Can a pump actually transport live fish? !

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The spiral centrifugal impeller was invented by Swiss engineers in the 1960s to transport live fish. It has both spiral propulsion and rotational centrifugal effects. The impeller flow channel is smooth, the blades are long, the energy gradient is low, resulting in high efficiency (up to 85%), a low net positive suction head, and it is not prone to clogging. It is suitable for transporting live fish, seafood, fruits and other soft materials, as well as urban sewage, pulp (with a concentration of up to 12%) and other highly viscous fluids; it can even transport crushed animals (including bones) without the need for water. Screw centrifugal pumps utilize both screw propulsion and centrifugal force. This view leads some scholars in our country to believe that spiral centrifugal pumps are composed of a spiral propeller and a centrifugal impeller, and designed based on this concept; their efficiency is only 50%–60%. In fact, for this type of spiral, there is no clear boundary in the centrifugal part. To be precise, it consists of the front ends of the blades of a single- or double-blade mixed-flow pump extending further toward the inlet side; this extended portion operates on a principle similar to that of an axial-flow pump. Therefore, during design, the variation law of Vu*r should be specified first to ensure a smooth distribution of the relative velocity, and then the shape should be drawn based on the two-dimensional theory.