Visit any mainstream manufacturer's website & you will find a selection page which will give you the shaft power requirement from your input conditions. RPM will usually be 3575, for the 1st stage, motor/compressor match.

There are formulae but the web is a far better place than the textbook. ■

Dear Maryam,

The formula to be used is depending on the type of compressor (piston, lobe blower, screw compressor with internal compression, etc.) and the degree of cooling.

Intake volume, internal leakage (or internal volume displacement) as well as compression ratio (external and internal) are necessary data for a calculation.

Then you can use the formulas from your thermo dynamics book.

If you know the manufacturer and the type, you can visit their website or contact their representative.

Calculating the power demand or power delivery through enthalpy drop (as often done in steam installations) is not usual for compressors.

best regards

teus ■

Look at Ingersoll Rand; Atlas Copco & Howden websites. ■

dear Maryam,

I overlooked the word “centrifugal” in your original question.

For the calculation of a centrifugal compressor, you must know the geometry of the fan (or blades) and from the housing.

This is not a simple task and should be left for an experienced expert.

When using a centrifugal fan, you must know the complete pressure-volume curve.

Using a centrifugal fan in pneumatic conveying is usually not advisable.

success

teus ■

ISBN-0-471-48680-7 "Chemical Process Design & Integration" Robin Smith - Wiley; Chapter 24 gives a worked example of a propane refrigerant cycle. You will need to input the chiller conditions to derive your coefficient of performance & then you will have to factor (0.6 ??) to estimate the mechanical work. The factor is built in to the manufacturers' web pages. Extra mechanical work for subcooling, against downstream flashing, is also required if your plant is hot weather.

How many TR are you talking about; so that you can qualify this thread for a bulk handling topic? <500 TR is hardly enough. ■

I had presumed that the book would be on the shelf in the technical bookshop in the Singapura Centre opposite the Beras Basa MRT station, but.

TR is tons refrigerant. One TR is, if I remember right, 12K BthU/hr which is supposed to be the enthalpy change rate while freezing a ton of water. I've never cross checked the units but it seems right. As an idea, the bigger units, screws, will produce about 900 TR for 2.5MW.(2.8MW motor framing To suit API 619 (I think)) ■

This may be of assistance --

http://committees.api.org/standards/tech/docs/619ti.xls ■

For a centrifugal compressor the estimated polytropic efficiency is 0.017lnF+0.7 where F is the inlet flow in m3/sec. This seems to almost match the units of refigerant flux you mention: if N is for normal? ■

Dear Myryam,

Yes, I am following your post with great interest (as all other posts)

When the subject changed to refrigeration, I was ruled out as I am not familiar with that technology enough.As I am working in the field of pneumatic conveying installations, I can handle the application and theory of positive displacement compressors (pistons, screws, vanes, waterring, roots type, etc)

The calculation of this type of pumps is fairly easy.

Displacement is volume times rpm.

Compression principle can be adiabatic, isochoric, isothermal, or polytrophic.

All the relevant formulas are in your thermo dynamic handbook.

The calculation of a turbine or ventilator is more complicated, because of the way the energy is transferred to the gas. (transfer of impulse)

Then the performance is pressure dependant and the calculation uses velocity vector diagrams, determined by the shape of the impeller blades.

(Application of adjustable diffuser vanes etc.)

Using enthalpy calculation in steam installations give you the available energy in the steam, which can be converted into mechanical energy.

How that is done, is a completely different technique. (Turbines, piston engines etc.)

Your question covers the technology for which an expert needs years of studying.

best regards

teus ■

TR is not the refrigerant flow rate. It is the capacity of the system. Don't run before you can walk. Read a good book which covers the technology.

Refrigeration plant consists of complex compressor stations & simpler vessels & heat exchangers hopefully working safely (827,000 cubic metres per hour of propane is not to be sniffed at)(phew) harmoniously. One expert told me that in refrigeration the first 18 years were the hardest! ■

Hello Maryam,

I haven't got my copy of Smith's book handy so I can't comment yet.

Hello Stngoh,

Liquid Piston Compressor sounds like a Liquid Ring Pump. They are manufactured to the Elmo patent which ran out in the early part of the last century. There is an excellent description in the Hick Hargreaves Handbook, they are now part of BOC Edwards but still based in Bolton, Lancs UK. Nash are another manufacturer but I can't vouch for their publication strengths. LRP's are used extensively for filtration duties & large scale evacuation processes. Factors to consider are the seal water qualities & temperatures; the latter has great influence on the system efficiency because 90% of the work done goes into the seal water. Hope it helps. ■