3 replies to this topic

[mdteng]

Please, I need help in a basic compressor issue.
I need to calculate the change in power consumption of a rotary screw compressor (displacement compresor) changing from 100% propane to 100% nitrogen at the same inlet/outlet pressure conditions and inlet temperature.
I've found several equations but in none of them the fluid density is reflected (the attachment shows one of them). If the volumetric flow (Q)and the pressure range is the same, How can i show the power change.

I'll appreciate your help !!!!

Thanks.
Martin

Attached Files

•  Equation.JPG   63.06KB   103 downloads

[breizh]

HI Martin ,
Let you try Perry 7th edition section 10-39 :

The work during compression is the product of the adiabatic head * mass flow of gas handled :
Work = mass* Had = k* mass*R*T1/(k-1) * ((p2/p1)^(k-1)/k -1))

as you know mass = Qv*Ro = Qv* P1/(R*T1) (perfect gas)

then Work = Qv * P1 * k/(k-1) *.....

Hope it helps

Breizh

[ankur2061]

Martin,

All PD compressors are evaluated on an adiabatic compression cycle. If you see the basic thermodynamic equations for adiabatic compression, density does not play a role in the power calculations. The specific heat ratio (Cp/Cv) however does play a role & is a function of the gas handled. The density only plays a role if your flow rate is given in terms of mass flow rate & if it is the same for two different gases then the volume flow rate will change based on the density of the gas in consideration.

You may refer the following post where I have posted a spreadsheet for estimation of power for adibatic & isothermal compression:

http://www.cheresour...r-calculations/

Hope this clarifies calculation procedure.

Regards,
Ankur.

Edited by ankur2061, 13 March 2010 - 10:55 AM.

[mdteng]

Thanks Guys.
I'll try.

Martin