Re: Aquatic Plants Digest V1 #102

> From: Kevin Conlin <kcconlin at zola_cae.ca>

> > One issue was that heat coils IN the substrate would provide better
> > granularity for convection currents for better over-all circulation.
> > OK, I buy that.
> I have a bit of trouble with this assumption.  If I were to uniformly heat a
> container of water from below, I would expect to see the formation of
> roughly hexagonal convection cells, each with warm water rising in a
> narrow column at the center and cool water subsiding around it.  Buried
> wires presumably give rise to linear cells.  For a given amount of heat
> applied to the system I would expect the same rate of water transport
> through the substrate.  

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.

> Why would either system have any advantage over the
> other?  How can a plant distinguish between linear and hexagonal convection
> cells?

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. 
You'll probably start running into side effects such as... oh... having to
buy a chiller to remove that excess heat that you're adding with the pad. 
That has got to be more expensive than just buying a cable. 

    - Erik

Erik D. Olson                		"I'd rather be right here."
olson at phys_washington.edu			- A. Belew