Selective Multidimensional Particle Fractionation Applying Acoustic Fields

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript reports experimental results on the acoustic fractionation of airborne microparticles. The study primarily focuses on two experiments:

(A)    Phase-Doppler Anemometry (PDA): Used to measure particle accumulation of particles and size distribution at nodes and lobes of an acoustic standing wave.

(B)    Particle Deposition Experiments: Conducted using an acoustic fractionation device to analyze deposition patterns.

 The reviewer recommends a major revision of the manuscript based on the following points:

                         

(1)

The manuscript, particularly the introduction to line 230, is excessively length and redundant. If this is intended as an original research article (as opposed to a review/perspective paper), the reviewer strongly suggests that the authors substantially simplify their explanations on physical background and conventional knowledge. It would greatly improve readability and impact.

 (2)

Numerous typographical errors throughout the manuscript diminish its readability. A thorough proofread and correction of all error are essential to enhance the quality of the text.

 (3)

In page 8 and Table 2, the manuscript describes the use of four different particle sets but fails to clarify the role of the three larger particle types (i.e., those other than SPG5000). It is unclear in which specific experiments these larger particles were utilized. Please provide explicit details linking the larger particles to the relevant Figures.

 (4)

The connection between the PDA measurements, deposition experiments, and conventional theory is not adequately addressed. The reviewer raises the following concerns:

(a)    The authors state that conventional theory predicts larger particles accumulate at the lobes and smaller particles at the nodes (e.g., as shown in Fig. 3a).

(b)    PDA measurements, however, indicate that larger particles accumulate at the nodes, even at lower power inputs (Figs. 9, 10, 11).

(c)    In contrast, deposition experiments show that more particles are found at the lobe positions in the downstream region.

(d)    The authors attribute the half-wavelength offset between (b) and (c) to a secondary flow pattern generated within the fractionation device (as shown in Fig. 14).

The authors should provide a clearer explanation reconciling the discrepancies between the theoretical predictions (a) and the PDA results (b).

 (5) 

Figure 14 presents a simulation, but the manuscript lacks detailed information about the methodology, assumptions, and parameters used. The reviewer recommends including a comprehensive description of the simulation setup and results to ensure transparency and reproducibility.

Author Response

Dear Reviewer,

we prepared the attached rebuttal.

Thank you and best regards,

Krischan Sandmann

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The paper presents a comprehensive experimental investigation into acoustic particle fractionation in a gaseous phase, providing crucial empirical evidence for phenomena primarily explored through numerical and analytical approaches. Advanced measurement techniques like Phase-Doppler-Anemometry (PDA) add credibility and depth to the study, enabling precise observations of particle behavior under varying acoustic field intensities. Additionally, the paper effectively bridges the gap between theoretical predictions and real-world applications by discussing practical challenges such as secondary flow effects and particle redistribution. The structured approach, involving both in-situ and ex-situ characterizations, strengthens the validity of the findings while integrating computational insights further enhances the overall rigor of the study.

Comments to paper:

1. Line 66. The phrase "latest experimental investigations" implies novelty but does not specify how this work advances or differs from prior studies. Provide a clear explanation of the unique contributions of this research.
2. The section “2.2.4 Filter deposition set up”. The use of fused deposition modeling for fabricating the device is described but does not address how its precision may impact experimental outcomes. Consider discussing this aspect.
3. The description of probability histograms (Figure 7) for particle velocity distributions should include details on statistical methods or data processing used to derive them.
4. Line 467. The term "rarefaction" in the context of particle concentration changes in lobes is unclear. Rephrase or explain better understanding.
5. Lines 602-605. The critical particle size calculation from Danilov et al. is referenced but not compared to experimental findings. Discuss agreements or discrepancies to enhance scientific rigor.
6. Lines 612-614. The suggestion to move baffles upstream is insightful but lacks quantitative evidence or simulation results to support it. Provide more substantiation.
7. Line 639. The challenges of entrainment and remixing due to secondary flow effects are acknowledged but potential design modifications to mitigate these effects are not discussed. Include recommendations for future work.

The manuscript is well-structured and contributes significantly to gas-phase acoustic particle fractionation. Minor revisions are needed to enhance clarity and rigor: specify the study’s novelty, address the precision of fused deposition modeling, clarify statistical methods for probability histograms, and rephrase "rarefaction”. Additionally, compare critical particle size predictions with findings, provide evidence for upstream baffle placement, and suggest solutions for secondary flow challenges. These refinements will further strengthen the paper's impact.

Author Response

Dear Reviewer,

we prepared the attached rebuttal.

Thank you and best regards,

Krischan Sandmann

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript is clearly written, interesting and rich of convincingly generated and discussed results and conclusions. I can recommend to publish the manuscript in the current form.

Author Response

We would like to express our gratitude for your time and effort in reviewing our manuscript. Your contribution to the assurance of scientific quality is greatly appreciated. We are pleased that our manuscript meets the scientific requirements.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

No additional comment.