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Posted by schooner on January 28, 2006, 8:05 pm
 
Few links:
http://www.hobby-boards.com/catalog/main_page.php
Lots of good info here on what it is, how it works, etc.

http://www.aagelectronica.com/aag/index.html?target=p_1.html&lang=en-us

http://www.digitemp.com/documentation.shtml

http://www.maxim-ic.com/products/ibutton/

When I get some spare time I plan to put together an app for logging BTUs
from a solar air collector.



Posted by Gary on January 29, 2006, 5:21 pm
 
schooner wrote:
Hi,
...

I've been looking for an inexpensive flow meter  as well.  The cheapest I have
found (not that cheap) are:

GEMS paddle wheel flow meters: http://www.gemssensors.com/index.asp

Dwyer has a couple: http://www.dwyer-inst.com/
Look for the RMV series and the HF series,
or the UV or VFC visual venturi meters.

Omega has some venturi meters: www.Omega.com
Look for the Fl46302, FL45101, ...

Beware that some of these meters might have too much internal pressure drop, or
not enough temperature capability for some solar applications.

----------

Omega.com also has a pretty good writeup on flow measurement:
http://www.omega.com/techref/flowcontrol.html
and,  http://www.omega.com/techref/table1.html

-------

DIY flow meter?
Since most of flow meters are based on the pressure difference caused by a
disruption in the flow (e.g. an orifice or venturi), I am wondering if one could
do a cheap version by:  1) create a suitable disruption in the flow using a
standard plumbing fitting(s), and 2)install pressure taps upstream and just
downstream of (or at) the disruption, 3) Then measure the pressure difference
between the pressure taps to get the flow rate.

What could the standard pipe fitting to create the flow disruption be?  Maybe
two reducers installed back to back to create a crude sort of venturi?  This
would not have the nice pressure recovery of a real venturi, but still would
have the low pressure area at the constriction?
Maybe a homemade orifice plate soldered inside a fitting (a coupling?)?

How would you measure the pressure difference?  Maybe a Magnehelic pressure gage
could be used to measure the pressure difference -- these are $0 new from
Dwyer, but are commonly available on ebay much cheaper.
http://www.dwyer-inst.com/htdocs/pressure/Series2000Intro.cfm   I have a couple
of these -- nicely made -- lots of uses.

It would have to be calibrated -- this could be done very accurately by timing
flow into a bucket of known size.

Gary







www.BuildItSolar.com
gary@BuildItSolar.com
"Build It Yourself" Solar Projects










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Posted by daestrom on January 29, 2006, 6:07 pm
 

I've played around with these GEMS ones myself.  Got some pretty cheap from
ebay.

But the OP should these things measure *volume* (i.e. gallons or liters per
minute) not mass flow.  To get a really good idea of the heat collection,
you also need to know the mixture ratio pretty accurately.

The density and specific heat capacity of water and glycol mixtures can be
found on the 'net.  To find the actual heat transferred.....

Energy Delivered = <volume flow rate>*<density>* <heat-capacity> *(Tin -
Tout) * time

(get all the units converted/cancelled out too)

daestrom



Posted by Gary on January 29, 2006, 7:43 pm
 Hi,

Any thoughts on the DIY flow meter?
I bought $.27 worth of plumbing fittings this morning to give it a try :-)

Gary



daestrom wrote:

www.BuildItSolar.com
gary@BuildItSolar.com
"Build It Yourself" Solar Projects









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Posted by Steve Shantz on January 29, 2006, 8:30 pm
 Best of luck in your endevour!

I would suggest that rather than adding restrictor fittings into your
line...what if you measured the pressure boost across the pump?  Place
one transducer just after the pump, and one right before the pump, and
measure the differential pressure.  At zero flow, no pressure drop.  As
the pump speeds up, there will be an increasing pressure change across
the pump.  The signal might be noisy and may need filtering, but the
idea seems good to me.  If across the pump is too noisy, how about
measuring the pressure drop through your collectors?  One transducer on
your out-bound (cold) pipe, and one on the the hot return pipe.  I'm
not sure this would really make a difference though, as compared to
just measuring across the pump.  You would get the largest signal by
measuring across the pump.

Are there any (cheap) piezzo transducers and signal conditioners that
would enable the signal to be fed into a processor?

Steve


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