in a turbine The calculation of NPSH in a reaction turbine is different to the calculation of NPSH in a pump, because the point at which cavitation will first occur is in a different place. In a reaction turbine, cavitation will first occur at the outlet of the impeller, at the entrance of the draft tube. Denoting the entrance of the draft tube by e, the NPSHA is defined in the same way as for pumps: Applying Bernoulli's principle from the draft tube entrance e to the lower free surface 0, under the assumption that the kinetic energy at 0 is negligible, that the fluid is inviscid, and that the fluid density is constant: Using the above application of Bernoulli to eliminate the velocity term and local pressure terms in the definition of NPSHA: Note that, in turbines minor friction losses () alleviate the effect of cavitation - opposite to what happens in pumps. NPSH design considerations Vapour pressure is strongly dependent on temperature, and thus so will both NPSHR and NPSHA. Centrifugal pumps are particularly vulnerable especially when pumping heated solution near the vapor pressure, whereas positive displacement pumps are less affected by cavitation, as they are better able to pump two-phase flow (the mixture of gas and liquid), however, the resultant flow rate of the pump will be diminished because of the gas volumetrically displacing a disproportion of liquid. Careful design is required to pump high temperature liquids with a centrifugal pump when the liquid is near its boiling point. The violent collapse of the cavitation bubble creates a shock wave that can carve material from internal pump components (usually the leading edge of the impeller) and creates noise often described as "pumping gravel". Additionally, the inevitable increase in vibration can cause other mechanical faults in the pump and associated equipment. Relationship to other cavitation parameters The NPSH appears in a number of other cavitation-relevant parameters. The suction head coefficient is a dimensionless measure of NPSH: Where is the angular velocity (in rad/s) of the turbo-machine shaft, and is the turbo-machine impeller diameter. Thoma's cavitation number is defined as: Where is the head across the turbo-machine. Some general NPSH examples (based on sea level). Example Number 1: A tank with a liquid level 2 metres above the pump intake, plus the atmospheric pressure of 10 metres, minus a 2 metre friction loss into the pump (say for pipe