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MER 439 - Design of Thermal Fluid Systems Cavitation & NPSH Professor Anderson SpringTerm 2012

MER 439 - Design of Thermal Fluid Systems Cavitation & NPSH Professor Anderson SpringTerm 2012. Cavitation. Low pressures are commonly encounter-ed on the suction side of a pump

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MER 439 - Design of Thermal Fluid Systems Cavitation & NPSH Professor Anderson SpringTerm 2012

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  1. MER 439 - Design of Thermal Fluid Systems Cavitation & NPSH Professor Anderson SpringTerm 2012

  2. Cavitation • Low pressures are commonly encounter-ed on the suction side of a pump • Cavitationoccurs when a liquid pressure at a given location is reduced to the vapor pressure of the liquid. Vapor bubbles form and the liquid starts to boil. • Causes loss in efficiency and structural damage to the pump.

  3. Cavitation - NPSH • To characterize the potential for cavitation the difference in the total head on the suction side near the pump impeller inlet and the liquid vapor pressure head is used:

  4. Net Positive Suction Head (NPSH) • The required NPSHR is the value that must be maintained to avoid cavitation. • The available NPSHA represents the head loss that actually occurs for the system.

  5. Example 1 Q = 0.5 ft3/sec NPSHR = 15 ft T = 80 oF P = 14.7 psi kL = 20, D = 4 in Determine the maximum z1 for no cavitation

  6. Example 2 A pump (NPSHR = 35’) is to pump 24,000 gal/min of water at 1170 RPM from a reservoir whose surface is at 14.7 psi. If the total head loss from the reservoir to the pump inlet is 6 ft, where should the pump inlet be placed for water at (a) 60 F, Pv = 0.26 lbf/ft2, SG = 1 and (b) 200 F, Pv = 0.11.52 lbf/ft2, SG = 0.9635?

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