Velocity Measurements in Sprays

1. A Brief Guide on Key Spray Characteristics: Drop Size and Velocity The importance of spray characterization has increased significantly since the last decade. Many diverse applications, such as evaporative cooling, spray drying, fire suppression, gas conditioning, tablet coating, spray painting, and agricultural spraying, require this information so that sprays can be effectively used. Thus, it is becoming more critical for engineers to understand the basics of the atomization process and learn how it is evaluated. The technology of atomization has advanced dramatically as the applications of sprays have become more sophisticated. When it comes to grasping the basics of atomization or spray nozzle operation, the one thing that matters the most is droplet size. However, for better understanding, let’s first discuss what atomization exactly means. Though the term “atomization” sounds intimidating, atomization is nothing but a process of generating drops. Atomization occurs when a liquid is forced through a nozzle. The liquid emerges in a form of ligaments when the potential energy of liquid and the geometry of the nozzle work together. These ligaments then break up into very tiny pieces, usually called droplets. Understanding Spray Characteristics - Drop Size and Velocity Drop Size Each spray can cause liquid to emerge in a range of drop sizes, and this range is called drop size distribution. Different spray nozzles come with different-shaped orifices and hence, produce different spray patterns, such as hollow cone, flat spray, full cone, etc. The drop size distribution depends on the nozzle type and varies greatly from one type to another. Other factors that affect drop size distribution include properties of the liquid, nozzle capacity, spraying pressure, and spray angle.

2. Velocity Typically called spray velocity, drop velocity is the speed at which a drop of the spray transfers from the orifice to the landing surface. In general, bigger droplet sizes travel at higher drop velocities, and smaller droplet sizes at lower velocities. Thus, the spray velocity is largely affected by not only the nozzle type, but also the droplet size. Increasing the spray liquid pressure typically results in a finer spray for most nozzle designs and also causes an increase in the velocity of droplets. But as spray becomes finer, the risk of drift also increases. However, after a certain point, an increase in pressure doesn’t result in a further increase of drift. In fact, with some nozzle designs, a further increase in pressure may even result in a decrease in drift because of the dominance of the droplet velocity effect. Therefore, accurate information on spray velocity measurements along with drop size evaluation is essential to achieve the best results. The relationship between droplet size and velocity is something that must always be taken into account whenever you want to come up with the best spray nozzle design or spray equipment that offers higher efficiency. Source: https://www.enurga.com/velocitymeasurement.htm