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Ewan · 10-16-2003, 07:21 AM

Megalomando:

Unfortunately your ideas are completely wrong. If an engine is rated at a certain effect (100 hp for exampple) then it is assumed that this is the mechanical effect of the engine. The engine will infact use a lot more energy than this (a good engine is about 40% efficient, the remaining 60% being heat that goes out the exhaust).

A pump is however generally rated at it's maximum electrical energy draw, in this case 46W. From the pump curves you can often get the pumps efficiency at the operating flowrate, say 60%. This information isn't generaly provided for small pumps because no one is realy concerned about losing a few watts here and there. It's often provided for industrial pumps where efficiency is important.
The pumps efficency is then calculated by how much power the pump draws compared to how much kinetic energy is added to the pumped fluid. The inefficency is heat, either from impeller friction, or motor inefficency. Electric motors are pretty efficient though (say 90%) so the remaining inefficiency is friction in bearings and impeller friction against the pumped fluid.
Both of these heats will be added to the water. So basicly we have given up 10% of the pumps power to heating the air from the motor, 30% to heating the water from other inefficiancies and the remaining 60% becomes kinetic energy given to the water.

However what does the kinetic energy do?
It can do 3 things:
1) accelerate the water
2) add potential energy (height) to the water
3) create heat

For point 1, we can obviously tell that there is no acceleration going on since the water in the cooling loop flows at the same flow rate all the time, so we're not doing any accerlating.
For point 2, we can see that the water isn't being pumped to a higher point, because it's in a closed loop and comes back again. So we aren't adding potenital energy.
That leaves point 3. All kinetic energy is converted to heat via pipe friction.

So infact the only part of the pumps power that doesn't heat the water is the small faction due to the motors inefficiency.
The pumps sole purpose is to overcome the pipe friction. Its what the restriction is that everyone is talking about. All friction is converted to heat and it pretty much all absorbed by the water.

So your 46W pump will heat the water with about 43 watts.

10-16-2003, 07:21 AM	#10
Ewan Cooling Neophyte Join Date: Jun 2003 Location: Sweden Posts: 30	Megalomando: Unfortunately your ideas are completely wrong. If an engine is rated at a certain effect (100 hp for exampple) then it is assumed that this is the mechanical effect of the engine. The engine will infact use a lot more energy than this (a good engine is about 40% efficient, the remaining 60% being heat that goes out the exhaust). A pump is however generally rated at it's maximum electrical energy draw, in this case 46W. From the pump curves you can often get the pumps efficiency at the operating flowrate, say 60%. This information isn't generaly provided for small pumps because no one is realy concerned about losing a few watts here and there. It's often provided for industrial pumps where efficiency is important. The pumps efficency is then calculated by how much power the pump draws compared to how much kinetic energy is added to the pumped fluid. The inefficency is heat, either from impeller friction, or motor inefficency. Electric motors are pretty efficient though (say 90%) so the remaining inefficiency is friction in bearings and impeller friction against the pumped fluid. Both of these heats will be added to the water. So basicly we have given up 10% of the pumps power to heating the air from the motor, 30% to heating the water from other inefficiancies and the remaining 60% becomes kinetic energy given to the water. However what does the kinetic energy do? It can do 3 things: 1) accelerate the water 2) add potential energy (height) to the water 3) create heat For point 1, we can obviously tell that there is no acceleration going on since the water in the cooling loop flows at the same flow rate all the time, so we're not doing any accerlating. For point 2, we can see that the water isn't being pumped to a higher point, because it's in a closed loop and comes back again. So we aren't adding potenital energy. That leaves point 3. All kinetic energy is converted to heat via pipe friction. So infact the only part of the pumps power that doesn't heat the water is the small faction due to the motors inefficiency. The pumps sole purpose is to overcome the pipe friction. Its what the restriction is that everyone is talking about. All friction is converted to heat and it pretty much all absorbed by the water. So your 46W pump will heat the water with about 43 watts.