Rotary Atomizer Research Articles

Characterization of the Residence Time Distribution in Spray Dryers

In this work it is presented a study on the residence time distribution (RTD) of particles in a co-current pilot-plant spray dryer operated with a rotary atomization system. A nuclear technique is applied to investigate the RTD responses of spray dryers. The methodology is based on the injection of a radioisotope tracer in the feed stream followed by the monitoring of its concentration at the outlet stream. The experiments were performed during the drying of aqueous suspensions of gadolinium oxide. The RTD responses obtained experimentally presented good reproducibility, indicating that the technique applied is well suited to investigating fluid-dynamics of spray dryers. In addition to the experimental investigation, a mathematical model was used to describe the RTD experimental curves.

Characterisation of coal blends for pulverised fuel combustion

The results of extensive experimental and predictive studies of nitric oxide (NO) and particulates (unburned coke) emissions from a large-scale laboratory furnace, fired by a heavy fuel oil (HFO) swirl burner with a rotary cup air blast atomizer are presented. A detailed in-flame data archive of gas temperature and O2, CO, CO2, and NO concentrations has been obtained for five flames for differing excess air levels (15% and 20%), swirl numbers (1.05 and 1.2), primary air-to-fuel ratios (2.5 and 3.0), and atomizer cup speeds (1.0×104 and 2.0×104 rpm). A wider range of operating parameters has been established to quantify their effects on NO and particulate concentrations at the exit of the furnace. In a parallel modeling study, a two-dimensional computational fluid dynamics code for the prediction of HFO spray combustion and NO and particulates emissions has been constructed. Validation of the code against the experimental data reveals reasonably good quality predictions in the near burner region. The code is capable of simulating the measured trends of flue-gas NO and particulates emissions with useful precision for a wide range of atomizer/burner operating conditions. A scrutiny of the in-flame and flue-gas data, with the aid of the predictions, has provided an enhanced understanding of combustion and combined NO/particulate emissions characteristics of the HFO flames generated by the rotary cup atomizer and establishes the foundation for future work in optimizing combustion and emissions performance.

SPRAY PENETRATION INTO THE CITRUS TREE CANOPY FROM TWO AIR–CARRIER SPRAYERS

Field experiments were conducted to investigate the effect of sprayer type, application volume rate, and airflowrate on spray deposition along depth of the citrus canopy. The trees were sprayed from one side using a tower sprayer withcrossflow fans and rotary atomizers (Curtec) at three spray volume rates and a tower sprayer with an axialflow fan andhydraulic nozzles (Titan) at two spray volume rates and two airflow rates. Spray deposition was determined with fluorometryusing cotton ribbons as targets within the entire canopy depth at two heights.<br><br>For both sprayers, deposition decreased with canopy depth, and spray penetration was improved as the volume rateincreased. The effect of volume rate became significant after about 1 m and 2 m depths for the Curtec and Titan sprayers,respectively. At the highvolume rate, mean depositions of the two sprayers were not significantly different. In general,operating the Titan sprayer at 1600 rpm (lower airflow) gave mean deposition comparable to that at 2225 (rated) rpm (higherairflow). The effect of airflow on spray penetration was significant beyond about 2 m depth.

