Hybrid Car – More Fun with Less Gas

Air Flow measurements

register ::  Login Password  :: Lost Password?
Posted by Jeff on January 30, 2007, 3:19 am
 
   I'd like to measure air flow/velocity and perhaps pressure. Any ideas
of homemade or commercial products?

   My Solar Air Collector is in test mode, but operational. Some details
were discussed in an earlier thread on temp glazing. Roughly 25' long  x
8' tall, the absorber is two layers of black fiberglass screen spaced
1/4"  apart ($3 at Home Despot). The supply plenum is roughly 14" wide
by 5" high with 1 1/2" holes every foot that feed the airspace between
the glazing and the absorber screen. The outlet is two opened jallosy
windows, rougly 16 square feet each, although I only have one open now.

  I had some trouble finding "clear" polyethelene for the temp glazing.
Mostly the clear is really really cloudy. I did find some painters drop
cloths that looked good but patching three together was more than I
wanted to do! Ace had some 4 mil that was hazy (but much better that
everyone else's), and I went with that. It does seem that the poly is
indeed mostly transparent to IR and I can get good spot readings with my
IR thermometer. With the fan off, the system thermosyphons through the
windows. The top of the collector is much warmer than the bottom. With
the fan on the absorber is nearly the same temp all over. The plenum
plumps and it takes a bit of finger pressure to push the poly back in,
so it seems that I could either add more holes or enlarge the ones I
have. I think  first though, I'd like to measure airflow (and perhaps
fan current draw) with the plenum in operation and with the plenum
opened up. I have this sealed with painters masking tape so tinkering is
easy!

   I'll post some pics on my site later.

   Jeff

Posted by Duane C. Johnson on January 30, 2007, 12:53 pm
 
Hi Jeff;

Jeff wrote:

 > I'd like to measure air flow/velocity and perhaps
 > pressure. Any ideas of homemade or commercial products?

Try this hot wire anemometer. It works very well:
http://www.redrok.com/misc1.htm#anemometer

 > My Solar Air Collector is in test mode, but
 > operational. Some details were discussed in an earlier
 > thread on temp glazing. Roughly 25' long  x 8' tall,
 > the absorber is two layers of black fiberglass screen
 > spaced 1/4" apart ($3 at Home Despot). The supply
 > plenum is roughly 14" wide by 5" high with 1 1/2"
 > holes every foot that feed the airspace between the
 > glazing and the absorber screen. The outlet is two
 > opened jallosy windows, roughly 16 square feet each,
 > although I only have one open now.

 > I had some trouble finding "clear" polyethylene for
 > the temp glazing. Mostly the clear is really really
 > cloudy. I did find some painters drop cloths that
 > looked good but patching three together was more than
 > I wanted to do! Ace had some 4 mil that was hazy (but
 > much better that everyone else's), and I went with
 > that. It does seem that the poly is indeed mostly
 > transparent to IR and I can get good spot readings
 > with my IR thermometer. With the fan off, the system
 > thermosyphons through the windows. The top of the
 > collector is much warmer than the bottom. With the
 > fan on the absorber is nearly the same temp all over.
 > The plenum plumps and it takes a bit of finger
 > pressure to push the poly back in, so it seems that
 > I could either add more holes or enlarge the ones I
 > have. I think  first though, I'd like to measure
 > airflow (and perhaps fan current draw) with the
 > plenum in operation and with the plenum opened up.
 > I have this sealed with painters masking tape so
 > tinkering is easy!

 > I'll post some pics on my site later.

 >   Jeff

Duane

--
     Home of the $5 Solar Tracker      Receiver
    http://www.redrok.com/led3xassm.htm       [*]
   Powered by             \  \     \        //|
  Thermonuclear   Solar Energy from the Sun / |
Energy (the SUN)           \  \     \  /  /  |
Red Rock Energy             \  \     /   /   |
Duane C. Johnson   Designer  \  \  /  \ /    |
1825 Florence St  Heliostat,Control,& Mounts |
White Bear Lake, Minnesota    === \   / \    |
USA      55110-3364                ===   \   |
(651)426-4766        use Courier New Font \  |
redrok@redrok.com     (my email: address)  \ |
http://www.redrok.com   (Web site)          ===

Posted by Gary on January 30, 2007, 9:23 pm
 Jeff wrote:

Hi Jeff,

You have probably already seen these, but just in case:

The Kestrel type wind gages are good -- these are little one inch diameter
turbines that run on sapphire bearings.  They will measure down to about 80 fpm,
up up to a lot (80 mph?).  I used this on my thermosyphon collector, and it
works well.  About $0 and up, but generally useful for measuring wind speed etc.

