The scroll compressor (Figure 3.12) uses one stationary (fixed) and one orbiting scroll to compress refrigerant gas vapors from the evaporator to the condenser of the refrigerant path. The upper scroll is stationary and contains the refrigerant gas discharge port. The lower scroll is driven by an electric motor shaft assembly imparting an eccentric or orbiting motion to the driven scroll. That is, the rotation of the motor shaft causes the scroll to orbit (not rotating) about the shaft center.
This orbiting motion gathers refrigerant vapors at the perimeter, pockets the refrigerant gas, and compresses it as the orbiting proceeds. The trapped pocket works progressively toward the center of the stationary scroll and leaves through the discharge port. Maximum compression is achieved when a pocket reaches the center where the discharge port is located. This happens after three complete orbits. The compression is a continuous process. When gas is being compressed in the second orbit, another quantity of gas enters the scrolls and a quantity of gas is being discharged at the same time. This ensures a smooth compression process with low noise and low vibration compared to other compression technologies. Studying this time lapse series carefully gives a true picture on how the trapped gases are progressively compressed as they proceed toward the discharge port.
Scroll compressors are a relatively recent compressor development and are expected to eventually replace reciprocating compressors in many cooling system applications, where they often achieve higher efficiency and better part-load performance and operating characteristics.
