A closed vessel contains ‘liquid nitrogen’. This vessel could be used in a ‘cooling room’ to cool fruit and vegetables (5°C), for example. Is that cooling ‘eternal’?

Answer

You can cool a room with liquid nitrogen, but contrary to what you suggest, it is not the pressure that causes the cooling and the cooling is certainly not eternal.

Liquid nitrogen boils at -196°C and this evaporation removes heat from the environment, cooling it down. All of the heat is used to convert liquid nitrogen into gaseous nitrogen and the temperature remains constant at -196°C. This immediately shows that the cooling effect ceases as soon as all nitrogen has evaporated.