Discharge conditions for a radial compressor

[akr768]

I'm new to rotary type compressors. I have a radial compressor prototype with the impeller diameter of about 5 cm (yes, it is a small machine). Based on the known inlet conditions and compressor performance characteristics, the calculated pressure and temperature rise across the compressor is about 4 bars and 3 C. Is this a normal range for these types and of such a small size? I feel that this is too low for any useful capacity. Please let me know your thoughts. Also let me know if you need additional information to provide an answer. Since I'm new to this tech, I'm at a loss for providing sufficient information.

 

[rotw]

I'm new to rotary type compressors
rotary compressor is not a radial compressor.
- What is the application? dual use (military/civil)?
An impeller of 5 cm diameter, I have never seen but it must be spinning extremely fast.

Based on the known inlet conditions and compressor performance characteristics, the calculated pressure and temperature rise across the compressor is about 4 bars and 3 C. Is this a normal range for these types and of such a small size?

- Pressure increase in compressor is normally expressed in terms of pressure ratio, an absolute differential is not very useful to compare performance;
- Temperature rise depends upon many factors including gas molecular weight / composition and pressure ratio.

I feel that this is too low for any useful capacity

- First define what you mean by useful. What is too low ? pressure rise? How do you infer capacity, which usually is flow, from pressure rise?

- If you have the performance curves and have derived the pressure and temperature curves following appropriate procedures, why asking then? Is this a sanity check exercise that your procedures have been applied properly? added: if pressure and temperature curves are already provided by vendor, then what is exactly the question?


Life is not about waiting for the storm to pass. It's about learning dance in the rain.

 

[akr768]

Thanks for your response, rotw. Apologies for being so vague in my question.

The application is for a small-scale distributed gas (co2) power plant, and yes the RPM is about 50k.
The pressure ratio across the compressor is about 1.1. By useful, I mean the pressure ratio across the compressor. If the pressure ratio is very small, then the system might not reach sufficient exit pressures for efficient gas power cycle operation. Accounting for the rest of the system (pipelines, valves etc) might add further pressure losses.

Yes, this is a sanity check to understand if this is typical of the radial compressors. I have worked with positive displacements compressors (piston, scroll) before, where the pressure ratios are typically about 2-3, hence this radial compressor's pressure ratio seemed awfully low. So, I wanted to understand if it is normal for such small compressors.

 

[rotw]

At 50000 rpm your peripheral speed is approx. 130 m/s which is relatively low for a single pinion shaft.
Considering that the max. limit can be up to >400 m/s for open type impeller / titanium.
Check the rotor-dynamic report and verify the max. shaft speed limit reachable.
If you want to increase the pressure ratio, you need this little tinny thing to spin faster.
How did you arrive to 1.1 pressure ratio, vendor figure or your own calc. ?
If your own, you can post your calc. procedure here and I can check it.

NB: The speed for operation when at full potential peripheral speeds, should more about 100k-150k rpm.
Problem is, is the manufacturer capable to construct such a machine.