Dynamics of Droplets

1R36. Dynamics of Droplets. - A Frohn and N Roth (Inst fur Thermodynamik, Univ of Stuttgart, Pfaffenwaldring 31, Stuttgart, 70550, Germany). Springer-Verlag, Berlin. 2000. 292 pp. ISBN 3- 540-65887-4. $82.00.Reviewed by Y Chisti (Inst of Tech and Eng, Massey Univ, Private Bag 11 222, Palmerston N, New Zealand).Many natural and technical processes depend on generation of droplets and interaction among droplets and other phases. Droplet dynamics influence processes as diverse as cloud formation, rain, spray painting, and dispersal of aerosols. Because of its wide-ranging significance, substantial research literature has accumulated on droplet dynamics, but not many books treat this subject. This book provides a useful discussion of droplet dynamics in a compact volume. Some of the theoretical aspects relevant to drop dynamics are covered in an extensive first chapter. The major topics discussed include surface tension and internal pressure; liquid-liquid and solid-liquid interfaces; charged droplets; small-amplitude droplet oscillations; internal circulation; instability of droplets; instability of jets; relaxation phenomena; thermodynamics; phase transition processes; droplet evaporation; and interaction of light with droplets. Topics, such as internal circulation and how it is affected by droplet dimensions and the presence of surfactants, are addressed quite poorly despite the importance of these topics in many processing scenarios. A chapter is devoted to droplet generation. This subject is discussed in less depth than some of the other topics in the book. Much practical information exists on design, selection, and operation of spray nozzles and other droplet generation devices, but the book does not reflect this knowledge. Pressure atomizers, rotary atomizers, and ultrasonic atomizers are barely mentioned. A chapter entitled “Droplet systems” addresses topics such as sprays, streams and arrays of droplets, and single droplets suspended by various means. An extensive chapter deals with the relevant measurement techniques such as the photographic methods, techniques of measuring velocity and size, measurement of optical properties, temperature, and surface tension. Not all available methods are discussed sufficiently or thoroughly. In most practical droplet systems, droplets interact among themselves with the suspending gas and with the suspended solids. Methods for the study of such physical interactions in flow systems are devoted a chapter. Many droplet-related processes involve phase transitions. Examples are condensation of water vapor into clouds, evaporation of fuel droplets during combustion, and spray-drying of droplets to powders. Some of the experimental methods for study of phase transition in droplet systems are discussed in an extensive chapter devoted entirely to this subject. Combustion related phase transition phenomena are discussed in particular depth. Some of the applications of droplet dynamics are outlined briefly, perhaps superficially, in a chapter entitled “Miscellaneous applications.” The applications mentioned include everything from ink jet printing to gaining an understanding of development of condensation trails of high-flying aircraft. The book covers many topics, but also leaves out a great deal. Nevertheless, this book should prove useful to anyone working on droplet dynamics and related fields such as spray technology and aerosol science. The book’s emphasis on experimental methods is one of its strong points. The book cites more than 500 references and is illustrated with more than 200 figures of generally good quality. On the negative side, the writing is needlessly verbose and sometime irritatingly so. The book’s short index is not especially useful, but this shortcoming is partly compensated for by a detailed table of contents. The text is hardbound, of good quality, and is reasonably priced ($82.00) for a specialist monograph. Dynamics of Droplets is a recommended acquisition for research libraries and individuals working on droplet dynamics.

Smoke precipitation by charged water aerosol

Experiments on the removal of smoke particles by charged droplets were carried out. The droplets were charged inductively during their spraying by a rotary atomizer. The electrical charging of droplets significantly increases the efficiency of removal of smoke particles from air as compared to the uncharged aerosol.

Feasibility of Rotary Cup Atomizer for Slag Granulation.

At the present molten slag from a blast furnace (B.F.) is granulated by impinging much water without any recovery of its much sensible heat (1 823 K), polluting water and atmosphere. To solve these problems, we studied the dry granulation of molten slag by Rotary Cup Atomizer (RCA), in which the influence of the rotating speed of the RCA on slag drop size was mainly examined. In the experiment, the molten B.F. slag was supplied to the center of RCA with air blast. Slag drops flown from the cup lip due to centrifugal force were collected and examined from viewpoints of shape, dimension and the flown distance of the drop.Most significantly, molten slag was successfully granulated under the dry conditions without water impingement. The rotating speed of the RCA influenced the diameter and shape of slag drop very strongly. The higher rotating speed made the slag drops smaller, more spherical and more uniform. Drops with 5 to 6 mm of average dimension were obtained at the rotating speed of 15 rps (900 rpm), and drops with less than 1 mm, at that of 50 rps (3 000 rpm). In the former case, the shape of drop obtained was distributed, changing from sphere to stick at the further place from the center of RCA. The results revealed a possibility of alternative, new slag granulation process with many benefits.

