Thermal Evaluation of a Hybrid Dryer with Solar and Geothermal Energy for Agroindustry Application

Round 1

Reviewer 1 Report

This paper presents a very interesting study on the design of a solar dryer for small agribusiness in Ecuador.  The major contribution is the technical details on the balance between energy saving and final product quality.  I have only one major comment related to the “discussion and conclusion” of the paper. Others are related to the writing errors and editorials.

Comments for author File: Comments.pdf

Author Response

General comment

This paper presents a very interesting study on the design of a solar dryer for small agribusiness in Ecuador.  The major contribution is the technical details on the balance between energy saving and final product quality.  I have only one major comment related to the “discussion and conclusion” of the paper. Others are related to the writing errors and editorials.

 

In P12, Discussion and Conclusion:It is a very good idea to design a solar dryer to save energy use,especiallyfor small agribusinessin ruralareaswithlimited access to energy supply. To build such a dryer, there are many parts and components which may require a very efficient supply chain. Please discuss whether there is such an industrial basis in Ecuador to support this experimental designand what kind of support is needed to make it a practical solution.

 

Response to the reviewer:

Authors appreciate the positive comments about the paper

Line 448-453: The change of the energy matrix of Ecuador promotes the implementation of renewable energy in the framework of distributed energy systems as a mechanism to achieve sustainable development and an important alternative with impacts in the social and economic development of the Ecuadorian population. The built dryer meets these requirements, and could be considered as an alternative solution for development local, being used by small and medium industries that need to dry their products

 

Specific comment 1

P1, Abstract, line22-26: There are two incomplete and poorly written sentences.

Response to the reviewer:

The text has been revised

Line 22-28 Among the problems presented for these types of dryers are; heat losses in the drying chamber because it is not thermally insolated, lack of temperature control (above 60°C) and drying speed, excessive fuel use and 10% burned product, being essential to control these parameters to obtain a quality product and savings in the energy consumption of the dryer. With regard to the problem raised above, is has been done the design and construction of a hybrid dryer that works 80% with thermal solar and low enthalpy aerogeothermal energy and 20% with electric power, in order to optimize the drying process and ensure a quality dry product

 

Specific comment 2

P2, line 46-51line 56-60, line 63-67: These are very long sentences. Please breaktheminto two or three sentences.

Response to the reviewer:

The text has been revised

 

line 48-53. In relation to the evaluation of the energy efficiency of the process several authors have reported in general terms that the consumption heat to dry grains varies between 2,330 to 2,790 kJ / kg of water eliminated when natural air is used, on the other hand, when an artificial source of air is used (turbulent flow), this rate varies between 2,790 to 3,490 kJ/kg of evaporated water. Finally, for Batch-type dryers the evaporation rate is usually 3,490 to 4,650 kJ /kg of evaporated water and for high-temperature dryers without recirculation the rate is 4,650 to 6,980 kJ/kg of evaporated water.

 

line 57-63. The FAO in the year 1996 published in the series of the booklet "Post-harvest Technology" the document entitled "drying of grains and dryers", the basic procedures for the evaluation of drying behavior at the industrial level. This document highlights that there are two procedures. The first procedure consists in the realization of technical tests under norms or regulations previously recognized by accredited institutions with a high cost of execution. The second procedure of lower cost is based on gathering information from the data provided by the manufacturers themselves in their manuals or brochures or those that are acquired by direct contact with the owners of the dryers.

 

line 66-70. Likewise, it is necessary to indicate that many dryers in the agroindustry sector of the Ecuador are of the artisanal or semi-artisanal type. These dryers have problems due to not controlling the temperature and drying speed by the hot gas in the chamber. This causes inhomogeneous drying, and an extra consumption of fuel unnecessary for its operation.

 

 

Specific comment 3

P2, line 68-70: Please elaborate how to design a dryer that usesdomestic materials with a cost limit of “$77000”?What isthe normal price range of an imported dryer versus adomestic dryer in Ecuador? It could be much cheaperto buy an imported dryer.But if you take into considerationthe costsof maintenance (parts, laboretc.)the cost could be quite different,and vice versa.Investing in a dryer may also involvecredit provisions (interest rate) in thelocal area.

