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Re: [APD] Re: Bubbles? -- or - Some hard topics

Cool, two things:

1: I said a 3/4" nylon tube to a 1.5" PVC was a 2x growth in volume,
that's just false.  Just a 2x growth in diameter, and thus a 2xPi growth
in volume, being more then 6 times growth!  For a second I was going to
try to figure out the flow rate through the tubes and PVC, but it's been
too long and I'll definately miss something, but I would almost want to
assume 1/6'th water flow rate (velocity) through the reactor then the
nylon tube to achieve the same result of 500g/hr.  There's no way for me
to even begin guessing at how fast it really is, how much pressure is
exerted on a bubble of size X, and the resulting direction of said
bubble :-(  I'll just have to find out tonight when I get to fiddle some
more :-)

2: I agree, the tap _should_ be acting as a venturi, why it doesn't? 
Your guess is as good as mine.  It's a flat pipe.  I'll just move it and
stop asking questions.  Originally I used it on an earlier reactor
design in which the flow was desired.  As you can imagine, the reactor I
built had far too small flow rate and esentially did nothing :-(  The
good 'ol stickin it near the impeller did well, until I became
disatisfied with my CO2 ppm and usage.

Ok, three points ;-)  My tank continues to produce bubbles, interestingly
my money wort is producing some on the bottom side of the leaves thus I
suspect O2 production.  Some stem plants that had a trim recently are
still showing damag and shoving off small streams of bubbles, looks like
a stream in a beer/soda bottle!  Out of curiosity I think I'll do some
readings tonight to find out what made them so happy.

Four, you say?  Ok ;-)  I took a reading recently of GH in my tank.  To
my surprise and fear, it read 30!  I thought it couldn't be right and
redid the test, yet again it was 30!  'Uh oh' I thought, as I quickly
went to the tap to test source water...2 degrees!  WOW, what in the H*LL
could be causing my GH to rise so sharply?  KH, btw, was 2 and pH 7.  I
have laterite substrate, 'normal' freshwater aquatic plants, 2-3mm
gravel and the wet/dry setup I showed earlier in the thread.  I dose
text book pmdd 2-3x/wk and don't use any sort of buffers...think I could
*knock knock* on my water soon!

-Dave T.

On 2/4/2004, "S. Hieber" <shieber at yahoo_com> wrote:

>Stab # 3 at the first question:
>If there are no other devices inbetween the irrigatin tap
>and the reactor, the pressure should be the same at the
>current location and at the reactor.
>If the tap extends into a length of the water tube/pipe
>coming off the pump utput, and is *not* angled (even
>slightly) so that it is pointed towards the water flow,
>then it should act more like a venturi and tend to suck gas
>in from the CO2 tube rather than push water up the CO2
>tube. If you can't get a venturi effect, close off the tap
>and move the CO2 connection to the reactor where the
>increase in the water line diameter should reduce the water
>line pressure relative to the CO2 line pressure.
>If you increase the CO2 out put pressure, that should
>prevent water going up the CO2 line. The water pressure is
>likely not very high; few aquarium pumps develop more than
>a few psi unless you have the output constricted (for
>example with a ball valve) and the CO2 is between the
>constriction and the pump. Even constricted, most aquarium
>pumps develop only a few psi.
>Question # 2:
>The bubbles *will* trap and tend to collect at the top but
>only up to point. The water will flow through the CO2 at
>the top of the reactor and down and out the reactor. If the
>water flow is too strong, then it might carry out small CO2
>bubbles with it -- in which case put the reactor on a
>Teed-off line from the main line so that it gets a lower
>flow or use a larger diameter reactor.
>If the water flow is too low or the CO2 rate too high, the
>CO2 will collect in the reactor faster than it can be
>absorbed, eventually filling the reactor with gas and
>leaking out the bottom opening of the reactor, which is a
>waste.  In that case, increase the water flow or decrease
>the CO2 output. If decreasing the CO2 doesn't yield a high
>enough CO2 level in the aquarium water or a higher flow
>blows out CO2 bubbles, then use a larger diameter reactor
>to support the higher water flow.
>You might need to go back and forth a bit to get a useful
>balance, but the set shouldn't be very sensitive to the
>amount of water flow and you'll be able to control CO2
>levels by adjusting the CO2 flow rate. If the set up is
>very sensitive to the water flow rate, and you have to keep
>fidling with the CO2 rate and water flow rate to get a
>stable reactor and CO2 levels, then use a larger diameter
>NOte that these suggestions are "IF/thens".  I think you
>can probably get where you want to go with the reactor you
>have, inverted so water enters the top, with a few
>adjustments to flow rates.
>2 examples on hand:
>I have a 3" x about 12" reactor on a 1/2" water line
>flowing about 200 gph. That can maintain 15-30 ppm in a 150
>g aquarium.
>I have a 2" reactor, about 12" on 3/8" water line flowing
>about 50 gph -- that works on a 30g. It might even work on
>the 150g, with higher flow rates but I never tried it.
>Scott H.
>--- David Terrell <Dave at terrellclan_com> wrote:
>> Actually, let me rephrase to clear this up, this being
>> the third time
>> someone misunderstood my problem I guess it was just
>> clearer in my head.
>> The airline from my CO2 tank comes out of the needle
>> valve, through a
>> check valve then down the line to the intake for the
>> reactor (but not
>> _at_ the reactor).  Now, I didn't drill a hole in the
>> reactor
>> specifically for the airline.  I had an irrigation tap in
>> the output
>> line from the pump (nylon return tube).  I put the
>> airline on that
>> tap...so when the pump is on water is forced up the
>> airline.  There is a
>> check valve after the needle valve (you can see it on the
>> left in the
>> reactor picture) so I wasn't nervous about it returning
>> to the tank and
>> causing problems.  However, it seems I won't get a
>> regular flow when the
>> airline has to build pressure to go back to the pump
>> return.
>> The question is/was:  How can I reduce the backpressure
>> of water on the
>> airline from the pump return to the CO2 tank?
>> My next question is, if I turn over the flow through the
>> reactor (so it's
>> closer to the proper design ;-) are the bubbles really
>> going to flow
>> upwards/trap?  I have a 750g/hr. pump, rated at this head
>> it flows
>> ~500g/hr.  I don't know fluid dynamics so this is a big
>> problem!  The
>> pump return is a 3/4" nylon tub that goes to some
>> adapting fittings of
>> PVC pipe, which eventually reaches 1-1/2" PVC, so a 2x
>> growth in volume.
>>  Will the flow be slow enough to allow the bubbles to
>> rise/trap in the
>> ractor chamber?
>S. Hieber
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