NPSH(required) decreased with the increasing of temperature... what is the reason??

Question

i have to do my report for pump characteristics but i still blur about the quetion above.... help me please?
From the theoretical, NPSHr is increased with increasing temperature...

Answer 1

net positive suction head is a tricky subject, but this question is actually quite simple.

the whole idea of NPSHr is that it is larger than the vapor pressure of the fluid being pumped. when the temperature goes up, the vapor pressure goes up.

you actually state two contradicting things in your question, one says NPSHr decreases with increasing temperature, and the other says the opposite.

if the temperature is increased, the vapor pressure goes up, and the NPSHr is increased. thats the story

Answer 2

NPSH is an acronym for Net Positive Suction Head. It shows the difference, in any crosssection of a generic hydraulic circuit, between the pressure and the liquid vapor pressure in that section.

NPSH is an important parameter, to be taken into account when designing a circuit : whenever the liquid pressure drops below the vapor pressure, liquid boiling occurs, and the final effect will be cavitation : vapor bubbles may reduce or stop liquid flow.

Considering the circuit shown in the picture, in 1-1 NPSH is :

NPSH = P0 + H − Y − Vt

(to be solved with coherent measuring units), where Y is the friction loss between 0-0 and 1-1, and Vt the liquid vapour pressure at the actual temperature in section 1-1.

In pump operation, two aspects of this parameter are called respectively NPSH (a) Net Positive Suction Head (available) and NPSH (r) Net Positive Suction Head (required), where NPSH(a) is computed at pump inlet port, and NPSH(r) is the NPSH limit the pump can withstand without cavitating.

Answer 3

To prevent cavitation, the pressure in all sections of a pump must be above the vapor pressure of the liquid being pumped. Vapor pressure increases with temperature.

Answer 4

You can draw cold water up a thick clear plastic tube (etc.) (using a vacuum pump?) only about 34 feet (similar to the 30 inches of mercury in a barometer). If you heat the water in the tube the level will decrease (with increased water vapor pressure) until the level will be zero at the boiling point of water.

Answer 5

You don't say what the fluid your pumping is, so I assume the reason for the decrease is the fluid has a lower viscosity at the higher temperatures.