What is the primary method of achieving capacity control in a centrifugal compressor?

The primary method of achieving capacity control in a centrifugal compressor is through the adjustment of the impeller inlet pre-rotation vanes. This mechanism allows the compressor to modulate its performance by altering the angle at which the incoming air or refrigerant enters the impeller. By changing the pre-rotation angle, the vanes influence the flow characteristics and speed of the fluid entering the compressor, effectively controlling the capacity and efficiency of the system.

This method is particularly advantageous because it allows for a continuous range of capacity adjustments without sacrificing the overall efficiency of the compressor. It also helps maintain optimal performance across varying operational conditions, which is crucial in applications where demand may fluctuate.

Other methods can influence compressor operation but may not provide the same level of fine-tuned control as adjusting the inlet pre-rotation vanes. For example, variable speed control impacts the operational speed of the compressor overall but may not achieve the same immediate responsiveness to load changes as adjusting the vanes. Adjusting the discharge pressure tends to be a reactionary measure rather than a proactive method of capacity control. Bypassing refrigerant can manage load but may compromise system efficiency and performance, thus making the vane adjustment a superior choice for administering effective capacity control.