| | Two bodies of water inside a well insulated tank are separated by a so-called Peltier device (Fig. 1). This is a particular type of thermoelectric device. It can be hooked up to an electric power supply. If we set up a voltage across the device, we observe that one of the bodies of water becomes warmer whereas the other one gets colder (see the diagram in Fig. 2, and Movie 1). Overall, both bodies of water heat up if the tank is sealed.
Interpretation The body of water getting warmer is gaining heat, (*) the other one is losing heat. It makes sense to assume that the heat added to the former is taken from the latter. Since here the heat goes from a cold to a hot body, it does not flow by itself from a higher to a lower thermal level. Heat is said to be pumped by the thermoelectric device. Like any other pump, this one also needs energy to do its job. The Peltier device produces heat as it pumps heat. Therefore, the heat of the two bodies of water taken together increases, and the average temperature rises. A thermoelectric device is a material that conducts electricity (electric charge) and heat. There are no moving parts, and no fluids transporting heat. Therefore, it appears that in a thermoelectric device electric charge can transport heat (and vice-versa: the flows of heat and charge are coupled).
 (*) Note: The technical term for quantities of heat is entropy. What we call heat, and what is officially called entropy by engineers and physicsist is closely related to what scientisits before 1850 called caloric. When presenting phenomena in terms of standard language, it makes sense to keep using the word heat for what we normally call entropy.
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