Which type of impeller is known for being the most efficient in energy transfer?

A closed impeller is recognized for being the most efficient in energy transfer, primarily due to its design. The closed configuration, which consists of two parallel discs (the cover plate and the back plate) that encase the blades, allows fluid to move through the impeller without significant turbulence or leakage. This design minimizes energy losses by ensuring that a greater portion of the energy imparted by the impeller blades is converted into fluid kinetic energy.

In addition, closed impellers provide better hydraulic performance with higher pressures and flows, making them suitable for applications where efficiency and performance are vital. The contained nature of the closed impeller helps maintain a streamlined flow, reducing drag and enhancing the smooth transition of fluid through the impeller.

Contrastingly, open impellers lack these enclosing plates, which can lead to increased turbulence and less energy efficiency. Mixed flow and variable pitch impellers serve specific applications and have their advantages, but in terms of overall efficiency in energy transfer, the closed impeller remains superior due to its effective design and ability to channel energy more efficiently into the fluid.