Improvements and Evaluation on Bitter Orange Leaves (Citrus aurantium L.) Solar Drying in Humid Climates

Round 1

Reviewer 1 Report

The presented work is a very interesting approach to the problem of energy consumption in drying operations. The proposed method (preliminary air drying) is not new, but the use of renewable energy sources (PV) to power the air preparation (drying) system is a very interesting and innovative approach. This solution is also in line with the current research trend aimed at developing energy-saving processing technologies that use green energy.

The structure of the work does not raise any objections, the goal was well defined, and the results obtained and their discussion confirms its implementation. The work requires a detailed linguistic correction due to slight but common mistakes.

 

General comments:

1. From the point of view of the drying kinetics, in my opinion, the process has been unnecessarily prolonged. Graphs 8 and 9 clearly show that after reaching the humidity of 0.6 (after about 150 minutes), the drying process slowed down considerably and it could be completed. This is probably the effect of the material reaching close to equilibrium moisture under given thermodynamic conditions. In this case, it is not possible to obtain further significant drops in humidity. The different value of the final moisture is due to the difference in temperature of air in the individual dryers. What is important, carrying out further drying increases the energy consumption and significantly influence the quality of products. Can the authors justify this extension of drying?
2. The added value is the use of an air preparation system (dehumidifier). However, it is not entirely clear to me how the system works. I would suggest rewriting the description in (lines 138-144) and supplementing the work with the IS layout diagram. Figure 1 is confusing. I am also wondering about the lack of difference between the humidity in the RD dryer and the IS dryer (figure 5) after reaching the "process equilibrium" at 9:40. This is strange because there is no dehumidifier in the RD system, so the air humidity should probably be higher than in the IS. If I am wrong and the results are correct, I do not fully understand what is the point of using dehumidification after reaching the "process equilibrium" humidity (Figure 5, @9:40), since the humidity in the RD dryer was exactly the same. There is no doubt that the air preparation system allowed to shorten the time of air drying. However, his work after achieving operational equilibrium seems unjustified. However, it affects the values of energy coefficients.
3. Several thin-film models were analyzed in the paper. Standard statistical coefficients R2, RMSE, and Chi2 were used to assess the goodness of fit. However, none of these parameters takes into account the number of degrees of freedom (DOF) of the models used. In such a situation, models with a higher number of degrees of freedom may be over-parameterized lead to overfitting. I suggest using statistical parameters that are taking into account the DOF of models (adjusted R squared and reduced chi squared). It could be also beneficial if authors assessed the models used with some likelihood criteria (e.g. AIC or BIC).

Moreover, why authors stated that only thin-layer drying models can be used for dryer design? There are many phenomenological models which can be used as well. Please justify.

4. Lac of statistical analysis. Considering the duration of a single drying process and the variability of the raw material, I would not expect an analysis of variance, as is often found in research studies. However, not even the standard deviation or an estimated measurement error is a serious oversight. In such a situation, it is difficult to evaluate the results obtained.

Detailed comments:

Line 84: Consumed or PRODUCED energy?

Line 124: Water activity is dimensionless.

Line 127: Please provide the color space. CIELAB?

Line 147: The PV panels were powering the air dehumidifier and storing part of the energy which can be used for cloudy days, am I correct?

Line 157 and so: Please provide the units for each symbol used in the equations.

Line 172: Equation 4 seems to be incorrect, please provide a reference. What is MR1 – mean value?

Line 201: Table 2, please change “humidity” to “moisture content”. Please provide the information about the basis of moisture content calculation (wet/dry basis).

Line 248: Please provide the reference for the value of pf = 0.9.

Line 251: Please revise the number of days.

Line 256: Please recall the reference for 0.582 value.

Line 259: Please recall the reference for 0.135 value.

Line 271: Figure 9 – please revise the unit of moisture content.

Lines 280-284: This part should be moved to the methodology of the study.

Line 285: Please revise the Table number. I would also suggest removing the photos of the samples. They are illegible and made with a different light condition – differences in appearances follow mainly from the exposure.

Author Response

Dear reviewer, we are very grateful for the time spent on your review. We are sure that you have helped us a lot to improve the document and we hope that we have complied with your suggestions.

