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Suction head coefficient, abbreviated as $$C_{NPSH}$$, a dimensionless number, is used to describe the efficiency of a pump or a similar fluid handling device in creating suction to draw fluid into the system.  It's an important parameter in pump design and analysis, especially when considering the behavior of fluids under negative pressure or suction conditions.  The suction head coefficient is typically used in conjunction with the Bernoulli equation and the pressure difference between the suction side of the pump and the surrounding fluid to assess the pump's ability to lift fluid.

The suction head coefficient indicates the ratio of the actual suction head to the theoretical suction head based on velocity.  It is a measure of the effectiveness of the pump's inlet design and its ability to create the desired negative pressure to draw fluid into the pump.  High values of the suction head coefficient indicate efficient pump designs that can effectively handle negative pressure and prevent cavitation.  Engineers use the suction head coefficient to optimize pump inlet designs, avoid pump cavitation, and ensure the pump's performance matches the intended application requirements.

In summary, the suction head coefficient is an important parameter in pump engineering that helps assess the efficiency and behavior of pumps under suction conditions, aiding in the design and operation of fluid-handling systems.

$$S = g \; NPSH \;/\; ( 2 \; \pi \;/\; t )^2 \; d^2$$
$$C_{NPSH}$$ = suction head coefficient $$dimensionless$$
$$g$$ = standard gravity $$ft \;/\; sec^{-2}$$ $$m \;/\; s^{-2}$$
$$NPSH$$ = net positive suction head $$ft^3 \;/\; sec$$ $$m^3 \;/\; s$$
$$\pi$$ = Pi $$3.141 592 653 ...$$
$$t$$ = period $$rad \;/\; sec$$ $$rad \;/\; s$$
$$d$$ = turbomachine impeller diameter $$in$$ $$mm$$