A Mesoscale Simulation Approach to Study the Flow Field in an Axial Granular Bed Filter

Round 1

Reviewer 1 Report

This manuscript attempts to develop a simulation method for the investigation of an axial granular bed filter. The main concerns include:

1.      Based on the title and the discussion of the manuscript, this is a NEW method. The description is not genuine. The method is not new. The main contribution is “combining the macroscopic calculation models into the porous media model and the source term of the conservation equations.”

2.  The method has not been clearly described. More information needs to be added to clearly differ the present method and the methods used in the previous study. More discussion should also be provided to demonstrate that the change is reasonable and necessary from the view of theories and/or physics.

3. In section 2.4, published experimental results have been compared with the present simulation results. What are the results if the previous methods are used? Can the present model get better results?

4. In Section 3, the dependence of pressure drop and dust removal efficiency on some parameters and conditions is considered. It is stated that the variation trend is consistent with those obtained in some references. Similar trends are not enough to validate the model. What are the conditions and methods used in these references? More detailed comparison needs to be conducted with the previous methods to show the advantage of the modified models in the simulations.

5. What are the limitations of the modified models? Such information is important for its future application.

6. In addition, the whole manuscript needs to be checked carefully regarding its writing. There are many editorial issues and vague descriptions. Some examples are

6.1 Line 9, what are the “macroscopic calculation models”? Need to make the concept clearer.

6.2  Lines 18 and 19, what does “WHO” represent? “stipulate” should be “stipulates”. It is better to rephase the sentence.

6.3  The format to cite the references is not correct. For example, Line 45,  “Xiao [6], Robert [7], Denis [8], Yin [9] et al.” should be “Xiao el al. [6], Robert et al. [7], Denis [8] and Yin et al. [9]”. Reference citation in the whole text needs to be checked.

6.4  Line 109, ref. [29] is mentioned, but on Line 129, [16] is given. Any error here?

6.5  Line 122 and other parts, change “a Baseline working condition” to “a baseline working condition”.

6.6  In fig.1, words and coordinates are too small.

6.7 Line 152, “which are not described here”. It is better to add references here so that the readers can find them elsewhere.

6.8 Lines 167-170, the equation should be given before the parameters are defined. The parameters should be defined when they appear first.

6.9 Line 190, “which is” should be “which are”.

6.10 Lines 189 - 191, the sentence is unclear.

6.11 Line 204, what is the meaning of “Where”? Does it mean “Eq. [12]”? The sentence needs to be revised.

6.12 Line 124, “which is compared to it” is vague.

6.13 Figures 3 and 4, the captions are unclear. What are the values of other parameters in each small figure?

6.14 Line 277, “in Figures”, which figures?

6.15  Lines 345 and 361, change “the Reference” to “References”.

Author Response

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Reviewer 2 Report

The manuscript "A new mesoscale simulation method in an axial granular bed filter" is of interest to readers. However, there are a few points that need to be clarified.

1) Figure 1 (a). Cite to article [16] 2018. The same figure is presented in the article [29] of 2016. It seems that you need to provide a cite to the original article.

2) Section 2.1. The authors suggest changing the voidage from 0.35 to 0.55. It is generally accepted that the value of voidage is affected by the ratio Dt/dg. Dt is the cylinder diameter, dg is the granule diameter. For example, in the work of 'Benyahia, F. O'Neill, K.E. Enhanced voidage correlations for packed beds of various particle shapes and sizes. Part. sci. Technol. 2005, 23, 169–177.' the results of experimental studies and formulas for granular beds with different particle shapes are presented. The standard void for a very dense packing of spheres with a large cylinder is 0.39. For the selected 58 mm diameter cylinder and for 10 mm diameter granules, the void should not exceed 0.45. What are the reasons for choosing the range 0.35-0.55 and how can these values be implemented in practice for such granules and tube sizes?

3) Section 2.2.1. Equations (1)-(3) are not clear. Each term has a multiplier \epsilon_0. Is it possible to divide all equations by this factor? The meaning of \epsilon/\epsilon_0 is not clear. It is necessary to explain the meaning and contribution of all variables.

4) The authors use the Gidaspow model for interfacial interaction in the momentum conservation equation. It is generally accepted that this model works well for dense fluidized bed cases in the Euler-Euler approach. How applicable is this model for modeling the movement of dust in a filter? Provide links to publications where the suitability of this model for similar tasks has been proven.

Author Response

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Round 2

Reviewer 1 Report

The authors have modified their manuscript based on my comments/suggestions, but mainly based on my minor concerns. Most of my main concerns still exist. They have explained, but not provide the information in the manuscript.

The first main concern is the description of the approach. They claimed that this was a new approach. Is “combining the macroscopic calculation models into the porous media model and the source term of the conservation equations.” new? Has the treatment not been used in other systems by other people? If not, more discussion should be provided to demonstrate that the treatment is reasonable from the view of theories and/or physics. If it has been used for other systems in literature, the treatment/approach is not new. More explanations need to be added to highlight this, including change pf the title.

In section 2.4, published experimental results have been compared with the present simulation results. It is stated that the same conditions have been used. What are the exact conditions, i.e., the values of the paraments, in the simulation and experiment? Are you sure that they are the same?

Variation trends are claimed to be consistent with those obtained in references. The conditions and methods used in these references should be provided in the text. If the conditions in this work and the references are different, the influence on the results should be explained.

In Conclusion, the new results obtained in this work should be highlighted. They should be clearly discussed, separately with those obtained in the previous studies even using different methods. 

Author Response

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Reviewer 2 Report

The authors of the manuscript revised the text and tried to answer the questions of the reviewer. However, some questions were not answered. I will reiterate the remaining major remarks:

1) To justify the choice of the voidage of 0.35-0.55, the authors give an example from article 'Powder Technology, 2018,333. (doi:10.1016/j.powtec.2018.04.019)', where 'the voidage in Fig. 5 is about 0.485'. That's right, the upper limit of voidness can be large depending on the value of Dt / dg. At the same time, the authors left the lower limit of 0.39 unanswered. Provide links to sources where a packed bed of spheres with a porosity of less than 0.39 is implemented in practice.

2) The rationale for choosing the Gidaspow model is not provided. In the reference to the work of Cloete J H, Cloete S, Municchi F, et al. The sensitivity of filtered Two Fluid Model to the underlying resolved simulation setup[J]. Powder Technology, 316 (2017) 265-277. （http://dx.doi.org/10.1016/j.powtec.2016.11.064）the filtered model is considered, which uses additional mathematical filtering by the two-fluid model parameter. This model differs significantly from the classic Gidaspow model. Also the Gidaspow model in the Fluent software is only applicable to the granular secondary phase using the kinetic theory of gases. The corresponding equations are not presented in the manuscript.

The manuscript can be considered for publication after additional processing.

Author Response

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