The Effect of Varying the Air Flow in a Solar Collector on the Quality of Arabica Coffee Beans
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe article "The Effect of Varying Air Flow Solar Collector on the Quality of Arabica Coffee Beans" has been reviewed, finding points of improvement that are numbered below.
Abstrac: This is very long and should focus on the key points and main findings of the research; please shorten it.
It is possible that the introduction can be reinforced with this work: https://doi.org/10.1016/j.renene.2019.09.018
Figure 1 should be improved, it is not necessary to enlarge the solar collector since it is always similar to that of any literature. Just specify that it is double-glazing.
Line 189, as the transmissivity of the glass or glazing system was measured, the optical analysis is not observed. Likewise, how was the absorptivity of the plate determined?
Improve figure 3 The photos are of poor quality, and the nomenclature is the same
Why is theoretical radiation included in the graph? how was it calculated? What is the relevance of doing so? I consider it necessary to eliminate this theoretical radiation, justify its relevance, or indicate in which calculations this information was used.
Table 1 correct "Energi"
How was the temperature of the absorbent plate measured? It is not observed in the methodology section.
Is it interesting to observe that with such low radiation, there is such a high difference in ambient temperature and the drying chamber?
Where are these camera measurement points? (enhance image)
What influence does thermal analysis of the drying chamber have? What is the temperature gain through the chamber? In any case, should you only take the air inlet temperature?
How do you explain that there is greater efficiency in the collector at higher speeds but low drying efficiency, obtaining grains with a higher moisture content?
The results are little or not discussed at all and compared with other works. There are many jobs related to drying coffee beans.
A broad explanation of the method of determining losses, heat transfer coefficients, energy, etc. was made. but no graph of the evolution of these parameters is shown, and they were even less discussed in the work. I consider that the quality of the presentation of the results and the available information should be significantly improved.
The conclusions are very poor, and they must be improved substantially.
Author Response
Thank you very much for taking the time to review this manuscript. For detailed review improvements, we have uploaded them in the following document file.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThis paper states that the conventional method of drying coffee beans is less hygienic and requires a larger area than one using forced convection. Moisture content of the beans needs to be low to give a long shelf life but the percentage range for the moisture required is not given. Presumably the ground area can be reduced by stacking drying racks within the drying cabinet and the time required for drying also reduced compared to drying in the open sun. But is the area needed for open air drying a problem?
The authors should quantify the problems with open air drying- is the moisture content too variable; the time required too long; is exposure to rain or loss from birds and dust too costly. One significant advantage of the traditional method is that it is cheap; but is it too labour intensive? The costs of a drying cabinet should be less than that from losses in the traditional method. (Any forced convection could be solar powered to be low carbon.)
The tests that were carried on 1500 g samples indicated that the average temperature of the absorber didn’t just depend on the air speed. Repeating the measurements several times would have helped in establishing the optimal conditions. Protein, carbohydrate, and fatty acid content are also important, but no comparison is made to what is obtained in open air sun drying, and what are the desired percentages for these components?
Moreover, the sample size is very small compared to the amount of coffee required to be dried in practice, and extrapolating results from such small sample sizes may be unreliable. Tests carried out on a full-size drying box and the results compared to those from open air sun drying would be more persuasive. The final taste and cost of the coffee are clearly important.
A good paper on developing a solar dryer for coffee beans is:
edepot.wur.nl/91838
This paper describes drying using natural convection. In this paper, it states that the optimal value for the moisture content is 12%. It also points out the importance of a design that is acceptable to the community.
Comments on the Quality of English Language
Some phrases are a bit awkward, but generally sense is clear.
Author Response
Thank you very much for taking the time to review this manuscript. For detailed review improvements, we have uploaded them in the following document file.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsRemark and suggestion:
-Table 2 shows average values ​​with up to 5 decimal places. In my opinion, it is not possible to provide such precision in this measurement. I suggest also add the standard deviation of this parameter.
-Chapter 4.3.1.: In this chapters Authors presented the change of mass of product during time, it is not drying rate. Drying rate curves are generally plots of the rate of water removal versus time or moisture content. Figure 9 should be changed.
-The airflow velocity has the effect on the drying rate only during the constant rate period. Thus the wide analysis of the rate value during the constant rate period, duration of this period should be done.
-Authors did not discuss results.
-Chapter conclusions contained only statements not conclusions.
In my opinion, the article in its current state requires thorough improvement and additions.
Author Response
Thank you very much for taking the time to review this manuscript. For detailed review improvements, we have uploaded them in the following document file.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe conclusions look incomplete, possibly it is an outdated version. please correct it
As for the rest, the authors have addressed the comments made.
Author Response
Thank you for the Comments and Suggestions given, here we attach a response to each Comments and Suggestions given.
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsAn air flow of 1.0 m/s is found to be sufficient to reduce the moisture content to the dry standard of 12% after 25hr of direct sun, with higher air flows somewhat less effective. However, without data from lower speeds it is not possible to say that this is optimal. [The authors note in the text that a drying velocity of 0.18m/s was optimal for carb pulp.] The authors could say that 1.0 m/s is sufficient.
If the moisture content after 25hr of direct sun with no forced air flow is known, then this number should be given and would strengthen the investigation. Data from lower speeds is really needed for the authors to conclude that air flow is beneficial.
Just knowing and stating that drying without any forced air flow takes significantly longer would be sufficient.
In any case the abstract needs to say that air flow was varied (from 1-3m/s), and that 1.0 m/s is sufficient to dry the beans to 12% moisture content in 25hr of direct sun. The protein, carbohydrate, and fatty acid content should also be given for 1.0 m/s. Add that higher speeds gave similar protein and carbohydrate values and fatty acid content less than 0.1%, but somewhat higher moisture contents.
[Do not give more decimal points than the accuracy of a measurement justifies]
The authors might add their comment: The sample size used in drying in this research is on a laboratory scale, however the coffee quality testing carried out has followed the approximate test standards at the Medan Industry Standardization and Service Center.
Figure 4 caption should just say: Measured solar radiation (a) ….
4.3.2 Quality of coffee bean
The quality of the bean should presumably be the values for when the moisture content is the dry standard ie those of DB1 air speed 1.0 m/s and not those of DB2 which gave a moisture content of 13.6%
The wording of the present conclusion needs changing.
The conclusion should match the abstract where you say:
Based on this research, it is found that the best quality coffee is using tool 1 (DB1) at a drying air speed of 1.0 m/s.
i.e. the results for 1.0 m/s should be given in the conclusion as this air flow reduced the moisture content to the dry standard of 12.0%.
Author Response
Thank you for the Comments and Suggestions given, here we attach a response to each Comments and Suggestions given.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe paper was corrected acording the remarks. The ppaer was improved.
Author Response
Thank you for the Comments and Suggestions given, here we attach a response to each Comments and Suggestions given.
Author Response File: Author Response.pdf
