Influence of Fluid Properties on Intensity of Hydrodynamic Cavitation and Deactivation of Salmonella typhimurium

Round 1

Reviewer 1 Report

Statistical information is missing. The authors should specify how do they analyze the data. 

Author Response

Reviewer #1

Comment #1:

Statistical information is missing. The authors should specify how do they analyze the data?

Response to reviewer comment #1:

The data is presented as the mean of three software-based bacterial colony measurements. The corresponding explanation is added to the revised version of the manuscript in line 468.

Reviewer 2 Report

Reviewer's comments to processes-722619:

The paper titled "The combined effect of hydrodynamic cavitation and salmonella thyphimurium presence in the working fluid" demonstrates the effects of thermophysical properties of fluids, including density, vapor saturation pressure, and surface tension, as well as S. Typhimurium suspension on the effectiveness of hydrodynamic cavitation (HC). Meanwhile, the deactivation of S. Typhimurium by HC has been proven using an optimal microfluidizer. I read the work with great interest. After major revising, the manuscript can be accepted. The comments are prominent in the following aspects:

1. The article title should be modified to accurately reflect the motivation and content of this study. For example, "Influence of fluid properties on intensity of hydrodynamic cavitation and deactivation of S. Typhimurium".
2. In the Introduction, the main sterilization methods and their pros and cons should be briefly introduced. The authors should pay attention to the application, mechanism, influencing factors and advantages of hydrodynamic cavitation in sterilization and deactivation of microorganisms. A lot of introducing the background of germs should be avoided (lines 88-115). In addition, the results of the study should not appear in the Introduction (lines 126-129).
3. In Materials and Methods, the initial discussion should be moved to the Introduction or deleted (lines 134-141). In addition, 'Methods and Materials' are generally written as 'Materials and Methods'. The main hydraulic parameters of the equipment should be listed in Table 1 and other tables, such as the flow rate at different inlet pressures, and so on. Clarify the meaning of these abbreviations: a <100> silicon wafer, using MLA 150 maskless aligner, 2 µm thick layer of AZ-ECI.
4. In section 2.4, how to measure the volume flow rate of the system?
5. Table 2 appears to be an incomplete form. There seems to be a lot of data missing.
6. Line 246, the unit in the following sentence seems wrong. "Growth medium was centrifuged at 5000 g for 5 minutes".
7. Line 289, what is the cavitation flow? Is it related to the volumetric flow rate of the system (line 276)?
8. Line 339-341, what are the difference among bubbly flow, bubble cloud, and cavitating flow?
9. What are twin cavities?
10. In Fig 4 – Fig. 8, the different parts of the microfluidic devices were selected for taking photos. Can you please point out the reasons for the choice? Can you use the photos taken the same parts, for example, the microchannel and extension part?
11. Line 359-360, the following statement is not correct. “Where the pressures corresponding to the same intensity of cavitating flows (cavitation number of about 0.8) are 4.14 MPa and 2.41 MPa for the cases of water and PBS, respectively”. In fact, the values are 0.84 and 0.81, respectively. If 0.84 and 0.81 are about 0.8, how is 0.86? Is 0.86 equal to 0.84?
12. Line 468, 474, the meaning of the following description is not clear: "The SEM image of the bacteria suspension (Figure 10-a), Figure 10. a) SEM image of the sample after the experiments".
13. The following writing errors need to be revised:l  The word “thyphimurium” appears in the title, and this word also appears in many places in the text, but sometimes “typhimurium” appears. Please use the correct word.l  Section 2.1 was not found. Therefore, the numbers of the sections must be modified.l  Line 272-274, where the alphabetic symbols do not match those in Equation 1.l  Table 3 should be placed on the same page, and one space is needed between Table 3 and the text below.l  The red text of the article should be revised to black. 

Author Response

Reviewer #3

The paper titled "The combined effect of hydrodynamic cavitation and salmonella thyphimurium presence in the working fluid" demonstrates the effects of thermophysical properties of fluids, including density, vapor saturation pressure, and surface tension, as well as S. Typhimurium suspension on the effectiveness of hydrodynamic cavitation (HC). Meanwhile, the deactivation of S. Typhimurium by HC has been proven using an optimal microfluidizer. I read the work with great interest. After major revising, the manuscript can be accepted. The comments are prominent in the following aspects:

Comment #1:

The article title should be modified to accurately reflect the motivation and content of this study. For example, "Influence of fluid properties on intensity of hydrodynamic cavitation and deactivation of S. Typhimurium".