The other is the Dwyer vane type air velocity meter.  About $5.  Very good for
thermosyphon, in that it will register very low velocities --  maybe down to 20
fpm.  The vane has just about the right amount of damping, so the readings don't
jump all over the place, but react to velocity changes over a few seconds.
One disadvantage is that the air flow being measured has to be horizontal.
The top end is is up at 200 to 400 fpm.

I also have a Testo Velocity Stick, which is a fairly inexpensive hot wire
anemometer.  To me, its not damped enough and difficult to get good readings
with.  You have to take half a dozen readings over a few seconds and average
them to get anything that is useful.

A bit more here:
http://www.builditsolar.com/References/Measurements/measurments.htm





It would be interesting if you could figure out a way to see how uniform the
flow velocity is throughout the collector.

If you got something like the Kestrel meter, it would be interesting to know how
much the outlet velocity from each of the 1.5 inch holes varies over the 25 ft,
and whether it would be worthwhile using larger diameter holes toward the far
end or not.

Since its temporary glazing, maybe you would not mind poking a some holes in the
glazing to get your velocity measuring device in the air stream :)

Gary


 Posted Via Usenet.com Premium Usenet Newsgroup Services
----------------------------------------------------------
    ** SPEED ** RETENTION ** COMPLETION ** ANONYMITY **
----------------------------------------------------------        
                http://www.usenet.com

Posted by Jeff on January 30, 2007, 10:46 pm
 Gary wrote:

   Hello Gary, Duane,

 > Jeff wrote:
 >
 >>   I'd like to measure air flow/velocity and perhaps pressure. Any
 >> ideas of homemade or commercial products?
 >
 > Hi Jeff,
 >
 > You have probably already seen these, but just in case:
 >
 > The Kestrel type wind gages are good -- these are little one inch
diameter
 > turbines that run on sapphire bearings.  They will measure down to about
 > 80 fpm,
 > up up to a lot (80 mph?).  I used this on my thermosyphon collector,
and it
 > works well.  About $0 and up, but generally useful for measuring wind
 > speed etc.

   That's an interesting idea. I wonder if the little CPU fans would work.

   I'm think along Duane's filament anemometer at the moment. It appears
to be logarithmic and measures low flow well. Considering I just need
relative measurements and I probably have all the ingrediants, I'm going
to give a go.

   I may have at some of Duane's other projects as well, specifically
the  differential temp controller. I now have some uneeded scrap polyiso
for the insulation tester as well.
 >
 > The other is the Dwyer vane type air velocity meter.  About $5.  Very
 > good for
 > thermosyphon, in that it will register very low velocities --  maybe
 > down to 20
 > fpm.  The vane has just about the right amount of damping, so the
 > readings don't
 > jump all over the place, but react to velocity changes over a few
seconds.
 > One disadvantage is that the air flow being measured has to be
horizontal.
 > The top end is is up at 200 to 400 fpm.
 >
 > I also have a Testo Velocity Stick, which is a fairly inexpensive hot
wire
 > anemometer.  To me, its not damped enough and difficult to get good
 > readings
 > with.  You have to take half a dozen readings over a few seconds and
 > average
 > them to get anything that is useful.
 >
 > A bit more here:
 > http://www.builditsolar.com/References/Measurements/measurments.htm
 >
 >
 >
 >
 >>
 >>   My Solar Air Collector is in test mode, but operational. Some
 >> details were discussed in an earlier thread on temp glazing. Roughly
 >> 25' long  x 8' tall, the absorber is two layers of black fiberglass
 >> screen spaced 1/4"  apart ($3 at Home Despot). The supply plenum is
 >> roughly 14" wide by 5" high with 1 1/2" holes every foot that feed the
 >> airspace between the glazing and the absorber screen. The outlet is
 >> two opened jallosy windows, rougly 16 square feet each, although I
 >> only have one open now.
 >
 >
 > It would be interesting if you could figure out a way to see how uniform
 > the
 > flow velocity is throughout the collector.
 >
 > If you got something like the Kestrel meter, it would be interesting to
 > know how
 > much the outlet velocity from each of the 1.5 inch holes varies over the
 > 25 ft,
 > and whether it would be worthwhile using larger diameter holes toward
 > the far
 > end or not.
 >
 > Since its temporary glazing, maybe you would not mind poking a some
 > holes in the
 > glazing to get your velocity measuring device in the air stream :)

   I think I'll do almost exactly that. Since I have the window open, I
can get to the back of the absorber screen and measure airflow there.

