Design, construction and evaluation of a standing wave thermoacoustic prime mover

Abstract

A standing wave thermoacoustic prime mover (TAPM) has been succesfully designed, constructed, and evaluated. It consists of a resonator with length of 128 cm, a stainless-steel wire-mesh stack with 14 mesh number, two heat exchangers, and air at atmospheric pressure as the working gas inside the resonator. The stack is placed inside the resonator near one of its closed-ends and has 4 cm length. The hot and ambient heat-exchangers are attached at each end of the stack to provide a large temperature gradient along the stack which is required for generating acoustic energy. An electric heater with maximum power of 400 W is used to supply thermal energy to the TAPM. The temperatures and dynamic pressures are measured by using type-K thermocouples and pressure transducers, respectively. We evaluated the prime mover by experimentally investigating the influence of heat input power on the onset temperature difference, time to reach the onset condition, sound frequency, and sound pressure amplitude. It was found that input power below 255 W could not generate sound, and its increase from 255 W to 400 W did not significantly change the onset temperature difference and sound frequency, namely of around 258 °C and 141 Hz (at temperature difference ΔT across the stack of 300 °C), respectively. In addition, the increase of input power in the range of 225 W − 400 W has raised the pressure amplitude from 3.3 kPa up to 4.5 kPa (within ΔT of 300 °C – 320 °C). Moreover, we found that the time to reach onset condition was inversely proportional to the input power. We also checked the influence of temperature difference across the stack on the sound frequency and sound pressure amplitude. It was observed that the frequency was slightly increasing from 139 Hz to 142 Hz and pressure amplitude was getting higher from 1.4 kPa to 5.1 kPa when the temperature difference was rising from 280 °C to 350 °C, with input power of 353 W.