A food processing plant wants to re-purpose a pump they used to pressurize the cold water...

A food processing plant wants to re-purpose a pump they used to pressurize the cold water system (35° F) to pressurize the hot water system (180° F). In every regard the cool and hot water systems are identical - only the temperature of the fluid is different. What is the correct impact on the net positive suction head available (NPSHa)?

Solutions

Expert Solution

To calculate the Net possitive suction head, we must consider the atmospheric pressure, status head, friction losses and also vapur pressure.
Usually water temperature is not an important factor while calculating NPSH. But when the pumping fluid is of higher temperature, vapur pressure increases exponentially and will have huge impact on NPSH.
Vapur pressure is the pressure required to boil the liquid at a given temperature.
As temperature rises so does the vapur pressure, but not at the same rate. As the temperature rises above 32°F, the vapor pressure rises slowly but as the temperature rises above 100°F, vapourpressure rises exponentially.
In the given case, this concept is crucial to understand because the temperature of liquid affects the vapir pressure which intern affects the NPSH.
At water temperature of 35°F, vapour pressure is 0.23 ft.
At water temperature of 180°F, vapour pressure is 17.125ft.
In this case the NPSH avaiabke with be less than half after the rise of temperature.

Ally Wells answered 2 months ago

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