December 2019
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11 Reads
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1 Citation
The Proceedings of the International Conference on Nuclear Engineering (ICONE)
In this paper, the driving power conversion rate of a twophase natural circulation loop is analyzed numerically. In operation of the two-phase natural circulation loop, part of thermal energy is converted into driving power, that is, the gravity difference between steam and water in vertical loops. The power drives circulation flow in this loop and it is converted into kinetic energy of the fluid, which is partially dissipated eventually with flow resistance. In steady state, the conversion rate is equal to the dissipation rate. In this study, modeling and simulation of a general two-phase natural circulation loop are performed. The dissipation rate of kinetic energy with flow resistance is calculated, which is equal to the driving power conversion rate in value. Furthermore, the conversion rate from thermal energy to the power is obtained with the conversion rate calculated indirectly and heat transfer rate of the heat source. Simulation results indicate that the conversion rate can be as low as 0.01%. Based on this result, design improvement of the natural circulation loop is proposed. In this design, the thermoelectric material Bi2Te3 is attached outside part of the heat exchanger tubes. With the material, the temperature difference between fluid inside and outside the heat exchanger leads to voltage, and the heat exchanger with the material actually works as a thermoelectric generator (TEG). In this way, part of thermal energy is converted into electricity with an efficiency which is much greater than that of original two-phase natural circulation loop. The electricity converted is further used to enhance circulation flow of water through a pump and natural convection outside the heat exchanger with a group of agitators. With this design, the driving power conversion rate of the two-phase natural circulation loop is increased, the driving force is enhanced, circulation flow and heat transfer can be improved.