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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.
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]
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.
Cavitation—the net positive suction head of the system is too low for the selected pump; Wear of the impeller—can be worsened by suspended solids or cavitation; Corrosion inside the pump caused by the fluid properties; Overheating due to low flow; Leakage along rotating shaft.
The equation for the NPSH should ADD the delta Z (not a minus) Furthermore, nothing is said about the velocity head in the flow. Total energy grade line (EGL) is the hydraulic grade line (HGL) plus the velocity head (V*V/2g), therefore, the "pressure" or the HGL that the fluid (and potential to cavitate) sees is the EGL - V*V/2g ..... or the Po + delta Z - Losses - V*V/2g
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 ...
Another example of point-of-care work involving a capillary pressure-related design component is the separation of plasma from whole blood by filtration through porous membrane. Efficient and high-volume separation of plasma from whole blood is often necessary for infectious disease diagnostics, like the HIV viral load test.