## Screw Compressor Calculation

How the screw compressor power is calculated for oil flooded screw compressor.

2. Work done is something like PdV isn't it? Oil used is synthetic, terribly expensive & should be consided as incompressible. It has no bearing, oops, on the amount of work done on the gas. There is a small additional power requirement related to viscous shear & you also have to consider the demands of the oil heater, required for cold start-ups, as well as the lube/reticulating oil pump powers. I recently worked with propylene compressors with 2.5MW shaft power demand & the oil demand was another 90kW. Most vendors will help you out on this quest; after all you are spending a fortune on the things.
Atlas Copco are now(today) boasting of a totally oil free delivery screw machine but can't tell you how to buy one.

3. Is this what you are looking for ?

N(th.dyn) = n/(n-1) * V1 * p1 * ((p2/p1)^((n-1)/n) - 1) – (p2-p3) * V1/((p2/p1)^(1/n))

BR
teus

Dear Teus,

Thanks for the formulae u had given.

I want to know how to calculate V1 of the screw compressor.

For reciprocating compressors we will calcualte V1 using piston volume and number of strokes.

5. dear Sir,

In the previous attachment, I made an error, which is corrected in the next attachment.
Sorry for the inconvenience.

V1 is the displaced volume by the compressor and is determining the required power.

Eventual internal air leakage is accounted for in the volumetric efficiency.

Vol.eff. = (displaced volume – internal leakage) / ( displaced volume )

= ( delivered volume ) / (displaced volume )

As your compressor is oil filled, there is no internal leakage.
In your example of a piston compressor,

V1 = 3.141593 / 4 * bore * bore * stroke * rpm

For a screw compressor the same procedure applies, but is much more difficult.
Only the manufacturer knows the entrapped volume of air per revolution, as the shape of the screws is very complicated.
More over the internal compression ratio has to be known as well.
Do not forget the power necessary for the oil circulation
Also the inlet control valve and the outlet pressure regulation for the oil separator have to
taken care off.

If you need the compressor for pneumatic conveying an oil free compressor may be a better option.

I am afraid that you need the manufacturer’s information.
If you still have to purchase a compressor, visit www.aerzener.de

success
teus

6. Join Date
Feb 10
Posts
1
Dear Teus,

we are manufacturing open type twin screw compressor in ammonia and freon so iwant to know the formulas to find out the swept volume and many things i want your personal e-mail id my e-mail id is sbmec91@yahoo.co.in plz reply i am waiting for ur msg.

7. kurraprashanth Guest
1.1 Total service air requirement ---- Nm3/hr

1.2 Total air requirement Nm3/hr Item 1.1

1.3 Margin for leakage at 10% Nm3/hr (0.1 x Item 1.2)

1.4 Total air quantity considering leakage losses Nm3/hr (1.2+ 1.3)

1.5 Margin for contingency demand at 10% Nm3/hr 0.1 x Item 1.4

1.6 Total capacity of working compressors. Sum of items 1.4and 1.5

NOTE: The FAD capacity will be calculated after suitable correction for the air quantity at Normal Temperature and Pressure (NTP) conditions

The capacity of air receivers will be calculated by the following (2 methods and the highest value will be adopted.

(Method 1 V = 1.6 x SQRTV1/60) ( Method 2= V = T x V1 x PA/Pr max- Pr Min)

Where

V = Volume of air receiver (m3)

V1 = FAD of service air (m3/hr)

T = 10 seconds which is the time for standby compressor to cut in

PA = Atmospheric pressure – kg/cm2

Prmax – Prmin = Difference between maximum and minimum receiver pressures will be maximum 0.4 kg/cm2.

8. Originally Posted by sbmec91
Dear Teus,

we are manufacturing open type twin screw compressor in ammonia and freon so iwant to know the formulas to find out the swept volume and many things i want your personal e-mail id my e-mail id is sbmec91@yahoo.co.in plz reply i am waiting for ur msg.
Hello sbmec91,

Let me get this straight: You are manufacturing screw compressors for refrigeration service and you are trying to get key design information from a remotely associated forum. Is that really correct? If this is so, this is the strangest way how I have seen a manufacturer go about designing a piece of precision machinery.

9. Registered User
Join Date
Mar 03
Posts
1,641
Originally Posted by RalfWeiser
Let me get this straight: You are manufacturing screw compressors for refrigeration service and you are trying to get key design information from a remotely associated forum.
Heaven help anyone who buys something they have manufactured
Mind you, I expect it will be cheap