Backyard Aquaponics
A place to discuss aquaponics

Frank
Just talking about nighttime and solar chimneys.
The earth 'radiates' heat in the Infra red bands, space is dammned cold. This radiation is effected by humidity and cloud cover, why deserts freeze at night. Good absorbers of IR are also good emitters of IR. If your chimney has a good view of the sky, and this I think would be in the design, it will radiate heat to space. If the objects around are radiating less IR than the chimney is emitting the chimney will loose more heat than its surroundings. (dewpoint and wind can also effect this).

Nice try again Frank, but injecting air on the suction side of the pump has a magnitude of inefficiency for pumping. You are now promoting inefficiencies!!! WTF?


And yet your happy enough to continually tell people on this forum that you now better and that they have it all wrong...

Mylesau, have you even tried to google on protein skimmers or needle wheel impellers???

I am not promoting inefficiencies, not even promoting pressurized Venturi's
as I think them not to do what is promised

but if someone insists on using them, I am trying to be of help and suggesting methods to make them as efficient as possible
that is the opposite to promoting inefficiencies

please play the ball, not the player

frank

A long but interesting link ftp://ftp.fao.org/FI/CDrom/FAO_Training ... e02.htm#9a

Have you? Look at the design of the impeller and tell me that they will efficiently pump water!


Go back and read, actually read, what I quoted and what I replied previously Frank - this is exactly what you have done in relation to placing a venturi on the suction side of a pump.


You are the one playing games Frank, accept that what others have input to this discussion has shown your earlier statements to be less then correct...

with my huge knowledge of pumps, wouldn't this produce cavitation within the pump and eventual pitting and ruination of the impeller? or the pump will just stop working?

WTF - - - what is a pressurised Venturi ? ? Is that not actuated by a pump either air or water? ?
+1 - if the impeller (of a pump) gets air/bubbles it makes it very inefficient and it will stop pumping.
It also depends where the pump is positioned eg. above the water level or below the water level.
(Suction or pressure)
So you could do away with the pump as such and just use your 'pressurised venturi' ? ?

Yay we're all on the same page

indeed, Jaymie, cavitation is very bad for a pump
thanks for bringing that up
you have coaxed me into fleecing (is that an understandable English word? ) my rusty brain to better understand the phenomenon
cavitation is the phenomenon where a vacuum is created by suction to such an extent where the medium (in our case water) starts to boil (this sounds incredible, but water can be made to boil at very low temperatures by applying vacuum to it just like water can be brought to high temperatures without boiling by applying pressure, like in a pressure cooker) and forms steam bubbles (not air bubbles, but vacuum cavities filled with steam)
these "bubbles" are not the problem on the suction side
but when they come to the pumped side, they implode by the abrupt pressure increase and are transformed back from steam into water
an implosion is just as destructive as an explosion
it can rip away particles of the impeller (the pitting you mention)

so a pump should always have ample access to the medium it is supposed to pump to avoid cavitation
a Venturi means a restriction
so is not a good thing to put in the inflow of a pump
... unless...
unless free access is given to another medium (in our case air) to fill the cavities
if enough air (in our case, but it can be i.e.e a chemical too) fills the cavities, no cavitation will occur
as when an air bubble moves from the suction side to the pumped side, pressure will increase inside the bubble and the bubble size will diminish, but the bubble will not implode

this is one of the reasons why Venturi's, though they seem and are simple enough, are horribly difficult to design well:
wherever you install them, they should have free access to the second medium for best performance
restricting this access will diminish efficiency
energy will be transformed in heat and sound (slurping)
if it is on the suction side of a pump, restricting access of the second medium will increase risks of cavitation

so the only good way to design a Venturi is to determine the restriction and leave access to the second medium untouched
that is quite a challenge

frank

frank

a submerged centrifugal pump needs water for only two reasons:
for cooling the motor and for lubricating the moving parts
any centrifugal pump, submerged or not, will last as long as you wish (normal wear excluded)
if you lubricate it and cool the motor
you can run a centrifugal pump "dry" if you regularly add a few drops of oil
it will suck up whatever medium that it can dispose of
if there is water it will pump water
if there is air it will pump air
very inefficiently, but still...
as long as you keep the moving parts lubricated and the motor cooled no harm will come to the pump (normal wear excluded)
as a centrifugal water pump is not designed to pump (only) air it will be very inefficient at this
as a centrifugal water pump is designed to pump water it will be more or less efficient at this
if it is pumping a mixture of water and air the efficiency will depend on the mixture

frank

Afraid not C1 , Frank will never be on the same page as anyone...

Just reading the Ebara Optima manual.... Page 3, section 7.1d... verbatim...



I'd have to suggest that the manufacturer inserted that clause for specific reason...

that doesn't depend on me, Mylesau
it depends on the size of the paper and you all allowing me to have a small corner of it.
please be generous

frank

Re: " Pressurised Venturi " Why did I asked this question ?

A VENTURI is a VENTURI - - - is a VENTURI !

IMHO -- a " PRESSURISED VENTURI " is NOT a VENTURI - - but an INJECTOR, injecting air into the inflow/intake of a pump.

an injector uses the Venturi principle, Heka:
http://en.wikipedia.org/wiki/Injector

the Venturi principle needs pressure to allow it to work
this pressure can come from a pump
or from gravity, which in that case is your pump

I have admitted my nomenclature to be questionable
do you have better suggestions?

frank