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Nozzle performance and service data

Distribution of liquid

The essential operating data of spray nozzles is

  • flow rate
  • spray angle
  • liquid distribution
  • spray impact
  • droplet size


Flow rate, pressure and spray angle

Flow rates and spray angles are dependent on feed pressure and viscosity of the liquid to be sprayed. We have measured the flow rates stated in the catalogue with painstaking accuracy, using inductive flow meters.

The spray angle is determined right at the nozzle’s orifice. The indications given on spray widths and coverage diameters are more useful at larger distances from the orifice. Air friction losses and ballistic phenomenons influence the spray behavior and the size of the impact area in dependence on the chosen service pressure.

The pressure (p) is the feed pressure above atmospheric, which is available at the liquid inlet into the nozzle. The spraying operation is performed under counterpressure, the flow rate is dependent on the differential pressure. Minimum and maximum pressures are adjusted to the required flow rates and the spray quality.

 

Distribution of liquid

Distribution of liquid

A uniform distribution of liquid is of paramount importance, e.g. for coating. We have developed special measuring methods which instantaneously deliver test results that are repeatable any time. Thanks to our electronic image processing measurement accuracy is approx. +/- 1 %. The test results are documented and made available to customers for design and construction tasks. Thus they’ll be sure in advance that Lechler spray nozzles exactly comply with their requirements.

 

Spray impact

For measuring the jet distribution of the spray impact and the impact itself a highly sensitive device is guided through the jet pattern. The measuring values detected by the sensor are transformed into electric signals and stored in a computer. Jet impact measurements show how uniformly the jet impact is acting on the impacted area. This data is very useful, in particular for high pressure applications where a maximum of pump energy has to be transformed into cleaning power.


 

Spray impact (i)

Spray impact (i)

The spray impact, i.e. the effect a jet exerts upon a surface, is defined in various ways. For assessing the efficiency of spray nozzles, the spray impact definition N/mm2 (impact), commonly used now, proved especially reliable. This is the conversion of the total spray force into the impact force acting upon the impacted area.

Low spray pressures are generated by full cone nozzles of wide-angle flat fan nozzles.

High spray pressures are typical for flat fan nozzles with narrow spray angles (15°-60°).

Extremely high spray pressures are produced by solid stream nozzles.



Droplet sizes and droplet distribution

Droplet sizes and droplet distribution

The droplet distribution of a nozzle must be known for many applications. The Laser Doppler Particle Analyzer has proved to be one of the most precise measuring devices for this purpose.

This method allows to measure simultaneously droplet sizes and droplet speeds. A full description of the spray characteristics can be obtained as a result.

 

Considering that the various spray patterns do not necessarily disintegrate into uniformly sized droplets, we use the Sauter diameter d32 to document the droplet size distribution.

Starting from this parameter, primarily used in process engineering, other droplet size definitions can be deduced, such as the arithmetic mean diameter d10, the mean volume diameter MVD, the logarithmic deviation LS. In the same way, other measured values may be processed to compile a full description of a measured droplet distribution.