Last updated: 19 July 2017
Tools and equipment
- Scissors, knife, glue, tape, thermometer
- 1 or 2 liter clear plastic soda bottle
- 12 oz. aluminum soda can
- Corrugated cardboard box approx. 16” x 16” x 16”
- Aluminum foil or reflective plastic from inside chip bags, etc.
- Tape (lables from some bottles make good tape)
From a 1 or 2 liter clear plastic soda bottle (right) cut off the top, 1" below where it becomes straight.
Cut slit 1" long into the side of the top (dotted line) to make it easy to insert into the bottle bottom.
A 12 oz. aluminum can with a dark lable or coat the can with carbon black from a candle or wood fire.
Put the can filled with water into the plastic bottle bottom and insert bottle top and press down to lock can in place.
To make the reflector (right), start with a corrugated cardboard box approximately 16" x 16" x 16". Cut off the top and two sides of the box. Cover the two remaining sides and bottom with aluminum foil or potato chip bags with silver coating facing out. Use wheat paste, glue or tape to adhere to cardboard box. Place bottle on the reflector and place in sun. Keep bottle shadow centered on back of solar panel.
Caution: Water is very hot do not drink from bottle until cool.
To pasteurize, water must be heated to 65 °C (149 °F).
© Eric Marlow 2012 All rights reserved
The soda water bottle pasteurizer shown here may have better performance than the one shown at above. It may also be slightly simpler to fabricate.
The cut off base, inverted, provides a stand for the blackened pop can (or other suitable black container). The taper of the inverted base eliminates the need for tabs--the cut off top just jams down over the inverted base.
Performance might be better for three reasons. First, the stand raises the pop can so that its bottom can be illuminated. (Be sure to blacken the bottom of the pop can.) Second, raising the pop can improves its bottom insulation. Third, the air leaks are below the bottom of the pop can. Since all of the air in the bottle above the stand is hotter and lighter than outside air, this stable arrangement of cool outside and hot inside air resists air leaks. In the design of Soda bottle pasteurizer, the air leaks are above the pop can, promoting outward leakage of hot air and inward leakage of cool air.
A possible further improvement
As the water in the pop can gets hot, most of the heat loss will occur from condensation of water vapor on the upper inner sloping sides of the soda bottle. We should be able to reduce the rate of heat loss from this condensation by double glazing the upper part of the soda bottle using the top portion of a second soda bottle as a hat on the first soda bottle.
The hat should accelerate the final portion of the temperature rise, or allow reaching a higher temperature (to make tea?), or allow successful pasteurization on less sunny days.
For lots more great projects made from Everyday Recyclables go to: http://www.recyclabits.com
A copy of this project may be made for personel and educational purposes only. © Eric Marlow 2012 All rights reserved