| Summary: | In this Comment, we analyze the performance of a microwave plasma device presented by Ye et al. [AIP Adv. 10, 055002 (2020)]. The efficiency analysis, using conservation of energy, shows that the methods used by the original authors predict up to 8000% device efficiency. Our analytical model is based on a control volume analysis of the original authors’ experimental setup and conditions, indicating that blocking the exit of the device yields stagnation pressure rather than jet pressure. The results from this analysis are consistent with the reported experimental data, demonstrating that the measured pressure using this method is internal chamber pressure and cannot be used to estimate thrust.
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