How to calculate what size turbine for a known output

Hi

I have just learnt that - the turbine needs to operate within an optimal speed which must then drive a gear box which is used to drive the crank to get the desired torque.

So obviously this opens up a tremendous amount of possibilities.

You're right about the number of possibilities. Sounds like you want the turbine to do 4000rpm (gearbox input), but need 20Nm at the gearbox output.

To calculate the power output, need to know gearbox output speed. Also to estimate the volume of air required, need to know air input pressure.

Codey

Have you tried going to a local tool supply shop and inquire about a pneumatic torque wrench?

4000rpm = 420 radians per second.

420rad/sec * 20Nm = 8.4kW.

So the turbine needs to deliver a shaft output power to the load of this amount.

There are air-motors that will do this sort of delivery, so the answers to the remainder can be had by looking at various suppliers' information, including air pressure/consumption charts, prior to selecting a unit that will do the job.

Hello PW - that power is correct if the 20 Nm is at 4000rpm, but his post #1 suggests it isn't, it's after a gearbox.

Codey

Thanks for all your replies - forums amaze me. An outpouring of help.

I think I have sorted it -I did some drawings and worked out volume of air in the turbine and from that was able to workout the Pressure required to turn the crank.

Pressure = Force / Area

So I 'll go an put my money in an engineers pocket to build it for me.

Your calculations were spot on from what I can make out.

Thanks again