Performance Characteristics Of Thermoelectric Resonant Tunneling Refrigerator

Seebeck effect and Peltier effect was found as early as the early of19th century, in which the interconversion of heat and electricity was a strong complement to the law of energy conservation. No moving parts and infinite energy conversion brought ecstasy, but low conversion efficiency caused people being discouraged. With the development of electrical technology since from the20th century, thermoelectric effect was focused again on, and how to improve the thermoelectric conversion efficiency has already become a hot topic.The thermoelectric devices stem from thermoelectric effect such as thermoelectric heat engine and refrigerator which work have been widely studied and applied. In early thermionic emission-absorption thermoelectric device, heat flow can be described by the Richardson formula, which is not applicable to the hot small-size devices nowadays. Landauer formula is a good solution to the quantum tunneling in such small-size thermoelectric devices. A thermoelectric device can be simplified as the sketch composed of hot/cold electronic reservoir and electronic conductor, and it can work as a thermoelectric heat engine and refrigerator if the chemical potential of the cold electronic reservoir is higher than the hot electronic reservoir. The efficiency of this kind of thermoelectric device, shown in many researches, depends primarily on the electronic conductor, and it can be close to the Carnot limit as the electrons transmitted selectively.At the beginning of this thesis, The Landauer formula with the same interface area of the two reservoirs was derived by the informal theory. In addition to temperature, chemical potential and the electron transmission probability, found in the analysis of the Boltzmann transport equation, the area of electronic reservoir used to transmit electron also had an impact on the performance parameters except the efficiency. The transmission probability of electrons in the multi-layer barrier and well can be calculated by using transfer matrix method, where the transmission resonance peak in the calculation can be regarded as a good energy filter. The thermoelectric refrigerator had been studied in this thesis. With the same interface area of the two reservoirs (referred to here as the "symmetry"), the impact of conductor in thermoelectric refrigerator had been studied in Chapters3and4. The kx/kr momentum selective mechanism can be applied to the thermoelectric refrigerator, in which the electrons were transmitted by the single/double resonance, and it is shown that the cooling rate of double resonance refrigerator should be larger than the single resonance one, while the coefficient of performance is just the reverse. From the comparison of the two momentum selective mechanisms, it can be obtained that the coefficient of performance of the n-dimensional thermoelectric device can be possible to approach the Carnot value after using the n-dimensional filter. A model of double-barrier rocked ratchet thermoelectric device was described in Chapter4, where a directional current existed during one cycle of the input square wave-voltage and the difference in temperature of the two reservoirs can cause the device working as a refrigerator. After given the bias voltage amplitude V0, a higher the temperature of the electronic reservoir made a wider refrigerator region, a greater maximum cooling rate, but a smaller coefficient of performance.In Chapter5, the performance characteristics of thermoelectric refrigerator with two asymmetric electronic reservoirs were studied. Found from the derived results, the net current of the asymmetric thermoelectric refrigerator is proportional to the minimum area of two electronic reservoirs, and so did the heat flux and entropy increase. The asymmetric thermoelectric refrigerator may be equivalent to the parallel-plate style refrigerator with the minimum area of the two reservoirs as the interface area to transport electrons, then, the model would return to the general situation described by the Landauer equation. With the double-barrier-single-well structure as an electronic conductor, the performance parameters of the refrigerator can be optimized by economic criteria and ecological criterion. The economic optimized area between the maximum cooling rate and maximum coefficient of performance can be obtained by numerical method. Similarly, the ecological optimized area under the optimization criterion EQ of high cooling rate and low entropy increase can also be obtained, and so did the optimization criterion ECOP of high efficiency and low entropy increase. These optimum results had important theoretical significances in both theory and application.