Compressors are used all over the world. They have become a vital part of all industries. There are multiple types of compressors, and an axial compressor is one of them. The axial compressor is the most famous type of dynamic compressor from the category of centrifugal compressor. In the previous article, we discussed different types of centrifugal compressors. Therefore, in this article, we will mainly discuss the axial flow compressor.
What is the Axial Compressor?
A compressor in which the flow of air or gases is parallel to the axis of rotation is called an axial compressor. In simple words, in an axial compressor, the gas enters axially or parallel to the rotor axis and also discharges in the same direction (axially). Therefore, it is called an axial compressor.
It is a mechanical device that continuously pressurizes the working fluid. This is a compressor that only allows gases or air to flow parallel to the shaft axis. This compressor works at constant pressure—external conditions like mass flow rate (density) and inlet temperature affect the efficiency of the compressor.
These compressors are generally lighter and smaller compared to centrifugal compressors but run faster. These compressors usually use in applications that require a high flow of gas and low head. It consists of a drum with blades of a particular shape. Due to these dynamic compressors‘ high speed, they can generate electricity in combination with a gas turbine.
These compressors are used in different applications like propane dehydrogenation, fluid catalytic cracking air, large-capacity air separation units, and blast furnace air. These are also utilized in aircraft engines due to their highly flexible operation during flight and high reliability.
Although these have very high costs but the price per high flow rate is lower than other types of compressors.
Read More: Different Types of Compressors
Explanation of Axial Flow Compressor with an Example
Dynamic compressors use one or more rotating elements to accelerate and reduce the air speed. This acceleration, followed by a sharp drop in speed, leads to an increase in air pressure.
Imagine a large freeway (like a freeway in the US or a freeway in Germany) and a car is an air molecule. All the cars are moving very fast and usually have adequate spacing; that’s low pressure. Now let’s block half of the lanes after the cars have gotten to full speed. When the cars approach the blockage, they slow down and get closer together. When the cars (air molecules) are packed tighter together, that is an increase in pressure.
The axial flow and radial flow centrifugal compressors are similar in that way; they speed up the air fast and then slow it down somehow. The speeding up and slowing down processes of these compressors are somewhat different, as described below.
The axial flow air compressor speeds up the air by using rotating airfoils and then slows it down because the axial compressor puts a roadblock in the way (a stationary element). Here’s a good picture of it:
The air gets a high speed from the rotating blades, and then it slows down because it has to go through the stationary components (blades). This is done several times in the compressor, and every time the air speeds up and then slows down. In this way, the air pressure increases.
Working Principle of axial flow compressor
The working principle of an axial flow compressor is given below:
First of all, the working fluid enters the compressor through the inlet. The working fluid flows in a parallel direction to the rotor axis.
When the gas or other working fluid passes through the rotor blades, then the blades provide kinetic energy to the gas. This kinetic energy increases the velocity of the gas.
After the rotor blades, there is a series of stator blades on the shaft of the compressor. After passing through the rotor blade, the gas passes through the stator blade fixed with the casing of the compressor.
When the gas passes through the stator blades, then the kinetic energy of the gas converts into static pressure energy. After that, this final output gas collects through the outlet section of the compressor. This final output gas exits the compressor axially.
In straightforward wording, in an axial flow air compressor, the rotor blades increase the velocity of the gas, and the diffuser’s stator blades convert this increase in velocity into pressure energy.
The design of a diffuser channel increases the pressure on standard functionality. This leads to a more significant increase in pressure in each stage that makes up the rotor and the stator.
Read More: How does a radial flow compressor work?
Components of Axial Flow Compressor
The main components of the axial flow air compressor are given below:
The casing acts as a protector that protects the internal components of the turbine from any damage. The stator blades fix with casing. It makes of cast iron or steel.
2) Rotor Blades
The blades of the rotor are moveable. They rotate continuously. The blade provides kinetic energy to the gas and increases its speed.
3) Stator Blade
The stator blades are static and fixed. These blades convert the velocity of the gas into pressure energy.
4) Collector or Outlet
A collector is an area from where final pressurized gas collects. So, the collector includes in the most important axial compressor components.
Advantages and disadvantages of the axial flow compressor
The advantages and disadvantages of the axial flow compressor are given below.
Advantages of Axial Compressor
- A high punching performance can achieve with a straight flow.
- A small area of the anterior lobe for a given flow.
- High peak efficiency as compared to the centrifugal compressor.
- The increase in pressure due to the increase in the number of stages increases, and the loss is negligible.
- These dynamic compressors have a large mass flow rate.
- These are more efficient than reciprocating compressors.
Disadvantages of Axial Flow Compressor
- Efficient in a narrow speed range.
- Mostly, these have manufacturing problems due to their complex design.
- High price as compared to the centrifugal compressor.
- The axial flow compressor has heavyweight.
- High power demands on the starting power.
- The axial compressor has an intricate design as compared to the centrifugal compressor.
Axial Compressor Applications
- These types of compressors use where a high flow rate is required.
- These dynamic compressors are most commonly used in aircraft turbojet engines.
- They are used in ship engines for high speed.
- They use for various industrial applications such as propane dehydrogenation and blast furnaces.
Difference between Centrifugal Compressor and Axial Compressor
- Axial compressors are more complex to design than centrifugal compressors.
- Axial compressors have the ability to control more gas flow than centrifugal compressors.
- The centrifugal compressor is easy to maintain than the axial compressor.
- Centrifugal compressors have low cost than axial compressors.
- Centrifugal compressors can’t work more efficiently than axial compressors.
- The pressure ratio per stage in the axial compressor is lower than in the centrifugal compressor.
Why is it called an axial compressor?
In an axial compressor, the gas enters axially or parallel to the rotor axis and also discharges in the same direction (axially). Therefore, it is called an axial compressor.