Preparation of redispersible dry emulsions by spray drying

Development of stable dry emulsions being able to reform the original o/w-emulsion by reconstitution in water is presented. Dry emulsions were prepared by spray drying liquid o/w-emulsions in a laboratory spray dryer. Three hydroxypropylmethylcellulose (HPMC) types were applied as solid carrier and emulsifier. The lipid phase was fractionated coconut oil. The ratio of solid carrier to lipid phase influenced the reconstitution properties. It was possible to prepare redispersible dry emulsions of a lipid content up to 40% dry powder mass. The different HPMC types had no noticeable effect on the reconstitution properties, but too viscous liquid o/w-emulsions were difficult to atomise. The type of rotary atomizer, or the rate of rotation did not affect the technical properties of the dry emulsions containing 40% lipid. It was concluded that low viscosity HPMC was a useful solid carrier. The dry emulsions remained physically stable for at least 6 months.

Technical optimisation of redispersible dry emulsions

Preparation of dry emulsions suitable for tablet processing was examined in this study. Liquid o/w-emulsions were spray dried in a laboratory spray dryer applying hydroxypropylmethylcellulose (HPMC) as a solid carrier and emulsifier. As the lipid phase, fractionated coconut oil was used. The ability of various excipients to increase the density of dry emulsions was investigated. Adding sucrose to the formulation, redispersible dry emulsions with higher density were obtained. The type of rotary atomizer did not affect the dry emulsions containing sucrose nor the rate of rotation of the atomizer applied in the spray drying process. By wet granulation, using ethanol as a binder, free-flowing and compactable dry emulsions were obtained and simultaneously the reconstitution properties were preserved. It was concluded that dry emulsions could be optimised for tablet processing by wet granulation. Tablets having a lipid content up to 20% had proper tablet properties.

Rotary atomizer

Rotary atomizer

Rotary atomizer

Rotary atomizer

Rotary atomizer

Fluorescent polymeric coatings can find interesting applications in the field of solar energy as thin-film luminescent solar concentrators (LSCs). At present, polymers such as polycarbonate (PC) or poly(methyl-methacrylate) (PMMA) are commonly used as dye-doped host matrix materials in LSCs. However, LSC devices based on these polymers still present limited lifetimes resulting from the intrinsic poor photostability of the polymeric carrier. In the attempt to achieve high-durability LSC devices, a series of new crosslinked fluoropolymeric systems is presented in this work as potential alternative host matrix coating materials for LSC applications. The chemical, physical and morphological modifications occurring to the crosslinked fluorinated coatings when subjected to long-term UV–vis light exposure (over 1000 h of accelerated weathering) are found to correlate well with the photovoltaic response over long-term operation of functioning LSC devices. In particular, better operational stability compared to reference PMMA-based devices can be obtained with the new crosslinked fluorinated coatings by appropriate selection of crosslinking agent. In addition, the effect of radical scavengers on LSC device operational stability is also investigated and it is found that in the long-term light exposure regime (>600 h) these additives may lead to improvements in LSC device lifetime. The results of this study allow a greater understanding of structure–property relationships in crosslinked fluorinated coatings subjected to long-term weathering and provide useful guidelines for the design of high durability fluorescent coatings for light management and photovoltaics.

Rotary atomizer

Rotary atomizer

Production of boron powder by arc volatilization : T.Hagio et al.J. Mater. Science, Letters, vol 17, no 22, 1998, 1937–1939

This chapter provides an overview of furnace oil burners. Fuel oils burn readily only in vaporized or gaseous state. The pot-type vaporizing burner can be used for the lighter fractions of gas oils, but combustion appliances using heavier fuel oils require special atomizing equipment for efficient combustion. Fuel-oil atomizers operate on two principles: (1) atomization by mechanical means, for example, pressure jet and rotary cup atomizers and (2) atomization by means of an atomizing fluid, for example, air at low, medium or high pressures, or steam. Pressure jet burner is the oldest type of mechanical atomizer and is still commonly used for large land and marine boilers. Rotary cup burner is a comparatively new burner, suitable for use with small installations and capable of using a variety of oil feeds without major modification. The chapter also discusses combustion characteristics of fuel oils. Combustion takes place initially in the vapor phase, so that evaporation or atomization must be sufficient to initiate combustion. After ignition, heat is supplied by the flame and by surrounding heated surfaces. With heavy residual oils and coal-tar products, a large oil film area is necessary to maintain combustion.

