Air Blowers Defined
An air blower is a device which uses a rotating impeller in a housing to draw in air, pressurise it then expel it in a defined direction to achieve a desired effect. The relationship between impeller type, blade size/design, housing size/design and supply power is crucial to ensure that the right air volume is being discharged at the correct pressure for a given application – and without wasting energy.
Types of air blower
There are various types of air blowers – find out more here – but essentially, they fall into two main types, depending on the design of their impeller and housing and how they move the air:
- Axial fans – they move air parallel to the axis on which they are mounted. Imagine a propeller on a shaft; the air moves parallel to the shaft.
- Centrifugal fans – these ‘hamster wheel’ impellers move air from the centre then blow it out at a tangent. Air is pushed out at angles that are divergent to the axis, instead of parallel to it.
Some 99% of the air blowers that we manufacture and/or supply feature centrifugal impellers. This is because the combination of volume/pressure output from centrifugal fans is much more useful in a wider range of applications than axial types.
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Misconceptions And Mistakes Involving Air Blowers
Probably the biggest misconception that most people have about air blowers relates to their sheer size. Some impellers – and therefore their housings – can be very large indeed; so big that you can climb inside one. Our largest air blower is around 7ft x 7ft x 5ft (2.1m x 2.1m x 1.5m) in the EV-BPR range, though we also manufacture air blowers as small as a human fist (the VBM3).
But the biggest mistake that some users make is something else entirely. It relates to the wiring of the air blower (especially where a three-phase supply is concerned)…
If you wire in an axial fan and a centrifugal fan incorrectly, they behave in completely different ways:
- Axial fan – the blade rotates in the wrong direction. It pushes air back out of the inlet instead of pulling it in. So an error is very easy to diagnose.
- Centrifugal fan – get it wrong with the impeller rotating in the wrong direction, and it will still pull air in the inlet and push it out of the discharge but only at around 50-60% of the rated performance. For this reason, performance issues can be harder for non-specialists to diagnose – because they assume (wrongly) that everything is fine, simply because the air is flowing the right way.
Air Blowers Vs Air Knives
You will sometimes hear the terms ‘air blower’ and ‘air knife’ being used interchangeably but in reality, these are two complementary technologies.
Both have housings so the air can be pressurised and then discharged in a pre-determined direction, and both are designed in accordance with the Fan Laws to ensure optimum performance and energy efficiency for their intended application(s).
- An air blower generates a volume and pressure of air that may be used by an air knife.
- An air knife system requires a blower to discharge the air generated through a plenum (blade) designed to prevent turbulence. This uniformity of direction and flow ensures there are no low-pressure areas that underperform or high-pressure areas that waste energy.
To find out more about air knife systems, view our detailed guide.
How The Fan Laws Affect The Design Of Air Blowers And Air Knives
These are the three Fan Laws:
- First Fan Law (Volume of Air) – the volumetric air flow rate (cubic metres/hour) varies in direct proportion to the rotational speed (rpm) of the impeller. If the speed increases by 10%, then the volumetric air flow rate will also increase by 10%.
- Second Fan Law (Pressure) – this outlines the relationship between the rotational speed of the fan and how much pressure is created as a result. Total static pressure will increase by the square of the change in speed – ie, if impeller speed increases by 10%, total static pressure will increase by 21%.
- Third Fan Law (Power) – this outlines the power needed to deliver the performance change required for the application. Power requirement will increase by the cube of the change in fan speed – ie, if fan speed increases by 10%, then the power needed to run the fan must increase by 33.1%. So you can see how even small reductions in fan speed can save a lot of energy.
View our resources section to find out more about fan engineering, the Fan Laws and how to understand fan performance curves. You’ll also find a handy glossary section there.
How ACI’s Air Blowers And Air Knives Solve Technical Challenges
View our case studies page and discover how ACI’s advanced air blowers and air knife technology help a wide range of industries to:
- improve quality and performance
- increase production and boost output
- cut costs and increase efficiencies.
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