compressor basic

8/11/2019 Compressor Basic

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What is a Compressor? A mechanical device that increases the pressure of a gas

by reducing its volume.

Similar to a pump Increases the pressure on a fluid andtransport it through a pipe.

What is key difference between a Fluid and a Gas? Compressibility a gas is compressible

What happens to gas volume as it is compressed? Decreases

What happens to the Temperature of the Gas as itis compressed? Increases


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Compressors are classified by how they work

Two Categories of Compressors Positive Displacement

Dynamic

What is a Positive Displacement Compressor?

A compressor that confines successive volumes of gaswithin a closed space in which the pressure of the gas isincreased as the volume of the closed space isdecreased. Intermittent Flow

What is a Dynamic Compressor? A compressor using a rotating mechanism to addvelocity and pressure to gas. Continuous Flow


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Two types of Positive DisplacementCompressors: Reciprocating

Rotary

Two Types of Dynamic Compressors Centrifugal

Axial


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Reciprocating Compressors How does it work?

Piston movement in a cylinder connected to a rod andcrankshaft

Downward piston motion, low pressure gas enters thechamber

Upward piston motion, gas is compressed and exitsthe chamber

Video
http://www.youtube.com/watch?v=fTDkG1y5R34http://www.youtube.com/watch?v=fTDkG1y5R34


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Hermetically Sealed and Semi Hermetically

Sealed Compressors The compressor and motor driving the compressor are integrated, and

operate within the pressurized gas envelope of the system.

The motor is designed to operate and be cooled by the gas or vapor beingcompressed.

The hermetic uses a one-piece welded steel casing that cannot be opened

for repair. If the hermetic fails it is simply replaced with an entire new unit.

A semi-hermetic uses a large cast metal shell with gasketed covers thatcan be opened to replace motor and pump components.

The primary advantage of a hermetic and semi-hermetic is that there is noroute for the gas to leak out of the system.

Open compressors rely on either natural leather or synthetic rubber seals to retainthe internal pressure

Require a lubricant such as oil to retain their

sealing properties


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Rotary Compressors How do they it work?

When a rotating mechanism spins past the inlet valve, itcreates a vacuum.

The fluid flows out of the valve behind it, filling the vacuum.

As it approaches the outlet valve, the chamber shrinks,creating more pressure on the fluid.

The fluid has nowhere to go but out of the outlet valve, so itshoots out of it.

Then the rotating mechanism continues on to draw morefluid at the inlet valve.

How it works Video
http://www.youtube.com/watch?v=7BK7VJD8YOYhttp://www.youtube.com/watch?v=7BK7VJD8YOY


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Common Types of Rotary Compressors Screw

Vane

Scroll

Screw Two meshing helix screws

Rotors

Compact and smooth running

2 types - Oil Free and Oil Flooded

Oil Free No assistance from oil to cool and assist in sealing .

Oil Flooded Oil injected to aid in sealing and provide cooling.

Separator downstream to capture the oil


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Vane Compressors Vane housing on a off centered shaft

Vanes slide in an out always making contact withthe compressor walls

Gas enters in the largest opening Exits the smallest

Good for low pressure applications

Efficient

Heat controlled byoil injection


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Scroll Compressor How it works

2 Spirals

1 stationary, 1 orbits without rotating

1storbit entraps inlet gas

Subsequent orbits compresses gas and exited out the center Generally 2-3 orbits for a full cycle

Video

Advantages Compact

Steady flow Low energy use

Quiet

Smooth operation
http://www.youtube.com/watch?v=lRHkzSdjcFEhttp://www.youtube.com/watch?v=lRHkzSdjcFE


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What is a Dynamic Compressor? A compressor using a rotating mechanism to add

velocity and pressure to gas.

Continuous Flow

What are the Two Types of DynamicCompressors? Centrifugal

Axial


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Centrifugal Compressors Rotating disk (impeller) forces gas to the rim of the

impeller, increasing velocity

The diffuser converts the velocity energy to pressureenergy.

Primarily used for continuous, stationary service inindustries such as refineries, chemical plants and snowmaking operations

Single Stage and Multi-Stage Compressors

How a Centrifugal Compressor Works
http://www.youtube.com/watch?v=L65Fwh9cw50http://www.youtube.com/watch?v=L65Fwh9cw50


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Impeller

Most critical part of a centrifugal compressor Compressor performance determined by impeller:

Size

Shape

Speed

3 types of Impellers

Closed

Most common

Shroud covering both sides of the blade

Center eye hole for gas to enter Used in Multi-stage compressors

Semi open

Open


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Multi-Stage Compressors Diaphragm

Specially designed casing wall separating the stages

Gas passes through the difuser

Passes through the return channel in the diaphragm Controlling Axial Load on the Shaft

Bearing Review

Thrust Bearing
http://localhost/var/www/apps/conversion/tmp/scratch_3/Bearings,%20Gaskets%20and%20Seals.ppthttp://localhost/var/www/apps/conversion/tmp/scratch_3/Bearings,%20Gaskets%20and%20Seals.ppt


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Axial Compressors Gas flows parallel to the axis of rotation

Unlike centrifugal that has radial components

Has rotating and stationary components

Rotating airfoil rotor Stationary airfoil stator

Similar number of these on

a shaft

Video
http://www.youtube.com/watch?v=rD5bd_U-Al8http://www.youtube.com/watch?v=rD5bd_U-Al8


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Axial Compressors High Volume

High Efficiency

High Cost

Common Uses Gas Turbines

Jet engines

Power stations

Nickname Superchargers


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1. What is a Compressor?2. What happens to the temperature and the volume of a gas

as it is compressed?

3. What are the 2 categories of Compressors?

4. Explain the difference between a positive displacement and

radial compressor.

5. Explain how a reciprocating compressor works.

6. Describe a Hermetically sealed compressor.

7. Explain how a rotary compressor works.

8. Describe how a scroll compressor works.9. Explain how a multi stage compressor works.

10. What type of compressor is found on jet aircraft?

compressor basic

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