ABSTRACT
In this chapter, the author considers irreversible processes in systems not too far from equilibrium. Examples of situations of this kind are phenomena associated with thermoelectric effects and thermo-osmosis. Thermoelectric effects that involve a coupled electrical transport and heat transport were discovered in the nineteenth century. Thermo-osmosis with the related thermomechanical effect involves the flow of energy and particles between reservoirs at different temperatures and pressures. One of the most dramatic examples of the thermomechanical effect is the fountain effect that is found in superfluid helium. Microscopically, the origin of the Peltier emf may be understood by considering the Fermi levels in two conductors that are placed in contact. In general, the Fermi levels will be different in the two conductors, and transfer of charge carriers will occur to equalize the levels. When charge is transported across the contact between two different metals, heat is either absorbed or emitted, dependent on the current direction, to conserve energy.
