Why are the blades of centrifugal pumps generally designed to be curved backward?

It is beneficial for the shear action on the fluid.

Reducing energy loss is obvious.

The backward-curving blades result in an increase in potential energy that is greater than the increase in kinetic energy, which helps to improve energy efficiency

Impellers with closed blades that are curved backward are generally used, as they offer good performance and high efficiency. To increase the single-stage pressure ratio and achieve a simpler, more compact structure, an impeller with semi-open radial straight blades can be used, accompanied by a guide vane that twists the blades radially in order to accommodate the different circumferential speeds u1 of the airflow as it enters the impeller. To accommodate higher flow rates, when the current b2/D2 value is ≥0.06, a three-dimensional impeller with twisted blades can be used to improve performance and efficiency. To improve the performance of the impeller while reducing blade blockage in the inlet area, some impellers employ a structure with alternating long and short blades in order to increase the number of blades. As shown in Figure 1, the impellers of a multi-stage compressor can be arranged in the same direction or in opposite directions. By adopting a counter-arranged structure, the axial thrust on the rotor can be eliminated without the need for an additional balance disk. However, intake and exhaust pipes have been added, which meets the requirement for segmented cooling.

It is beneficial for the shear action on the fluid. The impellers of a multi-stage compressor can be arranged in the same direction or in opposite directions. By adopting a counter-arranged structure, the axial thrust on the rotor can be eliminated without the need for an additional balance disk. However, intake and exhaust pipes have been added, which meets the requirement for segmented cooling.

A backward-curving impeller can reduce drag, lower energy losses, and thereby improve efficiency. It’s all explained in the original book

I learned it in school; for the real principles, I suggest the original poster go through the books carefully again

The function of the impeller is to transfer the mechanical energy of the prime mover directly to the liquid, in order to increase the liquid’s static pressure energy and kinetic energy (with the static pressure energy being the main increase). The backward-curving impeller can reduce resistance; the liquid within the impeller flows around the blades, and during this flow the liquid exerts an upward force on the blades. In turn, the blades exert a force on the liquid that is equal in magnitude but opposite in direction to this upward force. This force does work on the liquid, granting it energy so that it can flow out of the impeller, during which both the kinetic energy and pressure energy of the liquid increase.

This is covered in textbooks on chemical engineering principles and other related subjects. The function of an impeller is essentially to transfer the kinetic energy of the motor to the fluid being transported. Throughout this transfer process, three different types of impellers have been used: straight impellers, forward-curving impellers, and backward-curving impellers. A forward-curving impeller functions like a spoon, enabling the fluid to achieve a high initial velocity; however, it cannot provide much static pressure energy to the fluid. As a result, the fluid has a high flow rate but low static pressure energy. The high flow rate leads to high energy consumption during the transfer process, which in turn results in low efficiency of energy transfer. Centrifugal pumps made with such impellers generally have an efficiency of no more than 50%, which is lower even than that of shielded pumps. It’s easy to see that such pumps have no practical value； The curved impeller primarily converts the kinetic energy of the motor into the static pressure energy of the fluid; thereafter, the fluid flows out of the pump due to this difference in static pressure. This type of impeller **reduces energy losses during the conversion process, thereby increasing the efficiency of the centrifugal pump, which can reach over 90%, haha!

This is covered in textbooks on chemical engineering principles and other related subjects. The function of an impeller is essentially to transfer the kinetic energy of the motor to the fluid being transported. Throughout this transfer process, three different types of impellers have been used: straight impellers, forward-curving impellers, and backward-curving impellers. A forward-curving impeller functions like a spoon, enabling the fluid to achieve a high initial velocity; however, it cannot provide much static pressure energy to the fluid. As a result, the fluid has a high flow rate but low static pressure energy. The high flow rate leads to high energy consumption during the transfer process, which in turn results in low efficiency of energy transfer. Centrifugal pumps made with such impellers generally have an efficiency of no more than 50%, which is lower even than that of shielded pumps. It’s easy to see that such pumps have no practical value； The curved impeller primarily converts the kinetic energy of the motor into the static pressure energy of the fluid; thereafter, the fluid flows out of the pump due to this difference in static pressure. This type of impeller **reduces energy losses during the conversion process, thereby increasing the efficiency of the centrifugal pump, which can reach over 90%, haha!