Forums: Index > Help desk > Solar heater for PVC safety seal bands

I have a small business in Haiti and the electrical situation is very bad. I would like to heat the PVC shrink bands that I put on my bottles using solar energy heat. Does anyone have any ideas how this might be done? 01:41, 2 March 2007 (UTC)

How high of a temperature do you need to reach? How many bottles would you want to seal at one time? Tom Sponheim 04:19, 2 March 2007 (UTC)
Typically 100 to 120 °C will shrink PVC. Do you want to do a batch at a time or is the process continuous, one after another? For the former, an oven is more suitable. A concentrator may work for a continuous process, but unless the band is uniform in light absorbing properties, direct heating with sunlight may cause uneven shrinkage. Instead, heating air with solar energy and using it to heat the PVC may give better results. Walter Siegmund 04:31, 2 March 2007 (UTC)

Thanks for the responses. I'm not sure how to apply what you said, Walter. Any suggestions as to how to heat the air and force it onto the bands? We currently use a heat gun and it pulls a lot of electricity. I'm hoping to find a low tech solution. As far as whether we want to seal in batches or one at a time, it doesn't matter, as long as it gets done.

How about cutting the point off of a cone pointed at the sun. Then insert the head of the bottle into the hole from the bottom. I'll draw you a picture if I'm not making sense. Tom Sponheim 23:02, 2 March 2007 (UTC)

I think I get what you're saying. Would the cone get hot to the touch? What are the best materials? Could I make it from cardboard and foil? How big would it need to be? Hotsoslil 15:12, 4 March 2007 (UTC)

You might start by making one as is shown in these plans. You can test with that and then decide on the ideal size and shape. Tom Sponheim 21:04, 4 March 2007 (UTC)
Handheld electric heat guns for shrinking plastic film are typically 1200 W or so and require a few seconds per shrink operation. The sun supplies about 1000 W per square meter of radiant power for several hours each clear day. So roughly 1 square meter of area would be a good place to start. Heating air would require concentrating the solar energy on a heat exchanger, which could be a radiator from an junked car. You might need a fan to blow air through the radiator, but that would take only 100 W, That is much less than required by a heat gun.Walter Siegmund 04:29, 6 March 2007 (UTC)

I have several questions. The first one is for Tom. I tried the funnel, but I'm not sure how the heat gets transfered to the shrink band. On the page you sent me to, it says to use a canning jar or a pot painted black. I tried the black-painted jar and indeed it did get quite hot. I understand that this black object absorbs the energy that is directed to it and then heats up. If I open the bottom of the funnel and insert the bottle with the shrink band on it, how does it heat up? What if the band is white or another light color?

My next question is for Walter. What type of design would you suggest to heat the radiator? We are coming into the rainy season. Do I need a reflector? This is my first attempt at using solar energy to heat anything. Please be as specific as possible. Thanks to both of you for your help! Hotsoslil 01:32, 19 March 2007 (UTC)

Since you have made a funnel cooker, you might try using it to heat water to boiling and using the hot water to shrink the tubing. Depending on the shrink band material, that may not be hot enough. As an alternative, you can try cooking oil. Cooking oil can be heated to a much higher temperature and must be handled with care to prevent severe burns. You may be able to dip the bottle with band into the hot fluid or pour the fluid over the band. Be sure to collect the used fluid for reheating.
Because of its lower heat capacity, air must be heated to several hundred degrees C to be effective. I think that means you need some sort of concentrator, e.g., Spherical reflectors, or one of the other concentrator designs. If you focus the light onto a ~100 mm square portion of a radiator from a car or the heat exchanger from an old refrigerator, it will get very hot. It will need to be supported in an enclosure with a transparent window in an airtight refractory low-thermal-conductivity frame. Firebrick and furnace cement might work, but alumina fiber boards would have lower conductivity. [1] You probably want to put the fan on the cold side of the radiator. The hot air, from the other side of the radiator, can be transported to the workspace by means of a high temperature duct. [2] A double wall and/or insulated duct will reduce the temperature drop between the radiator and the workspace. Walter Siegmund 18:07, 19 March 2007 (UTC)

Solar Water Heater

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