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Rotary Compressors

Rotary

A rotary compressor, commonly used in refrigeration and air conditioning systems, operates based on the principle of rotary motion to compress gas. Here's how it generally works:


Intake Phase: The compressor has a cylindrical housing and a rotating element (rotor). The rotor is mounted eccentrically within the housing, meaning it's not perfectly centered. As the rotor spins, it draws in refrigerant gas (or another type of gas/air) into the compression chamber through an intake valve.


Compression Phase: As the rotor turns, the refrigerant gas space gradually decreases. This is often achieved by the rotor’s eccentric motion within a stationary, curved casing or by the use of sliding vanes or screws that mesh together. The reduction in volume increases the pressure of the gas according to Boyle's Law (a gas law that states that a gas's pressure and volume are inversely proportional. When the temperature is kept constant, as volume increases, the pressure falls and vice versa).


Discharge Phase: Once the gas is compressed to the desired level, it is forced out of the compressor through a discharge valve. The compressed gas then moves on to the next component in the system, like a condenser in a refrigeration cycle.


There are a few types of rotary compressors, with the most common being the rotary vane and screw compressors:


  • Rotary Vane Compressor: Uses a rotor with longitudinal slots in which vanes slide in and out. The eccentric rotation of the rotor causes these vanes to slide out due to centrifugal force, pressing against the wall of the housing, thus forming compression chambers.

  • Screw Compressor: Consists of two helical screws, one with a convex profile and the other with a concave profile, which interlock. As these screws rotate, the volume between the meshing screws decreases, compressing the gas.


The key advantages of rotary compressors include their compact size, smooth operation with less vibration than reciprocating compressors, and efficiency, particularly in systems where a constant flow of compressed gas is needed.


A scroll compressor is considered a type of rotary compressor. However, it operates on a somewhat different principle compared to other rotary compressors like rotary vane or screw compressors.


A scroll compressor consists of two interleaved spiral-shaped scrolls. One scroll is stationary (fixed scroll), and the other (orbiting scroll) moves in a small circular orbit. 


The motion is not rotational like that of a wheel but rather orbital, and because of this motion, pockets of gas are trapped between the scrolls. As the orbiting scroll moves, these pockets of gas are pushed toward the center of the scrolls, simultaneously being compressed into smaller and smaller volumes until they reach the center, where they are expelled through the discharge port.


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