When a direct current voltage is applied to the module terminals, electrical current flows from the supply voltage's positive terminal to the negative terminal. In the configuration shown in Fig. 5, this is represented by an anticlockwise current flow. The positive pole of the supply voltage attracts and repels the negative charge carriers, i.e. the electrons, in the n-type bismuth telluride pellet. Similarly, in the p-type material, positive charge carriers, i.e. holes, are attracted by the negative potential of the supply voltage and repelled by the positive potential, and move in the opposite direction to the electron flow.
Heat is transferred from one side of the thermoelectric couple to the other in the direction of charge carrier movement by these charge carriers. The charge carriers in the n-type pellet are negatively charged electrons that absorb heat from the 'cold' side of the thermoelectric couple and transfer or 'pump' it to the 'hot' side of the couple in a clockwise direction. Similarly, the positively charged carriers in the p-type pellet, the holes, absorb heat from the cold side of the couple and transfer it in an anti-clockwise direction to the hot side of the couple. Several of these thermoelectric couples are connected electrically in series and thermally in parallel to form practical Thermoelectric Modules. Arranging the thermoelectric couples in this way allows the heat to be pumped in the same direction.
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