Study on Using Microbubbles to Reduce Surface Damage of Mercury Target for Spallation Neutron Source
and Shiqing Zou 4Round 1
Reviewer 1 Report
General Comments
This manuscript presents information from experiments with an ultrasonic horn system designed to simulate cavitation-induced erosion damage in liquid-metal spallation target vessels. The information provides insight into factor influencing cavitation-induced erosion damage and would be useful for the research community in this field. However, the current manuscript draft has many grammatical errors and a few technical inaccuracies (for example, the description of the SNS as a heavy metal solid target – the SNS uses liquid metal for the target material) that must be revised. The manuscript needs to be reviewed and revised by a technical editor that is fluent in technical English writing. I have provided some grammatical corrections, but there are many more that I did not identify.
In summary, I think this manuscript will be suitable for publication after the grammatical errors are corrected and the text is modified to address some of the technical questions I identified in my detailed comments.
Detailed Comments
Line 15: Correct grammar in: “…is severely pitting damaged caused…”
Line 36: The Spallation Neutron Source in the United States uses liquid mercury as the target material. The passage in line 36 “…a heavy metal solid target…” should be changed. I suggest, “…a liquid-metal mercury target…”.
Lines 36-40: These sentences need to be revised. They appear to contrast a “solid target” at the SNS to a liquid-metal target at the MLF. The target at the SNS is a 316L stainless steel target vessel containing flowing liquid mercury, which is very similar to the MLF target. The way it is current written in the text it suggests to the reader that the two facilities use different targets.
Line 43: Correct grammar in: “As the pressure recovery, the generated micro jet forms damage…”
Lines 47-56: Recently an open access paper was published by McClintock et al. (Materials and Design, 221 (2022) 110937) that showed the results of SNS targets operated with and without gas injection, as well as strain measurements of the target vessel in situ operated with and without small-bubble gas injection. This paper contains the latest findings on small-bubble gas injection to reduce cavitation-induced erosion damage. You may include if you would like, it is not required per my review.
Line 50: Correct grammar in: “McClintock et al. cut the test piece and…”. I suggest “McClintock et al. removed samples from SNS target vessels after service and…”
Line 58: Correct grammar in: “Wall cutting of target vessel which is SNS.” I suggest: “Sample from SNS target vessel after service. ”. Also, add [8] at the end of the sentence to acknowledge these images came from a referenced publication.
Lines 65-66: Correct grammar in: “…preformed through using the vibratory horn in bubbly water.” I suggest: “performed using a vibratory horn in bubbly water.”.
Line 67: In the experimental procedures section there is no mention of the bubble generator type used for this experiment. Please add some information or reference for the bubble generator used during this experiment.
Lines 69-70: Correct grammar in: “…target vessel stalled in the…”. I suggest: “…target vessel installed in the…”.
Line 70: Replace “Materials and Life Science Experimental Facility” with “MLF”, this abbreviation was introduced on line 34 in the Introduction.
Lines 72-73: Correct grammar in: “The mercury target system with 2.6 m…”. I suggest: “The mercury target system is 2.6 m…”.
Line 73: Please clarify what this means: “…is set on the workbench.” What is a “workbench”?
Line 81: Insert space between “detected” and “by”.
Line 83: Insert space between “in” and “the”.
Line 87: Insert space between “Experimental” and “specimen” in section title.
Lines 97-98: Revise “After experimental each step…”. Do you mean: “After each step…”?
Line 100: Add space between words.
Line 101: Add space between words and consider shortening the section title.
Lines 177-119: This information was already provided in section 2.2 (lines 88-90). Consider removing this section and moving lines 120-123 to section 2.3.
Line 126: Add space between combined words “differentexperiment”.
Line 159: Change “was” to “were”.
Lines 155-159: It is not clear what you are saying in this paragraph – I do not understand these sentences. Will you please revise this paragraph and clarify the discussion on the effect of microbubbles on damage?
Line 165: There was no mention of the bubble characterization in the experimental procedure sections earlier in the manuscript. I think it is important to describe how you imaged and characterized the bubble population, and this information should be provided in the description of the experiment. This information is helpful to understand the effectiveness of gas injection and should be included.
Lines 174-176: These sentences have a few grammatical errors. Please review and correct errors.
Line 176: Delete “was”.
Line 184: Consider combining (a) and (b) on the same plot for Figure 9. This would help the reader compare the two flow conditions.
Line 198: Add “are” between “air” and “shown”.
