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The droplet size produced by spray nozzles plays a key role in many applications such as cooling, smoke removal, fire protection, drying and agricultural spraying. Before we understand why droplet size matters, let’s take a look at how a nozzle produces droplets.

How does the atomization process of the nozzle work

This diagram shows an idealized process of how a nozzle’s water jet breaks up to produce droplets.

The accuracy of this theoretical model appears to be borne out by scientific studies which suggest that a liquid film forms as the liquid passes through the nozzle and past the edge of the orifice.
Due to the influence of aerodynamic force, this layer of film first decomposes into elongated oval or approximately cylindrical “liquid strips”, and then decomposes into droplets.

What determines the droplet size in a spray?

According to the guidance of the atomization process, it is easy to understand that the average diameter of the droplets produced by the nozzle is related to the following factors:

1 | Pressure
The higher the fluid pressure, the smaller the droplet size.

2 | Spray Pattern Types
In general, full cone nozzles produce the largest droplets, followed by hollow cone nozzles and flat plate nozzles. This classification applies to both hydraulic and air-hydraulic dual-fluid nozzles, although the latter produce finer droplets than hydraulic nozzles.

3 | Measuring equipment
Often, measuring the size of a droplet using different measurement methods gives very different results.

4 | Droplet position within the spray cone and distance from the orifice
Depending on the type of spray pattern and its position within the cone, the size of the droplets can vary widely.

5 | Types of spray liquids
Viscosity and surface tension increase the amount of energy required to atomize the spray. An increase in these two properties generally increases the droplet size.

6 | The density of the fluid
The specific gravity of the fluid will affect the overall flow rate and therefore the droplet size. The higher the specific gravity, the lower the flow rate and the smaller the average droplet size for a given pressure.

7 | Spray Angle
The larger the spray angle, the smaller the droplet size will be for any given flow rate.

Why is droplet size so important?

What makes understanding droplet size so important is that, for any given volume of fluid, the smaller the droplet size, the greater the surface area that can be sprayed. If you halve the average droplet size for any given spray, you double the surface area of the spray.

The surface area of a spray can affect its ability to produce a chemical reaction, or affect its ability to absorb or dissipate heat. Therefore, droplet size is one of the most critical elements to monitor in heat transfer and chemical reactions.

Droplet size is also critical when considering the total entrainment of fluid in a gas stream.

Smaller droplets are carried away more quickly in a moving fluid and can overload the atomization eliminator if the spray is too fine. In windy conditions, smaller sprays may be blown away from the target.

If you need to know more about spray nozzles, please visit our company’s official website. Our team of expert engineers are on hand to provide further advice and assistance in understanding nozzle performance and selecting the nozzle that best suits your needs.

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