A large thermionic cooling effect is reported. Temperature reduction as much as 81 C has been
observed on a functionalized carbon nanotubes (CNTs) cathode surface. This cathode utilizes a
thin coating of low work function barium strontium oxide emissive materials on top of the CNTs to
lower the surface work function. This, combined with the field effect induced by the CNTs, results
in an even lower effective work function, and thus strong thermionic emission. Strong thermionic
emission is the underlying reason for the large cooling effect observed, and the largest emission
current in this study is around 160 mA on a 0.0727 cm2 emitting surface at around 995 C. Multiple
samples were used in studying thermionic mission at cathode temperature ranging between 750 C
and 1100 C, and in establishing correlation between the cooling effect and the emission current.
Details of the cooling effect measurement are provided, and the measurement results show a clear
linear dependence of temperature drop on thermionic emission current. The possible implication of
this linear dependence is also discussed. VC 2015 AIP Publishing LLC.
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