Spray measurement technology - reliable measurement of drop sizes and velocities

Spray measurement technology is used to measure all resulting droplet diameters as well as the speeds of droplets in a spray. Most technical atomizers deliver a spray containing droplets of different sizes. Only if complete information about these drop sizes is available, the spray property can be reliably assessed.

Modern methods of spray measurement technology work here without contact and influence. This means that the spray properties are not altered during the measurement. This is of course particularly important in order to obtain reliable and reproducible information.

It is certainly not necessary to know complete drop size distributions and speeds for any nozzle and application.

However, if process or manufacturing processes have to be optimized, the use of spray measurement technology is often necessary. The same applies, for example, when determining whether the drops are respirable. This is often important in medical technology, but also in the field of occupational safety.

Mass and heat transfer processes, including combustion and cooling processes, can only be reliably calculated if the spray properties are known in detail. This information is also important when further CFD calculations for fluidic optimization are required. These are just a few examples of the sensible use of a suitable spray measurement technology.

Spray measurement technology and drop sizes - there are often misunderstandings!

Especially in connection with drop size distributions dangerous misunderstandings and misjudgements often arise!

Spray measurement technology - There are many misunderstandings and misjudgements!

This is often claimed!

The spray properties of two nozzles are comparable if a characteristic droplet diameter is known. This can be, for example, the mean drop diameter d50 or the Sauter diameter d32.

In addition, one of these values should be sufficient to perform procedural calculations or reliable assessments. However, this only works if the nozzle supplies a so-called monodisperse spray. A spray in which all drops are of equal size!

However, with very few exceptions, almost all technical nozzles and atomizers do not supply drops of the same size! But rather a droplet size distribution. It contains a certain amount of fine and coarse droplets.

An example of the importance of spray measurement technology.

Let's take a closer look at the spray of a technical atomizer. It contains a multitude of drops, with different diameters. First, an average droplet diameter must be defined. This is, for example, 50 µm in size. So 50% of the drops are bigger, 50% smaller than this value.

What does this say about the spray and its overall properties?

And what does this 50% actually refer to? Does this mean the number of drops or does this information refer to the quantity volume or mass? It is obvious that this makes a considerable difference.

A single value does not mean anything!

Because theoretically there are infinitely many and basically completely different droplet size distributions, all of which can have the mentioned mean droplet diameter! Two sprays, which therefore have an identical average droplet diameter or Sauter diameter, may nevertheless have completely different properties.

As a result, a single characteristic value says nothing at all about the respective proportion of particularly fine or extremely coarse drops in the spray of the nozzle! This means that the two spray properties cannot be compared, even with an identical Sauter diameter or average diameter. A comparison of both spray properties is therefore only possible by using spray measurement technology!

So what about overspray problems or undesired droplet deposits in pipelines or apparatus? What is the connection between the surface quality and the spray during coating?

These important questions cannot be answered reliably if only one characteristic drop diameter is known!

Further important arguments for the use of spray measurement technology!

This is often overlooked and leads to problems with the real operation of the nozzles.

Data on real drop size distributions for standard nozzles are usually not available at all.

If at least information on characteristic droplet diameters - usually mean droplet diameters - is given, these values refer to the atomisation of water.

If real liquids whose rheological properties differ from water are to be atomized, this incomplete information is absolutely pointless. The entire drop size spectrum changes when fluids other than water are used!

Of course, the operating conditions of the atomizers also play an important role! Drop size spectra change, for example, with the operating pressure of the nozzle. These changes can only be determined with a suitable spray measurement technique!

For process optimization with subsequent numerical flow calculations, the complete droplet size distribution must be known. It then makes sense to know the drop speeds. This also concerns questions regarding overspray effects or the undesirable deposition of drops on pipe or container walls.

Occasionally, splash and drop impact effects have to be investigated for certain applications. Of course, we also have the necessary equipment here. This allows such effects to be resolved in detail.

What does the use of spray measurement technology cost?

This depends on some boundary conditions. First of all, it must be clarified whether spray measurement technology should be used as a separate service for determining the spray properties of existing nozzle systems. Or whether it is about the use of spray measurement technology in the context of an ongoing joint project. The duration of use of the measurement technology and the specially trained personnel must also be taken into account.

Furthermore, it must be clarified whether certain spray measurement techniques should or can be used in your company.

A significant cost factor is which of the available spray measurement technology is to be used. If the volume flow to be atomized is not too high and no information on drop speeds is required, the use of a laser diffraction spectrometer is recommended. The measurement results are quickly available. In most cases, measurements can also be carried out on site.

If the spray is very dense or additional information on drop speeds is required, a 3D Phase Doppler Anemometer (PDA) can be considered. This is a high-resolution spray measurement technology. This procedure is more expensive and measurements are only possible in our test bench.

We can offer high-resolution one-dimensional spray measurements for the determination of drop sizes and their velocities on site in cooperation with one of our partners.

The laser diffraction spectrometer can also be used in your company upon request.

The laser diffraction spectrometer can be used in your company upon request. With this spray measurement technology, data can be quickly determined under realistic operating conditions. It is important that there is good optical accessibility and that the spray is not too dense.

The 3D phase Doppler anemometer provides comprehensive measurement data.

The phase Doppler anemometer provides high-resolution information on drop sizes and drop velocities.

We offer comprehensive services in the field of spray measurement technology that are otherwise difficult to find.

On request, you can receive spray measurements both as contract measurements on existing atomizers or, of course, as part of joint projects. It goes without saying that our experts for spray measurement technology check which method is necessary, target-oriented and at the same time cost-effective!

Let us advise you now without obligation about the possibilities of spray measurement technology.

We will be happy to answer your questions about spray measurement technology on our hotline:

+49 251 2 87 99 53-0

Or use our contact form. An employee will contact you as soon as possible to discuss your task in the analysis of spray properties.