Response to reviewer comment #1:

The title of the manuscript is now revised according to the valuable suggestion of the reviewer.

Comment #2:

In the Introduction, the main sterilization methods and their pros and cons should be briefly introduced. The authors should pay attention to the application, mechanism, influencing factors and advantages of hydrodynamic cavitation in sterilization and deactivation of microorganisms. A lot of introducing the background of germs should be avoided (lines 88-115). In addition, the results of the study should not appear in the Introduction (lines 126-129).

Response to reviewer comment #2:

The corresponding section in Introduction is thoroughly revised, and extra information is removed in the revised version of the manuscript. The new section could be found in lines 89-104.

Comment #3:

In Materials and Methods, the initial discussion should be moved to the Introduction or deleted (lines 134-141). In addition, 'Methods and Materials' are generally written as 'Materials and Methods'. The main hydraulic parameters of the equipment should be listed in Table 1 and other tables, such as the flow rate at different inlet pressures, and so on. Clarify the meaning of these abbreviations: a <100> silicon wafer, using MLA 150 maskless aligner, 2 µm thick layer of AZ-ECI.

Response to reviewer comment #3:

Lines 134-141 are now moved to Introduction in lines 53-58 and 116-118. The title of section 2 is revised as well. The range of the hydraulic parameters of all three devices is added to Table 1 in the revised version of the manuscript. <100> includes the crystallographic indices of the silicon wafer used for the fabrication of the microfluidic devices. Since fabrication of the devices is not the major concern of this study, this term is removed from the manuscript to avoid any ambiguity for the readers. Moreover, “MLA 150 maskless aligner” is the name and model of the photolithography device used in the fabrication process. The word “photolithography” is added afterwards for clarification. AZ-ECI is also the model of the photoresist used in microfabrication. The word “photoresist” is added to avoid any ambiguity in line 184 of the revised version of the manuscript.

Comment #4:

In section 2.4, how to measure the volume flow rate of the system?

Response to reviewer comment #4:

The volume flow rate is measured by dividing 20 ml of the exiting fluid by the corresponding elapsed time for this volume to leave the system. The corresponding explanation is added to lines 217-218 in the revised version of the manuscript.

Comment #5:

Table 2 appears to be an incomplete form. There seems to be a lot of data missing.

Response to reviewer comment #5:

Discharge coefficient, Reynolds number and microchannel width are added to Table 2 in the revised version of the manuscript.

Comment #6:

Line 246, the unit in the following sentence seems wrong. "Growth medium was centrifuged at 5000 g for 5 minutes".

Response to reviewer comment #6:

The correct unit is “rpm” instead of “g” as the reviewer mentioned. The sentence is revised accordingly.

Comment #7:

Line 289, what is the cavitation flow? Is it related to the volumetric flow rate of the system (line 276)?

Response to reviewer comment #7:

In section 3, the important parameters in characterization of hydrodynamic cavitation are introduced to the reader. One of these parameters is cavitation flowrate. The definition of this parameters is already included in the manuscript. The corresponding explanation could be found in lines 283-284 of the revised version of the manuscript. The readers are referred to reference [30] for further information.

Comment #8:

Line 339-341, what are the difference among bubbly flow, bubble cloud, and cavitating flow?

Response to reviewer comment #8:

The most important parameter in the formation of the flow regimes in microscale is the surface tension. Bubbly flow consists of larger bubbles while bubble cloud includes smaller bubbles. In bubbly flow, smaller number of bubbles exists, while the number of the bubbles is significantly larger in bubble cloud. Therefore, the reason for this observation is the surface tension difference between water and PBS as the working fluids. In addition, the previous results corresponding to water also indicated that bubbly flow is a less dominant flow [C. Mishra and Y. Peles, “Cavitation in flow through a micro-channel inside a silicon microchannel,” Phys. Fluids 17, 013601 (2005).]. The corresponding explanation is found in lines 335-337. Cavitating flow, on the other hand, is the general term referred to a two-phase flow as a result of sudden pressure drop.