Best regards

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript dealt with evaluation and optimization of bitter orange leaves (Citrus aurantium L.) solar drying in humid climates. I recommend thorough expert language revision before consideration for publication.

 

Author Response

Dear reviewer, we are very grateful for the time spent on your review. We are sure that you have helped us a lot to improve the document and we hope that we have complied with your suggestions.

Best regards

Author Response File: Author Response.pdf

Reviewer 3 Report

The problem of drying in a humid climate seems interesting. But the literature review did not show the scale of the problem. There is no optimization of the drying process in the paper, as indicated by the title. The purpose of the research was not formulated.
The experiments are poorly planned, and probably performed in 1 repetition (the authors do not provide it), but the absence of eg SD indicates the lack of repetition (eg tab. 2). The method of determining the parameters in the models is not described. Which program was used?
RD was carried out under natural convection conditions. IS under forced convection conditions. It is therefore not known whether the observed effect was not the primary effect of the airflow effect
The methodology is not clearly written. The chapter "apparatus" should not be separated, and the instrumentation should be indicated for individual methods
It is not described how the value of Me was determined
During drying RD temperature ranged between 50 ° C and 60 ° C, with an average of 55 ° C. It was not explained why the mean temperature was determined as the arithmetic mean, which allowed for such counting. It is not stated where the temperature during drying IS or the relative humidity was measured.
Why is an air velocity of 2.9 m / s designed?

Formulas (4) and (5) and (6) are unnecessary, because the authors probably did not count the values ​​of statistical parameters directly from these formulas, but used the statistical program
Fig 4 should be deleted - the table is available in the textbooks,
 Calculations in section 3.3. are redundant. The calculation methodology is given earlier.
The results are unreliable. Fig. 8 shows that the water content of the leaves at the end of drying was 0.6 to 0.7 g water / g d.s. which means that the material has a moisture content of about 40%. On the other hand, if the moisture content of the material was 7-8% (as shown in Table 2), the final water content should be about 0.07 to 0.08 g of water per g of dry substance).
The authors did not show the purpose for which they described the experimental drying curves using different models. How can this be used in practice?
The presented results were not statistically evaluated
CO2 emissions should be related to the amount of material dried, but also the value obtained should be assessed
 
Overall, the experiment is poorly planned, with no repetition or statistical evaluation, and unreliable results. The work does not bring any new news regarding drying. It has not been shown that the shorter IS drying time is due to air drying, and not to the air flow rate (change from natural to forced convection).
The conclusion "This work has found that solar drying of bitter orange leaves can be performed in a humid climate with significant energy saving with optimized parameters" is not supported by the test results

Author Response

Dear reviewer, we are very grateful for the time spent on your review. We are sure that you have helped us a lot to improve the document and we hope that we have complied with your suggestions.

Best regards

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

In my opinion, the authors significantly improved the manuscript and explained all the doubts raised in my previous review.

Author Response

Dear Doctor, we are very grateful for all the patience and help you have given us to improve our work. We have tried to do our best.

Author Response File: Author Response.pdf

Reviewer 2 Report

This paper dealt with improvements and evaluation on bitter orange leaves (Citrus aurantium L.) solar drying in humid climates. Major revision is recommended.

 

Abstract: The Abstract is too descriptive. Please add more data. Please eliminate English Grammar Errors.

Materials and methods: Please provide the manufacturing information on the instruments used in the study.

Lines 67-68, 84-87, and 95-97: Incomplete Paragraph.

Line 85: Please discuss the photovoltaics systems and the principles.

Line 117: Please add Citrus aurantium L..

Lines 193 and 179: Any references for equations 1 and 2.

Line 194: Please discuss the models in Table 1.

Line 200: Why the adjusted coefficient was applied?

Lines 226-230: More discussions in Results section are needed. Discussions in Results section for Table 2 are needed.

Lines 231-236: Discussions in Results section for Figure 4 are needed.

Line 242: Please delete Figure 5.

Line 253: Report statistics results for Figure 6, 7 and 12.

Table 4: Redraw Table 4, please.

Lines 400-412: Please reformat these into one or two paragraphs.

Lines 413-429: Please reformat these into one paragraph.

