Dynamics of Laser-Induced Shock Waves in Supercritical CO2
Round 1
Reviewer 1 Report
Manuscript title :
Dynamics of laser-induced shock waves in supercritical CO2.
Author(s) : Asharchuk, et al.
Journal : Fluids
Reviewer comments (for both the authors and the editor):
This manuscript reports the shockwave formation and propagation in supercritical CO2. This manuscript also reports some mechanical measurements of shockwave characteristics and reports the non-linear response of those in a region close to the critical line. The reviewer thinks the results and discussion presented in this manuscript are slightly abstract, but it does not mean the reviewer believes this paper cannot be published. As the reviewer, whose research expertise is different from a supercritical fluid, a more specified introduction that explicitly justifies the importance of this contribution would be desirable. This will be helpful for non-expert readers. However, the reviewer admits that other reviewers who are more familiar with the field can make better recommendations/suggestions. Therefore, the reviewer defers to them. In addition, the reviewer has some rather general comments/suggestions that might be considered before the evaluation is concluded. First, in the introduction, the reviewer thinks that a few more overviews of the existing research on laser-induced optical breakdown/shockwave/cavitation formation should be made. This will help the authors to show the originality of the work (the authors mentioned some works in the discussion section, though). Second, the reviewer would like to see some discussion comparing the results found and those in common fluids (say, water) for comparison purposes. The reviewer would think this would be helpful to show the unique behavior of the supercritical fluid, as such a topic sounds relatively new. Third, there are some areas in which the reviewer thinks more detailed/ careful explanations are appreciated. For example, the Mach number is used without defining it. The definition and remarking of the values used for calculating it would improve the completeness of the work. There are a few more aspects that could be improved, please consider addressing them. Last but not least, there are some typos, though the reviewer is not able to evaluate the English proficiency. The information provided in the captions needs to be checked again and enriched. The reviewer recommends the authors go through the manuscript to eliminate any possible distractions.
Author Response
First of all, we would like to thank the Reviewers of our manuscript for their valuable and stimulating comments. Following the reviewers` recommendations we modified our manuscript, the full list of corrections is presented in the red-line version of the paper. We also hope that our manuscript in the amended form would be accepted in Fluids.
Below is the list of corrections we made in accordance with their suggestions.
1) As the reviewer, whose research expertise is different from a supercritical fluid, a more specified introduction that explicitly justifies the importance of this contribution would be desirable.
Answer: We expanded the introduction, added extra references. We hope that in the current version introduction will be clearer to a wide range of readers.
2) In the introduction, the reviewer thinks that a few more overviews of the existing research on laser-induced optical breakdown/shockwave/cavitation formation should be made.
Answer: We added additional information and references to the introduction.
3) The reviewer would like to see some discussion comparing the results found and those in common fluids (say, water) for comparison purposes.
Answer: We added the comparison with water before the “Summary” section:
«Comparing the dynamics of laser-induced mechanical post-effects in water and scCO2 we distinguished the following main differences. The shock wave pressure and energy in scCO2 is about one order lower than in water (for similar laser energies and durations [27]); in water the shock wave is generated at delays two orders of magnitude less than in scCO2; in water the shock waves decays faster and travels shorter distances than in scCO2. Higher pressures and energies in water are caused by its greater density, moreover water can be considered as incompressible liquid. This fact also leads to a shock wave decay rate. The difference in the shock wave generation time is a result of slower decay time of bubble wall velocity, in a result the shock wave in CO2 travels with a bubble wall greater period of time (~100 ns in scCO2 and ~1 ns in water).»
4) Third, there are some areas in which the reviewer thinks more detailed/ careful explanations are appreciated. For example, the Mach number is used without defining it. The definition and remarking of the values used for calculating it would improve the completeness of the work.
Answer: We added some explanations to the Methods section; moreover, we defined the term Mach number.
- Last but not least, there are some typos.
Answer: We have tried to fix all typos.
- The information provided in the captions needs to be checked again and enriched.
Answer: We enhanced captions and added additional information to them.
With best regards,
Sincerely,
Authors.
