An experimental analysis on a simple thermoacoustic generator for solar energy application

Solar energy could be readily applied and converted into other forms of energy. Especially, there are many ways to exploit its thermal energy converting to high-grade forms of energy. This paper introduces an experimental work where thermal energy is converted into acoustic energy by a simple resonator tube. The resonator tube consists of a tube closed at one end and a stack (porous ceramic material) inserted into the tube. Here, the stack serves as a thermal insulator and prime mover inducing cyclic motion of air parcels in its channels similar to a Stirling cycle. A series of experiments were conducted to observe the development of thermoacoustic waves when different lengths of resonator tubes and stacks were used. The effect of thermal gradients across a stack was also investigated as it plays a key role in sustaining a cyclic operation of air parcels and sets up thermoacoustic waves in the resonator tube. As envisioned by the theory of thermoacoustics, only those of certain wave lengths (4 times the tube lengths) were sustained and eventually developed to steady standing waves inside the tube. It was also observed that onset of thermoacoustic waves is directly influenced by the stack position and the physical dimensions (diameter, length) of the resonator tube. For the resonator tubes of 10mm and 20mm in diameter (inner diameter), it took about 70 seconds (the maximum onset time) for thermoacoustic waves to be generated and detected. The minimum onset time ranged from 11 secs to 16 secs, which also depended on the conditions aforementioned.