Thermionic Power Generation Efficiency In Cylindrical Semiconductor Nanostructures

The electrical energy was the most commonly used and convenient energy form. But at present the fossil energy was still the main form in generating electricity which had brought the problems of environmental pollution and the energy-hungry that the whole world was concerning about. Along with the enhancement of people's environmental consciousness and as the worry of traditional energy scarce springs up, the scientists from different countries had been trying hard in seeking new way of converting and using energies that were highly effective and non-polluted. Until now we had achieved the aim of using afterheat and waste heat on industry and agriculture, automobile waste heat, geothermy, solar energy and sea temperature difference reasonably and effectively to generate electricity. Studies already showed that some researchers had made generating set with semiconductor or nanometer semiconductor materials. But the actual generating efficiency of electricity was not high. So to increase the generating efficiency of electric power facility had become the most important task at present. However we needed to further understand the hot phenomenon of nanostructure if we wanted to make it real manage and control the heat-carrying granule in this structure.We first systematically studied on basic theories and understood in detail the heat motion and recent development of the nanometer structure including nano-wire, nanometer tube, thin film, superlattice, and the nano-composite structure to lay a solid theoretical foundation for establishing the theoretical model of electric power facility. The generating principle of the electric power facility that we studyed based on the thermionic emission among which we had made the cooling system and the electric power facility. Simply speaking, the power generation and the cooling were two reversible processes. And in this thesis we introduced the thermionic power generation and thermionic cooling in detail. Also we would introduce the related thermionic emission theory and the famous Richardson formula.There were several appealing advantages in the energy converting plan of thermionic emission. First, it transformed directly the heat energy to the electrical energy, and heat energy on making electron emission to produce the electric current directly; Unlike most of other energy conversion device, it transferred the heat energy to the acting fluid before transforming through mechanics or other ways. In that way, it had greatly increased the efficiency by avoiding the loss that general acting fluid sluggish or the turbulent flow and so on. Second, the thermionic energy converter did not have transportable part, for example the traditional heat engine's pump or the turbine and so on, causing advantages of its high reliability, small volume and light weight. In 1998, Mahan had designed a multi-layered geometry periodic potential barrier semiconductor's thermionic emission installment. Inspired by the Mahan multi-layer theory, in 2006, Taofang Zeng proposed an electric power facility model based on the direct packing of nano-wire or nanometer granule on the electrode of nanometer contact surface. The researchers were trying hard in raising the efficiency of power generation through changing the electric power facility's material, structure and so on.Inspired by the proposal of P. Lyu and C. Zhang on the cylindrical semiconductor nanometer structure thermionic cooling system, we wanted to raise the power generation efficiency through changing the shape of the electric power facility. In the cylindrical semiconductor nanometer structural model of this thesis, we discussed two kinds of situations: Model one takes the outer layer as the hot electrode and the inner liner layer as cold electrode; Model two take the outer layer as the cold electrode and the inner layer as hot electrode. In these two models, the electron must traverse the potential barrier through the thermal excitation way while not discover the phenomenon that it put on the potential barrier.Using the law of Richardson and energy conservation, we had studied the thermionic power generation efficiency on the cylindrical semiconductor nanostructure. The numerical results show that the cylindrical structure which takes the outer layer as the hot electrode and the inner layer as cold electrode had higher power generation efficiency than that of the plate model and the cylindrical structure which takes the outer layer as the cold electrode and the inner layer as hot electrode was on the contrary. Also we had obtained the relation between power generation efficiency, inside circle radius, barrier width and hot electrode temperatures under the two situations. Our research had provided the possible way to raise the thermionic power generation efficiency through changing the shape of electric power facility.