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Re: Cheap Substrate Heating (G. Booth)

George wrote:

>You would probably want this to be a sealed system. Pulling aqaurium water
>in would bring detritus and clog the tube.  And dumping the water back into
>the tank might heat the tank too much IF all the heat was not transferred
>to the gravel.  I suspect the silicon tubing is a pretty good insulator. 

I do not quite agree with George saying silicon tubing
would be a pretty good insulator, it is rather the opposite.
Assuming Silicon tubing contains mostly Silicon, it actually
is a very good thermal conductor. Here are some thermal
conductivities to compare (in units of W/cm*C):
Silicon:           1.57
Steel:             0.97
Stainless Steel:   0.329
Iron:              0.803
If one wants to get a higher thermal conductivity than
Silicon, there are only a few options, e.g.:
Aluminum           2.36
Diamond           20.0    (WOW!)
Meaning one could use Carbon in order to get a very very high
In order to achieve a relatively even heat distribution in
the gravel, one could split the tubing coming from the ballast
into 4 or 5 tubes going to different places in the substrate
and then merging them back together, guiding the cooled
water back to the "ballast heater".