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I want to build a heatpipe to move heat (30 watts/hr) from the interior of my refrigerator to the exterior of my house Answered

during the winter. I am considering using a 1/2 copper tube capped filled with ethanol, water or acetone. I plan on Adding the fluid (how much?)to the open tube heating one end with a torch and soldering on the second cap to seal the tube and create a vacuum. any ideas would be appreciated.?


Hello, I worked for an electronics cooling company here in Lancaster PA for 18 years and if you have any questions on how to realy build a heat pipe just ask. It realy is not as difficult as others will lead you to believe. Using a fill tube is the best way and you can make a pinch off tool using a pair of wire cutters. If you round over the sharp edges and use this to pinch off the fill tube after you heat it cherry red to make it soft you will pinch it off with the tool and this is called a cold weld. If done right it will be leak tight. Also use Methanol not Acetone. Don't worry you will not blow yourself up. I am Writting a how to on heat pipes, thermosiphons ( which is what you are attempting to build ) heat exchangers and vapor chambers. I know all the secrets and how too's in all these forms of electronics cooling devices and am dying to let it out. I no longer work for the company I used to work for.

Re-design: RE: Air exchanger : My guess (and my reason) is that a heat pipe can transfer up to 100 times the heat as a solid rod of the same size. Depending on the application, that can be very important.

Yes building it dry and pulling the vacuum later would work, but there are other ways. Its pretty trivial to build it with a open end, fill, heat to well past the operating region, release pressure and seal. When the pipe cools down, you have a vacuum. Not as good as a pump would get you, but, it works.

seandogue: I think you are being facetious? While not with out risk, its also not much of one if done correctly (there are a number of utube videos to this effect, and I've done it a few times now). Yes I wear safety gear + have a 2nd party around, but I do that when welding or any other activity that has a level of danger. It is safer to build it dry, drill a VERY small hole (or use a filler tube) then insert the acetone. Heat, release, and seal. Using a filler tube you would crimp a long section that also has a solder in it. I did not have much luck but also did not explore all the options.

kevinhannan: Yes, nice and easy, and not the point (for me) I have 3 freezers, they use around 30$ electricity every month. Personaly, I am working on a heat based cooling system that would be the primary cooling . This will save me money. Assuming a 25% savings, that is $90/year. How much will that reduce my carbon footprint? lessen the load on my wind generator? I expect more of a savings when perfected. Yes, I might spend 3 or 4 years worth of money to get it right. Once there, I can do other things with it.

Mostly acetone and water are pretty easy to work with for DIY heat pipes when simple precautions are taken. The best one is to use no open flames. Ive recently started working with propane based heat pipe. This might get interesting, ill keep a camera going =-)

Why not make a heat exchanger using air? If you've got to use liquid you would be much better off building the system dry, then sucking a vacuum and then loading the liquid thru a valve?

It all depends on how badly burned you want to be after the ethanol or acetone goes ballistic while you're soldering the end cap on. Whole body experience or just exposed extremities?

My idea is much simpler: The main aim you want is to remove excess heat from the back of your fridge,plain and simple. Get a length of ducting and an in-line fan to match (the smallest diameter I am aware of is 4") - the length of this must go from the back of your fridge to an outside point. It's your choice whether this is a wall or a window or door. Then make/get a box or cover that will seal the fridge motor and heat-sink area of your fridge. Make a duct-hole towards the top of the cover (heat rises) and make a cool-air entry point of the same diameter towards the bottom of the cover. Don't make this hole at floor level to keep out critters/dust etc - you might want to put a basic stocking filter on this hole. Then attach it all and away you go. The idea is this: you need to remove heat so you need to seal in the area of heat. The ducting and fan removes this heat but you need cooler air coming in - don't try it without an air-entry hole! And then you need to protect the fridge from the air-entry point of dust and bugs. You could use an exiting hole in the wall, such as that for a tumble-dryer , or an old boiler exhaust point. Easy, or what? ;-)

I've built a few, though nothing of your scale or your temperature ranges. Most heat pipes have wicking material inside so the condensed fluid on the cold end can wick back to the hot end. Though this limits how long it can be since capillary action only goes so far and so fast. (The speed of the fluid return will determine hoe much heat you can move.) Otherwise you'll need to mount it vertically with the hot end at the bottom and return the fluid via gravity. You don't want a lot of fluid since a) you want it to boil easily, and b) too much and it'll get in its own way as it travels through the pipe. I found the right amount of fluid was whatever it took to fully dampen the wicking material. For gravity feed, I can only guess, probably 2 ounces per foot. Choosing the right fluid will be tricky since you need to have something that vaporizes at your hot end and condenses (but doesn't freeze) on the cold end. Acetone is probably the closest temperature range, but it's still not ideal since it's boiling point is 134 °F, a little hot for most refrigerators. As you mentioned you can bring that temperature down by dropping the pressure in the tube. But acetone is flammable and corrosive. Not something I'd want to use a torch around. You're going to have a hell of a time keeping anything like a partial vacuum in a hand-soldiered pipe. Nine times out of ten it's less trouble just to use a pump to pump fluid around or use a fan.