Thermoelectricity is the phenomenon of the direct coupling of transports of electricity and heat (entropy). Electricity carries entropy, or entropy carries electricity. In materials that show this phenomenon, the flow of entropy from high to low temperatures sets up a voltage, i.e., it makes a generator out of the material. Alternatively, if we make electricity flow through such a material with the help of a battery, entropy is swept along from cold to hot. The material acts as a heat pump.
Peltier devices implement these phenomena. When used as heat pumps or refrigerators, they can cool electronics such as CPUs of computers, or CCD imaging devices. They even have been used to cool biological samples (parts of the brain of rats to control seizures).
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