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

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1 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 and transport 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 it is compressed? Increases

2 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 gas within a closed space in which the pressure of the gas is increased as the volume of the closed space is decreased. Intermittent Flow What is a Dynamic Compressor? A compressor using a rotating mechanism to add velocity and pressure to gas. Continuous Flow

3 Two types of Positive Displacement Compressors: Reciprocating Rotary Two Types of Dynamic Compressors Centrifugal Axial

4 Reciprocating Compressors How does it work? Piston movement in a cylinder connected to a rod and crankshaft Downward piston motion, low pressure gas enters the chamber Upward piston motion, gas is compressed and exits the chamber Video

5 Reciprocating Compressors High Horsepower Applications Common in natural gas transmission lines. Processes for high pressure delivery of gasses Air Conditioning Compressors Some manufactures (Frigidaire ) use rotary compressors AC Compressors (and other small appliance applications) are Hermetic or Semi-Hermetic

6 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 being compressed. 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 that can be opened to replace motor and pump components. The primary advantage of a hermetic and semi-hermetic is that there is no route for the gas to leak out of the system. Open compressors rely on either natural leather or synthetic rubber seals to retain the internal pressure Require a lubricant such as oil to retain their sealing properties

7 Rotary Compressors How do they it work? When a rotating mechanism spins past the inlet valve, it creates 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 it shoots out of it. Then the rotating mechanism continues on to draw more fluid at the inlet valve. How it works Video

8 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

9 Vane Compressors Vane housing on a off centered shaft Vanes slide in an out always making contact with the compressor walls Gas enters in the largest opening Exits the smallest Good for low pressure applications Efficient Heat controlled by oil injection

10 Scroll Compressor How it works 2 Spirals 1 stationary, 1 orbits without rotating 1 st orbit 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

11 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 Dynamic Compressors? Centrifugal Axial

12 Centrifugal Compressors Rotating disk (impeller) forces gas to the rim of the impeller, increasing velocity The diffuser converts the velocity energy to pressure energy. Primarily used for continuous, stationary service in industries such as refineries, chemical plants and snow making operations Single Stage and Multi-Stage Compressors How a Centrifugal Compressor Works

13 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

14 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

15 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

16 Axial Compressors High Volume High Efficiency High Cost Common Uses Gas Turbines Jet engines Power stations Nickname Superchargers

17 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?