Dynamic Compressors Flashcards
How does a centrifugal compressor work?
They convert velocity in to pressure using diffusers, a volute casing or a combination.
Describe the single stage centrifugal compressor?
It is the simples type of centrifugal compressor consisting of a single impeller that attaches directly to an extended motor shaft.
What is used to increase efficiency and capacity of a single stage compressor?
It uses diffuser vanes fit to the inside of the housing. increasing the speed and also increasing the volume.
How many stages (impeller) can you put on a single rotor?
You can have as many as 12 stages present on a single stage?
What is an alternate design to multi-staging?
Is to have 4 or 5 individual impellers with their volute casing arranged around a central bull gear.
What are the three different casings designs for centrifugal compressor?
- Sectional
- Horizontally Split
- Vertically Split
Describe sectional casings and their use?
Sectional casings they consist of a number of sections, each bolted to another with tie rods. They are usually on small units with low-pressure ratio and small volumes.
Describe horizontally split casings and their use?
The casing splits along the centerline of the housing and bolts together , sealing it metal to metal, limited to less than 1000 psig.
What is a dynamic compressor?
Is a non-positive displacement compressor, and it has no positive seal between inlet and discharge.
Describe Vertically casings and their use?
They are cylindrical or barrel casing with removable front cover. They are used in high-pressure applications of up to 10,000 PSIG
What provides the acceleration velocity for the conversion into gas pressure?
The impellers, they are fitted on the shaft. and the rotor is dynamically balanced.
What is the most important part of a centrifugal compressor?
The Impeller.
What are the two (2) major classifications of dynamic compressors?
- Centrifugal Compressors
* Axial Compressors
How do dynamic compressors produce pressure?
They convert velocity in to pressure using diffusers, a volute casing or a combination.
What can be done to increase the efficiency of a single-stage compressor?
Diffusers vanes inside the housing allow you to achieve a slightly higher compression ratio.
What has to be done to increase the volume and overall pressure ratio of a centrifugal compressor?
You should add additional impellers and their individual diffuser sections to the rotor shaft.
Which casing design do you use for high-pressure applications (10,000 psig)?
The Vertically Split Design.
Name the three (3) styles of impellers in centrifugal compressors
- Open
- Semi-Closed/Open
- Closed
Describe open impellers and their purpose?
Open impellers are the simplest design. they are usually used in single stage applications and they consist of vanes that radiate out from a central hub. used in rough service and dirty environments.
Describe semi-closed/open impellers and their purpose?
Semi-closed impellers have blades that can be straight radial, backward leaning, forward leaning or combination of the blades depending on compressor design and can be used on single stage or multi-stage or even as the final stage in an axial compressor.
Describe closed impellers?
They are impellers with front and back vanes closed, used in single stage and multi-stage units on up to 12 stages, as well as on axial compressors as the last stage. With these impellers you can achieve higher pressure ratios and higher efficiency due to tight clearances between impellers and diffusers.
What are guide elements?
They control and direct gas flow into the compressor or from one stage to the next. they maybe stationary or movable inlet guide vanes, or adjustable or stationary diffusers.