By Matt Migliore
Today’s spray nozzle designs have benefited from advances in manufacturing techniques, enabling the production of more complex shapes in a wider variety of materials. For example, rapid prototyping (3D printing) allows spray technology manufacturers to test system designs at a much faster rate than was previously possible, thus reducing development time for new and custom products. Further, advances in droplet measurement systems provide better characterization of the spray from a nozzle, providing a better prediction of how the nozzle will perform in a given process.
Choosing the Right Technology
From an end-user’s perspective, the wide-ranging and sophisticated nature of modern-day spray technologies heightens the importance of the selection process. According to Mike Bruno, applications engineering manager for BETE Fog Nozzle, end-users should enter the technology selection process with a firm understanding of the function the nozzle will perform. For example:
1. Does the spray technology need to provide uniform coverage, or does it need to make a very small droplet size?
2. Does the spray technology need to provide a high impact or cover a big area?
“There are many, many styles of nozzle to choose from, and identifying its function in the process helps to select the correct one,” says Bruno.
Once the intended function of the nozzle has been determined, Bruno says the end-user should next consider geometry, which determines the spray angle for the application. Other key elements to consider during the spray technology selection process are flowrate and available pressure drop across the nozzle.
“For complex situations, it is often beneficial to call the nozzle manufacturer and speak with one of their applications engineers who have been working with nozzles for years,” says Bruno. “Their expertise can make the difference between a system that simply works, and one that works efficiently.”
Once the spray system has been designed and employed, there are some common application issues that may negatively impact the application and force the end-user to revisit the technology selection process. At the top of the list of negative results are corrosion, erosion and plugging.
Plugging, in particular, can be insidious. A completely plugged nozzle is often easy to diagnose – there is zero flow. However, a partially plugged nozzle may show only a small change in flow, but this partial plugging may result in a significant change in spray pattern or spray angle, which, in turn, can have a big negative impact on the overall efficiency of the spray system. To mitigate the plugging problem, Bruno recommends a nozzle with a large free passage. “Nozzles that have internal passages that are equal in size to the orifice diameter have the largest free passage possible,” says Bruno. “If the fluid contains materials larger than that, a filter upstream of the nozzle is needed.
Corrosion and erosion are material-related issues. Chemical attack causes corrosion, while suspended solid particles abrading the surface lead to erosion. “There is a very wide range of materials from which a nozzle can be made,” says Bruno. “Proper selection of the nozzle material will minimize corrosion and erosion problems.”
According to Bruno, the most common pitfall end-users encounter in the area of spray technology is waiting until the very end of the design process to consider the nozzle. “The nozzle is where the rubber meets the road, so to speak,” says Bruno. “Selecting the right nozzle with the right pressure drop and the right spacing can make a drastic difference in how the system operates. Knowledge of this up front can lead to better piping layouts and more appropriate pump selection.”
The Future of Spray
Going forward, Bruno says the continued evolution of computation fluid dynamics (CFD) software will play a larger role in the spray systems design process. “Coupling the system designer”s detailed knowledge of their process with our knowledge of nozzles and ability to measure critical performance characteristics like droplet size allows us to evaluate the proposed design,” says Bruno. “In addition to the overall process, we can also use CFD to focus on potential trouble areas; for example, we can identify if there is gas bypass, impingement issues, undesirable phase change, etc. The software provides a look inside the process, which is something that you usually can”t see even if you have a production unit in operation.”
Matt Migliore is the editor in chief of Flow Control magazine. He can be reached at Matt@GrandViewMedia.com.