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As the title suggests – does there exist a liquid with a lower specific heat then water but with a higher thermal conductivity?

I thought of this in the context of sous vide cooking: Ideally, the liquid involved would transfer heat to the food quickly (hence high thermal conductivity), but would also respond to quick changes in temperature (hence the low specific heat), reducing the risk / time of heater element overshoot.

So, are there such liquids? (preferable ones that stay liquid between 20 and 85 degrees Celsius).

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  • $\begingroup$ ...How toxic is the liquid allowed to be? $\endgroup$ – Richard Terrett Jun 4 '13 at 9:02
  • $\begingroup$ Let's start with anything the won't melt plastic or aluminum, and that doesn't burst into flames when in contact with water or oxygen. $\endgroup$ – nbubis Jun 4 '13 at 15:20
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    $\begingroup$ *crosses mercury, gallium, galinstan, caesium off the list, for one reason or another. $\endgroup$ – Richard Terrett Jun 5 '13 at 2:25
  • $\begingroup$ Do you actually need it to respond quickly to changes in temperature? Normally the water bath is kept at a constant temperature and the food is inserted/removed when needed. With a higher heat capacity there is less of a risk of overshooting the temperature as it will heat up/cool down slowly. $\endgroup$ – Nick Jun 7 '13 at 10:58
  • $\begingroup$ On reflection, that cooking method is fairly medium independent given its long timescales. What matters is a control system for holding a constant temperature over a long period of time. Startup effects on warming at the start will not matter at all. $\endgroup$ – matt_black Jan 17 '14 at 16:11
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Most heat transfer through fluids is actually convection rather than conduction, so you need something that expands a lot with heat and has a low viscosity. Mineral oils or silicone are used as heat transfer fluids when temperatures above 100 °C are needed, but they are much more viscous than water. However, for your system I guess that heat capacity is actually the most important number, as convection will be sufficient to ensure an equal temperature throughout the system (unless you actively impede it) even with a viscosity slightly higher than that of water.

Eyeballing some of the tables at http://www.engineeringtoolbox.com I’d suggest trying ethanol – its heat capacity is around half that of water, its viscosity is not much higher and it stays liquid over the desired range. Plus of course, unlike some of the more exotic solvents, it’s not a disaster if some of it does leak in to your food. If the food isn’t actually going to be eaten (just for demonstration purposes) then you could perhaps try toluene or petrol (gasoline).

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    $\begingroup$ Of course ethanol is highly flammable and this would matter if it was nearly boiling and the flammable vapour was flowing out of your vessel onto a gas flame or a glowing heating element. $\endgroup$ – matt_black Jan 17 '14 at 16:07

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