Investigation of Plasma Propagation in Packed-Bed Dielectric Barrier Discharge Based on a Customized Particle-in-Cell/Monte Carlo Collision Model

Round 1

Reviewer 1 Report

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Author Response

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Reviewer 2 Report

In this paper, the authors developed a PIC/MCC model using commercial software to simulate streamer propagation characteristics in a packed bed plasma reactor. They found that the speed of streamer propagation and the distribution of plasma are strongly influenced by the dielectric constant of the packed pellets. Generally, this topic holds significance in plasma catalysis and thus warrants thorough investigation. However, the authors have yet to fully realize the capabilities of their model, and the currently presented results are insufficient to substantiate such a topic. Additionally, the simulation results lack a comparison with previous research. Please take into consideration the following comments:

 

1. The first paragraph of the Introduction requires more references.
2. Line 138 indicates that only electrons and 3 types of N/O ions are considered. Could such a simplified setup impact the model's validity, given the exclusion of other crucial species like nitride metastables and other radicals?
3. In Line 164, the term "plasma density" lacks clear definition. While commonly used in industry, for a simulation study like this, it's necessary to specify whether it refers to electron or ion density.
4. When discussing the transient propagation process of surface streamers, the authors exclusively present plasma density and electric field distribution plots. While these plots already convey plenty of information, it's more intuitive to present both electron and ion density distribution. In this way, one can identify the space charge accumulation region, thereby aiding a better understanding of how the electric field distribution arises. If possible, please also consider including an ionization rate plot.
5. In Figures 2-4, how do these results compare with findings from previous studies?
6. In Figure 4, a dielectric constant of 400 is assumed, greatly exceeding typical dielectric material values. It would be beneficial to mention whether any dielectric materials fall within this range.
7. The authors should elaborate on how the discoveries in this paper specifically impact the design of a packed bed plasma reactor.

 

Author Response

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Reviewer 3 Report

This is an interesting, well-structured paper.

The key area for improvement prior to publication is the explanation for the width of the plasma region in Figures 2 and 3.  I frankly do not know if this requires a simple tutorial explanation or more in-depth examination. Points that this this reviewer had a challenge understanding include:

1.       You refer to the breakdown as consisting of “streamers” and given the geometry that seems reasonable. Streamers, however, typically have a diameter an order of magnitude smaller than shown in figures 2 and 3.  I have measured the growth of the plasma column due to the follow current after the electrodes have been bridged by a streamer. In this case, however, the dielectric barriers would reduce the follow current and radial growth would occur on much slower times than the ones in the figures.

2.    Figure 2a suggests a swarm of individual streamers with plasma at the tips or a tree-like structure seen in many other situations. The problem is that structure is rare in practice. One streamer tends to grow faster than others, reducing the driving electric field others experience, so they do not have a significant plasma at the tip. I have found that I had to include the relevant physics in my streamer growth models or risk the model producing unphysical results.

3.    What defines the width that you predict? It is likely a combination of the electron free-path distribution and the geometric field distribution. If it was mentioned, I missed it.

Without further discussion, it is impossible to understand the extent the results reflect the processes that occur or are simply reflections of poor assumptions. 

Author Response

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Reviewer 4 Report

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Round 2

Reviewer 1 Report

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The authors of this paper have examined my comments thoroughly and have revised their paper accordingly. They have addressed all the issues and greatly improved the quality of the paper. I now recommend the publication of this paper. 

Author Response

Thanks for the positive comments.

Reviewer 3 Report

The modifications are improvements and publication is approved

Author Response

Thanks for the positive comments.

Reviewer 4 Report

The authors have resolved my concerns/questions. I would like to recommend it for publication.

Author Response

Thanks for the positive comments.