mr.maroonsalty
New member
I believe 1 watt = a specific amount of heat; its its definition. Therefore, any say 100 watt submersible will put the same amount of heat in the system, regardless.
Watts=Heat Help me if I'm wrong
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der_wille_zur_macht
Team RC
Actually, assuming the heater is submerged fully in your water, ALL resistive electrical heaters will be 100% efficient - i.e. they will all turn one watt of electrical power completely into heat in the tank (just over 3 btu/h iirc). Things like element design and case design can minimally alter rate of thermal transfer, but not the overall amount of heat transferred.
Willistein
Active member
This is correct. Resistive heaters are basically 100% efficient. And a watt is a measure of how much heat output per unit of time (1 Joule per 1 second).
mr.maroonsalty
New member
A pump or power head is a "resistive heater?"
der_wille_zur_macht
Team RC
maroon, sorry, I think we were all assuming you meant a submersible heater. Aquarium heaters are just simple resistive heaters - there's a coil of wire inside with high resistance, such that it heats up when you apply voltage to it. This sort of heater is indeed 100% "efficient" in the sense that every watt dumped into it ends up as heat in the tank.
If you're talking about submersible pumps then, no, they're definitely NOT resistive heaters! Pumps are inductive loads. They produce some if their heat by resistance in the windings, some via frictional losses at bearing surfaces, some via frictional losses in the fluid being pumped, etc. Design of the pump and motor plays a large role in efficiency, and hence the amount of heat dumped into the surrounding environment. In other words, if you had two pumps that both consumed 100w, you'd have no way of knowing whether or not they both dumped the same amount of heat into the system, short of a full-on engineering analysis or just collecting data experimentally.
If you're talking about submersible pumps then, no, they're definitely NOT resistive heaters! Pumps are inductive loads. They produce some if their heat by resistance in the windings, some via frictional losses at bearing surfaces, some via frictional losses in the fluid being pumped, etc. Design of the pump and motor plays a large role in efficiency, and hence the amount of heat dumped into the surrounding environment. In other words, if you had two pumps that both consumed 100w, you'd have no way of knowing whether or not they both dumped the same amount of heat into the system, short of a full-on engineering analysis or just collecting data experimentally.
mr.maroonsalty
New member
Thanks, that's what I was wondering about. Is it true though that a x W pump produces a minimum of x Joule per sec? Sorry, its been 28 years since my last Physics course.
der_wille_zur_macht
Team RC
Well, the conversion from watts to Joules/s is always going to be constant. The variation from pump to pump will be where the energy ends up - does it end up heating the tank water, or moving the tank water?
In other words, you may have two pumps that consume 100w. One of them heats the water a lot and doesn't create much flow, while the other barely heats the water and creates more flow. Just knowing the wattage just tells you the energy used, it doesn't tell you where that energy ends up.
Willistein
Active member
Most pumps are probably putting most of the energy into moving the water and a small amount goes to heat.
mr.maroonsalty
New member
I'm a wee bit puzzled; You're saying heat is a product of efficiency, or lack of it, and a theoretical 100% motor produces 0º heat. I'sn't heat always a product of Work?
der_wille_zur_macht
Team RC
Yes, more or less. Power goes in to the pump. The result is some water movement, and some power getting wasted, mostly through heating of the surrounding environment (your tank water, in the case of a submersible pump). "Efficiency" is more or less defined as what percentage of the power gets converted into each of those two types of energy.
Yep, more or less. a 100% efficient motor would turn all of the electrical power it supplied into kinetic energy (i.e. it would convert electricity into motion with no loss).
The laws of thermodynamics say so, in the real world. But that doesn't stop us from "theorizing" about 100% efficient machines.
Willistein
Active member
No, the heat loss in a pump is from friction in bearings, and the resistance of the motor windings. This is usually anywhere from 10-30% of your total power. Your small pump is probably about 70% efficient.
There is a very small amount of heat created in the water itself due to viscous heating, but that's not even measurable unless you have an elaborate test setup.
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