Any idea where to find a 'constant' temperature material?

"RobertMacy"

The "material" is probably a liquid that boils at 140F when under vacuum.

.... Phil

Any phase change will do. But ideally, materials with exceptional heat capacity, like water (but do mind the mechanical expansion). To some extent, you can manipulate the melting point, but only downwards (pick a eutectic you like, usually involving something dissolved like sugar or salt, or a miscible liquid like ethanol or ethylene glycol).

Higher temperatures mean you have to start with something hot and bring it down, usually an organic compound or salt mixture. For instance, mixed alkaline nitrates are used in heat reservoirs (e.g. base load solar power plants) for a convenient ~300C range phase change.

There should be a chemical handbook somewhere listing a whole lot of physical properties e.g. latent heat, melting point, etc. Less likely, phase diagrams of suitable combinations (to find eutectics, likely combinations, etc.).

Tim

-- Seven Transistor Labs Electrical Engineering Consultation Website:

Try a Google search on "phase change", "temperature", and possibly "wax".

A short-lived product at a company I once worked for used heat sinks filled with wax that melted at a specific temperature, allowing the equipment to operate for a while at temperatures well above the chips' operating points, with long breaks in between.

mat'ls use freeze-thaw cycle usually. You hafta be specific, since the Devil's in the details, for these recipes. A RT system is Glaubers salts, hydrated sodium sulfate.

You tend to suffer super cooling problems and change in volume if the phase change is solid-liquid and slightly less so if liquid-gas although overpressure could result in an explosion.

Strong mixtures of washing soda and sodium thiosulphate will do something approximationg what you say you want after a fashion.

Certain reusable handwarmers use a variant of the supercooled liquid to crystaline transition. Basically it is a mug's game even trying.

even better! thank you!

My newsreader is somehow setup to display 'top' responses first, AND when I hit reply, left only your posting, so EVERYTHING went faster.

Hmmm...only come 'down' in temperature, perfect!

True, especially with organics. Boiling doesn't appeal to me as much because the temperature isn't constant. Perhaps dE/dT is enough to be worthwhile though.

Hmm, doesn't ring a bell!

Yep, supersaturated (melted, really) sodium acetate trihydrate. Or something to that effect. Popular YouTube plaything.

Others are magnesium and water (e.g. MRE heater packs), or for the opposite effect even, something very soluble like ammonium nitrate or urea dissolving in water.

Tim

google somehow has 'ruined' itself with links to 'dead' websites [you'd think they'd have 'bots checking] and a bunch of unrelated ads for ?? products disguised as search results.

Wax? kind of a poor man's 'heat pipe' for cooling ?

can accept a wide range, somewhere in the 67F to 90F range will work

Pictured that problem, too.

Do you know the temp range? And the caloric requirement?

Probably too hot, but the right idea.

Who can tell? The OPs problem is so ill specified that it is probably only possible with copious amounts of unobtanium.

The thiosulphate supercooling demo is a classic and a variant is the hand warmer formulation (which I may have misremembered or more likely the handwarmers use a safer formulation than I recall).

Trouble is most of them are either a modest effect or irreversible.

Rubber Chemicals Handbook...

Most practitioners are aiming higher still with the intention of hot molten slat eutectic mixtures for solar energy storage eg.

better be even more specific what you want. These salts are difficult to package. Glaubers salts is a prototypical favorite. Heat of hydration. If you can use a thermoelectric cooler, or a heater-feedback system, do it!

BTW, hand warmers are just iron powder, carbon black, salt, and saw dust.

Can't there's NO power available, and I can't even bring my own power.

Material should have a 'narrow' temp range, somewhere between 67F to 90F will work. Even if slope is over 10F, staying within that range is perfect.

Must be sealed, self-contained. Vessels to sustain pressure changes, and military temperatures of -55C to 125C

Must be allowed to ship this material between factories by international air without special 'explosive' or 'hazardous/poisonous chemicals' permits required.

Would like to get a LOT of calories required for transition.

Need more specs?

atmosphere.

This site:

says the heat of fusion is 8.04 x 10^4 J/kg so 20kg of Ga would supply about 0.45kWh of energy.

MSDS is not the scariest I've seen:

Transport regulations in liquid form would have to be looked into. It expands when it freezes.

Metal trading prices place the gallium at about $300/kg, so not too bad, but you'll probably have to pay several times that for retail.

Much more critical is that it causes aluminium to disintegrate into dust very quickly just like mercury will.

No. Only refined unobtanium will do what you require.

Yeah, I was going to mention that Al embrittlement inconvenience. It might make it pretty unpopular for airplane use.

When I used to transport stuff containing many kg of Hg we had to use surface means typically.

Here's what might be a useful paper on use of Glauber's salt and similar phase-change materials in solar heating applications:

--sp