How is the capacity of a centrifugal compressor controlled using variable guide vanes?

The capacity of a centrifugal compressor can be controlled using variable guide vanes by varying the passages of the vanes. When the guide vanes are adjusted, they change the angle at which the incoming air or gas enters the rotor of the compressor. This adjustment influences the flow characteristics and allows for better control over the compressor's capacity.

When the vanes are set to a more open position, the compressor can handle a larger volume of fluid, increasing its capacity. Conversely, closing the vanes reduces the inlet area, decreasing the capacity of the compressor. This method of controlling capacity is particularly effective because it allows for smooth and responsive adjustments without drastically altering other operating parameters. This feature is essential in applications requiring precise control over flow rates and pressures, providing efficient operation across varying demand conditions.

The other choices pertain to mechanisms that do not directly affect the flow capacity in the same way as adjusting the guide vanes. Motor speed adjustments can influence performance but are not as precise for capacity control as modifying the vanes. Changing the refrigerant type or modifying the pump inlet involves different principles and does not provide the same level of direct control over the compressor's capacity.