Friday, February 15, 2013

Breaking Time-Reversal Symmetry Reduces Thermodynamic Efficiency

This was reported a few days ago, but I've only had a chance to read it recently. It is an interesting calculation for the thermodynamic efficiency of a thermoelectric engine in the presence of an external magnetic field, thereby breaking the time-reversal symmetry.

In this spirit, Kay Brandner at the University of Stuttgart, Germany, and colleagues report in Physical Review Letters their calculated efficiency of a simple thermoelectric device that converts heat to electrical current (Fig. 1). They show that when the device operates in an external magnetic field—a condition that breaks time-reversal symmetry for the motion of electrons—the efficiency is significantly lower than previous studies predicted. The lower bound on efficiency occurs, they argue, because in addition to the requirement that entropy be greater than or equal to zero, charge must be conserved—a point that was missed in earlier work. Their findings improve our understanding of thermoelectric efficiency and may one day influence the design of thermoelectric devices for real-world applications.

The rest of the article has a very good detail on why this is such an important study. You also get a free copy of the paper in the link.


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