Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper investigates the pressure drop characteristics of the Komax Triple Action Static Mixer under various flow conditions, including single-phase liquid flow, gas-liquid two-phase flow, and slug flow inlet. The conclusions are clear. However, the following issues should be addressed before publication:

 

1. The term "empty pipe" appears twice in the manuscript (Lines 178 and 212). In Line 178, it refers to the validation of the experimental setup using single-phase liquid flow at different Reynolds numbers. However, the applicability of this concept to the calculation of ΔP₀ in Line 212 is unclear. Please clarify whether the same concept is used in both instances. If not, provide separate explanations.

 

2. The study consists of three main parts: single-phase pressure drop, gas-liquid two-phase pressure drop, and flow behavior under slug flow inlet conditions. While the first section discusses single-phase liquid flow, the primary application context of the mixer is gas-liquid two-phase mixing. It is not meaningful to simply discuss the flow characteristics in pure liquid phase? Additionally, it is recommended to include the condition where U_G=0 in the two-phase pressure drop comparison graphs.

 

3. In Figures 3, 7, 8, and 14, the y-axis represents pressure drop, and the numerical values are consistent across figures, but the axis scales differ. Please verify whether the pressure drop presented is the pressure drop or the pressure drop per unit length. For a 160 mm measurement section, the difference between the two is significant.

 

4. The authors discuss the pressure drop characteristics under different slug frequencies (Figure 14), but a clear trend of pressure drop first increasing and then stabilizing with increasing slug frequency is not evident. Would additional experimental points help demonstrate this trend? Alternatively, consider using a more explicit method to illustrate this relationship.

 

5. The primary objective of the mixer is to achieve homogeneous two-phase flow. The authors used a classical separated flow model to calculate the pressure drop, which is typically applied in cases with distinct gas-liquid interfaces. Please consider whether a homogeneous flow model might be more appropriate?

 

6. When comparing pressure drop characteristics with other mixers from the literature (Figure 8), the operating conditions (gas and liquid velocities) in most cited studies differ significantly from those in this work. Only the data from Kenics [22] fall within a comparable range. It is advised to select literature data with closer operational conditions for a more relevant comparison. Furthermore, the proposed correlation should be validated, and its applicable range clearly stated.

 

7. Figure 2(a) should be presented with higher clarity. The unit of the y-axis in Figure 3 is incorrect.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This paper focuses on the pressure drop characteristics of the Komax triple-action static mixer in turbulent single-phase liquid flow and gas-liquid two-phase flow. Through experimental measurement, flow pattern observation, and model development, it fills the research gap regarding this type of static mixer in turbulent flow and gas-liquid two-phase flow scenarios. Verification of the pressure drop in an empty pipe yields an average relative error of 1.94%. Using a piezoresistive pressure transducer, the friction factor f=1.2 and pressure drop ratio z=44 for turbulent single-phase flow is measured. A Lockhart-Martinelli model is further developed for the "stratified flow-intermittent flow" regimes, with a prediction error ranging from ±10% to ±20%. Additionally, it is confirmed that the pressure drop of the Komax mixer is lower than that of similar mixers, and its core findings provide reference value for the design optimization of static mixers.

However, the paper still has shortcomings in three aspects: the universality of experimental conditions, the in-depth analysis of flow mechanisms, and the correlation between mixing performance and pressure drop. Targeted revisions and improvements are required to enhance the completeness and persuasiveness of the research.

1. The Lockhart-Martinelli pressure drop model developed for the "stratified flow-intermittent flow" regimes in this paper was established solely based on experimental data from the air-water system in a horizontal pipe with a 40 mm inner diameter. It does not cover other gas-liquid flow regimes such as annular flow and bubbly flow. Is this model applicable to a broader range of gas-liquid flow regimes?
2. Only air and water were used as the working fluids in the experiment, without considering polymer solutions that are commonly used in chemical engineering. Is this pressure drop model applicable to gas-liquid two-phase flows involving non-Newtonian fluids?
3. In the paper, the Komax mixer was fixed with 3 inserts, and the effect of changes in the number of inserts and twist angle on pressure drop was not investigated. Is this pressure drop model applicable to Komax mixers with different structural parameters?
4. The model was calibrated only based on experimental data under room temperature and atmospheric pressure conditions, and did not consider the influence of temperature and pressure changes on the physical properties of gas and liquid in industrial scenarios. Is this model applicable under variable temperature and pressure conditions?
5. In this paper, although the swirling flow phenomenon can be directly observed through visualization, it fails to provide an in-depth explanation of the formation mechanism of the swirling flow. Furthermore, no CFD simulations have been conducted, making it impossible to quantify the details of velocity distribution, vorticity evolution, and energy dissipation inside the flow field.
6. In this paper, the correlation between mixing performance and pressure drop is missing. The core performance of a static mixer requires simultaneous consideration of both "pressure drop" and "mixing quality"; however, the paper focuses solely on pressure drop measurement and makes no mention of quantitative indicators for mixing quality. This makes it impossible to establish a trade-off relationship between "energy consumption" and "mixing efficiency," and difficult to comprehensively evaluate the comprehensive performance advantages of the Komax mixer.
7. In this paper, the literature review lacks sufficient citations of the latest models for other static mixers in gas-liquid two-phase flow over the past three years, making it impossible to fully compare the differences between this study and existing research outcomes.

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The paper conducted relevant research on static mixers. The paper is well-written, but further research on its limitations and verification are needed.

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

This is a very well documented study that has yielded data not only useful for applications but also verification data for computational modeling. While the topic of triple action mixers is important to a small fraction of the fluids engineering community, the results are informative and the study itself provides a sound template for analogous experimental investigations.

The literature review is an important contribution to the literature on its own.

Some minor suggestions for the authors in finalizing the paper:

• embed a few more design guidance remarks in the abstract
• reword the introductory sentence of the paragraph that begins on line 64 ('The reliability...') - it is confusing
• subscript O₂ and O₃ in line 99
• the clarity of Fig. 2 could be improved.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have revised the manuscript according to the comments. Therefore, this manuscript is acceptable in its current form.