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Phrugal phase change materials

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Posted by nicksanspam on May 19, 2007, 1:13 pm
 
George Lane is 75 years old and used to work for Dow Chemical and has about
150 patents, including US 4,613,444, "Reversible phase change compositions..."
issued on 9/23/1986, now expired, which describes adding a dash of sodium
chloride and potassium chloride and about 2% strontium chloride hexahydrate
to calcium chloride hexahydrate to help ensure phase change stability, ie
lots of cycles, freezing at 26 C and melting at 30. A similar German product
(Doerken DeltaCool24 or 28) in thin plastic pouches costs about 5 Euros/kg,
plus shipping. George says don't heat his mix much above 40 C, because that
will melt the nucleation centers, which might not return until the mix is
brought to 0 F.

Here's a link to his 12-page patent:

http://geocities.com/davidmdelaney/pcm/US-patent-04613444-Lane-Reversible-phase-change-composition.pdf

George says the containers need to be strong to avoid being scratched or
punctured by the mechanical actions of freezing and thawing. There's a 10%
volume change with phase, so the containers must be elastic or pleated or
have some air fill to reduce the peak pressure. They want to be well-sealed
to avoid losing or gaining water from surrounding air, with plastic walls
at least 0.035 inches thick, but this can be avoided by keeping the air at
an RH of about 35%, with something like the vapor pressure of CaCl2+6H20
at 90 F (a humidistat might open a solenoid valve with a soaker hose inside
a small room with an air heater. We can't add too much sodium or potassium,
saturation is fine, but too much or too little strontium gives the freezing
curve a slope vs a plateau. George says 1-liter soda bottles could work well
in 90 F air at 35% RH, or less. We might look at the water level and top up
1000 bottles every 10 years.

George made calcium chloride hexahydrate from DowFlake and PellaDow road
salt, at about 5 cents a pound (the strontium salt used in road flares
costs twice as much), by adding salt to water (for safety, since this is
exothermic.) The salt starts as a di- or tetrahydrate with desirable
impurities. When I suggested baking it in an oven to drive off the water,
then adding water to double the weight, he said that couldn't be done
without disassociation, but a university chem lab could analyze the water
content by various simple means. I wonder how...

One application might be a house in Calgary, Alberta, where 751 Btu/ft^2
of sun falls on a south wall on an average 18 F December day. It needs
about 144K Btu for 5 cloudy days in a row.

If 1 liter stores 225 Btu, we might have 144K/225 = 640 1-liter bottles
(about 40 ft^3) in a horizontal hexagonal stack in a small room with
an air heater or a south window made from 2 layers of GE HP92W 10 mil
Lexan polycarbonate film enclosing a 7" waterproof glazing cavity filled
with tiny cold soap bubbles (US R20-30) at night and filled with air
during the day, when 600 Btu/ft^2 of sun might enter the room over 6 hours.

If the store recharges in 5 days at 28.8K Btu/day and the bottles have
565 ft^2 of surface with a 1.5 Btu/h-F-ft^2 airfilm conductance so
the room air is 86+28.8K/6h/1.5/565 = 92 F during charging, 600A
= 28.8K+6h(92-20)A/2 makes the window area A = 58.5 ft^2, so an 8'x8'
window might do. An 8'x12' window could also provide some warm air
for the house on an average day.

Know anyone who can turn George Lane's patent into a foolproof DIY
cookbook recipe? This might be sold in a 1-pound kit with enough
strontium salt to treat a 50 pound bag of local calcium chloride.

Nick


Posted by Derek Broughton on May 20, 2007, 3:22 pm
 
nicksanspam@ece.villanova.edu wrote:


A professor at Dalhousie U in Halifax, NS, experimented with similar
phase-change storage systems in the 70s, and found he couldn't cope with
the corrosion problems.  I've wondered if, with modern plastics and
ceramics, it might not be time to revisit the method.
--
derek

Posted by dances_with_barkadas on May 21, 2007, 12:30 pm
 
    i'll see your history-of-engineering, and raise you five bucks:




    Here's  Baltzar Von Platen with the first commercially successful
absorption-cycle refrigeration

       www.freepatentsonline.com/1609334.pdf





    And here he is again,   55 years and 11 months later

      www.freepatentsonline.com/4354361.pdf


Posted by dances_with_barkadas on May 21, 2007, 12:31 pm
 
    i'll see your history-of-engineering, and raise you five bucks:




    Here's  Baltzar Von Platen with the first commercially successful
absorption-cycle refrigeration

       www.freepatentsonline.com/1609334.pdf





    And here he is again,   55 years and 11 months later

      www.freepatentsonline.com/4354361.pdf


Posted by Jeff on May 22, 2007, 2:04 am
 nicksanspam@ece.villanova.edu wrote:

http://geocities.com/davidmdelaney/pcm/US-patent-04613444-Lane-Reversible-phase-change-composition.pdf

   A few notes.

   First, I have some memory of talking with an artist that made
sculptures out of empty plastic pop bottles. He had a source for the
clean unused and it seems to me it was not much money. After all 640
bottles is not trifling. If anyone really wants a go with this I'll look
into it.

   Second, 28K BTUs is not a lot of energy per day. Is it really worth
making a store for that?

   Third, 40C upper storeage limit does not lend itself beyond storing
excess air heater BTUs. I can't help but think that a brine storeage
would  have a wider range of temperatures and would probably be easier
to charge for about the same energy density.

   With all that said, there is something about calcium chloride as a
cheap energy store. Now if I could only find it in the south in the
summer! Perhaps the Dowflake which is used for road construction (but is
rather low in purity) is the way to go.

   Jeff


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