Simulation of Single Vapor Bubble Condensation with Sharp Interface Mass Transfer Model

Round 1

Reviewer 1 Report

1. The variables in the formulas in the paper need to be explained.

2. section 2.2 - needs more discussion and expansion on the acronyms of the numerical models will help. MPLC, CBR, etc.

3. Some methods in recent references about vapor condensation in subcooled water is helpful to improve this article, such as:

Numerical investigation on thermal hydraulic characteristics of steam jet condensation in subcooled water flow in pipes. International Journal of Heat and Mass Transfer, 2022, 184: 122277.

4. How do boundary conditions such as temperature and pressure affect the results?

Author Response

Please check the attached document.

Author Response File: Author Response.pdf

Reviewer 2 Report

See enclosed file.

Comments for author File: Comments.pdf

Author Response

Please check the attached document

Author Response File: Author Response.pdf

Reviewer 3 Report

Review Thermo-1758010

The authors carried out a computational study on the instationary mass transfer processes at a vapor-liquid interface using a CFD solver. The authors obtain good agreement of the simulation results with experimental results form the literature. The approach provides new insight in the computational approaches and their benefits and drawbacks. However, there are some major and minor points that have to be addressed.  

The paper is well structured, but has some language issues. The language of the paper should be improved. The reviewer is no native English speaker and therefore refrains making individual suggestions for improvements. But there are some language issues, e.g. “In present study” should be “In the(!) present study”. There are several similar instances.  

Before the manuscript can be accepted, the authors should address the following points:

1. In the introduction, the authors line out an epistemic guided motivation that it “is vital to obtain an extensive knowledge on [the] condensing bubbles”. Very well. However, in the case of this approach, I miss the widening of the perspective on the vapor-liquid interface in the introduction. In particular, it is well known [Adv. Phys. 28, 2, 143 (1979) DOI: 10.1080/00018737900101365] [J. Phys. Chem. C 122, 43, 24705 (2018) DOI: 10.1021/acs.jpcc.8b06332] that a fluid interface has a finite width, where the thermophysical properties change smoothly. This point should be discussed clearly in the introduction from my point of view. 

2. There is a large body of molecular simulation studies on the mass transfer at vapor-liquid interfaces available. The authors should give a discussion on mass transfer simulation methods to give a more realistic picture of the state-of-the-art physical modeling approaches of mass transport processes at fluid interfaces and set this in relation to their own work. Examples are:  

• [Coll. J. 81, 5, 491 (2019) 10.1134/S1061933X19040021]

• [Fluid Phase Equilibria 481,1 (2019) 10.1016/j.fluid.2018.10.012]

• [J. Chem. Phys. 144, 044703 (2016) 10.1063/1.4940137]

• [Mol. Phys. 119, 3, e1810798 (2021) 10.1080/00268976.2020.1810798]

• [Int. J. Heat Mass Trans. 73, 303 (2014) 10.1016/j.ijheatmasstransfer.2014.02.010]

• [J. Chem. Phys. 151, 4 (2019) 10.1063/1.5111759]

3. In the equations used in the manuscript, several variables are not properly introduced and defined to the reader. Please revise this carefully. 

4. The authors consider a pure substance fluid. This is a reasonable starting point, but in real world cases (as in the experimental data used for comparison{!} ), there will practically always be mixtures, e.g. nitrogen, oxygen and carbon dioxide solved in the water. In such mixtures, a light boiling component will usually accumulate at the interface [Int. Rev. Phys. Chem. 39, 3, 319-349 (2020) 10.1080/0144235X.2020.1777705] [J. Phys. Chem. B 125, 25, 6968 (2021) 10.1021/acs.jpcb.1c03037] [Chem. Eng. Trans. 69, 295-300 (2018) 10.3303/CET1869050]. It is intensely discussed in recent years that this accumulation probably acts as hinderance for mass transfer [J. Chem. Phys. 144, 044703 (2016) 10.1063/1.4940137] [Mol. Phys. 119, 3, e1810798 (2021) 10.1080/00268976.2020.1810798] [Colloid J. 81, 491 (2019) 10.1134/S1061933X19040021]. It has been shown that even very small mole fractions of a low-boiling gas solved in the liquid might change the boiling dynamics of the system. The authors should address all this in their work. Moreover, this could favorably be studied by the authors’ simulation scenario – probably in a future work.

5. On page 1, the authors state “The interface tracking and capturing methods such as (..) phase-field [6] can be (..)”. Yet, the phase field model yields a (physically correct) diffusive interface, which does not(!) have a uniquely defined interface. (see the seminal discussion of Guggenheim on the question of the ambiguity of the definition of the dividing surface). Hence, the authors should avoid the impression that the phase field model would be a suitable method to ‘track the interface’. 

6. On page 2, the authors state “The two-phase flow is treated as an incompressible (..) fluid”. Was also the vapor phase treated as an incompressible fluid? This would obscure thermodynamics and would be a crude assumption. If this was done, please clarify this in the manuscript. 

7. On page 2, the authors write “..parasitic current..” What do you mean by that? If this is a standard term in your field, please give a reference where it is used first in the manuscript such that readers not familiar can look it up. (later in the manuscript, you introduce the term. Please introduce the term in the moment you use it the first time it is used..)

8. What is meant with the “interface transport equation”? Is a balance equation where the quantity ‘interface’ is solved or does this rather work as a boundary condition for the mass conservation law? Please clarify. 

9. On page 3, the authors state “The physical properties can be found in [8].” What is meant by that? 

10. Give references where the thermophysical property data was taken from, cf. page 4 lines 118 ff and on page 6 lines 134 ff. This is in fact crucial since the authors compare their results to experimental data and differences between the simulation and the experimental data might well arise from the thermophysical property data used. 

11. Moreover, why does the thermophysical property data stated on page 4 differ from that stated on page 6? Were the simulations reported and discussed on page 4-5 only preliminary works?! Please clarify. 

12. Was the value of nu for the gas and liquid phase truly the same? I don’t know what property it is (possibly the viscosity?!)..

13. On page 4, you write “The pressure boundary condition sets fixed value of zero”. What do you mean by that? Please clarify. 

14. In figure 5a, please add a length scale such that the reader can understand the width of the temperature transition region. 

15. What turbulence model was used? What are advantages and disadvantages? How is that related to the spurious current?! 

Author Response

Please check the attached document.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

the authors reasonably addressed the reviewers comments.