I might have to find a different forum altogether to get information. I'm just posting here because it seems people here are the most mechanically inclined. So, back to my question, which kind has the highest efficiency, theoretical and actual? Centrifugal? Axial? Piston based rotary based? Anything. Oh, any idea what the efficiency is of a screw-type supercharger?

depends on what you whant

The most efficient rapid compression you can get

i meen flow or pressure ?

ifyou need alot of flow and no pressure a supercharger centrifugal is good
if you need flow and some pressure screw type or a roots blower (used in old small engines)
if you need alot of pressure and little flow a piston conpressure is best

depends on your aplication all are effichiant in thair way

What are you building? Your requirements of range of operation will also limit your choices. Efficiency is the only requirement? What about size or operating RPM?

Greg

Not building a thing. Just thinking. Only requirement is highest efficiency compressor and no other requirements are necessary. Efficient to me is when you get the most compression for the energy you put in. The mechanism with the fewest losses. Centrifugal, piston, screw, anything. Doesn't matter to me.

There must to be other requirements other than efficiency. Certain types of compressors are good at high pressure, low volume, others have inverse properties. Efficiency is not pressure per unit power input. Efficiency is pressure and flow rate per unit power input.

If you are looking for highest pressure, then I think the previous post is correct with piston type. The volume might be pretty low depending on how much power is available.

What good is a highly efficient compressor if there is no application? ;-)

Greg

I read that screw is the most powerful, but with the most losses. This is nothing to do with efficiencu however.

I think for light applications centrifugal is best. Low loss, but low output.

A car's supercharger might require 100bhp to rotate it at full speed, however it releses 200bhp, so you gain 100 extra. Efficiency is therfore the ratio of energy used to energy released.

Screw is the most variable. You can "download" it (like throttling down) to 10~20% while maintaining a practical efficiency. It has to spin faster than centrifugal tho. This is talking about air conditioning plants. System efficiency is enhanced since energy is saved when only a small portion of the building is in use.

While you have no specific application, gravitational has to be the most efficient both theorectical and actual.

Clement

Most efficient compressor---
use logic to find the answer.-
a simple piston in a sealed sleeve.
move the piston - ALL the air is compressed ahead of the moving piston.move it slowly or rapidly -makes no difference if you disregard heat buildup.
This is --effectively--a positive displacement compressor.
for moving air -NOT just compressing air - an entirely different set of requirements -
A supercharger --can be made from many types of devices --including the piston in a sleeve. The types of superchargers are varied and depending on the rpm range and speed the flow / efficiency etc., varies dramatically..
Air movers for buildings are another catagory - lots of air is moved at a very slight increase in pressure
with the exception of the sealed chamber and piston , all other types have losses due to many reasons
The logic is this :
air will always take the path of least resistance
It may simply sneak around the impellors -or cavitate -
The reason most cars still use piston engines is that this is the most efficient method of controlling pressures .