I Hooked Up A 2hp Centrifugal Pump To A Closed Loop Of Piping That Held About 5 Gallons Through 2 Inch Piping.
Posted by admin on January 28, 2010 under Fluid Mechanics | 
2 Comments to Read
Why did it heat up?
Estimate how many degrees F per hour the water heated up and explain your reasoning.
tinkerta said,
It heats up because the friction of the flow results in heat.
Not all of the energy put into the pump motor will become heat in the water. Noise would be an example of a non heat generating energy.
Also some heat will be absorbed or radiated away from the piping.
The 2hp pump won’t have 2hp of load.
If you measure the current going to the motor and know the efficiency at the point on the pump curve for this operation- then you can start estimating the heat rise in the circuit.
Maybe your problem just expects you to estimate this load.
. said,
Conservation of energy, you put power into the pump, the energy has to go somewhere, so the water (also the pump and the pipe, but I’m going to ignore them) has to get warmer.
So, converting to SI units, you have 18.9L, or 18.9kg of water, 2hp is 1490W, of 1490 joules per second. the specific heat of water is about 4184 J/kg °K
So to raise the temperature of 18.9kg 1 deg will take about 79kJ, your 1.49kJ/s pump will take 53seconds, to raise the temp. 1°
1hr, or 3600s / 53s = about 68°C rise, or about 122°F rise
You know, this question sounds a lot like the one I got my very first “best answer” for, whatever happened to Floodtl (sp?) ?
[EDIT] BTW, you have “about” 1 significant figure in your data (“about 5 gallons”) so just how close do you want?
[2nd EDIT] I just noticed you didn’t say what is in the pipe, but I contend water is a reasonable guess.
Yes, not all the energy will end up in the fluid, but that lost to noise is going to be a small fraction, and, I sort of mentioned was ignoring loses; “(also the pump and the pipe [will be heated], but I’m going to ignore them).
While it is true that most 2hp pumps will not be heavily loaded with a loop of about 30ft of 2″ pipe (assuming sch. 40 steel ) but since we don’t have the pump curve, and don’t how the “loop” was formed (elbows can present significant resistance), I took the “2hp” at face value. One could make a very high flow, low pressure pump that would be heavily loaded under these conditions, and for all I know this is a nominal 20hp pump that is being subjected to a 2hp load, with this loop of pipe.
With a thermometer and an hours time one could get a better answer, but with the information given, I think my estimate is fairly good.
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