What kind of processes are there using which it is possible to change the temperature of a material as fast as possible.
You are allowed to use any material you want.
It should remain in the same state of matter (solid/liquid/gas) within the temperature range of 5 to 65 degrees celsius.
The material should be able to suddenly reverse the direction of temperature change - so if i want to reduce its temperature at a given rate and then suddenly increase its temperature after a short period (generally <1s) there should be least resistance to reversal of the direction of temperature change.
Bonus points for minimising the amount of energy needed to do the above per unit mass, per unit temperature.
Bonus points if you can think of a liquid to do the above.