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Re: Substrate flow rates (was: Heating coils revisited)

Roger Miller writes:

>Conditions will vary, but 1 cm head difference seems like way more than
>  enough to push water down the lift tubes at 5 cm/min.

Back when I was experimenting with my air-driven RUGF, I placed a drop of 
something colored, probably Methylene blue, into the intake of one of the 
tube assemblies.  I timed it going down the last tube (see diagram on the 
krib at <A HREF="http://www.thekrib.com/Filters/rugf-dixon.html">www.thekrib.c
om/filters/rugf-dixon.html</A> ).  I calculated the cross-section of the 
tube, and by extrapolation was able to set a flow rate of 35 gallons per hour 
in each tube using a 1/2 inch head.  That head included the air that was 
bubbling up the lift tube, so it wasn't as heavy as pure water (if there is 
such a thing).  You are welcome to turn that into metric and then spread it 
out over the area of the plate, or simply make your own observations with  
drop of whatever you want to use as a marker.  Okay, I didn't use flowmeters, 
digital lazer-triggered timers, or anything else.  OTOH, I wasn't trying to 
land a probe on the martian north pole, but I got numbers good enough for me 
to be comfortable feeding my plants through the "blow-hole".

One advantage this has over cables is that I can actually "see" the water 
running through the tubes.  I can then confirm by intuition that the water 
going down must be displacing water in the plate area, which in turn can only 
be escaping through the substrate.  All of the substrate?  Heck, I don't 
know.  So what?  Has anyone actually been able to measure the thermals 
flowing through a cable-heated substrate?  Maybe Dupla has, but I haven't 
seen or heard anything even closely resembling actual figures.  I'm not 
saying it isn't happening, I am just saying "Show me".

Bob Dixon
Cichlid Trader List Administrator