Study of Natural Convection of Lithium-Ion Battery Module Employing Phase Change Material
Round 1
Reviewer 1 Report
I am not particularly familiar with this topic, but I found the research interesting.
Some details need to be changed, such as the scale of the image on page 9, the title of Figure 5 on page 10, etc.
Author Response
Reviewer reports:
Some details need to be changed, such as the scale of the image on page 9, the title of Figure 5 on page 10, etc.
Authors’ reply:
We changed the scale of the image on page 9. We revised the title of Figure 5 on page 10 to “Comparison of the maximum temperature between the present method and Parsons [17].”
We revised “profle” in the title of Figure 6 on page 12 to ”profile”.
We revised the title of Figure 10 to “Variations of (a) the maximum temperature (b) average Nusselt number with time for different cases A, B, C and D under 1 mm amid cylinders.”
Reviewer 2 Report
Line 9 – Personally, I think the abstract gives too many fine details. It would be good to give a clearer “big picture” view of the work and what is done, along the lines of “We did this and this is why it is important”.
Line 39 - “internal thermal convection” what do you mean by this?
Line 51 – can you clarify what you mean by “trade-off structure”
Line 56 – I’m not sure it is true that most li-ion cells are cylindrical. Maybe you can qualify this by saying most cells in X application are cylindrical or give a reference? Also, all cells produce heat, but the sentence makes it sound like only cylinders produce heat. I think there are two separate points being made in this sentence.
Line 60 - what do you mean by “peak overall averaged Nusselt number”?
Line 68 – What “increases with an increase in Grashof number.”?
The third paragraph of the introduction is very long and reads like a disjointed account of other work. It would be good to discuss these referenced works in the context of your paper. I would consider restructuring the introduction to make it clear what problem you are trying to address and what your approach is in this paper.
Line 149 – do you mean PCM instead of CPM?
Line 160 – I’m not sure I follow your “single-region” technique. Are you just treating the pack as a homogeneous solid material with some prescribed heat source? But then you still need to say something about heat transfer with the surrounding environment? I think the formulation needs a more careful explanation. My understanding is that equations 1-3 are for the surrounding fluid or PCM, but in that case, the heat source from the pack would show up as a boundary condition? And it looks like you solve the heat equation in the cell too, with a prescribed heat source?
Line 174 – you define x as the Cartesian coordinate here, but it first appears on line 165. Also, need to define t.
Line 180 – You define the material properties as volume-weighted averages. Would you expect to have anisotropic thermal conductivity, for example? Can you comment on this?
Line 193 – can you explain where this source term comes from in more detail or give a reference?
Line 207 – should this be equation 12?
Line 221 – the boundary conditions need to be explained more clearly, and it looks like the notation used in the figure is different from that used in the equations. The “battery walls” are labeled as a boundary condition, but you give a volumetric heat source there?
The figures in section 2 appear to be stretched.
Figures 6 and 8– consider changing the colourbar limits since the max temperature is around 50 deg C.
In figures 8 and 9 it is hard to see much difference between cases B and D. Again, this might be improved by adjusting the colourbars. Or maybe there is a different plot that better illustrates the effect of including the fins.
Line 404 – you talk about relative errors here but I think you are actually talking about the difference between the current temperature and the steady-state?
In the conclusions can you comment on the practical implementation of the different cooling strategies? For example, you highlight that PCM gives better thermal performance, but does this come at a cost (financial or otherwise).
Overall, the paper presents a nice study, but the model formulation is poorly explained and should be improved. I think the manuscript could also be improved by modifying the introduction to place the paper in the context of existing literature.
Author Response
Comments and Suggestions for Authors
Line 9 – Personally, I think the abstract gives too many fine details. It would be good to give a clearer “big picture” view of the work and what is done, along the lines of “We did this and this is why it is important”.
Authors:
According to the reviewer’s comments, we had re-written the abstract
Line 39 - “internal thermal convection” what do you mean by this?
Authors:
According to the reviewer’s comments, we have revised as “When Biot number was lower than 0.1, the conduction heat transfer rate would be very faster than convective heat transfer rate at the surface.” in lines 38-40.
Line 51 – can you clarify what you mean by “trade-off structure”
Authors: It means trade-off structure between the cooling capability and cost. For clarification, we had added some statements in line 50 of our revised manuscript.
Line 56 – I’m not sure it is true that most li-ion cells are cylindrical. Maybe you can qualify this by saying most cells in X application are cylindrical or give a reference? Also, all cells produce heat, but the sentence makes it sound like only cylinders produce heat. I think there are two separate points being made in this sentence.
