Carnot temperature and microwave cooking
By Neil Stacey
Industrial chemical reactors are commonly understood as analogous to heat engines; chemical processes frequently require both heat (increase in energy) and work (decrease in entropy) to operate. Just like in a heat engine, work can be supplied along with the required heat, but this is limited by the temperature of operation according to the Carnot equation: W=Q.(T_hot-T_cold)/T_hot.
The Carnot temperature of a reaction is that temperature at which the reaction's work requirements are exactly met by supplying its heat requirements. Below this temperature, heat must be oversupplied in order to meet work demands. Microwave cooking avoids this drawback by supplying energy in a non-thermal form with higher work potential, and/or creating localized hot spots where high Carnot efficiency is achieved without high bulk temperatures.
This may explain some of the efficiency and cooking-time improvements achieved by microwaving. Not widely known, however, are the Carnot temperatures for most cooking reactions, which would indicate the preferred cooking modalities for different foodstuffs, based on the heat and work requirements of those specific chemical reactions. Broadly investigating Carnot temperatures for cooking reactions would yield a guide for selecting efficient cooking modalities. Some foods may also have different nutritional properties depending on cooking modality based on which reactions are favoured.