Droplet Generation by Disintegration of Oil Films at the Rim of a Rotating Disk

A fundamental study has been performed to examine oil film disintegration mechanisms at the rim of a rotating disk. The configuration investigated is an abstraction of one of the droplet generation sources in an aeroengine bearing compartment. The paper aims to contribute to both the determination of directly applicable droplet characteristics and the establishment of a database that can be used for the development of droplet generation models. The near-term objectives of the study are (i) to identify disintegration modes relevant with respect to aeroengine bearing compartment operating conditions, (ii) to determine droplet sizes under those operating conditions, and (iii) to measure individual droplet diameter/velocity relationships. The long-term objective is to incorporate this information into advanced CFD-based design tools. The disintegration modes identified here were similar to previously reported flow regimes generated by rotary atomizers. However, slightly different transition characteristics are documented for the turbine oil considered here, indicating a transition occurring at either higher speeds or higher flow rates. Droplet diameters and velocities are presented for relevant bearing compartment conditions. In this mode, droplet diameters appear to be insensitive to the volume flow rate, but show a finer atomization for increasing rotational speeds. Eventually a speed is reached beyond which no further droplet diameter reduction is obtained. For the first time, size class resolved droplet velocities are presented. A variation of operating parameters at a constant radial location does not have a significant impact on either the normalized droplet velocity or the flow angle. Radial traverses show a decrease of the droplet velocity with increasing distance from the rim of the disk and a transition from a more tangentially oriented droplet trajectory to a more radial motion.

Spray-dried lactose composite particles containing an ion complex of alginate-chitosan for designing a dry-coated tablet having a time-controlled releasing function.

The properties of novel spray-dried lactose composite particles suitable for the coating filler of a dry-coated tablet having a long induction period in drug release were investigated. To prepare spray-dried composite particles containing alginate-chitosan complex (SD(L/AL-CS)), an aqueous solution of lactose and sodium alginate and the acetic acid solution of chitosan were concomitantly fed into the rotary atomizer of a spray-dryer. The formation of the alginate-chitosan complex was confirmed by measuring the weight of insoluble portion in the mixture of sodium alginate and chitosan solutions. The dissolution properties of the dry-coated tablet were measured with the JP specified paddle method. The micromeritic properties of SD(L/AL-CS) were compared to those of the SD composite particles of lactose-sodium alginate, having a good compacting property. The drug release profiles of dry-coated tablet with SD(L/AL-CS) contained a long induction period followed by a rapid drug release phase in the artificial intestinal fluid. The induction period for drug release to occur was increased with an increase in the degree of deacetylation of chitosan and in the amount of chitosan in the formulation. The prolongation of induction period was attributed to the formation of an insoluble ion complex between sodium alginate and chitosan in the composite particles, which could form a rigid gel structure on the tablet surface. A time-controlled release tablet was designed with the composite particles of lactose containing the alginate-chitosan ion complex. The induction period of the dry-coated tablet could be prolonged in order to deliver the drug to the colon by controlling the type and amount of chitosan formulated in the composite particles.

Advances in Locust Spraying Technology

Whichever species of locust is considered, control strategy has always been limited by control technology. Early crop protection measures were confined to mechanical means. The development of synthetic insecticides and progress in application technology improved the efficacy of crop protection. Coupled with improved understanding of the biology and population dynamics of the major locust species, they also enabled strategic control in the form of plague and upsurge prevention.Baiting and dusting constituted simple but inefficient methods of pesticide application, but it was the development of ultra low volume (ULV) spraying that allowed man to interfere with the progression of locust plague cycles. The technology for ULV spraying has developed from simple early devices such as the exhaust nozzle sprayer to safer and more efficient sprayers equipped with rotary atomisers for hand-held, vehicle-mounted and aerial spraying use.Global positioning system (GPS) technology is a powerful new tool in locust control. The spatial accuracy and navigational guidance it provides simplify some of the most difficult tasks such as refinding targets and flying accurately spaced spray passes when no ground marker party is available. The technology also provides greater accountability in that the details of spraying operations can be recorded for later analysis.Despite these improvements in knowledge and technology, locusts still pose major problems due to their mobility, the remoteness and inaccessibility of their habitats and the inconsistent commitment to maintaining monitoring and control capacity for a sporadic and infrequent pest. Upsurges and plagues have occurred in recent years and are likely to continue to do so in the future, albeit with diminishing frequency and severity.

