Study on Fluidization Characteristics of Magnetically Fluidized Beds for Microfine Particles
Round 1
Reviewer 1 Report
The paper entitled 'Study on fluidization characteristics of magnetically fluidized beds for microfine particles' concerns the study of the influence of a magnetic field on the pressure drop, bed expansion rate and the minimum fluidization velocity registered in a fluidization column of a very small size. The paper contains rich and interesting experimental material which, in the reviewer's opinion, deserves a much better presentation. While formulating a very unclear objective of the research, the authors did not reveal what is the practical application of the obtained research results. This is highly desirable, since the use of the magnetic field in the fluidization engineering is relatively rare.
The paper requires a thorough improvement in editing. The research object is presented very poorly. Basic information on how the experiments were performed is missing. Conclusions formulated by the authors on the basis of the presented research results are ambiguous. The nature of pressure drop changes as a function of both the bed height and the varying magnetic field is so varied that it requires a more thorough analysis compared to that presented by the authors. In its present form, the provided description and interpretation of the obtained results raises many questions and doubts that must be eliminated in order for the content to be unambiguous and understandable to the readers. Therefore, a thorough re-editing of the paper is recommended, especially in the context of the analysis of the obtained results. Detailed comments are presented below.
The Introduction section is very poor. Authors should present there the general idea of fluidization using magnetic field, the purpose of using magnetic field in fluidization of granular materials, advantages and disadvantages of this solution, as well as achievements of other researchers in this field. Please also formulate more clearly the purpose of your research.
Line 33
Please provide additional more general literature on fluidization technology where readers can find comprehensive information. For example:
- Wen-Ching Yang: Handbook of Fluidization and Fluid-Particle Systems, Siemens Westinghouse Power Corporation, Pittsburgh, Pennsylvania, USA, Marcel Dekker Inc, Chap. 6, 200
- Nowak W., Mirek P., Circulating Fluidized Bed Combustion (CFBC), Chapter 16 in Fluidized bed technologies for near-zero emission combustion and gasification, Edited by F Scala, Woodhead Publishing, 2013, pp 701-764
- D. Kunii, O. Levenspiel, Fluidization Engineering, 2nd ed, (Butterworth-Heinemann, 1991)
Line 38
Please provide literature sources
Line 56
'A series of studies...' please specify literature references
Line 57
-0.045 mm?
Line 66
'true' -> 'real'
Line 67
'composition' -> 'distribution'
Please specify what type of magnetic granular material was used in the study.
Please specify whether the fluidization column contained only magnetic granular material or not?
Line 57
Since Figure 1 only shows the components of the measurement system and not the main parts mentions in the body of the text, please clearly show all four systems in the figure.
Line 73-74
‘an air distributor' - not shown in Fig. 1
‘plexiglas cylindrical bed' - not marked in Fig. 1
Are 'air plate' and 'air distributor' the same thing?
Line 83
How is the pressure drop across the fluidized bed measured? Please indicate on the diagram where the pressure taps for measuring the static pressure are located.
Section 2.2
This section of the paper lacks information about conditions under which the experiments were carried out. It is not known what is the value of the minimum fluidization velocity Umf, and what is the value of the terminal velocity for applied granular material Ut. Please also state for what values of the superficial gas velocity the experiments were performed.
Furthermore, the authors did not state in which fluidization regime the experiments were performed. Were the particles elutriated during the experiments?
Line 113
'With the gradual increase of the applied magnetic field strength, the bed pressure drop first increases and then decreases.' - This conclusion does not follow from the results shown in Figure 2
Line 115
'When the magnetic field strength H=1KA/m, 2KA/m, 3KA/m, the bed pressure drop gradually increases, and the overall bed pressure drop is higher than the bed pressure drop at H=0KA/m.' Since it is difficult to identify the data for H=0KA/m in Fig. 2, it is also not possible to verify the conclusion made by the authors.
Line 181
Please explain this sentence 'The bed is transformed into a needle-type fluidized bed, and the permeability of the bed becomes better.'
Line 184
Please explain the term 'sequence of magnetic field'.
Fig. 4
Please explain the difference between the results shown in Fig. 2 and Fig. 4.
Which curves shown in the figure represent 'adding magnetic field later' and which curves represent 'adding magnetic field first'?
Please explain how the Umf values for H=3, 4 and 5 KA/m were determined.
In one of the diagrams certain locations are marked with three ellipses. Since there is no explanation of this marking in the text of the article, please explain how this marking should be understood.
