What is the working principle of a thermoelectric cooler in an aquarium?

When a current is passed through a wire, heat is generated and the generated heat is called Joule heating. This heat is proportional to the current and the resistance of the wire. A thermoelectric cooler is made up of a hot side and a cold side. The cold side is made up of thermocouples and the hot side is made up of thermocouples and a heat sink. When a current is passed through the hot side, heat is generated and the heat is carried by the heat sink to the cold side. Fourier’s law states that the heat flowing from a hot object to a cold object is proportional to the temperature difference between the two objects and their thermal conductivity. Since the cold side is made up of thermocouples and has high thermal conductivity and the temperature difference is high, the amount of heat transferred is large. This heat is then carried by the cold side to the heat sink.