Thermionic cooling efficiency of functionalized carbon nanotube thin films

Abstract

A large thermionic cooling effect is observed from a functionalized carbon nanotube cathode surface, and the cooling efficiency, defined as thermionic cooling power as a percentage of total input heating power to the surface, is reported. The cathode consists of a thin tungsten ribbon covered with low work function barium strontium oxide coated carbon nanotubes. It has both a low work function surface and a large Schottky field effect induced by the carbon nanotubes. The combination of the two leads to a strong thermionic emission and hence a relatively large thermionic cooling effect and high cooling efficiency. Detailed measurements of the cathode temperature profiles are presented together with the analysis of the cooling efficiency. The highest cooling efficiency obtained in this study is 5.9% at 1099 °C of cathode temperature and 114.5 mA of thermionic emission current. The dependencies of the cooling efficiency on the cathode temperature and on the emission current are also presented. Prospects of further improvements are discussed as well.