Fig. 5
The authors claim 'When the microfine particles are fluidized without magnetic field, the pressure drop of the bed is stable at Po'. Unfortunately, this conclusion is not supported by the results shown in the figure. Stabilization of the pressure means that this parameter does not change with time.
Moreover, the authors claim that 'With the addition of magnetic field, the pressure drop stabilizes to Pm over time.' This conclusion is also not supported by the results presented.
Lines 229-232
Please do not write in a scientific article that some researchers believe something and others do not. Science is based on facts and not faith. The dependence of Umf velocity only on grain properties is due to the fact that the fluidization condition was studied only in a gravitational field. It is obvious that the introduction of a new field changes the behavior of particles especially if they are ferromagnetic ones. This type of information should be included in the Introduction section.
Author Response
Please see attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Please find the attached Review file.
Comments for author File: Comments.pdf
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
This article studies the effect of magnetic field on the particle fluidization, which has reference and guiding significance for industrial applications. The following are some suggestions:
1. Please mark the type of the particle in the article.
2. The trend in Figure 2 is not obvious, maybe you could use the data to explain.
3. In lines 140 and 141, the parameters of H and Mb are used to divide the area, but Hf already exists in Mb to indicate the effect of the external magnetic field. What is the difference between H and Hf? Is it possible to only use dimensionless numbers for regional division? Why is H not considered when dividing the area at line 144?
4. "Magnetic chains" appears many times in the article. Does it mean chains formed by magnetic particles under the magnetic field? Please explain the term when it first appears.
5. There are multiple signs in the formula, please add the list of symbols.
6. What phenomenon does formula (2) explain?
7. When multiple graphs such as Figure 4 and Figure 5 are arranged horizontally, you should better keep the same coordinate axis range for easy comparison.
8. You can add the error bar in Figure 6 to make the data more convincing to the results.
9. Can you explain the direction of the force in formula (6)? The direction of the viscous force and collision force between particles should not be determined.
9. In Lines 304-306, is the object of force analysis all bed materials? Need detailed explanation.
10. How to avoid defluidization caused by the fluidization of the magnetic particles in your experiment?
11. You explain the experimental phenomenon by citing formulas from other articles. So what is the novelty of the article?
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
After carefully reading the revised version of the article, I find that the authors did not follow all the comments raised in the first review. Further, it is still not known what is the practical application of the obtained research results. In addition, while reading the text, many errors and ambiguities were noticed that require correction. I present their list below. Moreover, I find that the article has not been properly corrected linguistically.
Line 56
'fine-grained fluidized media'
In the literature, a fluidizing medium always refers to a gas and not to a solid material.
Line 68
'This indicates that magnetic field fluidization of magnetic particles can be achieved and that the basic fluidization properties have been extensively studied and progressed.'
A sentence that makes no sense. Please change the used time: have been => should be
Line 74, 74
'magnetic beads of 0.045-0.074 mm as fluidization media'
Fluidization medium is usually air, not grains
Line 76
'as separation media to separate fine coal'
Please explain what the authors understand by 'separation media'?
Line 78
'All of the above studies show that the applied magnetic field can fluidize magnetic particles'
The magnetic field is not used as a fluidizing medium. Gas usually plays this role.
Line 80
'but the mechanism of magnetic field magnetic particles is not yet perfect'
Please correct this part of the sentence from the grammatical point of view.
Please explain what it means that 'mechanism of magnetic field magnetic particles is not yet perfect'?
Line 81
'In this paper, Geldart A+C magnetite powder is used as fluidization medium'
The grains cannot be a fluidizing medium, only the gas!
Line 100
Since Figure 1 only shows the components of the measurement system and not the main parts mentions in the body of the text, please clearly show all four systems in the figure.
Line 122
'The experiments were carried out at room temperature.'
As the term 'room temperature' has different meanings, please give a specific temperature value.
Line 130
' The magnetic field strengths were 1KA/m, 2KA/m, 3KA/m, 4KA/m, and 5KA/m, and 0KA/m was set as the control experimental value.'
This sentence makes no grammatical sense. Please correct it.
Line 134
'.... and the gas velocity as well as the regulated power supply were adjusted to record the bed pressure drop values as well as the bed height variation values under different static bed height conditions, and the data were processed by computer.'
This sentence is difficult to understand and needs to be re-edited.
Line 141
'The static bed height is set to 40 mm, 50 mm and 60 mm respectively,…'
This information appeared earlier on line 133.
Line 143
'… the rotameter valve is opened to measure the pressure drop at'
The rotameter is not used to measure the pressure drop!
Line 159
Intervention -> influence or impact
Line 171
What does 'the original cause' mean?
