Experimental Investigation of the Heat Transfer between Finned Tubes and a Bubbling Fluidized Bed with Horizontal Sand Mass Flow
Round 1
Reviewer 1 Report
The manuscript (formerly number 20869946) underwent a number of edits during the first revision, also taking into account the reviewers' recommendations. I would only comment on the results:
(1) R^2 is used in most graphs. The regression coefficient only expresses how well you have chosen the function for interpolation of points, but nothing and statistical evaluation of the data set! In addition, a value of 0.25 or less is more indicative of randomness. In addition, there are conflicting trends that are not described. Descending / ascending (fig. 9 × 10), …
(2) In fig. 11, 14 no more points are drawn, which raises questions of the parties to the evidence.
From the above, I recommend "Major Revision"
Author Response
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Author Response.pdf
Reviewer 2 Report
Comments in attached file
Comments for author File: Comments.pdf
Author Response
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Reviewer 3 Report
The paper sounds. The contribution can be accepted, even the conclusions can be expand in terms of paper original results expression.
Author Response
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Reviewer 4 Report
The article matches the scopes of this special issues “"Advancements in Heat Transfer and Fluid Mechanics “ and can contribute to advancing state-of-the-art related technology.
There are minor issues that may be improved listed below:
- I invite the Authors to consider if it is possible to link the paper better to the journal so as to enhance the current discussion in Energies. Therefore, the Authors may consider previous work to which they are contributing. It may be possible to consider the article that was published recently in the journal: “Jabbar, Noman, Muhammad B. Hafeez, Sameh Askar, and Umar Nazir. 2021. "Non-Coaxially Rotating Motion in Casson Martial along with Temperature and Concentration Gradients via First-Order Chemical Reaction" Energies14, no. 22: 7784. https://doi.org/10.3390/en14227784” and/or others.
- Include more details on TU Wiend where the sandTES technology was developed, specifying that it is in Austria.
- Strengthen the connections between different paragraphs.
- Include how the paper is structured in its different sections at the end of the introduction.
Author Response
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Round 2
Reviewer 1 Report
As part of the revision, the manuscript underwent modifications reflecting the reviewer's recommendations. Therefore, I recommend publishing the manuscript in the submitted state.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
The paper entitled: "Experimental Investigation of the Heat Transfer between Finned Tubes and a Bubbling Fluidized Bed with Horizontal Sand Mass Flow" describes the research results that are a continuation of previous studies. The tests were carried out on three replaceable measuring sections of one test stand. The authors of the paper write about three measuring stands, but the research was conducted basically on one stand - it should be changed. The research topic is current, the Peer-reviewed Paper has a scientific value, it was written in a legible way. I propose to publish it in ENERGIES journal taking into account the following comments:
What do the Authors mean by "Previous simulations suggested the narrower tube spacing performed better...". Sounds unscientific. Provide values ​​or range.
On what basis was the production of helical fins found to be less expensive? "Helical fins, which are more widely available and therefore cheaper to produce than longitudinal fins." Is there any evidence for this in the literature?
Figure 2 - the diagram of the stand is hardly legible. Not much comes out of it. How was an even distribution of the airflow ensured?
The statement Virtual Heat Transfer Coefficient is incorrect, it sounds colloquial. I suggest to beware of such statements.
There is no information on the measurement uncertainty of the apparatus. This should be completed.
Reviewer 2 Report
Review of the Energies-1384719
AUTHORS: Stefan Thanheiser, Markus Haider, Paul Schwarzmayr
TITLE: Experimental Investigation of the Heat Transfer between Finned Tubes and a Bubbling Fluidized Bed with Horizontal Sand Mass Flow
The work is experimental. Unfortunately, the authors did not provide basic information on the conditions under which they performed the experiments.
It is not known how fluidization was forced. There is not even a schematic drawing showing the apparatus with the air flow directions marked. The authors did not report the flow velocities they used to force fluidization. The authors only report velocity in relation to the minimum velocity of fluidization. They calculated this minimum speed using the Richardson correlation. The authors did not write why they chose this correlation and did not provide the formula they used. The authors also did not provide the temperature of the air entering the system.
The authors wrote that they used sand of three different average diameters in the tests. However, they have nowhere given the distribution of the grains' diameters. The diameter distribution is essential for the fluidization process.
In the whole work, I was unable to find any information regarding the physical interpretation of the phenomena occurring, in particular regarding heat transfer.
Most likely, the continuous contact of the heating element with air compared to the momentary contact with the sand grains causes the heat to be transferred from the heating element to the air by convection. Further, the air in contact with the sand transfers heat to it, also by convection. If so, the boundary layer next to the heating element plays a key role. The thickness of this layer is primarily due to the actual air flow velocity. Therefore, comparing the results for the speed related to the minimum speed does not make sense.
Recapitulation
Considering the above, the article is not suitable for publication and should be rejected.
Reviewer 3 Report
The present manuscript deals with heat transfer in a bubbling fluidized bed. I would like to make a few comments on it
(1) a relatively brief introduction, where there is no reference to similar research to prove novelty
(2) for the model and subsequent data, I lack measurement uncertainty / error up to HTC
(3) In the introduction there is a reference to the VDI Heat Atlas and therefore I would expect that some configurations / results will be compared at least with this literature or other publications.
Based on the above, I recommend "Major Revision".
