2, University of Virginia, Charlottesville, Virginia, United States
The design rules for active cooling systems of electronic devices or batteries are quite different from those for Peltier refrigeration. Peltier modules made from tetradymite materials  are used commercially for refrigeration, pumping heat opposite the natural direction, but have yet to compete in active cooling where the heat flux from a hot source to a cold sink is the parameter that must be optimized. In particular, a high thermal conductivity is beneficial in the materials used for active cooling, since it allows a higher heat load to be carried away from the device to be cooled, whereas it is obviously detrimental to the ZT of a Peltier element used in refrigeration mode. The real objective of active cooling is to maximize the effective total thermal conductance, due to both the Fourier and the Peltier heat fluxes, rather than the ZT, which determines the minimum reachable cold temperature in a refrigeration application. Optimal materials for maximum active cooling are those with high thermoelectric power factor and high thermal conductivity .
Metals with large thermopower due to magnon drag offer such a prospect. A cooling module is constructed from several possible n and p-type metals with high thermoelectric power factor. It is connected so as to pump heat from a variable-power heater into a heat sink. The thermal conductance is first characterized against the temperature gradient in the absence of a Peltier current (passive cooling mode). It is then characterized again in the presence of an electrical current that maximizes the Peltier heat flux (active mode). The ratio of the thermal conductance of the cooler in active and passive mode is shown as a function of temperature drop and background temperature. The dynamic response is further analyzed and compared to the time constant predicted by thermal resistance and capacitance.
1. Heremans et al., Nature Review Materials, 2 17049 (2017)
2. Zebarjadi, M. Electronic Cooling Using Thermoelectric Devices. Appl. Phys. Lett. 106, 203506 (2015); doi:10.1063/1.4921457