1. Registered User
Join Date
Jun 06
Posts
8

## compressor power

How do you calculate compressor power given the pressure and capacity (volume per minute).

2. dear dror,

Compressor power is calculated along the thermodynamic laws and formulas, appropriate for the type of compressor in question.

Types of compressors are:

- positive displacement without internal compression (Roots-type blowers)
- positive displacement with internal compression. (screw compressor, vane compressor, water-ring compressor, piston compressor)
- Turbo compressors

Additionally, it is important whether the internal compression is isochoric (blower), adiabatic, isothermal or a combination of these. (depending on the internal compression ratio and the delivery pressure)

Compressor suppliers state the power requirements of their compressors in the data sheets.

Also auxiliary equipment to the compressor is important.

If you can inform us of the compressor, you might be referring to, we can help you more specific.

The compressor choice is a very important choice, because it influences the energy costs.

A buffer tank calculation spreadsheet is attached.

best regards,

3. Registered User
Join Date
Mar 03
Posts
1,641
Why calculate it?
If you are buying a compressor for a specific duty the manufacturer will supply it with the correctly sized drive motor.

4. Registered User
Join Date
Jun 06
Posts
8

## Re: compressor power

Originally posted by dror
How do you calculate compressor power given the pressure and capacity (volume per minute).
I obviously know how to compare suppliers tables for motor size for a given compressor duty.
I am interested in the thermodynamic aspect of the compression process and would like to examine it for a two stage screw compressor with an intercooler.
Regards,
Dror.

I worked for a compressor manufacturer in Hemel Hempstead who made any stage screw compressor packages driven by electric, diesel & wet process steam. In all that I never gave a toss about the thermodynamics.
This question is best answered by self help at a city library. Hick Hargreaves handbook is a good place to start.

6. ## compressor

To add to johns reply you also need to add the altitude that the compressor is going to be working at to add this to the mix of data.

7. Dear dror,

If you want to combine two screw compressors into a 2-stage compressor set, the following has to be clarified.

Type of screw compressors
Internal compression ratio
Oil free or oil filled.

Oil free (compression ratio approx. 4 , not cooled, adiabatic compression)
Oil filled ( compression ratio approx. 8-10, cooled, isothermal compression)

If stage 1 delivers the air compressed (cooled) at the intermediate pressure, then that delivered volume is the intake of the 2nd stage.

The 2nd stage compressor has to match that volume, otherwise the intermediate pressure will change and thereby the load of the compressor stages.

This is quit a complicated matter (though very interesting), but should be left to the experts, dealing with compressors daily.

This requires the full knowledge of thermo dynamics.

Success

PS As I disciovered an error in my file in cell G4, hereby an update.

8. Registered User
Join Date
Apr 06
Posts
12

## power of blower

is there anyone helps me on my project...

my question is...

is there any method to calculate the power of blower without having any given data....

9. No. Do you know what calculations are?

10. Dear Mr Ahsan,

One data, you have, is that your subject is a blower.
The working principle of a blower is :

a positive displacement compressor with isochoric compression.

As the performance of a compressor is set by the intake conditions (suction or atmospheric), the appropriate formulas are as given below.

Positive displacement pumps

Characteristic data for a blower are :

p1 = pressure at inlet
p2 = pressure at outlet
q0 = internal displaced volume per rotation
n = number of rotation per minute
Q0 = internal displaced volume per unit of time
Qv100 = internal leakage-losses at a dp of 100 mbar per unit of time.
Qv = internal leakage-losses at dp per unit of time
Q1 = External displaced volume at p1 per unit of time

Roots-type blower :

Q0 = n * q0

Qv = Qv100 * SQRT ((p2-p1) * 1,293) / (100 * rho(l)))

in which : rho(l) = 1,293 * p1 * 273/(273+t(amb))

follows :

Qv = Qv100 * SQRT ( ((p2-p1) * (273 + t(amb))) / (100 * p1 * 273))

Q1 = Q0 - Qv

eta(vol) =Q1/Q0 = (Q0-Qv)/Q0

P(th.dyn) = Q0 * (p2-p1) (isochoric compression)

P(shaft) = P(th.dyn) + P(losses)

As Mr John Gateley stated, no calculations without figures.

But, if you pose a question, you must have a real issue at hand, to which your question relates. If you explain that real situation to the forum members, a more specific advise can be given.

success