Line 206: There is no discussion on the effect of flow and possible reasons why the damage observed during testing with flow was more than testing in stagnant water. This contradicts observations made by Riemer et al. (for example, WNR experiments published in J. Nucl. Mater.) and at the SNS during PIE examinations of the target vessels after service. There are several papers in the literature that show fluid flow helps to mitigate cavitation-induced erosion damage compared to the stagnant condition. While a mention of the flow case was included in lines 156-160, this is not a convening argument and does not adequately address this significant contradiction from other experiments. Please add a discussion in section 4 to address this contradictory data you present in this paper and explain why flow would increase erosion damage.
Lines 207-226: The simulation results presented in this paragraph were not mentioned in the experimental procedures section. This information is good to include. However, the reader does not know what was simulated and how it is relatable to the data from the ultrasonic horn experiments. What geometry was simulated? How is this simulation similar to the button-shaped specimen exposed using the ultrasonic horn? Please add some section earlier in the manuscript describing the simulation work that was presented in lines 207-226.
Line 288: The reference is missing a “J.” in front of “Nucl. Mater.”
Author Response
Line 15: Correct grammar in: “…is severely pitting damaged caused…”
Line 36: The Spallation Neutron Source in the United States uses liquid mercury as the target material. The passage in line 36 “…a heavy metal solid target…” should be changed. I suggest, “…a liquid-metal mercury target…”.
Line 43: Correct grammar in: “As the pressure recovery, the generated micro jet forms damage…”
Line 50: Correct grammar in: “McClintock et al. cut the test piece and…”. I suggest “McClintock et al. removed samples from SNS target vessels after service and…”
Line 58: Correct grammar in: “Wall cutting of target vessel which is SNS.” I suggest: “Sample from SNS target vessel after service.”. Also, add [8] at the end of the sentence to acknowledge these images came from a referenced publication.
Lines 65-66: Correct grammar in: “…preformed through using the vibratory horn in bubbly water.” I suggest: “performed using a vibratory horn in bubbly water.”.
Line 70: Replace “Materials and Life Science Experimental Facility” with “MLF”, this abbreviation was introduced on line 34 in the Introduction.
Lines 72-73: Correct grammar in: “The mercury target system with 2.6 m…”. I suggest: “The mercury target system is 2.6 m…”.
Line 81: Insert space between “detected” and “by”.
Line 83: Insert space between “in” and “the”.
Line 87: Insert space between “Experimental” and “specimen” in section title.
Lines 97-98: Revise “After experimental each step…”. Do you mean: “After each step…”?
Line 100: Add space between words.
Line 101: Add space between words and consider shortening the section title.
Line 126: Add space between combined words “differentexperiment”.
Line 159: Change “was” to “were”.
Line 198: Add “are” between “air” and “shown”.
Line 288: The reference is missing a “J.” in front of “Nucl. Mater.”
Response: Thanks for reviewer’s careful comments. All of the related grammar and words expression have been revised in the manuscript.
Lines 36-40: These sentences need to be revised. They appear to contrast a “solid target” at the SNS to a liquid-metal target at the MLF. The target at the SNS is a 316L stainless steel target vessel containing flowing liquid mercury, which is very similar to the MLF target. The way it is current written in the text it suggests to the reader that the two facilities use different targets.
Response: Thanks for reviewer’s comment. The sentences of line 36-40 have been revised. The similar target was used in USA and Japan. We want to express that JPARC change it since the proton beam with MW level enters the target.
Lines 47-56: Recently an open access paper was published by McClintock et al. (Materials and Design, 221 (2022) 110937) that showed the results of SNS targets operated with and without gas injection, as well as strain measurements of the target vessel in situ operated with and without small-bubble gas injection. This paper contains the latest findings on small-bubble gas injection to reduce cavitation-induced erosion damage. You may include if you would like, it is not required per my review.
Response: Thanks for reviewer’s comment. We have read and cited this paper in the manuscript.
Line 67: In the experimental procedures section there is no mention of the bubble generator type used for this experiment. Please add some information or reference for the bubble generator used during this experiment.
Response: Thanks for reviewer’s comment. The bubble generator was customized, not a standard product. The status of generated bubbles mainly depends on the flow rate of liquid and gas. So, the related information of bubble generator is not introduced in the manuscript.
Line 73: Please clarify what this means: “…is set on the workbench.” What is a “workbench”?
Response: Thanks for reviewer’s comment. The “workbench” is a track platform.
Lines 177-119: This information was already provided in section 2.2 (lines 88-90). Consider removing this section and moving lines 120-123 to section 2.3.
Response: Thanks for reviewer’s comment. According to your suggestion, it has been revised in the manuscript.
Lines 155-159: It is not clear what you are saying in this paragraph – I do not understand these sentences. Will you please revise this paragraph and clarify the discussion on the effect of microbubbles on damage?
Response: Thanks for reviewer’s comment. This paragraph has been rewritten in the manuscript.
