On the Efficiency of Air-Cooled Metal Foam Heat Exchangers

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Title is misleading. The manuscript is not about Air cooled metal foam heat exchangers. It is about the heat exchanger already reported in previous publication [10]. The manuscript presents extended analysis of already published data. As such, does not meet criteria of acceptance for publication. Authors should make an effort to more clearly explain novelty of the manuscript

Author Response

Please refer to the attached document. 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

 The paper presents an experimental investigation of the thermal performance of metal foam heat exchanges. The paper is well-written and conveys a significant amount of information, and the results are interesting. I have the following comments:  

 

1- The authors must describe the freeze-casting method that they used to produce the foam.  

2- The particle size of the particles used, and the solidification speeds used.  

3- How much do the authors have control over the flow paths in the metallic foam?  

4- Are there any estimates about the pressure drop of the heat exchanger?  

5- Which is the criteria that the authors used to quantify the flow in the natural or forced convection regimes? I did not see any denominational number that they used, The  Grashof for Rayleigh numbers must be included.  

 

6- The authors must consult the literature for the porous media flows to quantify their observations. 

 

7- The authors must include the definition of the Reynolds number.   

 

Author Response

Please refer to the attached document. 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The authors are using aluminum foam to enhance the heat flow rate in a heat exchanger.

The paper is only implicitly specifying that the foam is an open cell foam. It is not clearly stated anywhere. In Fig. 1(a) and (b) it appears that the foam is partially closed cell and not fully open cell foam.

In Fig. 1(b) it is not clear how the copper tubes are placed in the foam block, it appears that the foam is also inside the tube? More clarity would be helpful.

In Equation (3) the efficiency should be termed as Ideal efficiency and not maximum efficiency, because the former is most likely not achievable.

The air flow measurements and use is unclear. The air velocity in the tunnel is measured, however the surface over which the air flows is not like a smooth plate but a rough and grooved surface. Thus, use of far field air flow for modeling is questionable.

The utility of this work is limited by unclear experiments and authors could include a paragraph on the effectiveness of this work in heat exchanger design.

Author Response

Please refer to the attached document. 

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

This paper reported experimental results on forced convection in metal foam heat exchanger. It shows the heat transfer efficiency under different flow rates. The topic is very interesting and the results are helpful for engineering design. However, this paper has some problems.

1. The results can be enhanced with temperature field inside metal foam.

2. What is the thermal boundary for the convective heat transfer? It is heated up by the electrical heater or constant temperature boundary? If it is heated by electrical heater, i.e, a constant heat flux boundary is mantained. Then the temperature on the thermal boundary should be measured.

3. How to measure the size, shape, pore distribution of metal foam used in this study?

4. The measurement uncertainty must be added and analyzed.

5. The literature review is far not enough to support the problem description or innovation of the current study. Applied Thermal Engineering 2023, 229, 120584 may be helpful for characterize the thermophysical properties of metal foams.

6. Could the authors compare their results to others in literature, such as the heat transfer coefficient or Nu number as a function of Re number.

Author Response

Please refer to the attached document. 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript still requires in my opinion some modifications. I suggest to change the title into something like "On efficiency of air cooled ...". If possible underline precise measurements of heat transfer. Remove Figures 4 and 5. 

Author Response

We want to thank the reviewer for their valuable inputs. Please find our response in the attached document. 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Thanks for the effort of the authors in revising the paper. There no further comments 

Reviewer 4 Report

Comments and Suggestions for Authors

accept as is

Author Response

Thank you for your time and valuable input, which have significantly improved our manuscript.