Characterization of bidirectional impulse turbines for thermoacoustic engines

Abstract

A bidirectional impulse turbine to convert thermoacoustic power into electricity is investigated. Experimental measurements are done with a loudspeaker for varying acoustic conditions and turbine loads. The results are used to characterize the turbine performance and compare it to steady flow turbomachinery and turbines in oscillating water columns. A dimensional analysis is done to identify the variables that influence the turbine performance, after which a scaling is determined that uniquely determines the efficiency of the turbine. The work is finished by providing the impedance of the bidirectional turbine such that it can be implemented in a thermoacoustic engine.

Optimizing bidirectional impulse turbines for thermoacoustic engines

“…Furthermore, the maximum efficiency that can be reached for both cases is independent of the turbine load. Finally, just as shown for the unshrouded rotor in previous work, 8 it is found that the acoustic frequency has a negligible influence on the turbine efficiency for the shrouded rotor. It can therefore be said that the shrouded rotor outperforms the unshrouded rotor for all investigated operating conditions.…”

“…A more elaborate explanation about the experimental procedure, including processing, validation, and error estimation, can be found in previous work. 8 The raw data, processing scripts, and processed results for all experiments presented in this work can be found in a supplementary data publication. 11 The experimental setup is shown schematically in Fig.…”

“…Subsequently dividing the shaft power with the acoustic power drop yields the efficiency of the bidirectional impulse turbine, g t . Following the error estimation procedure from previous work 8 and extrapolating for the current turbines, it can be said that results that show more than 0.8% difference in turbine efficiency can be regarded as reliable.…”

“…7 Previous work has confirmed that a bidirectional impulse turbine can also convert acoustic power into electricity for a range of thermoacoustic conditions. 8 This work has mainly focused on proving the concept and characterizing the performance of a first turbine prototype. The maximum efficiency of the turbine was found to be 25%, which is significantly lower than the 37% efficiency for the turbine in an OWC on which the first prototype was based.…”

Implementing a bidirectional impulse turbine into a thermoacoustic refrigerator

“…5 In previous work, a bidirectional impulse turbine was characterized under thermoacoustic conditions to identify the relevant performance indicators, and provide rules of scaling. 6 Subsequently, the turbine has been optimized under thermoacoustic conditions to reach an efficiency of around 36%, 7 which is in the same order as found for OWCs. 8 For both OWCs and the previous work, the turbine is used under atmospheric conditions with air as a working fluid.…”