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# Can I use a fan to make a compressor? Answered

I have seen many centrifugal compressor designs on the net, I was wondering if a ducted fan can be used, duct's diameter at the intake of the air would be smaller, and after the air passes through the fan and is accelerated, the diameter of the duct would increase, I think this should lower the velocity of the air and as a result the pressure should increase, according to Bernouli's princinple, I am not asking like which one is efficient, the usual type of fans used in centrifugal compressors (don't know what they'r called) or this one, just asking if this would work and increase the pressure of the air.

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## Discussions

An axial fan would "compress" the air, only not very much, only a few mm of air pressure. Its actually calculable, given the duct dimensions, and the volumetric flowrate. Look for venturi-effect

Theres a reason why ducted fans aren't used - their efficiency is terrible,.

Then the type of fans used, I think they'r called the centrifugal fans, why are they more efficient, they do the same thing an axial fan does, take in the air and then blow it out.

Because you extract the pressure from a different place in the system to the axial fan. In the axial case, the high pressure region is only a blade width from the low pressure region, in the centrifugal case, the air is accelerated (and pressurised into a separate area of the fan, where because of the energy imparted into it, it can't reverse into the low pressure side.

Thanks, I understand now, but the type of fans used in the compressors of jet engines are axial, what about them?

Have you seen the actual design of them ? They are not just fans in a tunnel !!!!!

Yes I have seen them but I didn't study it in detail and didn't know that they play any role in compression, so according to you what type of fans would be the best for a turbine, that could convert most of the kinetic energy of the airflow and convert it into rotational motion, high rpm?

Take a look at how they build model jet engines for some ideas of the techniques needed.

You can't convert a simple desk fan type impeller into a component for an axial compressor. You need LOTS of blades.

It will increase the psi and velocity like a wind tunnel however I don’t know by how much.

No - at any pressure over the pressure produced by the fan air will slip back through the fan.

Compressors are active pumps - like a motorised bike pump.

Then why doesn't it happen in centrifugal compressors which are used in turbochargers, they also have sort of fans.