Volumes of petroleum spray oil required for control of Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae) in mature citrus orchards

Studies on the relationship between volume of spray and suppression of citrus leafminer (Phyllocnistis citrella) oviposition by petroleum spray oil on 4 m‐high mature orange trees showed a negative exponential relationship between spray volume and the number of mines per leaf. Significant reductions in the number of mines per leaf compared to unsprayed trees was achieved at spray volumes of ≥ 3300 L/ha using oscillating boom and at ≥ 3200 L/ha using rotary atomiser sprayers. However, improvements in efficacy at volumes over 3200–3300 L/ha were not significant and so of little practical value. The optimal spray volumes for citrus leafminer control are therefore suggested to be 3000–3500 L/ha. No significant difference in effectiveness was found between the oscillating boom at 3300 L/ha and a rotary atomiser at 3200 L/ha. The effect of oil spray on the citrus leafminer parasitoid Semielacher petiolatus (Girault) (Hymenoptera: Eulophidae) was inconsistent. Improved droplet deposition and coalescence may enhance the coverage of new growths and increase the efficacy of oil spray for protection of plants from oviposition.

Ultrasonic atomization for spray drying: a versatile technique for the preparation of protein loaded biodegradable microspheres

Bovine serum albumin (BDA) loaded microspheres with a spherical shape and smooth surface structure were successfully prepared from poly(lactide-coglycolide) using an ultrasonic nozzle installed in a Niro laboratory spray dryer. Process and formulation parameters were investigated with respect to their influence on microsphere characteristics, such as particle size, loading capacity, and release properties. Preparation of microspheres in yields of more than 50% was achieved using an ultrasonic atomizer connected to a stream of carrier air. Microsphere characteristics could be modified by changing several technological parameters. An increased polymer concentration of the feed generated larger particles with a significantly reduced initial release of the protein. Moreover, microspheres with a smooth surface structure were obtained from the organic polymer solution with the highest viscosity. Microparticles with a low BSA loading showed a large central cavity surrounded by a thin polymer layer in scanning electron microspheres. A high protein loading led to an enlargement of the shell layer, or even to dense particles without any cavities. A continuous in vitro release pattern of BSA was obtained from the particles with low protein loading. Glass transition temperatures (T g) of the microspheres before and after lyophilization did not differ from those of the BSA loaded particles prepared by spray drying with a rotary atomizer. Analysis of the polymer by gel permeation chromatography indicated that ultrasonication had no effect on polymer molecular weight. Molecular weight and polydispersity of the pure polymer, placebo microspheres prepared by spray drying, and placebo microspheres prepared using the ultrasonic nozzle were in the same range. In conclusion, ultrasonic atomization represents a versatile and reliable technique for the production of protein loaded biodegradable microspheres without inducing a degradation of the polymer matrix. Particle characteristics can be modified by adjusting formulation parameters and atomization conditions in a simple manner.

Rotary atomizer

This paper presents a methodology to design a cross-coupled bistage fuzzy controller for cross-coupled servomechanisms. In the bistage fuzzy inference, the consequence in the first stage is passed to the second stage as fact and the consequence of the second stage is used as the control input. The proposed approach is used to reduce the complexity of the fuzzy system. A more systematic method which is based on a performance index of the fuzzy control system is developed to generate bistage fuzzy rule sets. To show the effectiveness, the proposed approach is applied to control a cross-coupled biaxial servomechanism system which is difficult to obtain by an accurate nonlinear mathematical model in the case of a circular trajectory. Simulation results have shown that the desired contouring the accuracy can be achieved, and the proposed approach outperforms the uncoupled approaches.

Low volume spraying on cotton: a comparison between spray distribution using charged and uncharged droplets applied by two spinning disc sprayers

Two hand held spinning disc sprayers, one producing electrostatically charged spray, were assessed and compared on Egyptian cotton. The charged droplets produced greater overall deposition with a higher proportion on the undersurface of leaves. Spinning disc sprayers offer smallholder cotton farmers several advantages over higher volume sprays applied by knapsack sprayers, and it is suggested that charged rotary atomisers merit further consideration for controlling troublesome cotton pests such as whiteflies which are found on the undersurface of leaves.