# An odd thought on centrifugal compressors.

• Windman
In summary, the conversation discusses the concept of modifying the inlet of a centrifugal compressor to spin the air as it is sucked in, similar to what a cyclone separator inlet does. This would potentially reduce the power required to achieve the final velocity. The conversation also mentions examples of this concept being used in centrifugal pumps and water turbines. However, it is uncertain if this concept would have the same advantage in a gas compressor.

#### Windman

Hi everyone I'm new.

Take a normal straight veined compressor. Normally it just sucks the air straight in and has to accelerate it effectively from zero to however fast it ends up going.

But what of you modified the inlet a bit. Instead of being just a hole you configured it so it spun the air as it got sucked in. In a similar manner to what a cyclone separator inlet does. If you make it spin in the same direction as the impeller, then wouldn't it mean that instead of accelerating the air from zero, it would just have to add to its already rotating velocity and so require less power to achieve the final velocity?

Well I have thoroughly confused myself trying to work this out. So I thought if anybody could someone here can.

Hi Windman,

Welcome to PF...

Not sure about gas compressor examples, but what you describe is found on some centrifugal pumps and is called an inducer;

http://www.mcnallyinstitute.com/10-html/10-1.html

"An axial flow impeller called an Inducer (it works like a booster pump) can be placed ahead of the regular pump impeller, on the same shaft, to increase the suction pressure and lessen the chance of cavitation. In some instances this can allow the pump to operate at a higher speed with a given NPSH. The inducer will contribute less than 5% of the total pump head, and although low in efficiency the total efficiency of the pump is not reduced significantly. The total reduction in NPSH required can be as much as 50%."

As mentioned in the link above, the advantage in pumping liquids is reduced NPSH-R and consequent reduction in cavitation.

Another example is found in many water turbines;

http://www.statemaster.com/encyclopedia/Francis-turbine

"The Francis turbine was developed by James B. Francis. It is an inward flow reaction turbine that combines radial and axial flow concepts."

Again, these are liquid applications - not gas - so not sure about the advantage for your compressor idea.

.

## 1. What is a centrifugal compressor?

A centrifugal compressor is a type of dynamic compressor that uses centrifugal force to increase the pressure and velocity of a gas or air stream. It consists of a rotating impeller that accelerates the gas, and a diffuser that converts the kinetic energy into pressure.

## 2. How does a centrifugal compressor work?

A centrifugal compressor works by pulling in a gas or air stream through the inlet, which then passes through the rotating impeller. The impeller spins at high speeds, causing the gas to accelerate and move outward towards the diffuser. The diffuser then converts the kinetic energy into pressure, resulting in a high-pressure gas or air stream at the outlet.

## 3. What are the advantages of using a centrifugal compressor?

Some advantages of using a centrifugal compressor include its compact size, high efficiency, and low maintenance requirements. It also has a continuous flow of gas, making it ideal for high-volume applications.

## 4. What is the difference between a centrifugal compressor and a reciprocating compressor?

The main difference between a centrifugal compressor and a reciprocating compressor is their method of compression. Centrifugal compressors use centrifugal force to increase the pressure of a gas, while reciprocating compressors use a piston to compress the gas. Additionally, centrifugal compressors are more suitable for high-volume, continuous operations, while reciprocating compressors are better for low-volume, intermittent operations.

## 5. What are some common applications of centrifugal compressors?

Centrifugal compressors are commonly used in industries such as oil and gas, chemical processing, and power generation. They are also used in refrigeration systems, air conditioning, and gas turbines. Additionally, they are used in various transportation applications, such as aircraft engines and turbochargers for cars.