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In a hydraulic circuit, net positive suction head (NPSH) may refer to one of two quantities in the analysis of cavitation: The Available NPSH (NPSH A): a measure of how close the fluid at a given point is to flashing, and so to cavitation. Technically it is the absolute pressure head minus the vapour pressure of the liquid.
The cavitation number (Ca) can be used to predict hydrodynamic cavitation.It has a similar structure as the Euler number, but a different meaning and use: . The cavitation number expresses the relationship between the difference of a local absolute pressure from the vapor pressure and the kinetic energy per volume, and is used to characterize the potential of the flow to cavitate.
Specific speed N s, is used to characterize turbomachinery speed. [1] Common commercial and industrial practices use dimensioned versions which are of equal utility. Specific speed is most commonly used in pump applications to define the suction specific speed —a quasi non-dimensional number that categorizes pump impellers as to their type and proportions.
From an initial design point of view, engineers often use a quantity termed the specific speed to identify the most suitable pump type for a particular combination of flow rate and head. Net Positive Suction Head (NPSH) is crucial for pump performance. It has two key aspects: 1) NPSHr (Required): The Head required for the pump to operate ...
Suction cavitation is often identified by a sound like gravel or marbles in the pump casing. Common causes of suction cavitation can include clogged filters, pipe blockage on the suction side, poor piping design, pump running too far right on the pump curve, or conditions not meeting NPSH (net positive suction head) requirements. [46]
Discharge Head, is the net head obtained at the outlet of a pump. For a centrifugal pump, the discharge pressure depends on the suction or inlet pressure as well, along with the fluid’s density. Thus, for the same flow rate of the fluid, we may have different values of discharge pressure depending on the inlet pressure.
During the pump operation, there is a drop of the liquid flow in the center of the rotor, causing the inflow of the liquid through the suction port. In the event of an excessive pressure decrease, in some parts of the rotor, the pressure can be lower than the saturation pressure corresponding to the temperature of the pumped liquid, causing the ...
The net force exerted by the air occurs as a pressure difference over the airfoil's surfaces. [82] Pressure in a fluid is always positive in an absolute sense, [83] so that pressure must always be thought of as pushing, and never as pulling. The pressure thus pushes inward on the airfoil everywhere on both the upper and lower surfaces.