Compressor

The main distinction is that the focus of a compressor is to change the density or volume of the fluid, which is mostly only achievable on gases.

They can be either stationary or portable, can be single or multi-staged, and can be driven by electric motors or internal combustion engines.

[1][2][3] Small reciprocating compressors from 5 to 30 horsepower (hp) are commonly seen in automotive applications and are typically for intermittent duty.

Larger reciprocating compressors well over 1,000 hp (750 kW) are commonly found in large industrial and petroleum applications.

This type of compressor can compress a wide range of gases, including refrigerant, hydrogen, and natural gas.

The classifications of rotary screw compressors vary based on stages, cooling methods, and drive types among others.

Screw compressors have fewer moving components, larger capacity, less vibration and surging, can operate at variable speeds, and typically have higher efficiency.

Small sizes or low rotor speeds are not practical due to inherent leaks caused by clearance between the compression cavities or screws and compressor housing.

[5] They depend on fine machining tolerances to avoid high leakage losses and are prone to damage if operated incorrectly or poorly serviced.

As the rotor turns, blades slide in and out of the slots keeping contact with the outer wall of the housing.

They can be either stationary or portable, can be single or multi-staged, and can be driven by electric motors or internal combustion engines.

Dry vane machines are used at relatively low pressures (e.g., 2 bar or 200 kPa or 29 psi) for bulk material movement while oil-injected machines have the necessary volumetric efficiency to achieve pressures up to about 13 bar (1,300 kPa; 190 psi) in a single stage.

[16][17][18] They operate more smoothly, quietly, and reliably than other types of compressors in the lower volume range.

[1] The degree of flexing and the material constituting the diaphragm affects the maintenance life of the equipment.

Rubber or silicone diaphragms are capable of enduring deep pumping strokes of very high flexion, but their low strength limits their use to low-pressure applications, and they need to be replaced as plastic embrittlement occurs.

Diaphragm compressors are used for hydrogen and compressed natural gas (CNG) as well as in a number of other applications.

A submerged outlet from the chamber allows water to flow to the surface at a lower height than the intake.

A facility on this principle was built on the Montreal River at Ragged Shutes near Cobalt, Ontario in 1910 and supplied 5,000 horsepower to nearby mines.

With multiple staging, they can achieve high output pressures greater than 1,000 psi (6.9 MPa).

The stationary airfoils, also known as stators or vanes, decelerate and redirect the flow direction of the fluid, preparing it for the rotor blades of the next stage.

However, they are relatively expensive, requiring a large number of components, tight tolerances and high quality materials.

Some compressors outside of refrigeration service may also be hermetically sealed to some extent, typically when handling toxic, polluting, or expensive gasses, with most non-refrigeration applications being in the petrochemical industry.

A semi-hermetic uses a large cast metal shell with gasketed covers with screws that can be opened to replace motor and compressor components.

An open pressurized system such as an automobile air conditioner can be more susceptible to leak its operating gases.

A compressor can be idealized as internally reversible and adiabatic, thus an isentropic steady state device, meaning the change in entropy is 0.

dH = VdP Non flow isentropic processes like some positive displacement compressors may use a different equation.

Real world cycles have inherent losses due to inefficient compressors and turbines.

Adiabatic compression or expansion more closely model real life when a compressor has good insulation, a large gas volume, or a short time scale (i.e., a high power level).

In the case of centrifugal compressors, commercial designs currently do not exceed a compression ratio of more than 3.5 to 1 in any one stage (for a typical gas).

The inter-stage coolers (intercoolers) typically result in some partial condensation that is removed in vapor–liquid separators.