Experimental Optimization of a Venturi-Type Fine Bubble Generation System Based on Gas Absorption Rate
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsGabriel Toma et al reported a new design on how to optimize the postion of obstacle based on Venturi-type FBG. This research is interesting for industrial to design a high efficient generator to produce high concentration ultra fine bubbles. There are several comments need to answer or modify their manuscript.
1) in this research, the bubbles they measured are mainly ultra fine bubbles because microbubbles are unstable and could not be measured stably. therefore, it is suggested to only describe the significance based on ultra fine bubbles.
2)In figure 3, it is hard to understand the specific positions of obtacles. where is converging or diverging sections?
3) As for the size distribution of formed ultra fine bubbles with different days,it is better to measure the concentration of ultra fine bubbles with different days to compare each other to know how stable after generation. also, why can they stable 7days.
Author Response
The attached file has the point-by-point replies to the reviewer comments.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe work as a whole should be supported, since the problem of multi-purpose optimization aimed at finding optimal conditions for obtaining fine-dispersed bubbles (FB) has been solved. In the reviewer's opinion, the most evidence-based studies of Venturi-type FB Generators were during microscopic measurements of the bubble size distribution and zeta potential. It used dynamic light scattering and zeta potential methods in order to determine their size and charge, respectively. The Fine Bubble Generators (FBGs) were printed on a 3D printer. Under the best conditions, the FB remained stable for 7 days with a size distribution from 60 to 90 nm.
The selection of optimal FB generators based only on measurements of the kinetics of gas saturation looks inconclusive.
The main 5 comments of the reviewer relate specifically to these types of measurements and show in attached file.
Comments for author File: Comments.pdf
Author Response
The attached file contains the point-by-point reply to the reviewers comments
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors were interested in the rapid processes taking place.
Due to the experimental finding of the parameter K, which was found experimentally and controlled for a small-size distribution, the reviewer has no particular complaints about the formulas.
The formulas in the article are relevant at times corresponding to the experimental situation, although they are limited in general.
Author Response
Comment1: The authors were interested in the rapid processes taking place.
Reply1: thank you very much for all your comments and we apologize for the misunderstanding in the original draft. I hope the explanation is better in the revised version.
Comment2: Due to the experimental finding of the parameter K, which was found experimentally and controlled for a small-size distribution, the reviewer has no particular complaints about the formulas.
Reply2: Thank you very much for your comment. Indeed fine bubbles where generated under controlled conditions. The values of K were included just to differentiate between dissolved oxygen due to gas absorption by physical means until the saturation limit and dissolved oxygen due to fine bubbles existence. High values of K indicate that, the contribution to dissolve oxygen by physical means is larger than that by fine bubbles at the beginning of the experiment. However, the final values of dissolved oxygen are from fine bubbles.
Comment3: The formulas in the article are relevant at times corresponding to the experimental situation, although they are limited in general.
Reply3: Thank you for pointing out this issue. Typically, gas absorption has not been considered as a method to validate the existence of fine bubbles. Therefore, the theory of mass transfer must be revisited to include the effect of fine bubbles in gas absorption.
