Best Phase Change Materials for Flexible Heating/Cooling Membrane

[martinl]

Hi All,

I'm working on a project that requires a flexible membrane be heated and cooled about 2000 times.

During the cooling process, I require the material give off heat for as long a period of time as possible. I figure a phase change material will have the highest heat capacity and give off its latent heat, over an extended period of time, while cooling at it's melting point.

So, I'm looking for a phase change material that I can imbed in a thin layer of silicon rubber to form the heat sink part of my membrane.

I considered magnesium nitrate hexahydrate (melting point 87 C), but fear that it is too toxic and flammable. The final membrane will be handled extensively and twisted and bent many times over its lifetime.

Could someone please give me some more suggestions of what else to try?
As many as possible (I may want to mix them to even out the heat transfer over the temp range)

Thanks a lot. over its lifetime.

 

[Astronuc]

I am not sure magnesium nitrate hexahydrate would work. If one heats a hydrated salt and removes the water of hydration, the heat is generated when the dehydrated salt is rehydrated (as in heat of hydration). That is different from a phase change. Besdies, in a closed system, where would the water go?

It would seem one needs a material with a low thermal conductivity (which works against heat up, but allows for long slow release of heat) and high thermal capacity.

Hmmm. Interesting problem.

 

[martinl]

I'v pretty much given up on magnesium nitrate hexahydrate, but I think it would still work. The MNH would be completely surrounded by the rubber matrix, so the water would separate out and turn to steam (in a bubble inside the rubber), then as the substrate cools, the steam would condense to water and re-bond into the MNH - a mini closed system.

 

[Q_Goest]

I think at that temperature, the most common material is wax. There are a wide variety of formulations for wax that can give different melting points. Try http://www.thomasnet.com/nsearch.html?cov=NA&which=prod&what=wax&navsec=search&heading=93001808" for manufacturers and more information.

 

[chemisttree]

Try the various esters of palmitic acid. Find some that are liquid at slightly higher than room temperature. Some other compounds you might consider are, in a general class, saturated fatty acid methyl or ethyl esters, cholesteryl esters, rigid rod aromatic esters.