PCM with large volume change but low heat storage capacity

[eknifff]

I'm trying to find a Phase Change Material (PCM), but the entire industry is pretty one-minded when it comes to what it should be used for - energy storage. You can see by the wording of the Wikipedia article:
https://en.wikipedia.org/wiki/Phase-change_material
that they list advantages like "High volumetric latent heat storage capacity" and disadvantages like "Change of volume is very high"
However, for my project, I'm actually trying to find the opposite! I'm looking for a PCM with large volume change but low heat storage capacity. Finding it really hard to google this as the industrial bias means everyone is looking the other direction, so I'm putting this out here. Anyone knows of any PCM, or broadly any PCM type, that fits this description?
Thanks!

 

[Dr. Courtney]

It's hard to have a big change of volume without doing work (storing heat).

 

[eknifff]

Thanks Dr. Courtney! That makes good sense.

Speaking of this energy imbalance, I noticed that commercial providers rarely provide specifications on acceptable pressures, usually only giving operational limits in terms of temperature. Does this mean that it is fine for all reasonable pressures? That doesn't really make sense, because the expanding PCM might end up doing a lot of work if the external pressure is large, while the amount of heat energy input seems to be approximately a constant.

 

[Dr. Courtney]

It would e hard to hold providers to their specs at pressures that were not close to atmospheric pressures.

 

[eknifff]

So physically, what's happening when I put in enough energy to melt the PCM, but I constrain the material with a large pressure such that its expansion would result in more work done than the heat energy I put in?

 

[Baluncore]

What temperature transition are you looking for ?
Do you need a solid–liquid or liquid–gas phase transition ?

The traditional thermostat fitted to ICEs contains a blend of paraffin wax. That is selected because it has a large volumetric change over a narrow temperature range.

If you know the temperature of the transition then look at a table of melting points for organic chemicals. The CRC handbook has such tables, sorted in temperature order.

I once used that technique to find a chemical for a specific temperature sensor and found that Lewisite had the optimum properties. Unfortunately it is highly toxic, so check your selection carefully.