[Stoves] A simple water sterilization technique

ajheggie at gmail.com ajheggie at gmail.com
Sat Feb 16 09:36:15 CST 2013


[Default] On Wed, 13 Feb 2013 20:36:24 -0700,Ron
<rongretlarson at comcast.net> wrote:

>
>List. Cc Dale
>
>   I think Dale knows a lot on this topic.  Dale?

ale does indeed know a lot about WAPI amd has posted the reply below
with a large attachment which I have reproduced as text with two small
images AJH

"Why yes, I know a thing or two about WAPI?s.  

 

The original WAPI was designed in 1992 by me, taking advantage of
preliminary work that had been done by others.  I made the first 20 in
my kitchen, then I hired a student to make the next 300.  Since then,
probably about 200,000 have been made.  At least 2 other designs have
arisen, which in my opinion are better than the original plastic tube
WAPI.  

 

One alternative design is a glass tube WAPI, which you can see in the
attached file.  The other (best of all, in my opinion) is based on
memory shape wire.  You can bend it when cold, then it will straighten
out when it goes above its transition temperature, which would be set
to be the pasteurization temperature.  A little preliminary work has
been done on that one, but it?s not gotten past the first few
prototypes.  

 

The attached file is a mashup of parts of several other files,
including an article from one of the Ohio State Alumni Newsletters. It
shows 2 of the WAPIs listed above, and gives some directions for
making the basic type.    Some of the information is dated, but is
generally accurate.  

 

The petroleum wax is definitely better than the soybean fat.  It?s
more stable at high temperatures and lasts longer, also it is colored
and easier to see in the tube.  The wax and the fat are available in a
wide range of melting points, so WAPIs could be made at various
melting temperatures.  

 

The WAPI is indeed a way to save a lot of energy while providing clean
water, either by using solar energy to heat water or flame heating the
water to the pasteurization temperature rather than the boiling point.
I?m planning to give a talk about this at the next ETHOS meeting, and
we are hoping to give a presentation at the next Water and Health
Conference in North Carolina.  In the meantime, there is the internet
and people like us to get the word out.  Or, if someone wanted to take
on and develop the memory alloy WAPI, that would be great.  

 

Dale Andreatta, Ph.D., P.E."

Brief Description of WAPI (the following contains pieces of a couple
of other files that relate to the pasteurization indicator).  


Contrary to what many people believe, it is not necessary to boil
water to make it safe to drink.  Heating water to 65° C (149° F) for 6
minutes, or to a higher temperature for a shorter time, will kill all
germs, viruses, and parasites.  This process is called pasteurization.
A way of knowing that the water reached the pasteurization temperature
is needed.  An inexpensive device that does this was developed, and is
shown in the Fig. 2.  It is a plastic tube with both ends heated,
pinched, and sealed, and with a particular type of soybean fat in one
end that melts at 154° F.  The tube itself is buoyant, but is weighted
with a washer so it sinks to the bottom (coolest) part of the water,
with the fat in the high end of the tube.  If the fat is found in the
low end of the tube at any time after, the water reached the proper
temperature, even though the water may have since cooled down.  A
nylon string makes it easy to take the tube out without
recontaminating the water.  The tube is reused by flipping it over and
sliding the string through the other way.  This device works in any
size water container, costs about $5, and is available from Solar
Cookers International, 1919 21st Street, Sacramento, California, 95814
(916) 455-4499.  This device also works with fuel-heated water.  Since
heating the water to the pasteurization temperature rather than the
boiling point reduces the energy required by at least 50%, the fuel
savings offered by this simple device alone is considerable.  


Figure 2:  One type of WAPI (Water Pasteurization Indicator).  The
indicator would sit at an angle in the bottom of a water container.

Instructions for making water pasteurization indicators

First, note that they are commercially available from Solar Cookers
International, 1919 21st Street, #101, Sacramento, CA  95814,
telephone 916 455-4499, FAX 916 455 4498.    

To make an indicator, start with a polycarbonate (also known as Lexan)
tube, outside diameter 3/8 inch, inside diameter ¼ inch.  Do not use
acrylic tubes.  One source for the tubing is the McMaster Carr Supply
Company, see attached information, including part numbers.  