   The thermal mass of the screen is so small that changes in light
intensity (clouds, trees, etc..) are immediately apparent in the IR
temp. I may try adding a layer or two of aluminum screen over part of
the absorber and see what that does.

   Jeff

 >
 > Gary
 >
 >>
 >>  I had some trouble finding "clear" polyethelene for the temp glazing.
 >> Mostly the clear is really really cloudy. I did find some painters
 >> drop cloths that looked good but patching three together was more than
 >> I wanted to do! Ace had some 4 mil that was hazy (but much better that
 >> everyone else's), and I went with that. It does seem that the poly is
 >> indeed mostly transparent to IR and I can get good spot readings with
 >> my IR thermometer. With the fan off, the system thermosyphons through
 >> the windows. The top of the collector is much warmer than the bottom.
 >> With the fan on the absorber is nearly the same temp all over. The
 >> plenum plumps and it takes a bit of finger pressure to push the poly
 >> back in, so it seems that I could either add more holes or enlarge the
 >> ones I have. I think  first though, I'd like to measure airflow (and
 >> perhaps fan current draw) with the plenum in operation and with the
 >> plenum opened up. I have this sealed with painters masking tape so
 >> tinkering is easy!
 >>
 >>   I'll post some pics on my site later.
 >
 > Good!
 >
 >>
 >>   Jeff
 >
 >
 >
 > Posted Via Usenet.com Premium Usenet Newsgroup Services
 > ----------------------------------------------------------
 >    ** SPEED ** RETENTION ** COMPLETION ** ANONYMITY **
 > ----------------------------------------------------------
 >                http://www.usenet.com

Posted by Duane C. Johnson on January 31, 2007, 4:45 am
 Hi Jeff;

Jeff wrote:
 > Gary wrote:
 > > Jeff wrote:

 > > > I'd like to measure air flow/velocity and
 > > > perhaps pressure. Any ideas of homemade or
 > > > commercial products?

 > > You have probably already seen these,
 > > but just in case:

 > > The Kestrel type wind gages are good --
 > > these are little one inch diameter turbines
 > > that run on sapphire bearings. They will measure
 > > down to about 80 fpm, up up to a lot (80 mph?).
 > > I used this on my thermosyphon collector, and
 > > it works well. About $0 and up, but generally
 > > useful for measuring wind speed etc.

These types work very well and are quite linear.
Albeit, they are kind of expensive and a bit large
in size.

 > That's an interesting idea. I wonder if the little.
 > CPU fans would work

I just did some testing on several very small DC fans.
Two of them, a 1" and a 1.25" types.

They don't seem to work very well as anemometers for
the low air speeds used in solar collectors.

Problems:
1. They don't seem to be very efficient as alternators.
    Ok, efficiency is irrelevant. But what I mean is
    the voltage generated by the windings is pretty
    low. The circuitry in the fans inherently have the
    equivalent of 2 diodes in series with the windings.
    So the windings must produce quite a bit of voltage
    to over come them.

    The result is an output of less than a volt and
    the measurement is quite non linear.

    ( I will make some measurements with my car
      tomorrow using the 1.25" unit and report here. )

2. They have some magnetic "cogging" action so the
    air speed needs to be fairly high to get them
    started.
3. The fan has a bunch of magnetic "friction" so they
    present an obstacle to the air flow which affects
    the measurement. Especially in small confined
    spaces.

To fix these problems I would remove the magnets,
windings, and pole pieces, to remove as much friction
as possible. The bearings are quite good. I would then
install a photo interrupter to count blade rotation
speed. This is pretty much how the Kestrel anemometer
does it.