Line 165: There was no mention of the bubble characterization in the experimental procedure sections earlier in the manuscript. I think it is important to describe how you imaged and characterized the bubble population, and this information should be provided in the description of the experiment. This information is helpful to understand the effectiveness of gas injection and should be included.
Response: Thanks for reviewer’s comment. According to your suggestion, the bubble of evaluating method has been added in the manuscript.
Line 184: Consider combining (a) and (b) on the same plot for Figure 9. This would help the reader compare the two flow conditions.
Response: Thanks for reviewer’s comment. (a) and (b) have been combined in the same plot for Figure 9.
Line 206: There is no discussion on the effect of flow and possible reasons why the damage observed during testing with flow was more than testing in stagnant water. This contradicts observations made by Riemer et al. (for example, WNR experiments published in J. Nucl. Mater.) and at the SNS during PIE examinations of the target vessels after service. There are several papers in the literature that show fluid flow helps to mitigate cavitation-induced erosion damage compared to the stagnant condition. While a mention of the flow case was included in lines 156-160, this is not a convening argument and does not adequately address this significant contradiction from other experiments. Please add a discussion in section 4 to address this contradictory data you present in this paper and explain why flow would increase erosion damage.
Response: Thanks for reviewer’s comment. This study focused on the effect of microbubble injection on cavitation erosion through the ultrasonic horn experiments. From theoretical viewpoint, the fluid flow should mitigate cavitation-induced erosion damage compared to the stagnant condition since bubbles exist in water in fluid flow condition. The cause of the argument may be the fluid flow in the ultrasonic horn experiment is different from the fluid flow in actual working environment. By the way, we will investigate the change in pressure waves in the fluid flow condition through the numerical simulation. In the future work, we will further research the effect of fluid flow on cavitation erosion.
Lines 207-226: The simulation results presented in this paragraph were not mentioned in the experimental procedures section. This information is good to include. However, the reader does not know what was simulated and how it is relatable to the data from the ultrasonic horn experiments. What geometry was simulated? How is this simulation similar to the button-shaped specimen exposed using the ultrasonic horn? Please add some section earlier in the manuscript describing the simulation work that was presented in lines
Response: Thanks for reviewer’s comment. According to your suggestion, the related information of the simulation has been added in the experimental procedures section.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The paper aims to study the use of microbubbles in reducing cavitation damage in spallation neutron sources. Some sources, such as J-PARC subject mercury targets to pulsed proton beams. This pulsed loading leads to cavitation damage that may be reduced using microbubble injection. To further the understanding of that phenomena, the authors present experimental work studying cavitation damage to stainless steel in water under stagnant, flowing, and bubbly conditions. The authors then present information obtained from simulations of the experimental conditions with different bubble parameters. The experimental and simulation results are the novel contributions.
The paper as written does not address the applicability of water experiments to mercury cavitation. This reviewer recommends adding discussion of how this work fits into the on-going research in water and mercury cavitation. The reviewer notes that only three of the sixteen references are to publications from the last five years. The reviewer also noted that some details that would aid in understanding and potentially replicating the experiments and simulations were not provided. These are addressed further in the detailed comments below.
Line 17 - The paper states "we proposed a method of using microbubbles injection into the flowing mercury to suppress the pressure waves." J-PARC has been using this method for at least 5 years as noted in Reference 16. Please reword to clarify the authors contribution.
Line 21 - The paper states "we also developed a simulation code for analyzing the change in pressure waves in mercury." But the discussion in Line 208 notes that the code was developed by team members, and references 15 and 16 are provided as a reference. There does not appear to be any overlap between the authors of the current paper and those references. Please clarify to better describe the contribution of this paper.
Line 36 - The paper notes that "a heavy metal solid target has been adopted in the conventional spallation neutron source (SNS) which was used in the USA." The reference 3 listed describes the use of a liquid metal target in the USA at the SNS including installation and commissioning with a proton beam. This reviewer notes that they are aware of neutron sources in the US and across the world that do indeed use metal solid targets. Please clarify.
Lines 50-55 - In this paragraph, the authors appear to be discussing the double wall structure and its ability to reduce damage. This reviewer could not follow the discussion of "top and bottom" damage in the WNR tests and how it relates to the narrow channel effect described in the other sentences. Please clarify.
Line 64 - The authors note that they are attempting to quantitatively investigate the effect of microbubbles on microsecond scale cavitation. However, nothing is provided to link spallation targets to microsecond scale cavitation. The reviewer notes that the target at J-PARC is struck by 1 microsecond long proton pulses as described in Reference 16, but these pulses are provided intermittently at 45 pulses per second. In reference 16, for example in figure 10, the response of the target appears to occur over a time frame of milliseconds. Please provide information linking the microsecond cavitation response to spallation targets.
