Performance of an air‐cooled looped thermoacoustic engine capable of recovering low‐grade thermal energy

Abstract

Summary An air‐cooled looped thermoacoustic engine is designed and constructed, where an air‐cooled cold heat exchanger (consisting of copper heat transfer block, aluminum flange, and aluminum fin plate) is adopted to extract heat and the resonant tube is spiraled and shaped to fit to the available space. Experiments have been conducted to observe how onset temperature difference and resonant frequency are affected by mean pressure, working fluid, and diameter of compliance tube. Besides, the influences of temperature difference, mean pressure, working fluid and diameter of compliance tube on pressure amplitude, output acoustic power, and thermal efficiency of the system have been investigated. The air‐cooled looped thermoacoustic engine can start to oscillate at a lowest temperature difference of 46°C, with the working fluid of carbon dioxide at 2.34 MPa. A highest output acoustic power obtained is 6.65 W at a temperature difference of 199°C, with the working gas of helium at 2.58 MPa, and the thermal efficiency is 2.21%. This work verifies the feasibility of utilizing low‐grade thermal energy to drive an air‐cooled looped thermoacoustic engine and extends its application in the water deficient areas.

Performance of a Modified Two-Phase Thermofluidic Oscillator With Low GWP Working Fluids for Lowgrade Waste Heat Recovery

“…Recently, much interest has been drawn on low-grade waste heat recovery. Among the available technologies such as organic Rankine cycle [2], Kalina cycle [3] and thermoacoustic engine [4], two-phase thermofluidic oscillator [5] has received increasing attention, thanks to its ability to operate across a small temperature difference between heat source and sink. In 2004, Smith [5] constructed a two-phase non-inertive-feedback thermofluidic engine (NIFTE), which was featured as having no moving parts.…”