Or, hack the motor circuitry so only one of the
windings is directly brought out. Then you can directly
measure the AC voltage. This AC voltage should be
directly proportional to the RPM of the fan. You could
also just measure the frequency.

( I haven't done either of these methods myself so
   maybe there are other problems I am not aware of. )

 > I'm think along Duane's filament anemometer at the
 > moment. It appears to be logarithmic and measures
 > low flow well.

Actually, these are Hot Wire Anemometers are generally
linear with a smaller non linear component.
Easily calibrated though.
http://www.redrok.com/misc1.htm#anemometer

 > Considering I just need relative measurements and
 > I probably have all the ingredients, I'm going
 > to give a go.

You will be pleasantly surprised at how easy the Hot
Wire Anemometers are to make. The wind resistance is
small because of the small physical size.

Or for a more robust probe one can use a 1/8 watt
resistor heated to about 300F or so instead of the
lamp filament.

 > I may have at some of Duane's other projects as
 > well, specifically the  differential temp controller.
 > I now have some unneeded scrap polyiso for the
 > insulation tester as well.

Good luck and have fun.

 > > The other is the Dwyer vane type air velocity
 > > meter. About $5. Very good for thermosyphon, in
 > > that it will register very low velocities --
 > > maybe down to 20 fpm. The vane has just about the
 > > right amount of damping, so the readings don't
 > > jump all over the place, but react to velocity
 > > changes over a few seconds. One disadvantage is
 > > that the air flow being measured has to be
 > > horizontal. The top end is up at 200 to 400 fpm.

 > > I also have a Testo Velocity Stick, which is a
 > > fairly inexpensive hot wire anemometer. To me,
 > > its not damped enough and difficult to get good
 > > readings with. You have to take half a dozen
 > > readings over a few seconds and average
 >  > them to get anything that is useful.

A perfect example of where an old fashion analog
meter can be superior to the digital stuff.

 > > A bit more here:
 > > http://www.builditsolar.com/References/Measurements/measurments.htm

 > > > My Solar Air Collector is in test mode, but
 > > > operational. Some details were discussed in an
 > > > earlier thread on temp glazing. Roughly 25' long
 > > > x 8' tall, the absorber is two layers of black
 > > > fiberglass screen spaced 1/4"  apart ($3 at
 > > > Home Despot). The supply plenum is roughly 14"
 > > > wide by 5" high with 1 1/2" holes every foot
 > > > that feed the airspace between the glazing and
 > > > the absorber screen. The outlet is two opened
 > > > jallosy windows, roughly 16 square feet each,
 > > > although I only have one open now.

 > > It would be interesting if you could figure out a
 > > way to see how uniform the flow velocity is
 > > throughout the collector.

 > > If you got something like the Kestrel meter, it
 > > would be interesting to know how much the outlet
 > > velocity from each of the 1.5 inch holes varies
 > > over the 25 ft, and whether it would be worthwhile
 > > using larger diameter holes toward the far end or
 > > not.

 > > Since its temporary glazing, maybe you would not
 > > mind poking a some holes in the glazing to get
 > > your velocity measuring device in the air stream :)

 > I think I'll do almost exactly that. Since I have the
 > > window open, I can get to the back of the absorber
 > > screen and measure airflow there.

 > The thermal mass of the screen is so small that
 > changes in light intensity (clouds, trees, etc..) are
 > immediately apparent in the IR temp. I may try adding
 > a layer or two of aluminum screen over part of the
 > absorber and see what that does.

 > Jeff

 > > Gary

 > > > Jeff

Duane

--
     Home of the $5 Solar Tracker      Receiver
    http://www.redrok.com/led3xassm.htm       [*]
   Powered by             \  \     \        //|
  Thermonuclear   Solar Energy from the Sun / |
Energy (the SUN)           \  \     \  /  /  |
Red Rock Energy             \  \     /   /   |
Duane C. Johnson   Designer  \  \  /  \ /    |
1825 Florence St  Heliostat,Control,& Mounts |
White Bear Lake, Minnesota    === \   / \    |
USA      55110-3364                ===   \   |
(651)426-4766        use Courier New Font \  |
redrok@redrok.com     (my email: address)  \ |
http://www.redrok.com   (Web site)          ===

This Thread
Bookmark this thread:
 
 
 
 
 
 
  •  
  • Subject
  • Author
  • Date
please rate this thread