열음향파 발생장치의 열적특성에 관한연구

Abstract

Interest in new types of renewable energy is increasing at home and abroad because of rise in the amount of CO2emissions caused by the use of fossil fuels and because of security problems with nuclear power plants. Various technologies harnessing new renewable energy have been developed thanks to strenuous efforts made by scientists and engineers. Of these, some monumental progresses have been made regarding the development of thermoacousticsystems, which convert thermal energy into acoustic energy by applying thermodynamic principlesin forward or reverse processes associated with its conversion. Unlike most other energy conversion systems, thermoacoustic converters generally do not require complicated machineries in their operation, and accordingly their structuresare simple and also highly reliable. Above all, they are capable of generating power using solar heat,waste heat, and other energy sources. This versatility in energy utilization makes thermoacoustic converters more attractive when compared to other systems and environmentally friendly. The acoustic energy generated by athermoacoustic system can be utilized in many ways such as removing kidney stones, exploring mines, processing materials and promoting sanitation & hygiene (surface cleaning, sterilization, and so on). Air-coolers based on thermoacousticconverters are currently used in naval vessels and space shuttles. Moreover, they are effectively applied to generate sound waves and to produce electric energy by means of piezoelectric materials. This research work has been carried out to analyze the effect of geometric parameters and temperature changes on the sound frequency of thermoacoustic systems. The geometric parameters are the lengths of a stack and a resonator tube, which are the major factors affecting the temperature gradient across the stack. Resonator tubes with different lengths (50, 40, 30, 20 mm) were made of copper for the cooling rate, and stacks with different lengths (15, 10, 5, 4, 3 mm) were made of ceramic because of its high thermal resistance. The stack operates as an insulator between the hot and cold regions of the resonator tube, which creates a steep temperature gradient, improving the system's efficiency. It was observed that the sound frequency increased when the length of the resonator tube decreased and the length of the stack increased. It was also found that the steeper temperature gradient along the stack leads to a higher sound frequency. The maximum sound frequency was 3,006Hz when the resonator tube was 20mm in length and the stack was 5mm in length, and the average sound frequency was 2,600 Hz. When the ratio of the stack's length to the resonator's length was greater than 1/4, acoustic waves were rarely generated because of greater viscosity and thermal loss.