Centrifugal fan working principle
The motor turns the impeller. Air enters near the wheel’s centre and passes through the rotating blade passages, gaining energy as it moves outward. The casing collects and directs that flow into the discharge connection.
A common scroll-cased fan has an inlet aligned with the shaft and an outlet pointing in a different direction. Other arrangements package the same broad centrifugal principle differently. An inline fan can also use a centrifugal impeller.
The important practical result is a relationship between airflow and pressure at a stated speed. The fan does not deliver one fixed airflow regardless of what is connected to it.
The parts you will see on a drawing
| Component | Purpose |
|---|---|
| Impeller or wheel | Transfers mechanical energy into the moving air. |
| Casing | Contains and directs the flow to the outlet. |
| Motor and drive | Turn the wheel at the intended speed. |
| Inlet and outlet | Connect the fan to the intended airflow path. |
| Supports and access | Locate the equipment and allow inspection and service. |
The detailed arrangement varies. Motor location, bearings, transmission and access can all differ between models, so use the actual drawing when planning an installation.
Centrifugal fan uses and the required duty
Centrifugal fans are used in many ventilation and process systems. In laboratory extraction, the fan works with the cupboard, duct route and discharge arrangement to move the required air against system resistance.
Define a duty as an airflow and pressure requirement, with the pressure basis and air conditions stated. Compare that duty with the manufacturer’s fan curve. A maximum free-air figure is not the airflow you can assume through a completed duct system.
Branches, bends, transitions and other components contribute to resistance. The room’s replacement-air arrangement and the enclosure’s required performance are also part of the complete extraction design.
Blade design and speed affect performance
Centrifugal wheels can use different blade geometries. Forward-curved and backward-curved fans have different characteristics that should be assessed through the relevant curves.
Speed also changes performance. For the same fan under comparable conditions, the fan affinity laws relate speed to airflow, pressure and shaft power. A higher speed can demand considerably more power, so mechanical and motor limits must be checked.
Selection includes a suitable stable operating range, not just a curve point that appears to meet the maximum duty. The controls and expected operating modes should be included in that review.
What changes for chemical extraction?
The fan’s materials and construction must suit the extracted substances, temperature and possible deposits or condensate. The wheel principle does not make a general ventilation fan chemically suitable. Review casing, wheel, seals, shaft and motor arrangement against the process.
FumeCare supplies Fumeflow extraction fans. Our D250 and TD250 selection guide explains the information needed to discuss a model. Bring the chemical list and layout as well as the airflow target.
Plan access for cleaning, inspection and replacement. Retain the accepted curve, operating settings and commissioning records so maintenance staff can compare future performance with the intended duty.
Questions about what is a centrifugal fan
Does a centrifugal fan produce a fixed airflow?
No. The operating airflow depends on where the fan characteristic meets the connected system’s resistance at the operating speed.
Is a centrifugal fan the same as a blower?
The word blower is used in different ways across equipment catalogues. Compare the actual impeller arrangement, pressure-flow curve and construction rather than relying on the label.