Spraying Devices Research Articles

Wet electrostatic scrubbers for the abatement of submicronic particulate

Water electrostatic scrubber (WES) represents an alternative technology for the abatement of that submicronic fraction of particulate – belonging to the so-called Greenfield gap – usually hardly captured with other cleaning techniques. The promising potentialities of WES are recognized by the scientific and industrial communities, but the design of this kind of reactor is far from being optimized. This work reports a mathematical model to evaluate the particle removal efficiency in wet electrostatic scrubbers. The model is used to find out optimal working condition of WES units, through the maximization of the particle collection efficiency in function of different process parameters: contact time, specific water consumption, water/gas relative velocity, size and charge of sprayed droplets. The model has been validated by comparison with different experimental data available in literature, both for charged and uncharged scrubbers. Then it is applied to a reference case study to obtain generalizable results. The model shows that the process optimization for micronic and submicronic size particles follows different criteria. For micronic particles, the collection efficiency increases for higher water/gas relative velocity, with a small effect of droplet diameter and a moderate increase with the droplet charge. On the contrary, in the Greenfield gap, the water/gas velocity plays a secondary role in the capture mechanisms, while a substantial increase of collection efficiency by improving the droplet charge level and reducing the droplet size has been observed. With reference to the actual performances of water spraying and charging devices, the model predicts that a collection efficiency as high as 99.5% can be reliably obtained in few seconds with a water consumption of 100 ml/m 3 by adopting droplet diameters around 100 μm and charge to mass ratio from 1 to 3 mC/kg, corresponding to droplet charge equal to 10–30% of Rayleigh limit.

Electrospray on superhydrophobic nozzles treated with argon and oxygen plasma

We report on a simple process to fabricate electrohydrodynamic spraying devices with superhydrophobic nozzles. These devices are useful, among other things, in mass spectrometry and printing technology. The superhydrophobic nozzle is created by roughening the surface of the polyfluorotetraethylene (PTFE) by argon and oxygen plasma treatment. We have developed a polymer-based electrospray device with a flat, superhydrophobic nozzle capable of maintaining a high contact angle and stable jetting.

A procedure for constructing the normative characteristics of chimney-type evaporative cooling towers from the results of field measurements

A procedure for constructing the normative characteristics of chimney-type evaporative cooling towers equipped with different designs of heat-and-mass transfer (spraying) devices is developed using the results of balance tests carried out for many years on 34 cooling towers of different designs with areas ranging from 500 to 10000 m2.

High-pressure injection injuries

This article has been subjected to double blind peer review High-pressure injection injuries are caused by the accidental injection of fluid from high-pressure industrial equipment such as hydraulic systems or paint spraying devices. Schoo et al (1980) estimate that, in their emergency department (ED), these injuries account for only one in 600 hand injuries. But, despite their rarity, several of the features of high-pressure injection injuries make them worthy of examination. Human skin can be breached by pressures of 100 pounds per square inch, or 689kPa (Scott 1983). Many industrial devices operate at pressures of several hundred thousand kPa however, so the consequences of the injuries they can cause can be devastating, requiring for example surgical amputation of fingers or even hands. The first recorded high-pressure injection injury occurred in the 1930s. Rees (1937) describes the progress of a mechanic who, while using a fuel injection system able to emit diesel fuel at pressures high enough to penetrate skin and tissue, sustained a high-pressure injection into his finger. The incident left a wound that, at first, appeared as a pinpoint sized entry site but, after seven days, this became gangrenous. Eventually, the finger was amputated. Since then, a wide range of high-pressure industrial equipment, including hydraulic systems, paint spraying equipment and injection devices for vaccinating animals, has proven capable of causing similar injuries, either through poor working practices or equipment failure (Hart et al 2006).

Inhalational and dermal exposures during spray application of biocides

Data on inhalational and potential dermal exposures during spray application of liquid biocidal products were generated. On the one hand, model experiments with different spraying devices using fluorescent tracers were carried out to investigate the influence of parameters relevant to the exposure (e.g. spraying equipment, nozzle size, direction of application). On the other hand, measurements were performed at selected workplaces (during disinfection operations in food and feed areas; pest control operations for private, public and veterinary hygiene; wood protection and antifouling applications) after application of biocidal products such as Empire 20, Responsar SC, Omexan-forte, Actellic, Perma-forte; Fendona SC, Pyrethrum mist; CBM 8, Aldekol Des 03, TAD CID, Basileum, Basilit. The measurements taken in the model rooms demonstrated dependence of the inhalation exposure on the type of spraying device used, in the following order: “spraying with low pressure”<“airless spraying”<“fogging” indicating that the particle diameter of the released spray droplets is the most important parameter. In addition inhalation exposure was lowest when the spraying direction was downward. Also for the potential dermal exposure, the spraying direction was of particular importance: overhead spraying caused the highest contamination of body surfaces. The data of inhalational and potential dermal exposures gained through workplace measurements showed considerable variation. During spraying procedures with low-pressure equipments, dose rates of active substances inhaled by the operators ranged from 7 to 230 μg active substance (a.s.)/h. An increase in inhaled dose rates (6–33 mg a.s./h) was observed after use of high application volumes/time unit during wood protection applications indoors. Spraying in the veterinary sector using medium-pressure sprayers led to inhaled dose rates between 2 and 24 mg a.s./h. The highest inhaled dose rates were measured during fogging (114 mg a.s./h) and after-high-pressure applications in the antifouling sector (110–300 mg a.s./h). The potential dermal exposure of spray operators was lowest (dose rates from 0.2 to 7 mg a.s./h) in the areas of food and feed disinfection and private and public hygiene during spraying with low-pressure devices. During fogging, wood protection and antifouling applications, high-potential dermal exposures of the operators were determined. Dermal dose rates varied between 100 and 34,000 mg a.s./h.