Line 173
'When the same static bed height, the reason for the above variation in pressure drop lies in the competitive relationship between the applied magnetic field and the gas velocity.'
Grammatically incorrect sentence.
Section 2.2
This section of the paper (or other) still lacks information about conditions under which the experiments were carried out. It is not known what is the value of the minimum fluidization velocity Umf, and what is the value of the terminal velocity for applied granular material Ut. Please also state for what values of the superficial gas velocity the experiments were performed.
Please provide this information not to the reviewer but to readers!
Furthermore, the authors did not state in which fluidization regime the experiments were performed. Were the particles elutriated during the experiments?
The question is about the regime, not the state of fluidization.
Line 113
'With the gradual increase of the applied magnetic field strength, the bed pressure drop first increases and then decreases.' - This conclusion does not follow from the results shown in Figure 2
Line 181
Please explain for readers this sentence 'The bed is transformed into a needle-type fluidized bed, and the permeability of the bed becomes better.'
If the term 'needle-type fluidized bed' appears in the literature, please quote it.
Fig. 4
Please explain the difference between the results shown in Fig. 2 and Fig. 4.
Which curves shown in the figure represent 'adding magnetic field later' and which curves represent 'adding magnetic field first'?
Your response is as follows: Firstly, in the graph we use 'H' to represent the magnetic field added first and 'H' to represent the magnetic field added later.
I cannot see the difference between 'H' and 'H'.
Fig. 5
The authors claim 'When the microfine particles are fluidized without magnetic field, the pressure drop of the bed is stable at Po'.
Unfortunately, this conclusion is not supported by the results shown in the figure. Stabilization of the pressure means that this parameter does not change with time.
Moreover, the authors claim that 'With the addition of magnetic field, the pressure drop stabilizes to Pm over time.' This conclusion is also not supported by the results presented.
Unfortunately, your answer to my remark does not sound convincing. Please provide an appropriate explanation to the text.
Table 3
Data presented in the Table should be placed in a separate section.
Conclusions
Formulated conclusions are overly complex, which means they lose their integrity. I propose to formulate more specific conclusions.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
The paper has been substantially revised and improved. In general, it seems that the authors have managed to address my comments successfully. Therefore, I suggest accepting the paper.
Author Response
Dear reviewer, thank you very much for your approval of our research.
Reviewer 3 Report
after this revision, the authors have provided more information,so, it can be accepted for publication.
Author Response
Dear reviewer, thank you very much for your approval of our research.
Round 3
Reviewer 1 Report
Line 80
'but the mechanism of magnetic field magnetic particles is not yet perfect'
This sentence is still incorrect and must be somehow improved. In the present form it is unacceptable.
-> but the influence of the magnetic field on the fluidization process itself has several drawbacks, including ….
Cover letter – response 7
Thank you for your comments, the temperature of our experiment was 20°C, for which we have made changes in the article.
Your response is 20deg but within the body of the text there is 25 Celsius deg. Which of the values is true?
Fig 1
Unfortunately I must admit that your analysis of the results shown in Fig. 1 is confusing and not very convincing. When presenting the data for comparison it would be useful to show them in such a way that all curves end for the same velocities. Meanwhile, it is currently the case that some curves end at 12m/s while others end much earlier. This introduces unnecessary confusion.
What follows from this figure is:
- the higher the height of the bed, the greater the pressure drop across the range of gas velocities analyzed
- whether generating a magnetic field or not, the pressure drop increases as the fluidizing gas velocity increases
- it is difficult to see any pattern when it comes to the effect of the magnetic field intensity on the pressure drop. Therefore, based on the presented data it is not possible to unambiguously formulate a conclusion that an increase or decrease in magnetic field strength causes an increase or decrease in bed pressure.
Line 350
The introduction -> application
The application of the magnetic field changes the fluidization characteristics of microfine particles.
Line 353
'... while the bed pressure drop increases and decreases first.'
This sentence introduces unnecessary confusion. What does the word 'first' mean?
Line 355
and the air-flow action in the bed dominates -> and the gas flow has a major influence on the fluidization
Line 357
overall, and the bed is dominated by the magnetic field -> which means that the fluidization is mainly affected by the magnetic field
Line 359
' The sequence of magnetic field addition affects the fluidization state of the microfine particles, and the bed undergoes a ‘sudden pressure drop’ when the magnetic field is added later, and the time of the ‘sudden pressure drop’ increases with the magnetic field strength.'
This sentence is too long. Please divide it into two.
Conclusion 4
This conclusion is too long and thus too complicated. I recommend to divide it into parts.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
