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'[EE]: Fog generating system - ideas wanted'
2000\11\24@041326 by Russell McMahon

picon face
I want a small one off system that will produce a fine water fog (for
specialist plant propagation).
.
A local mall has a system which makes  a fog of droplets so fine that the
vapor floats in the air somewhat akin to "heavy smoke".
ie the general trend is downwards  but it wafts in air currents and is not
discernibly wet when you contact it.

My first guess is that this fog is generated ultrasonically.

Has anyone any experience of similar systems and are any details available.
Another (non electronic) approach would be very high pressure atomisation
through a standard nozzle arrangement.
My brief experimentation with air pressure and water does not produce a
fine-ness approaching that of the fog system.



TIA

       Russell McMahon

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2000\11\24@042156 by Spehro Pefhany

picon face
At 10:16 PM 11/24/00 +1300, you wrote:
>I want a small one off system that will produce a fine water fog (for
>specialist plant propagation).
>.
>A local mall has a system which makes  a fog of droplets so fine that the
>vapor floats in the air somewhat akin to "heavy smoke".
>ie the general trend is downwards  but it wafts in air currents and is not
>discernibly wet when you contact it.
>
>My first guess is that this fog is generated ultrasonically.
>
>Has anyone any experience of similar systems and are any details available.
>Another (non electronic) approach would be very high pressure atomisation
>through a standard nozzle arrangement.
>My brief experimentation with air pressure and water does not produce a
>fine-ness approaching that of the fog system.

Can you just canibalize a humidifier? That would surely be cheaper and
faster than trying to make a 1-2MHz high voltage drive circuit and sourcing
the piezo transducer assembly.  The droplet size is directly related to the
drive frequency.

There are industrial units available that do this, however the cost is
much higher than the domestic humidifiers, due to the heavy duty
stainless steel construction and so on.

Best regards,

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2000\11\24@042821 by staff

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face
Spehro Pefhany wrote:
{Quote hidden}

What volume of water do you need to vaporise and how big is your
target area? Is it going to condensate as soon at touches the sides
of the greenhouse enclosure and dribble down the sides?

Maybe you could buy/borrow one of those cheap ultrasonic cleaners
that jewellers use, and test what water amount it will vaporise
over the piezo?
-Roman

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2000\11\24@043443 by Spehro Pefhany

picon face
At 08:28 PM 11/24/00 +1100, Roman Black wrote:
>
>Maybe you could buy/borrow one of those cheap ultrasonic cleaners
>that jewellers use, and test what water amount it will vaporise
>over the piezo?
>-Roman

Unfortunatly, the frequency of those units is roughly  two orders of
magnitude  too low.

Best regards,

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2000\11\24@050642 by Morgan Olsson

picon face
Water+air nozzles driven with pressurized air are effective, small and relatively cheap.

Some works like ultrasonic whistle and generates very small water drops.

Cheaper alternatives like cyklon where air enters tangentially in a small cavity where air enters axially one end, and it all exits the other end.

/Morgan

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2000\11\24@063104 by Alan B. Pearce

face picon face
I would have thought it would use some sort of venturi system, with a blast of
air blowing across the top of a nozzle like a paint spray gun. The nozzle may
also be vibrated ultrasonically to help get droplet breakup to achieve the very
small drop size. With a suitably enlarging opening on the exit after the nozzle
(like a megaphone) the air speed would drop enough that it would leave the
droplets floating in the breeze.

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2000\11\24@095904 by James Korman

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face
Could you hack one the less expensive air brushes
that are on the market. Testors makes one that is
mostly plastic for about $20 US

  http://www.testors.com/Product.asp?product%5fid=A2203

Jim Korman

"Alan B. Pearce" wrote:
{Quote hidden}

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2000\11\24@151432 by Dwayne Reid

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face
At 10:16 PM 11/24/00 +1300, Russell McMahon wrote:
>I want a small one off system that will produce a fine water fog (for
>specialist plant propagation).
>.
>A local mall has a system which makes  a fog of droplets so fine that the
>vapor floats in the air somewhat akin to "heavy smoke".
>ie the general trend is downwards  but it wafts in air currents and is not
>discernibly wet when you contact it.
>
>My first guess is that this fog is generated ultrasonically.

<http://www.leevalley.com> has a fogger for small garden ponds.  They ship
over-seas.

I know there have to be other suppliers somewhere but I don't know
where.  But the Lee Valley unit may give you some ideas.

dwayne



Dwayne Reid   <dwaynerspamKILLspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

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2000\11\24@162251 by Bob

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face
Well, off the top of my head, the best way I can think of doing it would be to
use an ultrasonic tranducer, submerged just under water (about 1/4").  This is
how they make ultrasonic humidifiers, which can put out fairly large volume of
VERY fine mist.  I don't know what that type of transducer would draw for power,
but I think it's a lot (i.e., either use a big battery, or have it run off of a
transformer connected to 120VAC).

That type of system is typically stationary, although I think someone does make
ultrasonic spray heads (I seen it somewhere on the net...).  You'd also need a
water pump for that setup, and control both the transducer and pump so they shut
off at the same time (or your transducer will overheat with no water supply)
You could drive that with a PICF87x hardware PWM, and have it fully programable
too (you could even have memory presets by using the onboard EEPROM).

-----Original Message-----
From: Russell McMahon <.....apptechKILLspamspam.....CLEAR.NET.NZ>
To: EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU <PICLISTspamspam_OUTMITVMA.MIT.EDU>
Date: Friday, November 24, 2000 4:16 AM
Subject: [EE]: Fog generating system - ideas wanted


>I want a small one off system that will produce a fine water fog (for
>specialist plant propagation).

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2000\11\24@181001 by Brett Testerman

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face
Being the parent of a child with asthma I have had to use a nebulizer over the last
few years. The units that the medicine is put in are quite effective of generating a
fine mist using compressed air. The next time you visit the doctor you might ask for
one of those. They usually just dispose of them.

I also have an ultrasonic room humidifier which works even better, but is bulky even
without the water tank.

The units I saw at Natural Wonders for putting in miniature fountains were
ultrasonic and small. About 1x1x2 inches. But they wanted $40 for them.

Brett


Bob wrote:

{Quote hidden}

> {Original Message removed}

2000\11\25@054221 by Peter L. Peres

picon face
FYI most vaporizers meant for gardening use water pressure only for this.
I have one of those manual plastic bottles with trigger pump, and it makes
about 50% 'fog' and the rest heavier droplets. All these seem to work on
the well-known tangential injector principle (liquid attacks the output
nozzle tangentially). The same principle is used in most furnace injectors
for liquid fuel, and diesel engine injection nozzles. So it has to be
good. The only requirement is high liquid pressure (>4at at least).

Even finer particles can be made by blowing hot air over a hot water
nozzle and then allowing this to mix with ambient air. The result is a
miniature cloud. You can't get any finer than that imho.

The ultrasonic method works well only for small quantities, otherwise you
will need serious power input and protection issues for people will arise
afaik. The power required to drive a single water nozzle can easily be
>1000W, coming from the water works (pipe pressure). To match that
electronically you will likely need more power. Think of the consequences.

Peter

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