Flash freezing of erythrocyte suspensions

Freezing whole blood in bulk usually results in severe cellular destruction through the action of ice crystals and osmotic effects in the freezing liquid. The potential of flash freezing blood aerosols onto a liquid nitrogen surface as a means of inhibiting cellular damage was studied in this work. Three commercial spraying devices were employed to spray-freeze either whole blood or concentrated erythrocyte suspensions, using hydroxyethyl starch (HES) as a cryoprotectant. The integrity and viability of the processed cells were assessed by measuring gross rheological properties and the extent of hemolysis. Cells were found to be susceptible to the very high shear stresses imposed by some of the spraying devices. Bulk freezing of blood, even in the presence of the cryoprotectant, resulted in complete cellular destruction. Whereas flash freezing was capable of substantially reducing the level of hemolysis to 12.6% and preserving the cellular deformability.

An Adaptive System with an Identifier (ASI) for Control of the Temperature Profile in a Tubular Reactor

The paper is concerned with control of a catalytic reactor used for producing maleic anhydride from benzene. The objective of the control is the yield of the product synthesized and is obtained through control of the vertical distribution of the temperature profile in a reactor. A mathematical model is used which describes the dynamics of thermal and chemical processes in a reactor. The model parameters are updated by adaptive identification algorithms. An algorithm of adaptive identification with orthogonalized input variables improves the accuracy of parameter estimation when input variables strongly correlate. The computing load is so low that a micro-computer will do the job. An identifier updates the process parameters which is a crucial advantage since dynamic properties of a plant may change substantially due to different reasons, like catalyst ageing, changes in the environment air composition, stuffed holes in the benzene spraying devices, etc. Special attention was given to the system reliability. An algorithm was designed for protecting the information stored in RAM including the programs which use error-correcting codes.

A Quarter of a Century of Plasma Spraying

SUMMARY This review article marks the silver jubilee of plasma spraying. It is obvious that kno wledge about spraying has progressed more by experimental tricks than by scientific approach. This paper surveys the more scientific work done since 1957 and tries to make clear that even yet a gap exists between the theoretical work and the experiments. A consolidated spraying theory still does not exist. The main developments in 25 years are low pressure plasma spraying; spraying in an inert atmosphere; high-velocity, high-power plasma spray­ ing; and low-velocity, long, thick plasma jet spraying. The number of applications has expanded enormously, and spraying is now an accepted surface treatment. The paper is divided into three main sections: the sprayed coating, the transport of the particles, and the spraying devices. In each section a survey is given of the present knowledge and the present problems. At the end of each section some possible research topics are listed.

A Polyester Casting Process for Replicating Cliff Surfaces for Artistic Purposes

The first named author of this note set for himself the project to replicate parts of a forty-foot-high cliff in the Catskill Mountains of the State of New York, for which he developed the process described below. The molding process was begun by waxing the face of a cliff part with a product called a 'separator' to ease the removal of a sprayed rubber mold. Holes and crevices that were too deep to receive the rubber spray were stuffed with paper. Then numerous coats of rubber solution were applied (cf. Fig. 1). To strengthen the rubber layer, which was too thin and brittle to withstand its removal, a urethane foam was sprayed over the rubber. Most of the spraying devices were specially designed. Ten to fourteen

HYMENOPTEROUS PARASITES OF ECONOMIC IMPORTANCE IN S. INDIA

The study of economic entomology has in these days attained such dimensions that various methods of control are being advocated for checking insects injurious to crops. The mechanical methods of control such as the use of insecticides, spraying, fumigation and other artificial devices such as the use of light traps, etc., have been in some cases found impracticable and uneconomical. In view of the poisonous nature of the insecticides themselves, the prohibitive cost of the treat- ments in some cases, the frequency and thoroughness with which these treatments have to be given, the promptness with which these have to be done, and the several meteorological factors that influence the success or failure of the results obtained and lastly the temporary and palliative nature of the results obtained, mechanical methods of control frequently become very much limited in their scope.