Conservation of flow in a pump

1. Jul 19, 2012

natedogg1002

Hello.

I am writing a relatively simple simulation code for looking at transient temperatures in a surge tank, which reflects a real-world system. The tank is hooked up to a recirculation loop with a pump and a heat exchanger. The pump has an average flowrate of 500 GPM. Despite the temperature therefore density of the water it is pumping, the pump moves "500 GPM".

So my question is: When a centrifugal pump has a set flowrate of 500 GPM, is that equivalent to the conservation of mass or conservation of volume?

No amount of Googling seems to have brought me any conclusions, though I have come to understand that positive displacement pumps are different than centrifugal pumps when it comes to this particular topic.

2. Jul 19, 2012

For water (or any other "incompressible" fluid), the two are the same since density doesn't vary.

In a gas, this would refer only to volume flow rate.

3. Jul 20, 2012

natedogg1002

Ok, but what if the density does change over time? For example, my tank is hooked up to a recirculating loop with a heat exchanger. As time goes by, the water temperature in the tank rises about 100°F -- corresponding to a change in density of ~2 lb/ft³.

Is the pump actually moving 500 GPM, or the mass equivalent over time?

4. Jul 20, 2012

Travis_King

A gallon is a unit of volume, not mass.

5. Jul 24, 2012