Comment #9:

What are twin cavities?

Response to reviewer comment #9:

Twin cavity is referred to the gas-phase appearing in the extension part of the microfluidic device. Its use for the gas-phase in the microchannel (nozzle) section of the manuscript was an error, which is now revised. The word “cavity” is the correct one, which could be found in line 411 of the revised version of the manuscript.

Comment #10:

In Fig 4 – Fig. 8, the different parts of the microfluidic devices were selected for taking photos. Can you please point out the reasons for the choice? Can you use the photos taken the same parts, for example, the microchannel and extension part?

Response to reviewer comment #10:

The geometries of three microfluidic devices used in this study are different (Table 1). Thus, fluid behavior is different for each of them. The images were taken from the sections of the microfluidic device, where phase change phenomena were observed. The corresponding explanation is included in the text to avoid any ambiguity for the readers. It can be found in lines 337-339 in the revised version of the manuscript.

Comment #11:

Line 359-360, the following statement is not correct. “Where the pressures corresponding to the same intensity of cavitating flows (cavitation number of about 0.8) are 4.14 MPa and 2.41 MPa for the cases of water and PBS, respectively”. In fact, the values are 0.84 and 0.81, respectively. If 0.84 and 0.81 are about 0.8, how is 0.86? Is 0.86 equal to 0.84?

Response to reviewer comment #11:

The authors agree with the reviewer’s concern. However, the aim of this section is to compare the cavitation number for the same flow pattern. In other words, when the inception of cavitating flows occurs for both cases, the cavitation numbers are almost the same (0.87 and 0.86). At higher pressures, where the flow pattern is “developed cavitating flow”, the same trend can be seen. The cavitation numbers are 0.81 and 0.84 for this flow pattern. We are aiming to show the readers that the same cavitation intensity, characterized by cavitation number, is achieved at different inlet pressures for the cases of water and PBS due to the differences in thermophysical properties.

A better approach of illustration is adjusting the cavitation number to a specific value such as 0.80 and then to compare the inlet pressures. However, it is impossible to do this experimentally.

Comment #12:

Line 468, 474, the meaning of the following description is not clear: "The SEM image of the bacteria suspension (Figure 10-a), Figure 10. a) SEM image of the sample after the experiments".

Response to reviewer comment #12:

The corresponding descriptions are revised. The new version could be found in lines 464 and 471 of the revised version of the manuscript.

Comment #13:

The following writing errors need to be revised:l  The word “thyphimurium” appears in the title, and this word also appears in many places in the text, but sometimes “typhimurium” appears. Please use the correct word.l  Section 2.1 was not found. Therefore, the numbers of the sections must be modified.l  Line 272-274, where the alphabetic symbols do not match those in Equation 1.l  Table 3 should be placed on the same page, and one space is needed between Table 3 and the text below.l  The red text of the article should be revised to black.

Response to reviewer comment #13:

The correct word (typhimurium) is used in the revised version of the manuscript. The section numbers are revised. The symbols are also revised in the mentioned lines. Table 3 is placed on page 9, and the space is now added. The locations marked in red suggest for the revision. Now they are in black, while the new changes are marked in red.

Reviewer 3 Report

This study explores the usage of hydrodynamic cavitation reactors for ‘Water Treatment on Chip’ applications. Water and PBS were tested as the working fluids in the fabricated microfluidic devices. The whole study is interesting and contributes to the area of hydrodynamic cavitation. The following are the minor suggestions to be considered during revision. • “higher vapor saturation pressure”? check • “vapor saturation pressure”, check • “They could include the effects of viscosity and surface tension in their proposed model”? • “resulting energy release could be fine controlled”, clearly rewrite • “O-antigen as one the most flexible components occurs”, rephrase • “Pvap is the vapor saturation pressure”, check • “vapor saturation pressure directly affects this value”, check • “due to the high velocity of the fluid in the under discussion system”, rephrase • “Vapor saturation pressure (Pvap) [kPa]”, check and rephrase • “twin cavity movement along the microchannel area”, what do you refer to? • Line 432: “vapor saturation pressure” • “determine the antibacterial activity of the cavitation processes”, is it correct? • Recent works on the application (water treatment and nanoemulsion) of hydrodynamic cavitation could be referred: Ultrasonics Sonochemistry, 51, 526-532, 2019; Industrial and Engineering Chemistry Research, 52(34), 11829-11837, 2013; American Institute of Chemical Engineering Journal (AIChEJ), 59(1), 155-167, 2013;

