When the fan is installed in a device or a system, the inflow and discharge ratios and thus also the characteristic curve deteriorate to the characteristic curve
The mass flow rate through the impeller is reduced by additional disturbance components, especially on the intake side, such as guard grilles, angled inflow or turbulence areas in the inflow. Examples of unfavorable intake conditions are shown in Figure 3.5.2.b. The stronger the additional disturbances to the optimum flow through the fan wheel, the steeper the characteristic curve becomes (extreme case characteristic curve
On the downstream side, unfavorable flow guidance (such as sharp deflection behind the fan wheel or struts in the downstream) can also lead to system losses; in addition, it also quickly leads to a higher noise level on the downstream side.
If the operating behavior of a fan or fan system is to be determined or designed as accurately as possible in an installation situation that deviates significantly from the test bench setup defined in DIN EN ISO 5801, practical tests are required, since despite all the progress made in the field of fluid mechanics, it is not possible to determine the fluidic behavior exactly in advance.
For design questions, the installation situation should therefore be specified as precisely as possible. Our application experts will be happy to advise you on this.
Factors influencing the quantitative and qualitative characteristic curve are, for example:
- Intake / discharge in a free-running condition or via a duct system
- Use in a spiral housing
- Struts / Bearing crosses
- Deflections
- Obstructions (e.g. motor in impeller, etc.)
- Speed drop due to motor slip
- Gap flow / inlet cone-wheel overlap
- Construction tolerances
- Air density / compressibility
- Type of measuring device used