Technical aspects of flat fan nozzles

What you should keep in mind when planning

Different applications and ambient environmental or operating conditions require different flat fan nozzles. With its broad portfolio of flat spray nozzles, Lechler offers the optimum nozzle solution for every task. The following criteria are helpful in selecting the optimum flat fan nozzles.

Technical aspects of flat fan nozzles

Criteria for nozzle selection

Impact
Impact
Spray angle
Spray angle
Spraying behaviour
Spraying behaviour
Distribution of liquid
Distribution of liquid
Droplet sizes
Droplet sizes
Parameters on temperature behaviour of nozzle materials
Parameters on temperature behaviour of nozzle materials
Material
Material
Wear
Wear

Impact – Impact force is (almost) everything

The impact force of a liquid jet on a surface, for example, plays an important role for reliable cleaning or in surface technology in general. The impact is calculated as the quotient of the impact force and the impact surface.

Calculation of the impact force:


F: Impact force (spray impact)
A: Impact surface (impacted area)

Parameters that may influence the impact

Impact surface and jet shape

Impact surface and jet shape

The impact surface is the area where the droplets strike. This is the area affected by the liquid jet.

The smaller the surface area, the greater the impact values. Nozzles with high impact are, for example, flat fan nozzles with a narrow spray angle as well as solid stream nozzles.

(Image: Comparison of the cleaning result of three nozzles with identical pressure and flow rate.)

Impact – increase of pressure and flow rate

Pressure and flow rate

Increasing the connected pressure results in an increase in the spray impact. Doubling the pressure while maintaining the same flow rate results in a doubling of the impact.

Increasing the flow rate by using a larger nozzle increases the impact, assuming that the other parameters (spray angle, pressure and medium) remain the same.

(Image: Comparison of the cleaning result of three nozzles with pressure or flow rate increase.)

For a high impact, the droplet size is also very important – in addition to the impact force and the impact surface. Large droplets at high speed are advantageous for high impact. As the pressure increases, the droplet velocity also increases, but the droplet size decreases. This means that an increase in pressure above the recommended operating pressure will only have an impact close to  the nozzle. As the distance increases, the small droplets quickly lose speed and there is less impact.

Nozzle with large droplets at optimal pressure and with small droplets at too high pressure Nozzle with large droplets at optimal pressure (left) and with small droplets at too high pressure (right).

Optimal arrangement of flat fan nozzles and tongue-type nozzles

Basically, Lechler flat fan nozzles are designed for parabolic liquid distribution. Unaffected by transient pressures, they are suited for universal application. Their performance data are exactly defined. Operational values, such as flow rates, spray width, jet thickness and liquid distribution are readily available for a great variety of feed pressures. There are also special-design nozzles with rectangular or trapezoidal distribution of liquid.

Arrangement of flat fan nozzles with parabolic liquid distribution

Arrangement of flat fan nozzles with parabolic liquid distribution

Lechler flat fan nozzles provide a consistent, uniform coverage over the impact area. For this purpose, the spray widths B ought to overlap each other by 1/3 to 1/4. To avoid interferences of the sprays, the nozzle orifices must be offset 5 – 15° to the pipe axis.

B = Spray width, E = Nozzle distance, H = Installation distance of nozzles, α = Spray angle

Alignment of tongue-type nozzles

Alignment of tongue-type nozzles

In order to achieve an even surface coverage the nozzles need to be aligned in such a way that spray widths B overlap by 1/3 to 1/4. Therefore the nozzles should be inclined in an angle of 15° to the vertical of the horizontal axis of the tube (either with a weld base at an angle or a Lechler ball joint nozzle mount) in order to prevent a disturbance of the spray.

B = Spray width, E = Nozzle distance, H = Installation distance of nozzles, α = Spray angle

Flachstrahldüsen Gesamtflüssigkeitsverteilung Flat fan nozzles total liquid distribution

Spraying behaviour of flat fan nozzles

The spraying behavior of flat fan nozzles is determined by several factors:

  • Design of the geometric configuration at the nozzle orifice
  • Characteristics of the medium (density, viscosity)
  • Structure inside the nozzle (swirl inserts)
  • Inlet of the medium (tangential, axial)
Spraying behaviour of flat fan nozzles

Influence of viscosity on the spray behaviour of nozzles

Viscosity is a measure of the flowability of a fluid. The higher the viscosity, the thicker (less flowable) the fluid is. The lower the viscosity, the thinner (more fluid) the fluid is, i.e. it can flow better under the same conditions.

Examples for fluids with different viscosities:

  • Water: 1 mPa·s at 20° C
  • Coffee cream: 10 mPa·s at 20° C
  • Olive oil: approx. 80 mPa·s at 20° C
  • Honey (wild honey): 10.000 mPa·s at 20° C

The viscosity is specified dynamically (mPa-s or centipoise) or kinematically (m²/s or 106 centistokes).

viscosity scale Viscosity scale

The temperature has an enormous influence on the viscosity. It is therefore by no means negligible. This influence can be observed when olive oil is placed in a pan at room temperature (80 mPa·s at 20° C) and heated. As the temperature increases, the olive oil becomes more liquid (20 mPa·s at 60° C; 10 mPa·s at 80° C).

Spraying behaviour of a flat fan nozzle with increasing viscosity

The following example shows the changing spray behaviour of a 652 series flat fan nozzle at constant pressure and increasing viscosity.

The pictures clearly show how the spray angle becomes smaller and smaller with increasing viscosity. If a nozzle with a different performance size were used, it would also be apparent that the influence of viscosity also depends on the performance size of the nozzle. The spray angle at smaller performance sizes decreases more strongly.

The use of flat fan nozzles for viscous media is generally only recommended to a limited extent. The following statements apply primarily to flat fan nozzles, but can also be partially transferred to other nozzle types:

  • Flow rate: On the influence on the flow rate, the most precise information is available. A liquid with a different viscosity often has a different density than water. This difference in density leads to a difference in flow rate irrespective of the difference in viscosity.
    With increasing viscosity, the pressure loss in the supply line to the nozzle also increases. It is therefore recommended to measure the pressure directly at the nozzle. At very high viscosities (from approx. 100 mPa-s) a significant pressure loss already occurs within the nozzle, which then has an additional influence on the flow rate.

    Formula for converting the flow rate at different densities:

    VFI: Flow rate of the liquid whose density differs from 1
    VW: Flow rate water
    ρ: Density [kg/m3]

     

  • Spray angle: With increasing viscosity the spray angle becomes smaller. The influence of the viscosity on the spray angle also depends on the performance size or the geometry of the nozzle.
  • From measurement results, it can be concluded that flat fan nozzles with a larger flow rate are more angularly stable than those with a smaller performance size. However, no universal rule for the spray angle as a function of viscosity can be derived from the measurement results. Many factors play a role. An increasing pressure has a positive effect on the stability of the spray angle, especially at higher viscosities.
  • The viscosity definitely has an influence on the liquid distribution!

Flat fan nozzles: Further details and product porfolio

Further details about flat fan nozzles

Flat fan nozzles are often used for an intensive and uniform (water) jet. Find out more about the advantages of flat fan nozzles and different application examples. Flat fan nozzles

Lechler flat fan nozzles portfolio

Lechler flat fan nozzles are available for industrial, metallurgical and agricultural applications. Lechler offers the optimal solution for every application. Technical aspects of air nozzles