Horsepower equation for isentropic positive dispacement gas compressor 2

[spiraltooth]

I have been able to find the equation for an air compressor that takes into account RPM, CID, compression ratio and efficiency and I have seen the non-positive equation that takes into account the input temperature and pressure cp and cv of a gas but I haven't been able to find an equation for a positive dispacement compressor that takes the properties of the gas into account. Thank you to everyone who takes the time to help me.

 

[zdas04]

The equation that matches the ubiquitous compressor wheel (from Marks) has got gas properties compressed into a ratio of specific heats (k). The Coper Bessemer equation also uses the "k" factors. I can't find a hp equation that is any more detailed on gas make up.

David

 

[dcasto]

SPGR = specific gravity (90% + hydrocarbons)
VN = EXP(.344 - .18715 * (SPGR - .05))
CON = (VN - 1!) / VN
CPC = 708.75 - 57.5 * SPGR
CTC = 169.01 + 314.001 * SPGR
Ratio = Press Disch / press Suc
Temp Disch = ((temp suc + 460) * Ratio ^ CON) - 460!
TRG = (temp suc + 460!) / CTC
PRG = Press Suc / CPC
Zfac Suc = 1! + (.0703 * PRG / TRG) * (1! - 6! / TRG ^ 2)
TRG = (temp Disch + 460!) / CTC
PRG = Press Disch / CPC
Zfac disc = 1! + (.0703 * PRG / TRG) * (1! - 6! / TRG ^ 2)
Zavg = (zfac suc + zfac disch)/2

Brake Horsepower per MMSCFDM = (ts + 460) / 520 * (50.8 * (Ratio) ^ CON - 1!) * (Ratio) - .715)) / (CON * (ratio - .793)) * ZAVG

 

[spiraltooth]

SPGR = specific gravity (90% + hydrocarbons)
Brake Horsepower per MMSCFDM = (ts + 460) / 520 * (50.8 * (Ratio) ^ CON - 1!) * (Ratio) - .715)) / (CON * (ratio - .793)) * ZAVG
How do I get specific gravity for a gas? Isn't this dependent on pressure? Is there a conversion for perhaps molecular weight? Or should I use the density at the low pressure?

 

[dcasto]

spgr = mole weight of the gas / mole weight of air (29.9586)

 

[spiraltooth]

Thank you very much Dcasto. Does MMSCFDM mean the same thing as MMSCFD Million standard cu.ft./day?

 

[mucour]

I have never seen MMSCFDM. I only know of MMSCFD has defined by you.

 

[dcasto]

I had a typo, no M at the end

 

[25362]

A similar subject was discussed in thread71-109890.