Re: Screw Compressor Calculation
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. ■
Re: Screw Compressor Calculation
1.0CAPACITY (FAD) CALCULATION
1.1Total service air requirement ----Nm3/hr
1.2Total air requirementNm3/hrItem 1.1
1.3Margin for leakage at 10% Nm3/hr(0.1 x Item 1.2)
1.4Total air quantity considering leakage lossesNm3/hr(1.2+ 1.3)
1.5Margin for contingency demand at 10%Nm3/hr0.1 x Item 1.4
1.6Total 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
2.0 CAPACITY OF AIR RECEIVERS
The capacity of air receivers will be calculated by the following (2 methods and the highest value will be adopted.
(Method 1V = 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.
Hope this will be helpfull ■
Re: Screw Compressor Calculation
Originally Posted by sbmec91
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. ■
Re: Screw Compressor Calculation
Originally Posted by RalfWeiserHeaven help anyone who buys something they have manufactured 
Mind you, I expect it will be cheap 
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Re: Screw Compressor Calculation
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. ■
John Gateley johngateley@hotmail.com www.the-credible-bulk.com
Re: Screw Compressor Calculation
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))
see also attachement
BR
teus ■
Teus
Re: Screw Compressor Calculation
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. ■
Re: Screw Compressor Calculation
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
Attachments
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Teus
Screw Compressor Calculation
How the screw compressor power is calculated for oil flooded screw compressor. ■