Line 81 - Please provide clarification of the "electric mercury leaking sensor."
Line 91 - The paper notes "The surface was ground to a grain size of 1 micrometer." Please clarify, as the reviewer would expect grinding to affect the surface finish, not the grain size of the material.
Line 101 - This reviewer believes that additional information is needed to understand the experimental conditions described here and in in Figure 4. Please provide information on the flow velocity across the sample, or provide the information necessary to calculate it such as the size of the pump line or the depth of the water tank.
Line 107 - The authors note that the microbubble generator is composed of a flow meter, pump, and a water tank. The reviewer is unsure how that combination by itself generated the described bubble populations. Please provide information on the "micro-bubble generator" as noted in Figure 4(b).
Line 155 - Please clarify what is meant by "in the bubbling case, injected microbubbles deposited in negative pressure region and cavitation bubblers were remaining around the specimen." What is the negative pressure region in this experiment with an oscillating ultrasonic frequency? Did the authors see cavitation bubbles during operation? If so, is there any information no their size and frequency?
Figure 7 and Figure 11 - This reviewer found it difficult to distinguish the overlapping error bars of the different conditions. Please consider showing the different conditions in different sub-plots with matching axes for clarity.
Figure 8 - Please provide a scale for the figure. Based on the proceeding figures, it appears that the dark object is a specimen with a diameter of 26 mm. With that assumption, the size of the bubbles visible in the figure appear to be quite large compared to the diameter of microbubbles presented in Figure 9. Please clarify.
Figure 8 - In the images, it appears that there are several overlapping bubbles in the images. Please provide more detail on how the bubbles were counted and how image processing challenges such as overlapping bubbles were handled.
Figure 9 - Based on the above comments, it appears that there are a significant number of large bubbles, but the bubble size distributions show a maximum size of 130 micrometer. Please add information on how the distributions were obtained, and if possible what portion of the bubbles are represented by the bubble size distributions in this figure. If many large bubbles are present, how did the authors isolate the effects described to only the microbubble portion of the population?
Figure 9 - The (a) label appears to be repeated for subfigure (b).
Figure 10 - The 5 and 10 minute duration specimens at 4L/min in subfigure (a) appear to have long, bending lines of damage that are not seen in other specimens. Do the authors have any explanation for this phenomena?
Line 198 - The surface roughness was noted to be "remarkably smaller" at 5 L/min as compared to 4 L/min, but Figure 11 shows significant overlap in the error bars. Please clarify.
Line 207 - In this reviewers opinion, the simulation setup should be described in detail in the experimental section, not only discussed in the discussion. Currently, there is no detail provided of what was simulated. One might think it is a simulation of the experimental setup, but Line 21 notes that the code is for analyzing changes in pressure waves in mercury, not water as was used in the experiment. The authors references 15 and 16 are noted, but these do not appear to this reviewer to provide sufficient information on the code used in this paper. Please provide sufficient detail to understand the simulation method and setup.
Figure 12 and 13 - The figures show the response over a time frame of 1 to 100 microseconds (note typographical error in Figure 13 x axis states micrometers). The figures show a drop in the response due to the different size microbubbles. However, the experiment presented here describes a 20 kHz experiment, which correlates to a 50 microsecond repetition. Please clarify what was simulated.
Line 211 - The authors state that a comparison of the pressure waves in the simulations with and without microbubbles is provided in Figure 12. Please describe what microbubbles were considered in this simulation. Did the simulated distribution match an experimentally measured bubble distribution?
Line 222 - Please clarify how simulations were performed for the different microbubble sizes. Were only one size of bubbles included in the simulations? Were the simulations equal in the number of bubbles or in the total gas fraction?
Line 230 - The authors note that the paper "proposed a method that using microbubbles injection into the flowing mercury to suppress the pressure waves." As noted previously, this method is already in operation. Please clarify the contribution of this paper, such as quantitatively evaluating the effect of microbubbles through experiment and simulation.
Line 239 - For specificity, this reviewer recommends noting that the microbubble injection was able to mitigate damage in specimens in water with air bubbles. The paper does not provide sufficient information to generalize this to other conditions such as mercury.
Line 247 - The authors noted that "a numerical simulation code was developed" to investigate the effect of the microbubbles. As noted previously, the discussion appears to indicate the code was previously developed by others. Please clarify.
Author Response
Line 17 - The paper states "we proposed a method of using microbubbles injection into the flowing mercury to suppress the pressure waves." J-PARC has been using this method for at least 5 years as noted in Reference 16. Please reword to clarify the authors contribution.
