DIY Heat Pipe 2

[PHovnanian]

I'm putting together some homemade heat pipes using common hardware store materials (1/2" copper pipe and fittings, acetone).

Most of the web sites (for solar collectors) describe how to build and fill these as empty pipes, with some amount of acetone, evacuated and sealed. The wicking function (common in commercially available heat pipes) seems to be overlooked. Possibly because most commercial wicks appear to involve some sorts of sintered metal lining to the pipe. This is beyond the home DIY shop capability.

So my question is: Any suggestions for common hardware store material, compatible with acetone and a working temp up to about 150 C that would have the appropriate capillary properties to draw acetone up a 24" to 72" pipe?

My 'breadboard' design uses 24" pipes, but a finished prototype could be up to 6 feet long.

 

[moltenmetal]

Is the wick necessary if the orientation is proper already, i.e. boiler at the bottom, condenser at the top? Seems to me that the wick is only necessary if you need capilarity to fight gravity, but if it also provides some useful heat transfer area worth the extra pressure drop it represents, I'm sure someone will correct me.

 

[davefitz]

There are many published papers and texts on the subject, published circa 1980-1985. Many of the conference proceedings on this subject were thru the ASME. I think that if you vistied an enginering technical libray and searched their library journals titles you can find descriptions of experiments by researchers that were basically operating as a DIY homeowner.

 

[PHovnanian]

Is the wick necessary if the orientation is proper already, i.e. boiler at the bottom, condenser at the top?

It still might provide a useful function of wetting the walls of the pipe in the boiler section without having to fill that section with liquid acetone. And tube performance as a function of orientation is one factor I'd like to measure.

I've made a couple of pipes with varying amounts of acetone. The volume of my test pipe (24") is 75ml. I started with some Internet-gathered advice of using as little as 5ml acetone. But my boiler section will be about 18" of the pipes overall length. And by filling the entire boiler section (50ml), the transfer from the higher reaches of the boiler seems* to be more efficient. I'm guessing that some wicking will draw the acetone up from a small reservoir at the bottom to produce the same effect. It may also capture the condensate from the top and hold it against the tube sides more effectively. Either effect will serve to reduce the quantity of fluid required.

*Right now, I'm just making subjective judgments about the pipes' efficiencies by hold ing pipes under running hot water. My primary duty is to put together some instrumentation to evaluate installed pipe performance.

published papers and texts on the subject, published circa 1980-1985

Yeah. Just my luck. Before Al Gore invented the Internet. Google seems to find trade studies on all the micro channel, sintered wicking designs. I was hoping someone working the problem back in the day remembered some more common materials tried at the time. And with a bit more engineering behind it than the average homeowner (who I suspect just steal the wife's turkey baster and use whatever quantity that will hold).

 

[IRstuff]

There are some possibly useful articles on Google Scholar:
Scholar

Note that the original article: Structures of very high thermal conductance is available from AIP: AIP

there may also be articles of interest at DTIC:
DTIC

the original Eastman heatpipe article from SA:
Scientific American

TTFN
faq731-376

 

[btrueblood]

Dunno about hardware stores, but mesh lining like this might work:

http://www.mcmaster.com/#standard-cable-sleeving/=k8gm59

You might try window screen wrapped one or two layers thick...

 

[keefw1956]

If you don't need to reinvent the wheel, I'd recommend Heat Pipes: Theory, Design and Applications by Reay & Kew.

 

[telecomguy]

Maybe some good info here:

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19810065690_1981065690.pdf