EXPERIMENTAL AND THEORETICAL STUDY OF NONLINEAR HEAT TRANSPORT AT THE ENDS OF A HEATED STACK IN A THERMOACOUSTIC PRIME-MOVER

摘要

Thermoacoustic engines have been developed since three decades and appear nowadays as potentiality for niche applications at moderate powers, notably for the recovery of waste heat. However, there still remains open questions about the complex heat exchange processes occurring at the ends of the stack and of the heat exchangers. So, this paper aims at investigating such phenomena, and attention is focused on the experimental and theoretical study of nonlinear heat transport processes generated by large amplitude acoustic oscillations at the ends of the stack of plates in a standing wave thermoacoustic prime-mover. The experimental set-up is based on a time-resolved and full-field digital holography interferometry technique, which is applied to the measurement of the density fluctuations from the optical phase difference between two laser beams (a reference beam and a probe beam). This measurement of density fluctuations in the vicinity of the stack is performed for the case of (uncontrolled) self-sustained acoustic oscillations generated spontaneously in the thermoacoustic prime-mover, and then for the case of an assigned acoustic field whose amplitude is controlled by an external sound source. A theoretical model describing the nonlinear heat transport by gas parcels going back and forth through the ends of the heated stack is presented, and enables to predict the resulting large distorsion of temperature fluctuations. From the modeling, numerical simulations are carried out. The comparison between experimental data and numerical simulations is provided for several stack positions, several sound pressure levels, and several amounts of heat supplied to the stack. The results show good agreement between the experiments and the model. The potentiality of the experimental set-up to investigate other processes like the thermoacoustic amplification of sound within thermal boundary layers, or like the rate of unsteady heat released by flames within acoustic resonators will be also discussed.