All right, I've got to step in now. I knew this was headed this way!
There are more than one heat source, as far as a pump is concerned, but I'll talk about the only two relevant ones:
1-Heat from the pumping action. Yes, that's right, all that sloshing of the water actually creates heat. It can be calculated, based on flow and pressure, and can be measured in Watts. Many people have run the test, where they circulate water in a closed loop, and it does heat up, very exactly with the power applied to moving the water.
2-Heat from the pump motor coil. Those electrical coils do actually heat up, and that's the heat that we perceive as localised to the pump. If you know #1, you can then compare your pump's actual electrical power draw, to figure out just how efficient it is. But I digress... This heat is usually very well isolated from the water, because plastic is a poor transmitter for heat. Let me make this even clearer: even if the plastic reaches a temp of say, 65 deg C, there is only a little bit of energy that can travel through plastic. This is not a significant source of heat (unless the pump housing is metallic).
Bad or cheap pumps will run hot. As a result, some end up having to be cooled, by running submerged. Usually, this is not a problem, if you are running a pond, or an aquarium.
A good pump will have a very precisely wound coil, minimizing energy losses.
I ended up with a Little Giant 2-MDQ-SC which, by any standard, is a power hog: 182 Watts, with max flow of 550gph, and a max head of 14+feet. Luckily, there is a magnetic drive that turns the impeller, so the motor is completely isolated from the water, which circulates through a "glass-filled polypropylene" housing.
|