What is the primary way to achieve capacity control in a centrifugal compressor?

Capacity control in a centrifugal compressor is primarily achieved through the adjustment of the impeller inlet guide pre-rotation vanes. These vanes help control the flow of the gas entering the impeller by directing it at a specific angle, which influences the velocity and pressure characteristics of the gas as it passes through the compressor. This adjustment allows for better matching of the compressor’s capacity to the demand, enhancing efficiency and stability in various operating conditions.

By altering the angle of the guide vanes, the compressor can effectively handle fluctuations in load without compromising performance. This method is particularly beneficial in applications where the demand for compressed gas may vary significantly. It provides a more precise way to control capacity compared to other methods, which may not respond to changes in demand as effectively.

Other options, while they may play roles in the overall operation of a refrigeration system or compressor performance, do not directly control the capacity of the centrifugal compressor in the same way as adjusting the inlet guide vanes does.