×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

# Horsepower equation for isentropic positive dispacement gas compressor2

## Horsepower equation for isentropic positive dispacement gas compressor

(OP)
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.

### RE: Horsepower equation for isentropic positive dispacement gas compressor

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

### RE: Horsepower equation for isentropic positive dispacement gas compressor

2
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

### RE: Horsepower equation for isentropic positive dispacement gas compressor

(OP)
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?

### RE: Horsepower equation for isentropic positive dispacement gas compressor

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

### RE: Horsepower equation for isentropic positive dispacement gas compressor

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

### RE: Horsepower equation for isentropic positive dispacement gas compressor

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

### RE: Horsepower equation for isentropic positive dispacement gas compressor

I had a typo, no M at the end

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

#### Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a partâ€™s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!