Ultrasonic Nozzle Compatibility
The physical properties of the liquid play a central role in any atomization process. Factors such as viscosity, solids content, composition of the mixed solution, and fluidity of the liquid.
Pressure nozzles, whether hydraulic or pneumatic, are generally unsatisfactory for abrasive materials or materials that tend to clog small holes in the nozzle. In addition, it is often necessary to operate such nozzles at high pressures, which can result in overspray and consequent material loss.
Ultrasonic nozzles have many advantages over pressure nozzles, but still have technical limitations. Some of these advantages include gentle low-speed spray, controlled spray range, extensive spray forming capability and no clogging. The limitations of ultrasonic technology are usually the type of liquid.
Although there is currently no specific set of rules to measure whether liquids can be successfully atomized by ultrasound, we can give some general advice after 20 years of experience.
The liquids are classified as follows:
Pure one-component liquid (water, alcohol, bromine, etc.)
Aqueous solution (NaCl / water, alcohol / water, 10% KOH aqueous solution, etc.)
Solid mixture (coal slurry, polymer beads/water, silica/ethanol, etc.)
The principle that applies to most materials is that the higher the viscosity or solids content of the liquid, the lower the maximum flow rate at which a given nozzle can be atomized. Although the ultrasonic power and frequency are adjustable, for liquids with high viscosity and high solid content, no matter how the power and frequency are adjusted, the desired effect cannot be achieved.
1. Pure liquid, the only factor limiting the ability of ultrasonic atomization is viscosity. Generally, the upper limit of viscosity is about 100 cps. As the viscosity decreases, the maximum flow rate increases accordingly.
2. Aqueous solution, in most cases, the limiting factor is also the viscosity. But when the solution contains very long chain polymer molecules, the results may be different. This molecule can inhibit the formation of discrete droplets because the polymerized molecules may polymerize two to three droplets.
3. Solid mixture, there are three main factors affecting atomization: particle size, solid concentration and dynamic relationship between solid and carrier.
Granularity is a key parameter. In general, if the particle size ranges beyond one tenth of the median diameter drop, the mixture will not atomize properly. For droplets containing one or more solid particles, the size must be significantly larger than the size of the solid particles embedded therein. If this is not the case, the droplets formed by atomization will most likely not contain solid components, the solid components will be separated from the carrier, aggregated on the atomized surface and eventually dropped in the form of agglomerates.
The concentration of solids in the mixture is an important factor in its nebulization. Even if the particle size is appropriate, other factors, such as the viscosity of the carrier and the ability of the solid component to remain suspended, also play a role in the final atomizability. Therefore, there are no clear guidelines to enable us to establish the relationship between atomization and solids concentration. According to our experience, the actual upper limit of solids concentration is about 40%.