Response: Thanks for reviewer’s comment. According to your suggestion, we have revised it in manuscript.
Line 21 - The paper states "we also developed a simulation code for analyzing the change in pressure waves in mercury." But the discussion in Line 208 notes that the code was developed by team members, and references 15 and 16 are provided as a reference. There does not appear to be any overlap between the authors of the current paper and those references. Please clarify to better describe the contribution of this paper.
Response: Thanks for reviewer’s comment. We and the members of developed code in the same team, but research field and research work are different. We only used the simulation code for analyzing the change in pressure waves in water. So, there does not appear to be any overlap between the authors of the current paper and those references.
Line 36 - The paper notes that "a heavy metal solid target has been adopted in the conventional spallation neutron source (SNS) which was used in the USA." The reference 3 listed describes the use of a liquid metal target in the USA at the SNS including installation and commissioning with a proton beam. This reviewer notes that they are aware of neutron sources in the US and across the world that do indeed use metal solid targets. Please clarify.
Response: Thanks for reviewer’s comment. Japan and the United States always keep the close cooperative relations in the field of high strength proton accelerator, so the liquid metal target was also installed at the SNS in the USA.
Lines 50-55 - In this paragraph, the authors appear to be discussing the double wall structure and its ability to reduce damage. This reviewer could not follow the discussion of "top and bottom" damage in the WNR tests and how it relates to the narrow channel effect described in the other sentences. Please clarify.
Response: Thanks for reviewer’s comment. Through the double wall structure is able to reduce damage, Riemer et al. further research where in double wall structure was serious damage through a series of experiments.
Line 64 - The authors note that they are attempting to quantitatively investigate the effect of microbubbles on microsecond scale cavitation. However, nothing is provided to link spallation targets to microsecond scale cavitation. The reviewer notes that the target at J-PARC is struck by 1 microsecond long proton pulses as described in Reference 16, but these pulses are provided intermittently at 45 pulses per second. In reference 16, for example in figure 10, the response of the target appears to occur over a time frame of milliseconds. Please provide information linking the microsecond cavitation response to spallation targets.
Response: Thanks for reviewer’s comment. The effect of microbubbles on microsecond scale cavitation is important for the spallation targets. However, the proposed experimental conditions are not the actual working conditions of spallation targets. Thus, the microsecond cavitation is only for this simulation experiment, and it is unable to contact with spallation target.
Line 81 - Please provide clarification of the "electric mercury leaking sensor."
Response: Thanks for reviewer’s comment. The "electric mercury leaking sensor" is a sensor that if the mercury in the target leaks, the electrical components will automatically alarm.
Line 91 - The paper notes "The surface was ground to a grain size of 1 micrometer." Please clarify, as the reviewer would expect grinding to affect the surface finish, not the grain size of the material.
Response: Thanks for reviewer’s comment. We have revised it in the manuscript.
Line 101 - This reviewer believes that additional information is needed to understand the experimental conditions described here and in in Figure 4. Please provide information on the flow velocity across the sample, or provide the information necessary to calculate it such as the size of the pump line or the depth of the water tank.
Response: Thanks for reviewer’s comment. The status of generated bubbles mainly depends on the flow rate of liquid and gas. In this experiment, the flow rate of liquid and gas were respectively 75 L/min and 4 L/min (or 5 L/min) through adjusting the water flow valve and gas flow meter. The information of the flow velocity across the sample was shown in “Experimental conditions”.
Line 107 - The authors note that the microbubble generator is composed of a flow meter, pump, and a water tank. The reviewer is unsure how that combination by itself generated the described bubble populations. Please provide information on the "micro-bubble generator" as noted in Figure 4(b).
Response: Thanks for reviewer’s comment. The bubble generator was customized, not a standard product. The status of generated bubbles mainly depends on the flow rate of liquid and gas. So, the related information of bubble generator is not introduced in the manuscript.
Line 155 - Please clarify what is meant by "in the bubbling case, injected microbubbles deposited in negative pressure region and cavitation bubblers were remaining around the specimen." What is the negative pressure region in this experiment with an oscillating ultrasonic frequency? Did the authors see cavitation bubbles during operation? If so, is there any information no their size and frequency?
Response: Thanks for reviewer’s comment. In vibratory horn experiments, the pressure will be smaller with close to the vibration center. So the differential pressure (called negative pressure) is formed near the vibration center. That is called the negative pressure region. The cavitation can’t be directly seen during operation, but the cavitation can be indirectly reflected through the degree of surface damage. The cavitation was investigated by other members.
Figure 7 and Figure 11 - This reviewer found it difficult to distinguish the overlapping error bars of the different conditions. Please consider showing the different conditions in different sub-plots with matching axes for clarity.
Response: Thanks for reviewer’s comment. Figure 7 have been enlarged, and Figure 11 have been revised in the manuscript.
Figure 8 - Please provide a scale for the figure. Based on the proceeding figures, it appears that the dark object is a specimen with a diameter of 26 mm. With that assumption, the size of the bubbles visible in the figure appear to be quite large compared to the diameter of microbubbles presented in Figure 9. Please clarify.
Response: Thanks for reviewer’s comment. According to your suggestion, the scale has been provided in the figure.
Figure 8 - In the images, it appears that there are several overlapping bubbles in the images. Please provide more detail on how the bubbles were counted and how image processing challenges such as overlapping bubbles were handled.
Response: Thanks for reviewer’s comment. According to your suggestion, the bubble of evaluating method has been added in the manuscript. The bubble generator was customized, not a standard product. The status of generated bubbles mainly depends on the flow rate of liquid and gas. So, the related information of bubble generator is not introduced in the manuscript.
Figure 9 - Based on the above comments, it appears that there are a significant number of large bubbles, but the bubble size distributions show a maximum size of 130 micrometer. Please add information on how the distributions were obtained, and if possible what portion of the bubbles are represented by the bubble size distributions in this figure. If many large bubbles are present, how did the authors isolate the effects described to only the microbubble portion of the population?
Response: Thanks for reviewer’s comment. According to your suggestion, the bubble of evaluating method has been added in the experimental procedure sections as shown in Fig.5.
Figure 9 - The (a) label appears to be repeated for subfigure (b).
Response: Thanks for reviewer’s comment. Figure 9(a) and 9(b) have been combined in the same plot.
Figure 10 - The 5 and 10 minute duration specimens at 4L/min in subfigure (a) appear to have long, bending lines of damage that are not seen in other specimens. Do the authors have any explanation for this phenomena?
Response: Thanks for reviewer’s comment. The specimen need to be washed before observation. The long bending lines is caused by human operation when the specimen was washed.
Line 198 - The surface roughness was noted to be "remarkably smaller" at 5 L/min as compared to 4 L/min, but Figure 11 shows significant overlap in the error bars. Please clarify.
Response: Thanks for reviewer’s comment. "remarkably smaller" was changed to “slightly smaller”
Line 207 - In this reviewers opinion, the simulation setup should be described in detail in the experimental section, not only discussed in the discussion. Currently, there is no detail provided of what was simulated. One might think it is a simulation of the experimental setup, but Line 21 notes that the code is for analyzing changes in pressure waves in mercury, not water as was used in the experiment. The authors references 15 and 16 are noted, but these do not appear to this reviewer to provide sufficient information on the code used in this paper. Please provide sufficient detail to understand the simulation method and setup.
Response: Thanks for reviewer’s comment. We made a clerical mistake, this code is for analyzing changes in pressure waves in water. It has been revised in the manuscript. As considering the confidentiality of core technologies, the detailed simulation method is not allowed to be shown in this manuscript.
Figure 12 and 13 - The figures show the response over a time frame of 1 to 100 microseconds (note typographical error in Figure 13 x axis states micrometers). The figures show a drop in the response due to the different size microbubbles. However, the experiment presented here describes a 20 kHz experiment, which correlates to a 50 microsecond repetition. Please clarify what was simulated.
Response: Thanks for reviewer’s comment. Figure 13 x-axis has been revised. Since the response time of the pressure wave near the proton beam window of the mercury target vessel was less than 150 µs, the response time was set to 100 µs in the numerical simulation code.
Line 211 - The authors state that a comparison of the pressure waves in the simulations with and without microbubbles is provided in Figure 12. Please describe what microbubbles were considered in this simulation. Did the simulated distribution match an experimentally measured bubble distribution?
Response: Thanks for reviewer’s comment. Injecting 100 μm microbubbles were considered in this simulation. The simulation code only analyzed that the pressure waves were in water with the microbubbles of same size. However, since the experimentally measured bubble distribution was very complex, it was difficult to simulate. Thus, we only simulate the microbubbles of same size with different diameter. Moreover, we will keep the size of microbubbles as consistent as possible in the future work.
Line 222 - Please clarify how simulations were performed for the different microbubble sizes. Were only one size of bubbles included in the simulations? Were the simulations equal in the number of bubbles or in the total gas fraction?
Response: Thanks for reviewer’s comment. The simulations were performed for the different microbubble sizes through changing the diameter parameters of microbubbles. Only one size of bubbles was included in the simulations. The simulations were equal in the number of bubbles.
