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Re: 150 watt substrate heater cables

> Date: Tue, 21 Aug 2001 05:41:18 -0700 (PDT)
> From: "S. Hieber" <shieber at yahoo_com>
> But does what you are saying mean that the Dennerle cables and similar
> relatively lower wattage setups:
> 1) fail to optimize convection effects because they, intentionally, run
> constantly?

That is my opinion, yes. If they are on continuously, they need to be a low
wattage to avoid overheating the water. IMHO, that will not create a high
enough heat density to create convection currents. You will get some benefit
because a warmer substrate tends to speed up biological processes. But, to
me, the main benefit of substrate heating is to create convection currents
that move nutrients from the water column to the substrate where they can be
sequestered by negative binding sites and held until the plant roots adsorb

> 2) are not achieving the heat density required to go from conductive
> heating (no currents) to convection heating (micro currents)?

Yes, that is my opinion. I have had setups with low heat density (100 watts
in a 100 gallon tank) and I had poor results. I can only conjecture that
conductive vs convective heating is the difference. I have no proof other
than my observations.

I've thought about doing some experiments. I even went so far as to consult
some mechanical engineers at work who had some background in heat transfer.
But, alas, useful experiments sounded like more work than I wanted to do.

George Booth in Ft. Collins, CO (booth at frii dot com)
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