Hybrid Car – More Fun with Less Gas

pex vs copper - Page 2

register ::  Login Password  :: Lost Password?
Posted by Duane C. Johnson on September 10, 2005, 11:02 pm
 
Hi Nick and all;

nicksanspam@ece.villanova.edu wrote:
 > Bert Menkveld <bertATreentronicsDOTcom> wrote:

 > > I wonder if the large temperature drop from the
 > > fin to the circulating water might not be caused
 > > by the poor thermal conductance of the CPVC...

 > And limited contact area between the fin and the pipe.

 > http://www.boedeker.com/pvc_p.htm ... gives a thermal
 > conductance of:

 > > 0.9 BTU-in/ft^2-hr-F.  Compare this with aluminum
 > > at about 1500, or copper at 2700!

 > We need to divide by the wall thickness (less then 1"),
 > but copper is better. I'd like to see somebody make
 > "Big Fins" out of aluminum coil stock. Home Depot sells
 > rolls of 0.019"(?) Al painted white on one side and
 > dark brown on the other for 50 cents/ft^2. They might
 > make fine Big Fins with 4" wings if bent to a U shape
 > with a brake and attached to copper pipe with some
 > hardware. They could easily nest for shipping.

A Wrapping Jig.
http://www.redrok.com/misc1.htm#wrappingjig

Or a Beading Jig.
http://www.redrok.com/misc1.htm#beadingjig1

 > Nick

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 nicksanspam on September 11, 2005, 9:16 am
 


http://www.redrok.com/misc1.htm#wrappingjig

Nice :-)                                          .  .
                                               .  .  .  .
                   aluminum flashing   rivet . .  1/2"  . .  
                .........................|... .  copper  . .  
                .........................|... .   pipe   . .
                                       rivet . .        . .
                                               .  .  .  .
                                  --- .           .  .
                      .  
                                   |  . <--foil-faced foamboard
                                      .    on the back side?
...then open it up like this:         .  
                                      .           .  .
                                      .        .  .  .  .
     Home Depot sells dark-           .rivet . .        . .  
     brown-painted aluminum       ~5" ...|... .  copper  . .  
     roof flashing for $6.50         ...|... .   pipe   . .
     for a 50'x2'x0.027" roll.        .rivet . .        . .
                                      .        .  .  .  .
                                      .           .  .
     [View in Courier font.]          .  
                                   |  .    This solar collector might be
                                      .    60% efficient heating 120 F
                                  --- .    water inside an 80 F sunspace.

Nick


Posted by Gary on September 11, 2005, 3:05 pm
 Duane C. Johnson wrote:


Hi All,

Nice jigs.

Here is another one that I have used:

http://www.builditsolar.com/Experimental/CPVCCollector/jig.htm

It's Honda Powered :-)


Also like Nick's idea for using the using the fins from the wrapping
jig above -- somebody should give it a try.


--


Gary

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









----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com  The #1 Newsgroup Service in the World! 120,000+
Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

Posted by Gary on September 11, 2005, 5:22 pm
 Hi Bert,
...

Thats a nice site.

I had a go at calculating the theoretical temperature drop across the
CPVC tube wall using the the thermal conductance values you provided
above.  If I did the math right (see below), then it takes a delta T
of about 40F to transfer the incoming heat from the fin (and sun)
through the wall of the tube.  So, this says that as you suggest, most
of the thermal resistance seems to be in the CPVC wall.  And, it
agrees pretty well with the test thermocouples (except the one right
on the CPVC outer wall, which is a bit suspect since the only way I
could place it on the outer wall was to have it in the open part of
the U on the extrusion).

The PEX tubing I have has the same OD and ID as the CPVC, so the PEX
might be 2.1/0.9 = 1.9 times better, or about 20F to transfer the heat
through the PEX wall.


If the PEX causes the fins to run 20F hotter, then the extra losses
through R1 Glazing might be about (1 sqft)(20F)/R1 = 20 BTU/h-ft2  --
the efficiency hit might be 20/(290*0.9) = 8%.  This seems to me that
it might be getting into the acceptable range?  Especially given how
easy such a collector might be to build.  Wonder if a PEX one is worth
a try?
Hope Andre is still watching.


  Hey Nick, are you reading this?  What do you think? <--------- Yes

The wall heat transfer calc:

About (290 BTU/sqft-hr)(0.9 transmission) = 260 BTU/sqft-hr gets to
each sqft of fin.
Each sqft of fin (4 inch wide) is served by 3 ft of pipe.

CPVC half inch pipe:  r2 = 0.3875 inch, r1 = 0.3125 inch

Ucpvc = 0.9 BTU-in/ft^2-hr-F = 0.075 BTU-ft/ft^2-hr-F

The transfer through the CPVC wall is:

q = UA(Touter - Tinner)

UA = (2*Pi*L*K)/ln(r2/r1)
UA = (2)(3.14)(3ft)(0.075 BTU-ft/ft^2-hr-F)/(ln(0.3875/0.3125) =
       6.6 BTU/ ft^2-hr-F

(Touter-Tinner) = q/UA = (260 BTU/sqft-hr)/(6.6 BTU-ft/ft^2-hr-F) =

                   39F


--


Gary

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









----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com  The #1 Newsgroup Service in the World! 120,000+
Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

Posted by Gary on September 14, 2005, 1:43 pm
 Gary wrote:
...


Oops -- I made a mistake in the calculation in the post above.  I
assumed that the 90% of the solar energy that gets through the glazing
all gets transfered to the fluid in the tubes.  Actually (based on the
flow rates and temperature rise in the tube flow) only about 60% gets
to the fluid -- the rest is losses out the glazing.  I have plugged in
the corrected numbers below:


Corrected Version:
  I had a go at calculating the theoretical temperature drop across the
  CPVC tube wall using the the thermal conductance values you provided
  above.  If I did the math right (see below), then it takes a delta T
  of about 40F to transfer the incoming heat from the fin (and sun)
  through the wall of the tube.  So, this says that about 65% (26F/40F)
  of the thermal resistance seems to be in the CPVC wall.

  The PEX tubing I have has the same OD and ID as the CPVC, so the PEX
  might be 2.1/0.9 = 2.3 times better, or about 11F to transfer the heat
  through the PEX wall.


  The wall heat transfer calc:

  About (290 BTU/sqft-hr)(0.6 efficency) = 174 BTU/sqft-hr gets to
  each sqft of fin, and is transferred into the fluid.  The rest is
either
  not transmitted through the glazing or is losses out the glazing.
  Each sqft of fin (4 inch wide) is served by 3 ft of pipe.

  CPVC half inch pipe:  r2 = 0.3875 inch, r1 = 0.3125 inch

  Ucpvc = 0.9 BTU-in/ft^2-hr-F = 0.075 BTU-ft/ft^2-hr-F

  The transfer through the CPVC wall is:

  q = UA(Touter - Tinner)

  UA = (2*Pi*L*K)/ln(r2/r1)
  UA = (2)(3.14)(3ft)(0.075 BTU-ft/ft^2-hr-F)/(ln(0.3875/0.3125) =
        6.6 BTU/ ft^2-hr-F

  (Touter-Tinner) = q/UA = (174 BTU/sqft-hr)/(6.6 BTU-ft/ft^2-hr-F) = 26F




Gary

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









----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com  The #1 Newsgroup Service in the World! 120,000+
Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

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