Lecture8_ThermoelectricDevices

Lecture8_ThermoelectricDevices - ecture 8 Lecture 8...

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Unformatted text preview: ecture 8 Lecture 8 Thermoelectric Devices Focused on Generators for this class but coolers are designed nearly identically ECE 4833 - Dr. Alan Doolittle Georgia Tech Heat Flow in a Slab Hot Cold Surface Surface Since energy flows from high energy to lower energy, heat will from hot surface to cold surface Heat conduction (inside the material) can be mediated in several ways: Phonons Mobile carriers Metal: electrons and holes in a metal Doped Semiconductor: Either electrons or holes Ionic Conductor: Ions ECE 4833 - Dr. Alan Doolittle Georgia Tech History and Terminology hermoelectric Effect or Thermoelectricity: Differs from Thermoelectric Effect or Thermoelectricity: Differs from thermophotovoltaics in that thermophotovoltaics is merely small bandgap solar cellsthat can absorb and convert infrared heat energy. Critical work was performed by Jean Charles Athanase Peltier (French), and Thomas Johann Seebeck (German). Seebeck Effect is the generation of a voltage across a material as a result of a temperature difference. Peltier Effect is the opposite generating a temperature difference as a result of an applied voltage/current. This is used for refrigerant free cooling. ECE 4833 - Dr. Alan Doolittle Georgia Tech Heat Flow Normally Equilibrium Hot Cold Surface Surface N-type In a n-type material, hot electrons diffuse to the cold side and cold electrons diffuse to the hot side eventually resulting in a constant temperature structure. Note also that a high thermal conductivity (heat flow dominated by phonon transport) material will also result in a near constant temperature profile (equilibrium). N-type ECE 4833 - Dr. Alan Doolittle Georgia Tech Heat Flow from a Source to Sink Hot Cold +- Opposing Electric Field results that limits charge transfer and thus total voltage Surface Surface N-type If something changes the imbalance of hot/cold electron diffusion, a net charge can result on one side relative to the other. charge can result on one side relative to the other....
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Lecture8_ThermoelectricDevices - ecture 8 Lecture 8...

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