Re: Under-tank heating coils.

On Saturday, 3 June 1995, Erik Olson wrote:

> I don't think you're going to see the hex cell formation when you have 
> SUBSTRATE in the tank.  Your assumption is only good for a water-only 
> situation.  The substrate tends to trap the water in place.

The presence of substrate won't necessarily alter the convection
patterns in ways that hinder the transport of nutrients to the roots.
Given the very low flow rates, my feeling is that anything is possible
and only experimentation will resolve the issue one way or the other.
People have made all sorts of statements regarding convection patterns
in the gravel without (as far as I can tell) making any measurements
or citing any non-biased references.

> BECAUSE the amount of heat required to get convection in a "uniform"
> heating situation (especially when noting my above observation) is far
> more than the heat required to start water churning between cables. 

The fact that you have sharper temperature gradients in the vicinity
of the cables doesn't imply that the total water transport is different
in the two cases.  Remember that the enery input to the system assumed to
be the same with either heating system.
Kevin Conlin   kcconlin at cae_ca   "We're Canadians.  We HAVE to be polite"