Reviewer 2 Report
The manuscript entitled “Dynamics of laser-induced shock waves in supercritical CO2” by N. Asharchuk and E. Mareev is clearly written, original, and well-organized. Therefore, it will be of great interest to the audience beyond the field of superctitical fluids. Specifically, in this manuscript, the authors studied the dynamics of laser-induced shock waves in supercritical CO2. They demonstrated that cluster formation in the Widom delta leads to the decrease of the shock wave energy and pressure.
Importantly, the results presented in the manuscripts are novel. In contrast to the dynamics of laser-induced shock waves in water, the mechanical laser-induced post-effects are purely investigated. The background contained in this field is adequately represented in the manuscript, and appropriate references are provided. The cluster impact on the dynamics of optical breakdown in supercritical fluids is discussed for the first time providing new physical insights. Thereby I recommend this manuscript for publication in Fluids, and the manuscript is subject to minor revisions.
Minor comments to address/incorporate:
1) Fig.3c: What is the source of the data presented in the figure?
2) The authors performed experiments for one set of energies. What was criterion for the energy selection in these experiments?
3) In abstract, the values of p and T for the maximal shock wave energy are not specified. Please, specify.
4) What is the accuracy of pressure and temperature control?
5) In water, the shock wave is separated from the bubble wall ~ 1ns after laser impact. The authors proposed that in scCO2 the separation occurs at ~ 100 ns. What is the reason for such difference?
6) It will be interesting if the authors compare the well-known shock waves dynamics in water and scCO2.
Comments for author File: 
Comments.pdf
Author Response
First of all, we would like to thank the Reviewers of our manuscript for their valuable and stimulating comments. Following the reviewers` recommendations we modified our manuscript, the full list of corrections is presented in the red-line version of the paper. We also hope that our manuscript in the amended form would be accepted in Fluids.
Below is the list of corrections we made in accordance with their suggestions.
1) Fig.3c: What is the source of the data presented in the figure?
Answer: We added the reference to the caption (NIST database).
2) The authors performed experiments for one set of energies. What was criterion for the energy selection in these experiments?
Answer: In the manuscript, we concentrated on the role of scCO2 microstructure and do not vary the energy of the laser pulse. We chose the energy in such way, that the optical breakdown occurred with a 100% possibility and its shape was close to spherical. We added the following text fragment to the manuscript: “In the manuscript we concentrated on the role of scCO2 microstructure and do not vary the energy of the laser pulse. For the chosen energy, the optical breakdown is occurred with ~ 100% possibility. For higher energies the shape of the bubble and shock wave starts to deviate from spherical [29], that could possibly violate the shock wave dynamics.”
3) In abstract, the values of p and T for the maximal shock wave energy are not specified. Please, specify.
Answer: We specified the values.
4) What is the accuracy of pressure and temperature control?
Answer: The accuracy is 0.1 bar and 0.1 K. We added the information to the text of the manuscript.
5), 6) In water, the shock wave is separated from the bubble wall ~ 1ns after laser impact. The authors proposed that in scCO2 the separation occurs at ~ 100 ns. What is the reason for such difference? It will be interesting if the authors compare the well-known shock waves dynamics in water and scCO2.
Answer: We added the comparison with water before the “Summary” section:
«Comparing the dynamics of laser-induced mechanical post-effects in water and scCO2 we distinguished the following main differences. The shock wave pressure and energy in scCO2 is about one order lower than in water (for similar laser energies and durations [27]); in water the shock wave is generated at delays two orders of magnitude less than in scCO2; in water the shock waves decays faster and travels shorter distances than in scCO2. Higher pressures and energies in water are caused by its greater density, moreover water can be considered as incompressible liquid. This fact also leads to a shock wave decay rate. The difference in the shock wave generation time is a result of slower decay time of bubble wall velocity, in a result the shock wave in CO2 travels with a bubble wall greater period of time (~100 ns in scCO2 and ~1 ns in water).»
In addition, we have made adjustments to the section References and Links and corrected the text
With best regards,
Sincerely,
Authors.
