Effect of Surface Topography on Particle Deposition from Liquid Suspensions in Channel Flow

Round 1

Reviewer 1 Report

Review of “Effect of surface topography on particle deposition from liquid suspensions in channel flow” by Law, Zhu, and Ma.

Summary

The authors perform 2D DNS simulations of laminar flow over a corrugated surface to investigate the impact of factors such as particle size, rib structure, and velocity on the surface retention of particles, which is relevant in the context of fouling in certain types of particle-laden flows.

The work is high quality and results in some interesting and relevant conclusions.  There are issues that I believe should be addressed before publication, which are listed below.

Comments

1.      Section 2: the symbol u_f (bold u) is specified as the fluid velocity. When used in Eqs 1 & 2 (for instance) one would assume this is a vector field.  However, when used in Eq 4 and 9 (for instance) it would appear to be a specific value because it is subtracted from the particle velocity (a single point value) to obtain quantities such as drag force on the particle.  This should be clarified in the paper.

2.      Eq 6: The equation for drag coefficients is presumably for smooth particles, since surface roughness would be a factor at higher Reynolds numbers. The authors should clarify whether the analysis is limited to smooth particles, or whether the limitation of laminar flow makes this irrelevant.  (If the latter, it might be noted in the Re_p > 1000 notation in Eq 6).

3.      Line 176. When all the assumptions are brought together (meaning smooth particles, laminar flow, 2D, no electrostatic forces, no energy loss with collision), the simulations represent a fairly idealized system, which may not be representative of many real conditions. The findings are still likely to be valuable, but this would be a good thing to address directly in the introduction of the paper.

4.      Table 1. The values of H and h should be added to the table for easy reference on the size of the channel and ribbing.

5.      Figure 2. This figure is not legible when printed on paper. The authors should review to ensure that when published it will be at a resolution legible to the reader either electronically or in print.

6.      Line 240: “For all simulations, uniformly distributed 1000 particles are injected from the inlet…”  I assume this means the injected particles are spatially uniform across the inlet? If so, this represents a significant problem in the simulations, because well-mixed particulate flow will not enter streamlines uniformly across the inlet, but rather as a flowrate-weighted distribution. This means that Eq 16 should be integrated and particles distributed into uniform increments of inlet flow. The reason this is important is that a spatially uniform distribution will put too many particles along streamlines that enter near the walls of the channel, which in turn will affect the calculations of fraction of particle attachment.

7.      Lines 398-407. This paragraph is confusing and needs to be rewritten. Particular issues include: ‘Thereby, the effect of particle interaction with previously attached particle and the change…” (line 399): It’s not clear why 2D flows with Re range of 500-3000 have anything to do with whether the simulations consider previously attached particles, as indicated by “thereby.”  Also the statement that enlarged contact area effects are not evident because electrostatic attraction is not considered is not clear.

General: the paper contains a fair number of typos and grammatical problems.  Some of these are simple things that should have been caught by spell checking (lines 174-184 alone has “zerio,” “andrigid,” and “distacne.”), suggesting the authors could have taken more care before submitting the manuscript. Also, formatting (justification) of the equations is messed up in what my PDF reader created.  This is something I assume would be fixed prior to publication.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The article addresses a sound topic using well established and adequate research methods. The authors make an extensive review of the existing bibliography and uses it to justify the present work. The presentation of the methods and the description of the results is very clear. The figures are very well designed to help describing the results.

 

There are minor errors:

- The formulas of the van der Waals force (12) and van der Waals energy (15) are not consistent. They should be checked.

- There are issues with the grammar of the manuscript. The text has many typos which should be corrected before it can be published.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf