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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
http://cichlidtrader.listbot.com