Question on transfer of power from a pump to water.

Question on transfer of power from a pump to water.
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Posted by: cduran ^®

08/03/2005, 20:51:58

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There is a debate going on in another forum that is dedicated to marine aquarium keepers. The debate is on weather or not a pump rated at X watts circulating water in the aquarium will generate the same amount of heat as a water heater of X watts. In other words, will a pump of X watts raise the temperature of the water by the same amount of degrees in the same amount of time as a water heater of the same wattage.

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Re: Question on transfer of power from a pump to water.

Re: Question on transfer of power from a pump to water. -- cduran Post Reply Top of thread Forum

Posted by: kelly_bramble ^®

08/03/2005, 21:53:38

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Well, this is almost a trick question. Watts is a unit of power and may be converted into BTU's (British Thermal Units) using the following equvalent 1kW-hr = 3.413 X 10^3 BTU. Now alot depends on the efficiency of the pump. Assuming that all of the energy is disspated into thermal energy within the water (mechanical and electrical), the pump construction will effect the amount of heat dissipation into the circulating water, not to mention how the pump is submersed in the water (completely submersed, or draws the water out and circulated the water back).

If all pumps are roughly identical in mechanical efficiency, however are rated at different power consumptions, and are submersed within the water very simular. Then the pump with the highest electrical power consumption should heat the water more.

The same pretty much holds true for a remote located pump, as the water is the most thermally conductive fluid in contact with the pump (some thermal dissipation will occur to the air). The highest power rated pump should heat the water more.

A test case could be done as follows: Identical fish bowls (not large). Insulate all identically, allow to set within the same room long enough to stabalize in temperature with the pumps installed. Measure temperature in all then start pumps and allow to run until the temperatures in all fish tanks stabilize, which ever tank is the hottest, that your answer.

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Re: Question on transfer of power from a pump to water.

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Posted by: devitg ^®

08/03/2005, 21:38:01

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It all depend , if the punmp is submerged in the water , all power will be disipated as heat , one part as lost from the motor coil , and other for the equivalent heat from mechanical work.
The fact is taht the rated power is stated for a flow and head pressure, if you do not meet both the power disipated will be less than the rated.
Remember that the equvalent heat from mechanical work was obtained from the calorimeter where a blade was dirven inside water.

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Re: Question on transfer of power from a pump to water.
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