Author Response

Reviewer #4

This study explores the usage of hydrodynamic cavitation reactors for ‘Water Treatment on Chip’ applications. Water and PBS were tested as the working fluids in the fabricated microfluidic devices. The whole study is interesting and contributes to the area of hydrodynamic cavitation. The following are the minor suggestions to be considered during revision.

Comment #1:

“higher vapor saturation pressure”? check

Response to reviewer comment #1:

If the reviewer refers to the phrase “higher vapor saturation pressure” mentioned in the abstract in line 22, this value is higher for the case of PBS (Table 3). The effect of this difference on cavitation is discussed in Section 3 and Section 4.1 based on Equations 2 and 3.

Comment #2:

“vapor saturation pressure”, check

Response to reviewer comment #2:

The phrase “vapor saturation pressure”, the symbols (referring to it in the text and equations), the analysis using this parameter, and the reported values are checked in the entire manuscript. All the vapor saturation pressures are replaced with saturation vapor pressure throughout the manuscript.

Comment #3:

“They could include the effects of viscosity and surface tension in their proposed model”?

Response to reviewer comment #3:

Surface tension and viscosity are included in our analysis. The values reported in Table 3 and the flow pattern analysis and difference between the cases of water and PBS are explained in section 4.1.

Comment #4:

“resulting energy release could be fine controlled”, clearly rewrite

Response to reviewer comment #4:

The corresponding sentence is removed from the manuscript to avoid any possible ambiguity for the readers.

Comment #5:

“O-antigen as one the most flexible components occurs”, rephrase

Response to reviewer comment #5:

The corresponding section is thoroughly revised in the new version of the manuscript.

Comment #6:

“Pvap is the vapor saturation pressure”, check

Response to reviewer comment #6:

It is checked and revised.

Comment #7:

“vapor saturation pressure directly affects this value”, check

Response to reviewer comment #7:

It is checked and revised.

Comment #8:

“due to the high velocity of the fluid in the under discussion system”, rephrase

Response to reviewer comment #8:

The sentence is now significantly revised. The new version reads as “However, Reynolds number is high enough to lead to turbulent flow behavior as a result of the high velocity of the fluid inside the system”. The new version could be found in lines 307-309 in the new version of the manuscript.

Comment #9:

“Vapor saturation pressure (Pvap) [kPa]”, check and rephrase

Response to reviewer comment #9:

It is checked and revised.

Comment #10:

“twin cavity movement along the microchannel area”, what do you refer to?

Response to reviewer comment #10:

Twin cavity is referred to the cavities in the extension region. The word twin cavity was an error in this section. The word is now replaced with “cavity” in line 411 in the revised version of the manuscript referring to the gas phase in the microchannel.

Comment #11:

Line 432: “vapor saturation pressure”

Response to reviewer comment #11:

It is checked and revised.

Comment #12:

“determine the antibacterial activity of the cavitation processes”, is it correct?

Response to reviewer comment #12:

The authors aimed to study the disinfection or deactivation effect of cavitating flow in this section. We believe that this clause could be considered as a good opening for this section.

Comment #13:

Recent works on the application (water treatment and nanoemulsion) of hydrodynamic cavitation could be referred: Ultrasonics Sonochemistry, 51, 526-532, 2019; Industrial and Engineering Chemistry Research, 52(34), 11829-11837, 2013; American Institute of Chemical Engineering Journal (AIChEJ), 59(1), 155-167, 2013;

Response to reviewer comment #13:

The section related to recent studies on the application of hydrodynamic cavitation is extended, and the abovementioned studies are added to Introduction. The additions can be found in lines 105-115 in the revised version of the manuscript.

Round 2

Reviewer 2 Report

The authors provided clear explanation and the revised version can be accepted for publication on Processes (ISSN 2227-9717)