A dynamic compressor is a continuous fluid machine that accelerates the gas or air when it flows through a rapidly rotating element. This compressor converts the velocity of the gas or air into pressure with the help of a diffuser.
In a dynamic compressor, the air is drawn in between the rotating impeller vanes, which increases the airspeed. Eventually, the air or gas expels from the diffuser, and K.E of the air or gas is converted into pressure. In general, these compressors use as turbochargers with axial or radial airflow patterns. Dynamic compressors often design for high flow rates of the air or gas.
Dynamic compressors operate at static pressure and are classified based on axial or radial design. The functioning of a dynamic compressor affects by external conditions (e.g., changes in inlet temperature).
With this type of compressor, outside air escapes between the impeller blades, which rotate at high speed in the compressor. The air or gas is then purged into the diffuser. During this process, the kinetic energy converts into static pressure.
The dynamic compressor has more reliability than a positive displacement compressor because it does not have alternative parts that are subject to repeated load during working. These compressors can also be known as turbochargers because they can provide massive horsepower. Dynamic compressors mostly use in large industrial applications.
Dynamic Compressor types
The dynamic compressor has the following major types:
1) Centrifugal Compressor
It is the most famous type of dynamic compressor. The functional principle of a centrifugal compressor is to convert kinetic energy and speed into pressure energy with the help of a diffuser. Air sucks from the radial blades through the suction guide vane into the middle of the rotary impeller. After that, this air discharges from the centre by centrifugal force. This radial motion of the air leads to kinetic energy production and an increase in pressure energy. As the air or gas passes through the diffuser, the kinetic energy converts into pressure energy.
This compressor takes several steps to increase the pressure to an adequate stage to meet the needs of a typical industrial plant. Each stage is part of the total pressure elevation of the compressor unit. According to the pressure required for the applications, several stages can be connected in series to achieve a higher pressure.
Most popular centrifugal compressors have 2 to 4 stages for 100 to 150 PSIG pressure production, with a water-cooled charge air cooler and separator installed between each stage to eliminate condensation and cool the air.
Compared to other oil-free compressor designs, centrifugal compressors have the highest load efficiency. But functioning will transform expressively because of inlet conditions changes.
2) Axial Flow Compressor
Axial flow compressor can control large airflow. It has a small casing and adequate power requirements. The pressures in these compressors vary from low to medium. Axial compressors use a series of vanes that look like a jet engine to force air inside the smaller areas. These dynamic displacement compressors are not widely used in industries. This dynamic displacement compressor is smaller and lighter than a similar radial compressor and generally operates at higher speeds.
These compressors are typically multi-stage, and the gas or air passage area is reduced throughout the compressor in order to maintain the optimal axial Mach number.
Axial compressors can be very efficient; under their design terms, about 90% are polytropic. Axial compressors are designed to offer high capacity, high efficiency, and high reliability. These compressors have a relatively high price and require many parts, high-quality materials, and tight tolerances. They are used in natural gas pumping systems, medium to large gas turbines, and chemical plants.