Heat Transfer Performance of Fruit Juice in a Heat Exchanger Tube Using Numerical Simulations

Round 1

Reviewer 1 Report

The manuscript focuses on heat transfer of nonnewtonian fluid of fruit juice by using numerical simulation of ANSYS Fluent. The innovation of this study is investigation of modulation of the heat transfer in the nonnewtonian fluid by using CFD. However, the manuscript is insufficient for the publication as it is because there are several concerns as follows:

 

Though the introduction describes various studies from application and engineering aspects, few basic studies of nonnewtonian fluid are introduced. Authors should add validations of the flow simulation for the nonnewtonian fluid. The previous study using CFD conducted by Pawar, et al. shows more comparisons with experimental and the previous results. Authors should discuss this kind of comparison, qualitatively and quantitatively. Though authors discuss y+ for the grid dependency in Fig. 6, authors should clearly describe the computational condition with Reynolds number. Usually, y+ is discussed in the condition of turbulence for Newtonian fluid. If not, authors should demonstrate the reason why the discussion is carried out with the previous study. Authors should prepare 3 levels not 2 levels for the grid independency test. Moreover, both coarse and fine grids should be visualized for the comparison. The reason why the turbulence model was employed in this flow simulation should be specified with the previous study. The reason why the k-epsilon turbulence model was appropriate in this flow simulation should be clarified with the previous study. Authors should denote the definition of the Re in the line 152. Is the description of the reference in the line 504 correct? Authors should denote exact dimensions and specific locations in Fig. 1 and Fig. 4 for other researchers. I would like to recommend to simulate nonnewtonian flow through simple circular pipe without turned section due to the clarification of the centrifugal force. The visualizations of Fig. 7, Fig. 9 and Fig. 11 are hard to find the characteristic flow features. I hope that authors can prepare the visualizations which can focus on flow features more than now. The level of the contour should be matched as much as possible. Authors discuss only Nusselt number along with the planes in Fig. 8. However, averaged temperature, maximum temperature and these values in the case of the water should also be compared and discussed. What component of the velocity is employed in Fig. 10? Can the twin vortices structure be observed in the plane of the Fig. 10? Authors should also discuss temperature distribution in the same section of Fig. 11. Is the grid dependency clarified in the distribution of dynamic viscosity in Fig. 14? Is the discrepancy of the comparison in Table 5 acceptable? Authors should discuss the comparison including the previous studies.

Author Response

 

Please see the attachment file (Response to Reviewer 1)

 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

The article is very interesting and useful. Nevertheless, some points are to be considered. My comments and suggestions are:

Governing equations – eq.(3) and (4), the symbol of velocity – it is “u” (U) or “v” (V)? This should be unified. Rheological properties – Figure 3 is not required. Measurement uncertainty with the use of viscometer should be given. Validation procedure – the influence of the use of coarser grid compared to finer grid on average Nusselt number for water should be presented. Results – Local Nusselt numbers for fruit juice (Fig.8) should be compared with those for water at the same Reynolds number. References – there are editorial errors: in many positions titles of journals with lowercase letters, [26] – should be “Reynolds”, no “reynolds”.

Author Response

Please see the attachment file (Response to Reviewer 2)

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Though authors could reply to almost all the comments of the previous review, the most important point that no validation was demonstrated by the comparison with experiments or theoretical study is remained. This kind of comparison is highly required for the recent numerical studies. Moreover, some additional comments to the revised manuscript are appended.

 

As same as the first indication, we need comparisons with experimental results or theoretical values. The comments are denoted in the comment 3 of the previous review. Authors should prove the correctness of the current numerical study by the comparison with some reliable results. Authors can utilize friction coefficient and Nusselt number for a curved pipe based on theoretical values or experimental results from many previous studies. Please give us the validation and the comparison by using author’s numerical methodology. The comparison of the grid independency test is quite qualitative. It should be discussed by the graph quantitatively. The definition of the Reynolds number should be expressed. What are the representative length and the velocity? In the turbulent flow, we can define some Reynolds numbers based on different representative values. The comment is same as the previous comment 7. The governing equations authors added for the momentum and energy have no time derivatives. It is slightly unusual. Sometimes this kind of expression can be employed in order to get the steady solution. However, even in that case, the time integration is carried out as same as the time-dependent flow simulation. Please check the description of the governing equations. When the constant heat flux is imposed to the wall boundary, nondimensionalized temperature can be converged even though the dimensional temperature continues to increase. If authors insist the convergence of the temperature, graphs of the time history of the temperature at several locations should be demonstrated.

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf