Back to Ultrasonic Spray Nozzles
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| The breadth of applications throughout research institutions and industry for ultrasonic spray technology is wide. In addition to the electronics and medical/biomedical areas which are discussed elsewhere in this presentation, numerous other uses have been identified and perfected. It is not practical to identify all of them, but the following sample list should be indicative of the diverse nature of the areas in which this technology has been applied. |
| Coating moving webs of glass, fabric, and paper |
| Spray drying pharmaceuticals and ceramic slurries on a laboratory scale |
| Moisturizing various materials with a soft spray of water or injecting water into chemical reactors |
| Applying small amounts of fragrances, flavors, or oils to products |
| Coating food products with layered ingredients |
| Injecting small amounts of reagents into chemical reactors |
| Providing an atomized spray for the combustion of liquid fuels |
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Moving Webs The term "web-coating" covers a wide range of industrial applications, all involving the coating of continuously moving webs of material ranging in width from a few inches to several feet. Common examples are found in the fabric, paper, and glass industries. Ultrasonic spray technology is used for web-coating primarily because of the low-velocity spray that is produced. The low velocity assures that overspray is kept to a minimum. An additional benefit of the soft spray is found in applying substances to delicate materials, such as non-woven fabrics. The low-velocity spray prevents any damage to or distortion of the fabric. An example of a very successful application of this technology is in the manufacture of float glass, used for architectural structures, automobile glass, mirrors, doors, etc. Float glass is produced by "floating" the molten glass on a long bed of liquefied tin. The glass spreads out onto the surface of the denser tin and moves downstream. As it moves, the continuous sheet, as much as 14 feet in width, is gradually cooled until it solidifies. It then emerges onto rollers, where further cooling occurs. Finally the glass is cut into manageable rectangular sections by cutting tools over the web. The thickness of the plate glass produced is controlled principally by the rate at which the molten material is released from the furnace. Virgin glass, during its first days or weeks of being produced, has a tendency to develop areas of irreversible stain, which are unacceptable in many of its applications. The staining is caused primarily by moisture contained in the air. As humidity increases, the problem worsens. Protective organic acid coatings have been developed that eliminate this problem. These coatings, which are washed off before the glass is put into service, are usually applied onto the top surface of the moving web, prior to cutting. After cutting, the glass panes are stacked such that the uncoated surface is in contact with a coated surface, thereby providing protection to that surface as well. Ultrasonic nozzles spray systems are preferred for this application because of their low-velocity spray, which eliminates the overspray of these acidic chemicals. Typically, complex collection systems, used to entrain overspray, do not have to be employed. To produce wide sprays from a single nozzle, the nozzle is mounted within a specially designed air-handler that uses low-velocity air to both shear the spray to the desired width, and propel it forward in a uniform wedge-shaped pattern. Uniform spray patterns up to 20 inches wide can be produced. Thus, for coating a 14 foot wide web, as few as six (6) nozzle/air-handling assemblies are required. Typically, more than six (6) assemblies are used in order to achieve optimum uniformity across the entire extent of the web. Spray Drying Spray drying is a well-known technique used for the preparation of pharmaceutical products, ceramic-based materials employed in x-ray crystallography, and other related substances. Instant coffee is another example. The spray drying process involves the injection of a sample of atomized, solids-bearing material into the top of a heated, cylindrical chamber and the subsequent drying of the product as it falls to the bottom, where it is collected. The trajectory of the drops is controlled by induced air currents within the chamber that keep the drops suspended for as long as required to effect complete drying at the preset temperature. The shape and size of the dried particles are important. Several factors play a role in the determination of shape and size, the most important of which are
The size of the chamber plays a primary role in setting the boundaries for the process. In commercial applications in the food and pharmaceutical industries, drying chambers may be several stories tall because of the need to balance throughput with the drying rate, temperature and initial drop size conditions. Obviously, such chambers are not suited for use in the laboratory , where usually, only small amounts of material are processed, and where the size of the chamber becomes an important consideration. The principal reason that spray dryers are generally so large is that the standard pressure nozzles used to generate the spray impel the drops at high initial velocity, thereby dictating a large chamber volume in order to properly dry the material. The low velocity spray developed by ultrasonic nozzles brings new possibilities to the situation. Having only 1/10,000th the kinetic energy of pressure sprays, it is a much simpler matter to keep the drops suspended. The chamber size can be drastically reduced, to volumes small enough to fit on a counter top. Another important byproduct of using ultrasonic nozzles is that their ability to deliver very small quantities of material makes it possible to process samples of limited size. This is particularly important in many pharmaceutical applications where researchers are dealing with extremely small quantities of available material. Moisturization Some very specific applications exist for ultrasonic atomization in applying a water spray to certain products and in introducing moisture into reaction streams. The technology is not suitable for general humidification purposes, since the mean drop sizes are somewhat larger than desirable for that application. The ultrasonic humidifiers that are commercially available operate at much higher ultrasonic frequencies than do nozzles, resulting in a spray with mean diameters in the one(1) micron range, a region of drop size consistent with humidification requirements. Ultrasonic nozzles have a role in moisturization processes where the requirement exists to deliver a precisely metered water spray, usually in small amounts, and/or where a low-velocity spray is critical. One example of where this technology has been applied comes from the dried herb and spice industry. It is sometimes necessary to partially reconstitute herbs, which have previously been dried, with moisture in order to bring the product into specification. Directing a spray of water from a pressure nozzle at such a product can result in unacceptable dispersion because of its light and fluffy nature. Ultrasonic nozzles are used because of their characteristic "soft" spray and the high degree of control that can be achieved. Another application that benefits from the soft spray is the moisturization of delicate, non-woven fabrics. Fragrance, Flavors, and Oils There exists a wide assortment of potential uses for ultrasonic nozzle spray technology in applications where minute amounts of material must be applied to relatively large areas of product. The title of this section is somewhat misleading in that it names only three substances. Obviously, there are many more. An example, taken from the non-woven fabric product area, involves the application of a highly concentrated, perfumed scent onto a narrow, moving belt of loosely packed, fibrous material used in manufacturing certain personal hygiene products. Since the amount applied per unit area is necessarily minuscule, but at the same time, must be spread out to cover as much of the product as possible, the use of ultrasonic spray nozzles is ideal. Other substances, such as flavorings, vitamins, or oils used in food product manufacturing, often have similar coating requirements.
Food Product Coatings Coating food products with sprays from ultrasonic nozzles has been partially covered elsewhere on this page under Fragrance, Flavors, and Oils. Here we shall give an example that involves coating a food product on a larger scale. The example is taken from the frozen dessert industry. Ultrasonic spray nozzles are used to apply a substance used to prevent the product's outer coating from prematurely breaking apart when eaten. Ultrasonic nozzles are used because of their ability to provide a uniform, precisely controlled spray pattern with virtually no overspray. Chemical Reactor Injection The term "chemical reactor" covers a broad range of equipment designed to carry out chemical reaction processes. The reaction chamber can be under vacuum, under high pressure, at high temperature, at low temperature, etc. In some instances, small quantities of reactants must be injected into the reactor as a spray. Ultrasonic nozzles are used when there is a need to precisely control the injection rate and amount, when a low-velocity spray is desirable and/or when a generally small drop size will enhance the process. Typically the housing of a nozzle is fitted with a flange which is bolted to an inlet port of the chamber, with the atomizing tip of the nozzle protruding into side of the chamber. Both pressure and vacuum operation are possible. In cases where the internal temperature of the chamber is high, auxiliary cooling of the nozzle must be provided. Refer to the Operating Considerations section on the Additional Technical Information page for further limitations regarding operation at elevated temperatures. If you would like to discuss your specific application, please contact us at Sono-Tek.
Combustion The original application for ultrasonic nozzles was in the combustion of liquid fuels, which dates back to the early 1970's. Sono-Tek was the pioneer in this use of the technology for this purpose.
The attraction of ultrasonic nozzle technology as a means to atomize fuel prior to burning is its low flow rate capability, and the ability to deliver fuel over a wide range of flow rates. Oil burners based on this technology were developed first for the military market, for use in portable electric power generation equipment, and then for the commercial market, as an energy-efficient replacement for conventional, pressure spray burners. The prospect of being able to modulate the heat input to a furnace or boiler over a range of flow rates that is always consistent with the immediate heating requirements is attractive. Pressure nozzles used for residential oil burners fire at a fixed flow rate, which makes it impossible to adjust the flow rate to the instantaneous heating requirement. The approximately 5:1 turndown ratio possible with ultrasonic nozzles makes modulation possible. Moreover, these nozzles can deliver as little as 0.1 gph compared with a lower limit of 0.5 gph for pressure nozzles. The combination of low flow rate capability and adjustability is ideal for producing an extremely high efficiency burner. However, this burner, after all these years, is still not a commercial success. Unfortunately, the economic realities of the oil burner industry mitigate against the higher initial costs associated with ultrasonic oil burners. There are still many who are involved in combustion research that use ultrasonic nozzles in their work. The areas in which work is or has been conducted include:
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