Line 230 - The authors note that the paper "proposed a method that using microbubbles injection into the flowing mercury to suppress the pressure waves." As noted previously, this method is already in operation. Please clarify the contribution of this paper, such as quantitatively evaluating the effect of microbubbles through experiment and simulation.
Response: Thanks for reviewer’s comment. According to your suggestion, we have revised it in manuscript.
Line 239 - For specificity, this reviewer recommends noting that the microbubble injection was able to mitigate damage in specimens in water with air bubbles. The paper does not provide sufficient information to generalize this to other conditions such as mercury.
Response: Thanks for reviewer’s comment. The essential difference between water and mercury is their density. This paper only considers to simulate in water liquid. Other members in same team engaged in relevant mercury research.
Line 247 - The authors noted that "a numerical simulation code was developed" to investigate the effect of the microbubbles. As noted previously, the discussion appears to indicate the code was previously developed by others. Please clarify.
Response: Thanks for reviewer’s comment. Statement: we and code developed members are in the same team, but the research fields are different. So the simulation code was provided by others.
Author Response File: Author Response.docx
Reviewer 3 Report
This is a good paper, which will be interesting to readers. Scientificaly it is very well written, the diagrams are clear, and the results are good. The use of bubbles to decrease cavitation is an interesting concept, and the authorhave shown that it is a measurable effect. The only suggestion is that a native English speaker checks the manuscript, as there are numerous places where the grammar needs to be checked and correcteed. Other than this, the paper is an excellent addition to the literature on cavitation.
Author Response
This is a good paper, which will be interesting to readers. Scientificaly it is very well written, the diagrams are clear, and the results are good. The use of bubbles to decrease cavitation is an interesting concept, and the authorhave shown that it is a measurable effect. The only suggestion is that a native English speaker checks the manuscript, as there are numerous places where the grammar needs to be checked and correcteed. Other than this, the paper is an excellent addition to the literature on cavitation.
Response: Thanks for reviewer’s careful comments. We have tried our best to revise some related grammar and words expression in the manuscript.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
General Comments
In summary, I think this manuscript will be suitable for publication after the grammatical errors are corrected and the text is modified to address some of the technical questions I identified in my detailed comments. I attempted to list all errors I identified, however I suggest you have someone that is fluent in English review the manuscript to improve the readability.
Detailed Comments
Lines 12-13: There are grammatical errors in the first sentence of the abstract. Consider changing text, I suggest something similar to: “A liquid mercury target, which is used to explore the neutrons produced by spallation reactions, is operated at the…”
Line 15: Grammatical error. I suggest you replace “will be” with “are”.
Lines 18: Grammatical error. I suggest you replace “we developed” with “research was conducted with”.
Line 25: Grammatical error. I suggest you replace “…the pressure amplitude of the pressure wave was decreased…” “…the amplitude of the pressure wave decreased…”
Lines 36-40: These sentences are confusing, and it is not clear what you are trying to convey to the reader. The Spallation Neutron Source (SNS) is an operating facility and a proper noun; therefore, it should be capitalized. I think you are trying to say that both the SNS and the MLF are spallation sources that use liquid metal targets, that use mercury to produce neutrons and remove the heat produced during operation. Based on that I would recommend you modify the text to clarify for the reader, I suggest something similar to:
Liquid-metal mercury targets for spallation neutron production have been operated at the Spallation Neutron Source (SNS) in the United States and the MLF in Japan [3]. The mercury flowing through the 316L target vessels at the SNS and MLF not only serve as the target material, but also remove the heat produced during operation [4].
Line 42: I suggest replacing “…the aggressive cavitation generates in…” with “…aggressive cavitation occurs in…”.
Line 47-48: This is a confusing sentence, I suggest modifying it similar to: “The SNS in the United States has operated targets with MW-level proton beams, and the effect of operating conditions were studied and tested during post-irradiation examinations.”
Line 51: Grammatical error. I suggest you remove “as”.
Line 52: Grammatical error. I suggest you replace “…obtained the result of…” with “…observed…”.
Line 55: This reference you added needs to be in sequence with the reference list. Therefore, the “[17]” reference you added to the text should be reference [10], and all other references on your list from [10] to [16] will need to increase by one; they would become [11] through [17]. The reference listing throughout the manuscript text for all references affected will also need to be edited.
Line 59: The references [10,11] need to be changed to [11,12] – as mentioned above.
Lines 67-68: This sentence needs to be revised, as it is written it sounds like the simulations were performed using the ultra-sonic horn. I suggest rewriting the sentence to state that simulations were compared to the results from the ultra-sonic horn experiments. Perhaps something like: “…were performed and compared to samples exposed to cavitation erosion damage using a vibratory horn in bubbly water.”.
Line 76: The references [12,13] need to be changed to [13,14].
