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Dynamic Type Compressors
Dynamic type compressors or turbocompressors are a class of machinery that generates compressed air. They operate by imparting kinetic energy to the air and converting this velocity into pressure.
Dynamic compressors use a rapidly rotating impeller to accelerate the air and a diffuser to slow the air down and build up pressure. They operate continuously, providing a steady, large volume of air.
Dynamic compressors benefit large-scale industries because of their high efficiency at full load, high flow rates and low maintenance. In manufacturing, these units power assembly lines, pneumatic tools and paint spraying equipment. Other application examples include natural gas transmission, steel-making processes and gas turbine power generation.
What Are the Different Types of Dynamic Compressors?
The two primary types of dynamic compressors include:
- Centrifugal compressors: These units draw air into the center of a rotating impeller and throw it outward using centrifugal force. This radial movement increases air velocity and pressure. Before moving to the next stage or outlet, the air passes through a diffuser and volute, which convert kinetic energy to static pressure.
- Axial compressors: These machines move air parallel to the shaft. The air flows through rows of rotating blades, or rotors, and stationary blades, or stators. Rotors accelerate air, while stators convert this increased velocity into pressure. This process repeats through multiple stages to achieve the target pressure level.
FAQs
The difference lies in the compression method. A dynamic compressor increases air pressure by accelerating air to a high velocity and converting that velocity into pressure.
In contrast, a positive displacement compressor traps a fixed amount of air in a chamber and then mechanically decreases the chamber volume to raise the pressure.
Surge refers to an unstable operating condition that occurs when the flow rate through the dynamic compressor is too low for the pressure it is generating. It can cause a flow reversal, resulting in vibrations and potential unit damage.
A surge happens when the compressor’s impeller blades stall because they can no longer push the air forward against the pressure in the downstream system (backpressure).
Common causes for the stall include:
- Reduced system demand
- Increased inlet temperature
- Decreased inlet pressure
- Lowered compressor speed
- Increased contamination buildup on the impeller blades
Choke or stonewall is the operating limit at the maximum possible flow rate. It occurs when the air velocity reaches the speed of sound in the impeller. At this point, it cannot push out any more air, regardless of how fast it spins. Operating in choke causes inefficiency and vibrations but does not damage the compressor as violently as surge.
Dynamic type compressors are highly efficient when operating at full loads. This feature makes them ideal for applications requiring a large, continuous, relatively stable volume of compressed air, such as oil and gas, large-scale manufacturing, power generation and wastewater treatment industries.
A dynamic compressor achieves high efficiency within a specific operating range. The range of flow between the maximum efficiency point and the surge point is called turndown. Since the efficiency drops significantly outside this range, dynamic compressors are less suitable for applications with highly variable air demand unless paired with other controls.
Multiple stages allow dynamic compressors to efficiently achieve higher overall pressure ratios. They also provide air intercooling opportunities between stages, reducing the compression work and increasing overall efficiency.
Yes. Many dynamic compressors provide oil-free air, making them ideal for industries such as food and beverage and pharmaceuticals, where air purity matters.
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