Flow Viz... Re: Fwd: Re: [Beowulf] Earthquakes and raised floors...

[Jim Lux]

At 08:58 AM 1/9/2006, David Kewley wrote:

>Do any of y'all have suggestions for visualizing the air & heat flow in a
>room, or practical methods for reducing heat recirculation inside or around
>racks?


The traditional approach is using some form of smoke stream to visualize 
the air flow. Historically, one would use a bit of TiCl4, which combines 
with atmospheric moisture to create TiO2 as a very dense fine 
particulate.  The problem is that it also makes HCl, which is corrosive.

Some other convenient smoke sources are the stream of vaporized oil 
particles that come from an interesting device called a "Mole-Fogger" (made 
by Mole-Richardson) which has a hot element and a little plunger pump that 
squirts mineral oil into the element.  You get a dense stream of smoke 
which is very controllable.  There is also a device with the trade-name 
"Diffusion Fogger" which produces a fine (1 micron particles) mineral oil 
mist by mechanical means, so you don't have the smell and decomposition 
products, but it doesn't generate a nice dense stream. (If you have ever 
seen a theatrical presentation or concert where there was a sort of thin 
haze in the air to make the light beams show up, you've seen the output of 
the diffusion fogger.. about 10 mg/m3 is the peak concentration used)

The standard glycol based disco foggers are another possibility.  They 
basically superheat heat a mixture of propylene glycol and water (sometimes 
they add triethylene glycol), and squirt it out a tiny nozzle.  It flashes 
into vapor, which then condenses into a "fog".  The water evaporates 
quickly, leaving just the glycol as a smaller droplet.  Commercial units 
are often referred to as "water base" to distinguish them from oil units. 
They also sometimes add a fragrance to mask the distinctive glycol odor and 
taste. The glycol eventually evaporates, so to keep the "fog density" up, 
you have to keep pumping the glycol/water steam into the room.  This leads 
to a fairly high glycol vapor concentration.  The vapor is highly soluble 
in your saliva, so when you breathe in through your mouth, it dissolves, 
resulting in a very characteristic taste.  (I used to work with all of 
these things, and I used to be able to make a rough quantitative assessment 
of the fog juice composition just by smell and taste)

Anyway, we built a smoke probe for visualizing airflow using standard 
glycol fog juice, a small pressurized container, and a resistance heater 
with a temperature controller.






James Lux, P.E.
Spacecraft Radio Frequency Subsystems Group
Flight Communications Systems Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
tel: (818)354-2075
fax: (818)393-6875