What happens to the efficiency of a centrifugal compressor when the condensing pressure is lowered?

When the condensing pressure is lowered in a centrifugal compressor, the efficiency tends to increase. This occurs because a lower condensing pressure reduces the load on the compressor. As the condensing pressure decreases, the compressor has to do less work to achieve the same flow rate, leading to a reduction in the energy required for compression.

The improved efficiency is often due to the fact that lowering the condensing pressure can enhance the pressure ratio across the compressor. A smaller pressure difference between inlet and outlet allows the compressor to operate more optimally, resulting in less enthalpy increase per unit of volume of gas being compressed. Additionally, the reduced energy consumption typically corresponds with a decrease in thermal losses, thereby enhancing overall efficiency.

In essence, as condensing pressure is optimized, the performance of the centrifugal compressor often shows significant improvements in efficiency, thereby maximizing its effectiveness in various applications.