Solar/heat-driven thermoacoustic engine

Abstract

With its abundance and cleanliness, solar energy has been harnessed to generate power using various techniques. A thermoacoustic engine is described which was built, instrumented, and tested to demonstrate use of solar power to generate acoustic power. Sunlight is collected using a 3-ft-diam acrylic Fresnel lens and focused on one end of a ceramic ‘‘stack.’’ This engine has a total length of 40 cm and resonates at around 420 Hz. To permit testing on the abundant cloudy days in Pennsylvania, an electrical heater was also built and installed to provide a reliable thermal energy source for indoor measurements. Experimental results are in reasonable agreement with a DeltaE model. When running in solar mode, as a 1/4 wavelength open end resonator, the measured acoustic SPL can reach 120 dB easily at 1 m away from the open end on a clear day. The onset of sound generation can be achieved even with a 1-ft-diam Fresnel lens. While an impressive demonstration in terms of sound output, despite modest efficiency, real solar energy conversion will be improved with inert gas mixtures at higher pressures. [Work supported by ONR, lens provided by G. W. Swift.]