well, technically...

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Posted by Mokele on March 05, 2003 at 13:55:33:

In Reply to: Mr. Carmichael(or anyone with a large croc cage) posted by psusocr on March 05, 2003 at 12:52:45:

:since i know you have some rather large cages, i am seeking some advice and quick. My tank is going to hold about 200 gallons of water for my dwarf caimen. The problem is im having ALOT of trouble heating this and i cant put my croc in until the temps are right. Right now hes living in my bathtub!! which is very easy to heat, but anyway what do you think its going to take to heat this much water? maybe a 300 watt submersable and another 100 watt?

200gal = 757.08 L = 757082.4 cm3
1 gram of water = 1 cm3 at Standard temperature and pressure
1 cal = ammunt of energy to raise one 1 gram of water 1 degree C
1 cal = 4.1868 Joules

therfore you need 3169752.4 J to raise the water temperature 1 degree C. neglecting heat loss to the outside environment, It would take 3 hours for a 300 W heater to raise the water temperature 1 degree C, meaning raising it from 70F-80F (21-26C) will take 15 hours.

note, this is neglecting losses. according to Newton's law of cooling, you will lose heat at a rate proportional to the difference between the water temp and the surrounding environment. meaning if you have an 80F tank of water in a 70F room, and an 80F tank in a 60F room, the second one will lose heat twice as fast. also, surface area plays a large part: if there's a lot of surface area of the volume, your heat loss will be higher.

what does this mean? it means if your ambient temperature (air temp in this case) is too low, a 300W heater will never work. personally, i just heat my entire reptile room to a certain background temp, and let the cage heaters create a hotspot from there.

think of it this way: you know how big objects (trucks, boulders, linebackers) have a lot of inertia, making them hard to get moving, and hard to stop once they are moving? well, large amounts of stuff like water can have a lot of thermal inertia, meaning it's damn hard to heat it up, and damn hard to cool it down.

Mokele, your resident thermodynamicist

Follow Ups:

Just like an engineer (or engineering student)....... Bill Moss 03/06/03 (1)
- guilty as charged. ::grin:: n/p Mokele 03/07/03 (0)
Re: well, technically... psusocr 03/05/03 (1)
- Re: well, technically... Rob Carmichael 03/05/03 (0)