Thermionic Generators: Low Efficiency Explained

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SUMMARY

The discussion focuses on the low efficiency of thermionic generators and thermoelectric generators, specifically highlighting the limitations imposed by low potential differences and current leakage. It is established that thermoelectric devices require low impedance to maximize current, which necessitates closely spaced junctions that lead to significant heat loss through conduction. In contrast, thermionic devices suffer from heat radiation, and insulating them sufficiently can cause the collecting electrode to become an emitter, further diminishing efficiency.

PREREQUISITES
  • Understanding of thermionic emission principles
  • Familiarity with thermoelectric effect and Seebeck effect
  • Knowledge of electrical impedance and its impact on current flow
  • Basic concepts of heat transfer, including conduction and radiation
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  • Explore advanced thermoelectric materials and their efficiency improvements
  • Investigate methods to reduce heat loss in thermoelectric devices
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Engineers, researchers, and students interested in thermoelectric and thermionic technologies, particularly those focused on improving energy conversion efficiency in thermal systems.

sid_galt
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Why is the efficiency of generators working on thermionic emmission and the generators working on the seebeck effect (thermoelectric) so low?
 
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I believe it is related to the fact that the potential difference is low for a given temperature difference, and perhaps current leakage also limits the current.

You might wish to look at this paper - http://www.humphrey.id.au/papers/JAP2005.pdf
 
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I alway thought it was heat loss. In thermoelectric devices, since the voltage is so low, you need low impedance to get lots of current. To get low impedance, you have to place the junctions close together and the material connecting the junctions wastes a lot of heat by conduction between the juncitons.

With thermionic devices, they radiate lots of heat. If you insulated them enough to catch most of the heat, the collecting electrode would get hot and become an emitter, itself, counteracting the emitting electrode.---I think.
 

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