Lines 80-81: It would help the reader to specify that the safety hull is cooled by heavy water while the target vessel is cooled by mercury.
Line 82: The helium environment is “monitored” by the detectors not “detected by. It would be clearer to say: “…the helium gas around the mercury container is constantly monitored by the electric mercury leaking sensor,…”.
Line 99: Typographical error in section title – replace “proceed” with “procedure”.
Line 101: Grammatical error – I suggest you replace “…experiment of ultrasonic erosion was performed to…” with “…an experiment was performed to…”.
Line 109: You are writing about something that happened in the past, therefore you need to use past tense in the text. Also, you took several images, therefore “image” should be “images”. I suggest replacing “…the image of microbubbles is taken by the…” with “…images of the microbubbles were taken with a…”.
Line 110: Grammatical error with tense. I suggest replacing “…the obtained image of microbubbles is 2D processed.” with “…the images of the microbubbles were processed.”
Line 111: Grammatical error with tense. I suggest you replace “…different radius is…” with “…different radiuses were…”.
Line 120-121: The simulations you performed did not “prove” the effect of bubbles. They were used to compare theoretical behavior to observed behavior in experiments. I suggest you delete this text “…prove the effect of injection microbubbles on suppressing pressure wave and…”.
Line 129: Reference [14] needs to be changed to [15].
Line 134: This sentence reads awkwardly to me. I suggest you delete “difference”.
Lines 134-135: Grammatical issue – the “that” is not used correctly. I suggest you replace “…so-called that incubation period.” with “…the so-called incubation period.”.
Line 136: A space needs to be added between “with” and “26” in the table title. A space needs to be added between “20” and “kHz” in Table 1.
Line 139: Grammatical issue with tense. I suggest you replace “Figure 5 showed…” with “Figure 5 shows…”.
Line 143: It would read better to replace “since” with “as”.
Line 144: I suggest you replace “when” with “after”.
Line 145: This section of the sentence needs to be corrected. I suggest you replace “…the degree of losing gloss was…” with “…the degree of decrease in gloss was…”.
Line 151: Grammatical issue. I suggest you replace “…most…” with “…largest…”.
Line 158: What is “JIS B 6001-2001”? It is not clear to me from the text what this refers to, I suggest you either explain what this is or remove this text.
Line 168: I think you should be careful with your words here. You assume the bubbles remained “around the specimen”, however this was not directly observed and should not be mentioned. I suggest you modify this sentence by changing “…bubbles were remaining around…” to “…bubbles likely remained around…”.
Lines 170-172: I don’t agree with these two sentences and think you should really be careful with the declaration that flow made erosion damage more severe compared to the stagnant condition. Other experiments at the WRN facility and PIE observations at the SNS showed clearly that flow had a mitigating effect on erosion damage – flow decreased erosion damage. I suggest you only present the findings and include a statement saying it is not clear what the effect flow has on the erosion damage due to the lack of statistics (few pits to count) and additional results that support this finding.
Lines 179-180: Grammatical issues. I suggest you replace “…from the image which was taken by…” with “…from the images taken by…”.
Line 188: Grammatical issue, I suggest you remove “was”.
Line 221: References [15,16] need to be changed to [16,17].
Line 249: This section of the sentence reads awkwardly. I suggest you consider replacing “…in microbubbles case…” with “…during microbubble gas injection…”. I think this would more clearly convey your results to the reader.
Line 286: The journal name is not correct. It should be: Quantum Beam Sci.
Line 288: The journal name is not correct. It should be: Nucl. Instrum. Phys. Res. A.
Lines 303-317: These references all need to be increased by one after you insert the new reference [10].
Lines 318-320: This reference needs to be corrected and moved up in the list to line 303 and become reference [10], which is where in order it was inserted into the text. The correct reference citation for this paper is:
D. A. McClintock, Y. Liu, D. R. Bruce, D. E. Winder, R. G. Schwartz, M. Kyte, W. Blokland, R. L. Sangrey, T. M. Carroll, C. D. Long, H. Jiang, and B. W. Riemer, Small- bubble gas injection to mitigate cavitation-induced erosion damage and reduce strain in target vessels at the Spallation Neutron Source, Mater. Des. 221 (2022) 110937.
Reviewer 2 Report
The authors have addressed my previous comments. The changes made have significantly clarified the scope and procedures used. In the updated form, the paper describes testing performed which quantifies the effect of different conditions on cavitation damage in water subjected to an ultrasonic horn. The authors evaluate possible reasons for the observed changes in damage under those different conditions, and support their conclusions with simulation results.
This paper will be of interest to the readers of Coatings, and align with the stated topic of interest of "wear, corrosion, erosion."
