Influence of Temperature on Rising Bubble Dynamics in Water and n-pentanol Solutions

Round 1

Reviewer 1 Report

The manuscript entitled Influence of temperature on rising bubble dynamics in water and n-pentanol solutions is experimental study. I commented as follows;

1. Abstract and introduction is not clear. The author should revise them. Especially, the disadvantages of the previous studies and the advantages of the present study should be shown.

2. How about Capillary number?

3. The many symbols and letters are used. The author should summarize them as nomenclature.

Author Response

1. Abstract and introduction is not clear. The author should revise them. Especially, the disadvantages of the previous studies and the advantages of the present study should be shown.

The sentence in the abstract, highlighting the reason of use of the two complementary techniques has been added. It is now written that: “… The bubble velocity was measured by a camera, an ultrasonic sensor reproduced in numerical simulations. Results obtained by image analysis (camera) were compared to the data measured by an ultrasonic sensor to reveal the similar scientific potential of the latter …”.  The advantages and disadvantages of the presented study are discussed in the paper body and are summarized in the conclusion section.

2. How about Capillary number?

Thank you for this comment. Indeed, capillary number (Ca) could be a very nice parameter for comparison of the data taken under different physicochemical conditions of the aqueous phase. However, we focused in the paper on well-known models, where the Ca is not used. We will use the Reviewer idea for further analysis of our experimental results.

3. The many symbols and letters are used. The author should summarize them as nomenclature.

Reviewer 2 Report

Minerals-1366061

Comments on : Influence of temperature on rising bubble dynamics in water and n-pentanol solutions

• English must be revisited as there are typos and grammatical errors in the text needing further proofread.
• Authors should review more relevant articles in this area discussing two-phase flows in aqueous n-pentane solutions. This is important to highlight latest research conducted in this area and importance of this study to be done. For example, searching the literature, following papers are suggested to be read and used to enrich literature review:

Convective bubbly flow of water in an annular pipe: role of total dissolved solids on heat transfer characteristics and bubble formation.  Simulation of cavitation of spherically shaped hydrogen bubbles through a tube nozzle with stenosis.  Thermal analysis of a binary base fluid in pool boiling system of glycol–water alumina nano-suspension.  Boiling flow of graphene nanoplatelets nano-suspension on a small copper disk.  Boiling heat transfer characteristics of graphene oxide nanoplatelets nano-suspensions of water-perfluorohexane (C6F14) and water-n-pentane.  Pool boiling heat transfer to CuO-H2O nanofluid on finned surfaces.  Transient pool boiling and particulate deposition of copper oxide nano-suspensions.  Experimental study of the effect of various surfactants on surface sediment and pool boiling heat transfer coefficient of silica/DI water nano-fluid. 

• It is not clear how authors have obtained physical properties given in Table 1?
• An image of the test rig with proper labelling is suggested to be added to the paper to be a complementary figure to Fig. 1.
• A discussion on error and uncertainty analysis is required to be added to the paper.

All in all, the paper can be published once above comments are addressed.

Author Response

1. English must be revisited as there are typos and grammatical errors in the text needing further proofread.

English language of the paper was corrected by the professional service.

2. Authors should review more relevant articles in this area discussing two-phase flows in aqueous n-pentane solutions. This is important to highlight latest research conducted in this area and importance of this study to be done. For example, searching the literature, following papers are suggested to be read and used to enrich literature review:

• Convective bubbly flow of water in an annular pipe: role of total dissolved solids on heat transfer characteristics and bubble formation. 
• Simulation of cavitation of spherically shaped hydrogen bubbles through a tube nozzle with stenosis. 
• Thermal analysis of a binary base fluid in pool boiling system of glycol–water alumina nano-suspension. 
• Boiling flow of graphene nanoplatelets nano-suspension on a small copper disk.  Boiling heat transfer characteristics of graphene oxide nanoplatelets nano-suspensions of water-perfluorohexane (C6F14) and water-n-pentane. 
• Pool boiling heat transfer to CuO-H2O nanofluid on finned surfaces. 
• Transient pool boiling and particulate deposition of copper oxide nano-suspensions. 
• Experimental study of the effect of various surfactants on surface sediment and pool boiling heat transfer coefficient of silica/DI water nano-fluid. 

Thank you very much for the articles’ suggestions, which we found interesting. However, only two of them were found relevant to our studies – they describe problem of bubble hydrodynamics in tubes and associated phenomena like cavitation – it is very important problem from the point of view of industrial processes. These two articles have been incorporated into the revised paper as the Refs 3 and 4.

3. It is not clear how authors have obtained physical properties given in Table 1?

It is now written in the revised manuscript that (lines 351-354): “The values of surface tensio, density and dynamic viscosit at studied temperatures were taken from the engineering tables [29]. Details on the temperature-dependent physical properties of the water were taken from [29] and are given in Table. 1”

4. An image of the test rig with proper labelling is suggested to be added to the paper to be a complementary figure to Fig. 1.

Thank you for the suggestion. We decided not to add the rig photography. It is difficult to capture whole parts of the set-up with satisfactory accuracy and to make them readable. In our opinion the Fig. 1 reflects the real system used in the study very nicely and provides all information, allowing the rig to be reproduced by other authors.

5. A discussion on error and uncertainty analysis is required to be added to the paper.

A small paragraph was added in the revised manuscript (1315-1321), where it is written that: “… both for the ultrasonic and camera methods, the standard deviation values for average terminal velocity were quite small, indicating good reproducibility. It should be highlighted, however, that for camera method terminal velocity was calculated from only one experimental run. The ultrasonic sensor, because of its simplicity and swiftness of measurement, allowed for multiple measurements of a bubble velocity profile, which increased the statistical soundness of the terminal velocity values.”

Reviewer 3 Report

This article presents a detailed study on the influence of temperature on rising bubble dynamics in pure water and water+n-pentanol solutions in the range 5-45°C. The bubble velocity is experimentally measured using optical and ultrasonic techniques and compared to CFD calculations. The results are interesting and exploited in a good way but the article needs some modifications:

1. There is a lot of typo errors which makes the reading somehow difficult. A global and accurate revision of the English is absolutely required. Hereafter a non-exhaustive list of mistakes:

Line 38: show == shows

Line 49: He == They

Line 50: he == they

Line 57: are full == is full

Line 62: system == systems

Line 140: to analyzed == to analyze

Line 149: was == were

Line 156: It == Its

Line 156: was == were

Line 168: was == were

Line 202: represent == represents

Line 220: proofs == proves

Line 234: Fig 4 == Fig 5

Line 240: an assumptions == assumptions

Line 341: allow == allows

Line 449: shown == showed

Line 458: quantify == quantified

Line 474: allow == allows

2. You give in Table 1 the different properties of pure water for different temperatures (from Handbooks). However, when you mix pure water with n-pentanol, these properties will change, mainly surface tension. Have you measured the surface tension of water+n-pentanol at the corresponding concentrations to confirm or invalidate this?
3. Equations (4), (5) and (6) are valid, as said in the manuscript, for the incompressible liquid. In your case, you have a two-phase flow with an incompressible liquid (phase 1) and compressible gas (phase 2). How this two-phase flow is handled numerically to get the images in figure 3?
4. You have employed a non-ionic surfactant (n-pentanol) in the experimental part. You compare your results with those of Zhang et al. (2003) who used Triton X-100 which is also a non-ionic surfactant. How about the behavior with ionic surfactants? Is it the same?
5. Sound wave speeds are taken from engineering tables. This is available for infinite systems. Is this assumption fulfilled in your case or is there any interference with the walls of the box for example? This may explain partially the difference between the two techniques.
6. You affirm that the ultrasonic technique may be a reliable technique in the case of opaque or turbid solutions where optical techniques fail. In real industrial systems, we generally face turbid systems with a lot of bubbles. Is it possible to get information on the dispersed phase (velocity of the bubbles, their volume fraction, …) using the ultrasonic technique?

Author Response

1. There is a lot of typo errors which makes the reading somehow difficult. A global and accurate revision of the English is absolutely required. Hereafter a non-exhaustive list of mistakes.

We did our best to correct all typos and mistakes in the text. In addition, the English language of the paper was corrected by the professional service.

2. You give in Table 1 the different properties of pure water for different temperatures (from Handbooks). However, when you mix pure water with n-pentanol, these properties will change, mainly surface tension. Have you measured the surface tension of water+n-pentanol at the corresponding concentrations to confirm or invalidate this?

Certainly, the Reviewer is right. Addition of n-pentanol changes the properties of water. We are perfectly aware of that (we have measured the n-pentanol surface tension isotherm). We did not, however, provide this information, because Table 1 reflects the properties of pure water, in which the bubble behavior is analyzed in the first part of the paper. All the discussion and analysis (using dimensionless numbers), taking Table 1 as a reference is done for pure water, only. For n-pentanol we do not perform similar analysis, focusing only on kinetics of development of dynamic adsorption layer at the rising bubble surface.

3. Equations (4), (5) and (6) are valid, as said in the manuscript, for the incompressible liquid. In your case, you have a two-phase flow with an incompressible liquid (phase 1) and compressible gas (phase 2). How this two-phase flow is handled numerically to get the images in figure 3?

According to my best knowledge, the bubble is treated in the Gerris code as incompressible, as well. This is simple assumption but should work perfectly for most of the considered cases, where moving bubble volume changes are really small.

4. You have employed a non-ionic surfactant (n-pentanol) in the experimental part. You compare your results with those of Zhang et al. (2003) who used Triton X-100 which is also a non-ionic surfactant. How about the behavior with ionic surfactants? Is it the same?

In our opinion yes, it is this same. Usually, similar bubble behavior is observed for ionic surfactants but for more concentrated solutions comparing with non-ionic surfactants of similar carbon atom chain length. We use n-pentanol as an example, only. We are sure that similar trends and conclusions can be drawn for any other surface-active substance. The only difference will be the concentration regime.

5. Sound wave speeds are taken from engineering tables. This is available for infinite systems. Is this assumption fulfilled in your case or is there any interference with the walls of the box for example? This may explain partially the difference between the two techniques.

Yes, the Reviewer is absolutely right. We wrote in the paper that difference between velocities taken by both techniques can be caused by assumptions made on sound wave speed in water phase, whose values, for different temperatures, were taken directly from the engineering tables. Now we added in the revised manuscript additional sentence (line 1305): “… The difference could have been caused, for example, by wave interference with the column walls. …”

6. You affirm that the ultrasonic technique may be a reliable technique in the case of opaque or turbid solutions where optical techniques fail. In real industrial systems, we generally face turbid systems with a lot of bubbles. Is it possible to get information on the dispersed phase (velocity of the bubbles, their volume fraction, …) using the ultrasonic technique?

Yes, it is. Please, see for example: Batsaikhan, M., Hamdani, A., Kikura, H. Velocity measurement on two-phase air bubble column flow using array ultrasonic velocity profiler. Int. J. Comput. Methods Exp. Meas. 2018, 6, 86–97. It is Ref [25] in our manuscript.

Round 2

Reviewer 2 Report

Accept