured and discussed.     

锅炉蒸汽雾化油喷嘴性能分析与改进方案

针对燃油锅炉的油喷嘴雾化效果差、受热面结焦、喷嘴边缘裂纹、油嘴需要经常拆卸清透等运行方面的问题,对油喷嘴进行了雾化效果的分析,改进了油喷嘴的运行参数,提出了运行操作措施,使锅炉运行状态得到了提高。     

Influence of Plate Size on the Evaporation Rate of a Heated Droplet

The purpose of this study is to numerically investigate how the width of a plate influences natural convection around a droplet. Droplets evaporating on hot surfaces have many applications including drying of dishes and paint. Evaporation rate and deposition of particles withheld in the fluid are of great importance in both cases. As a first step to investigate how the drying rate and deposition mechanisms can be controlled, this work aims to investigate how the external flow around a water droplet influences the evaporation rate. Natural convection caused by the hot plate on which the droplet rests is considered and the effect of different widths is examined. Results show that an extension of the plate past the droplet will increase the maximum velocity in the domain due to natural convection while the flow close to the surface is decreased due to the no-slip condition and temperature gradient. A decrease of the evaporation rate is therefore observed when the plate is extended past the droplet as compared to the case when the plate and droplet have the same diameter. Simulations furthermore show that the results from the heat and mass transfer analogy only compare well to the results of Fick's law when the droplet and plate have the same width.     

螺旋喷嘴液滴分布特性的实验研究

以水为喷淋介质,研究了螺旋喷嘴的喷淋量与喷淋压力的关系,考察了雾化液滴的粒径分布特性。实验结果表明,随着喷淋压力的增大,喷淋量相应增大,并逐渐趋于平缓;螺旋喷嘴喷雾区喷淋量沿径向形成多个峰,随工作压力增大各峰沿径向外移,处在峰面上液滴的索特直径较峰面间的大;液滴平均粒径随压力升高而趋于均匀,且大喷嘴雾化形成的粒径比小喷嘴的略大。研究结果可为螺旋喷嘴的实际应用提供参考。