Cut the tube into lengths of about 2 ¾ inches.  Use some source of
heat to heat the last ½ inch of the cut tube.  The heat can be a
candle or gentle torch flame, or the flame of a gas stove.  Other
sources of heat can probably be used.  Twirl the tube to heat it
uniformly all around, and stop when you see the plastic get soft and
little bubbly.  Pinch the hot end of the tube closed with a pair of
pliers making a tab about ½ inch wide by about ¾ long.  Try to keep
the flame products out of the inside of the tube by holding the open
end of the tube up.  Combustion products contain soot and water vapor,
both of which could be bad for the soybean fat.   

When this is done slip a stainless steel washer over the tube and fill
the inside of the tube about halfway  or 2/3 of the way full of the
soybean fat, which is more properly known as a food-grade soybean
emulsifier.  The washers can again some from McMaster Carr, see
attached information for part numbers.  You can use part number
98017A204, 98017A205, 98019A500, or 98019A502.  I’d recommend the last
two numbers unless you want to fit the pasteurization indicator
through a small opening.  These washers are stainless steel.  You can
use ordinary steel washers but they will rust and give a funny taste
to the water.  The soybean fat comes from the Eastman Chemical
Company, PO Box 431, Kingsport, Tennessee (sorry I don’t have a phone
number).  The product name is Myverol and comes with a series of
numbers depending on the melting point.  I think you use Myverol
18-04, but ask for the one with a melting point of about 154? F.  

Heat and pinch the other end closed similarly to the first one.  When
you get a bunch of tubes made like this put them in a pot of hot
water.  This will melt the fat and make it run to the bottom of the
tube and make the indicator ready to use.  Also, if any of the tubes
have a little too much buoyancy they will float and should be
discarded.  

Put a hole, about 1/8 inch diameter, in each tab using either a drill
or hot iron.  The hole should be close to the end of the tab so that
you don’t accidentally pierce the cavity where the soybean fat is,
which should be permanently sealed.  Take a piece of nylon fishing
line about 3 feet long and run it through the holes in both tabs and
through the inside of the washer, that is, between the inside of the
washer and the outside of the tube.  Take two small stainless steel
washers, such a McMaster Carr part number 98019A330, and slip the last
3 to 6 inches of the fishing line through each washer.  Then make a
loop in each end of the fishing line with the washer in the loop and
tie it off.  I like to use a figure-8 knot, but any good knot will do.
See the sketch below.  This loop-washer system is used for holding the
dry end of the string in place.  You can hang it over the edge of the
water vessel and the weight of the small washer will keep it from
being pulled into the vessel.  Or, you can put a stick or hook through
the loop and that will keep the dry end of the string out of the
water.  The important thing is that only the indicator and its string
ever touch the pasteurized water.  Also, don’t get the nylon string
too close to a flame.  

The total cost for the parts is about $.50 and after a little practice
it takes about 10 minutes to make one indicator.  



Recently, a smaller WAPI has been developed by Solar Solutions of San
Diego for use with their Aquapak water pasteurizer.  Their information
is at www.Solarsolutions.info.  It is a 1-inch long glass tube,
containing a small amount of petroleum wax.  It doesn’t have any of
the washers and strings as the SCI indicator, so it must be used
differently.  It is intended to be attached to a wire or stick, or
held in a receptacle.   In my opinion, their WAPI is better in all
respects (smaller, cheaper, longer lasting) than the one from Solar
Cookers Int’l, as long as you can use it in your application.  

Recently a student design team in Prof. Dennis Guenther’s ME 564 class
took on the design of a Water Pasteurization Indicator as their class
project.  Their design, which has been built and tested, includes a
small glass capsule filled with petroleum wax which melts at about 67
degrees.  The glass capsule is held by a simple system of wires, such
that the wax starts out at the high end of the tube.  If at any later
time the wax is found at the low end of the tube, then the
pasteurization temperature was achieved and the water is safe to
drink.  The device is reusable indefinitely, and will cost less than
$1 if made in developing countries.

The six students who worked on the project are Arif Mohsin, Zaidi
Ahmad Latiffi, Khairil Azim Khairuddin, William Hunter, Shimpei
Narita, and Muhammad Yusoff Che-Lah.  Currently, Solar Cookers Int’l,
of Sacramento, CA is interested in produced the WAPI.  The project was
suggested by Dale Andreatta (BSME ’83, MSME ’84) who has worked with
Solar Cookers Int’l.  
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