Author Response

Dear Doctor, we are very grateful for all the patience and help you have given us to improve our work. We have tried to do our best. We attach the improvements to our work, according to your comments. Thanks again

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear authors Most of the comments were taken into account, but there is one very important one that needs to be taken into account

The authors did not respond to Note 13 regarding Figure 9 (in a revised version): "Fig. 8 shows that the water content of the leaves at the end of drying was 0.6 to 0.7 g water / g ds which means that the material has a moisture content of about 40%. On the other hand, if the moisture content of the material was 7-8% (as shown in Table 2), the final water content should be about 0.07 to 0.08 g of water per g of dry matter) "

Please check the calculations or units again:

Table 2 Moisture content wb (%)

Initial for RD 54.5%, which means 54.5 g of water in 100 g of wet material, i.e. 54.5 g of water for 45.5 g of d.m. which gives a water content of 1.19 g water / g dm, not with moisture content of 2.2  kg water / kg dry matter as shown in Figure 9

Final for RD 7.25%, which means 7.26 g of water in 100 g of material, i.e. 7.26 g of water per 92.74 g dm which gives a water content of 0.08 g water / g dm, not with an equilibrium moisture content of 0.506 and 0.596 kg water / kg dry matter as shown in Figure 9

Consequently, it is likely that the values in Figure 10 should be corrected 

Author Response

Dear Doctor, we are very grateful for all the patience and help you have given us to improve our work. We have tried to do our best. We attach the improvements to our work, according to your comments. Thanks again

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

The authors have addressed part of the concerns raised. However, I believe that the manuscript still has rooms for improvement. There are too many redundant expressions and English grammar errors in Abstract section, which should be eliminated.

Author Response

Dear reviewer, according to your suggestions, the document has been revised and corrected. We have preferred to send the document to a professional to ensure we comply with this point. We are attaching the manuscript with the corrections made. Kind regards.

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors improved the results, I have no further comments 

Author Response

Dear reviewer, we thank you very much for the time and attention paid to our document, we believe that it has helped us a lot to improve it and increase its value.

Author Response File: Author Response.pdf

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

Comments and Suggestions for Authors

     Manuscript entitled "Evaluation and optimization of bitter orange leaves (Citrus aurantium L.) solar drying in humid climates " presented to evaluate the effect of thermal and photovoltaic energy and regular solar drying on the kinetics, mathematical modeling, and colorimetry study as a quality parameter of the leaves.

Introduction section

Please add and explain more the effects of natural convection and forced convection on drying performance. These effects are pivotal to optimize the drying operation of orange leaves. Please add references.

Materials and Methods section

Please clearly elucidate the operation weight of the sample (e.g. orange leaves) when the drying performance of bitter orange leaves is evaluated.

1. line 142 Please clearly elucidate the meaning of the abbreviation "PVS".
2. line 158 The value of equilibrium moisture (Me) should be added in this study.
3. In Table 1 there are many typing errors for the equations, please correct them.

Results and Discussion

1. line 196, line 200, line 205, line 212, line 237, line 243 and line 276 should be added the number after the Figures (e.g. “Figure X”).
2. In Figure 2 the word of ISD should be revised to IS.
3. line 213 should be corrected.
4. line 255 and line 260 should be revised.
5. In Table 3, in order to compare the effects of natural convection (with regular dryer) and forced convection (with integrated system), the k value should be added with Newton model in the section of the Regular Dryer.
6. Please explain the difference of k value in between regular solar dryer and the integrated system under the Newton model.
7. In Figure 6, please calculate the area of graph (This area is usually referred to the values of thermal input) for RD and IS and explain the meaning of the difference of thermal input.
8. In Figure 7, please check the ticks along the vertical axis.
9. In Figure 9, “please denote the sub-figure (a or b) in appropriate place.
10. In Table 4, please add the images of the orange leaves.
11. Line 283 Please revise the sentence “ ….. reported by [46] ”

Reviewer 2 Report

Mansucript has not been proofread properly. Error! Reference source not found - this is found at many places. Please revise, check carefully and resubmit.

Fig. 3 is not numbered in text.

Same problem with Fig. 4

Results are not discussed with literature. Just saying your results agree with particular literature is not enough. Strongly recommend a separate discussion section for recommending acceptance.