Authors:
According to the reviewer’s comments, we have added some statements in line 55 and new reference [7].
Line 60 - what do you mean by “peak overall averaged Nusselt number”?
Authors:
According to the reviewer’s comments, we have revised as “the overall averaged Nusselt number reached the maximum value” in lines 60-61.
Line 68 – What “increases with an increase in Grashof number.”?
Authors:
This is a typographical error and we deleted this statement.
The third paragraph of the introduction is very long and reads like a disjointed account of other work. It would be good to discuss these referenced works in the context of your paper. I would consider restructuring the introduction to make it clear what problem you are trying to address and what your approach is in this paper.
Authors:
According to the reviewer’s comments, we have added some statements in lines 57-59, 69-70 and 74. We also deleted some references to make the paragraph shorter.
Line 149 – do you mean PCM instead of CPM?
Authors:
It is a typographical error and we revised it as “PCM”.
Line 160 – I’m not sure I follow your “single-region” technique. Are you just treating the pack as a homogeneous solid material with some prescribed heat source? But then you still need to say something about heat transfer with the surrounding environment? I think the formulation needs a more careful explanation. My understanding is that equations 1-3 are for the surrounding fluid or PCM, but in that case, the heat source from the pack would show up as a boundary condition? And it looks like you solve the heat equation in the cell too, with a prescribed heat source?
Authors:
According to the reviewer’s comments, we have revised the legend and pointing on Figure 2 (b) for avoiding misunderstanding. Considering fluid and cylindrical heat sources with a rectangular pack as one region means that cylindrical heat sources appears in the heat source in Eq. (3).
Line 174 – you define x as the Cartesian coordinate here, but it first appears on lines 165-166. Also, need to define t.
Authors:
According to the reviewer’s comments, we have revised some statements in lines 153-154 and line 162.
Line 180 – You define the material properties as volume-weighted averages. Would you expect to have anisotropic thermal conductivity, for example? Can you comment on this?
Authors:
Anisotropic thermal conductivity depends on the direction. Instead, this study assumes isotropic thermal conductivity. The volume-fraction-averaged properties are used for the control volume composed of different phases.
Line 193 – can you explain where this source term comes from in more detail or give a reference?
Authors:
According to the reviewer’s comments, we have added some statements and new reference [28] in lines 184-185.
Line 207 – should this be equation 12?
Authors:
According to the reviewer’s comments, we have revised “13” as “12” in line 197.
Line 221 – the boundary conditions need to be explained more clearly, and it looks like the notation used in the figure is different from that used in the equations. The “battery walls” are labeled as a boundary condition, but you give a volumetric heat source there?
Authors:
According to the reviewer’s comments, we have revised the label on Figure 2 (b) for avoiding misunderstanding. We have removed the statement “heat source: volumetric heat generation, 88914 (W/m3)” from the boundary conditions in line 246 and added the statement “cylindrical heat source with volumetric heat generation, 88914 (W/m3)” in lines 146-147.
The figures in section 2 appear to be stretched.
Authors:
According to the reviewer’s comments, we have revised the figures in section 2.
Figures 6 and 8– consider changing the colourbar limits since the max temperature is around 50 deg C.
In figures 8 and 9 it is hard to see much difference between cases B and D. Again, this might be improved by adjusting the colourbars. Or maybe there is a different plot that better illustrates the effect of including the fins.
Authors:
According to the reviewer’s comments, we have changed the colourbar limits in Figures 6, 8 and 9.
Line 404 – you talk about relative errors here but I think you are actually talking about the difference between the current temperature and the steady-state?
Authors:
According to the reviewer’s comments, we have revised the” relative errors” to ” relative differences” in line 381, which means the difference between the maximum temperature at some time and that at the previous ten minutes when time is after 70 min.
In the conclusions can you comment on the practical implementation of the different cooling strategies? For example, you highlight that PCM gives better thermal performance, but does this come at a cost (financial or otherwise).
Authors:
According to the reviewer’s comments, we have added some comments in lines 443-446 in the conclusions.
Overall, the paper presents a nice study, but the model formulation is poorly explained and should be improved. I think the manuscript could also be improved by modifying the introduction to place the paper in the context of existing literature.
Authors:
Thanks for the reviewer’s recommendation and comments very much. We have revised the manuscript carefully according to the reviewer’s comments. We also have revised the whole manuscript many times and managed to avoid any grammar or spelling mistakes we believe that the manuscript has been improved a lot.
Round 2
Reviewer 2 Report
Thank you for your careful revisions. The problem formulation is now much clearer.
