Numerical and experimental analysis of a transcritical thermoacoustic prototype

An experimental rig has been developed to study the thermoacoustic response of a supercritical fluid. A linear topology is employed to study standing waves in a system composed of a heater, a thermoacoustic stack, and a variable-length resonator. A linear analysis has been developed to aid with definition of the facility and a commercial refrigerant has been utilized as the working fluid. As this fluid is a compressed liquid at ambient temperature, a separate pressure regulation system is included whereby a bladder accumulator tank permits one to set rig pressure by adjusting nitrogen pressure on the other side of the bladder. An additively manufactured Inconel stack and a graphitic foam stack have been evaluated over a range of conditions. Acoustic frequencies from these experiments are in agreement with model predictions, but sustained oscillations were not obtained in either stack to date. Current efforts are aimed at improving the model to reflect the presence of the accumulator line with the hope that this will help explain the damped acoustic behavior.