Eventos Anais de eventos
COBEM 2023
27th International Congress of Mechanical Engineering
Performance evaluation of standing wave thermoacoustic engines for different geometries
Submission Author:
Caio Everton , SP
Co-Authors:
Caio Everton, Flávio Bannwart
Presenter: Caio Everton
doi://10.26678/ABCM.COBEM2023.COB2023-1977
Abstract
This work consists of a comparative study between two standing wave thermoacoustic engines that differ in the geometry of their resonant chambers, but hold the same internal elements and operate at the same fundamental frequency and boundary conditions. One of the engines consists of a straight tube of circular cross-section as its main part that defines a resonant acoustic waveguide, while the other one consists of, in addition to a similar straight tube, also a conical bulb connected to one of its ends acting as a coupled Helmholtz resonator. According to the literature, the Helmholtz cavity causes a higher pitch quality in the first harmonic mode, which is, for instance, of greatest interest from the energetic point of view; this better tuning, on its turn, causes a better engine performance. The main objective of this work is to verify and evaluate such an effect on the engine performance so that to explore its optimization by means of frequency and geometric adjustments. Atmospheric air is the working fluid, instead the usual and expensive high pressure He-Ar mixture. Both engines are simulated in the DeltaEC software, which enables determining and fixing the same internal positions for their respective heat exchangers and porous material, whose pores dimensions define the first frequency of resonance and, hence, all longitudinal dimensions. The temperature gradient necessary to trigger the thermoacoustic phenomena is ensured by the heat exchangers. DeltaEC, however, does not include harmonics other than the fundamental one. Despite this limitation, their results reveals better performance for the Bulb engine just because it incurs in less thermoviscous losses on the waveguide internal walls. As a consequence, the evaluation of the actual effects of difference in pitch quality will involve setting higher modes in DeltaEC by means of changing the engine configuration in the light of analytical models. Understanding of the influence of higher acoustic modes may lead to a better management of the thermoacoustic engine configuration towards higher thermal efficiencies.
Keywords
thermoacoustics, thermoacoustic engine, resonance, DeltaEC, harmonics, standing wave