Response to the reviewer:

Line 71-78 . Another important point of the current problems of drying in Ecuador is the need of build dryers with national materials avoiding the importation of Brazilian, German, Indian, Colombian and Chinese dryers, which have approximate cost $ 7700 dollars (the reference value includes the import cost) for a capacity of 909 kg of product. In any case, a local construction will reduce the cost of the dryer about 50%. It could even regulate different drying temperatures (40°C, 50°C and 60°C) with the purpose that it can be used to dry any type of product (rice, wheat, corn, cocoa) [4]. Finally, during the research phase it has been determined that a handcrafted dryer built with materials such as cement and brick costs $500 dollars, for a capacity between 227 to 454 kg/day of product.

 

Specific comment 4

P2, line 71: Please clarify why there is a special requirement for the dryer to be able to handle wheat with a drying temperature of 55ºC? Is wheat the main cereal produced in Ecuador?

Response to the reviewer:

Line 75-76 it could even regulate different drying temperatures (40°C, 50°Cand 60°C) with the purpose that it can be used to dry any type of product (rice, wheat, corn, cocoa)

Author Response File: Author Response.docx

Reviewer 2 Report

The idea of the submitted paper is very interesting. Authors recognized the problem in their “neighborhood” and immediately got an idea how to improve the current situation. Commendable. Unfortunately, there are some issues that need to be addressed. First of all, in the title instead “Thermal evaluation of a hybrid dryer with solar energy and geothermal for agroindustry application” there should be written “Thermal evaluation of a hybrid dryer with solar and geothermal energy for agroindustry application”. The language and grammar is not at expected level. There is no line in the text where isn’t problem with comma, dot or spaces between words, small or capital letter. It seems that some words are in Spanish too. Likewise, there are some mistakes with figures layout and captions. For example: Fig. 3 caption is not clear. Fig. 4 is missing the explanation of dots of various colors. Fig. 4a is not uniform (black) as others. Figs. 6 and 9 x-axis are not clear as well. Further, authors are using unit “quintal”. Why not kg or tones? In the text authors write units in centimeters and meters. Uniform this. In lines 72 and 168 authors write “a) Drying technology….” Where is the “b)”? What is the point of this “a)”? From line 138 to line 178 there are many equations with explanation of used variables. It is written too messy; need to be edited to be clearer. Line 391 sentence: “Error! Reference source not found. 8”; what is this??? Authors used 6 mm polycarbonate plates; why not glass plates instead? What is the total cost of constructing such system? Did authors thought about “scale up” of the presented hybrid system?

In the Result section authors mentioned that operating temperature in the laboratory was 27 °C and the outside temperature was 24 – 25 °C. Why in the laboratory temperature wasn’t 18 – 25 °C, which is usually a room temperature? Is there problem with air conditioning system? In terms of repeatability of the experiment conditions anywhere in the World it is important to have some variable which can be considered as basic and constant such is the laboratory temperature.

On Fig 2 authors showed reached average temperatures vs radiation. In the text above authors stated that temperature stabilization time is from 40 to 60 minutes. It would be very helpful to show incorporated, if possible, in Fig 2 Temperature vs Time or Radiation vs Time.

By viewing the whole paper it can be noticed that there isn’t any table present. Authors are advised to create at least two or more tables in which data can be more logical and clearer presented. For example, from line 93 to line 100 these data can be showed more easily in the table form. Results explaining the efficiency of the hybrid dryer can be showed in table form as well.

Overall, taking the whole idea into account and the results presented in this paper, authors are suggested (encouraged) to incorporate more meteorological data (temperature, humidity, rainy days, pressure,…) from area in which experiment was performed (average data through the year). This will bring more useful data. Likewise, authors didn’t mention what is the average initial humidity of product that needs to be reduced to 20-25%. This seems to be a crucial data to someone who is investigating the drying process and constructing the hybrid drying system.

Author Response

General comment

The idea of the submitted paper is very interesting. Authors recognized the problem in their “neighborhood” and immediately got an idea how to improve the current situation. Commendable. Unfortunately, there are some issues that need to be addressed. First of all, in the title instead “Thermal evaluation of a hybrid dryer with solar energy and geothermal for agroindustry application” there should be written “Thermal evaluation of a hybrid dryer with solar and geothermal energy for agroindustry application”. The language and grammar is not at expected level. There is no line in the text where isn’t problem with comma, dot or spaces between words, small or capital letter. It seems that some words are in Spanish too. Likewise, there are some mistakes with figures layout and captions. For example: Fig. 3 caption is not clear. Fig. 4 is missing the explanation of dots of various colors. Fig. 4a is not uniform (black) as others. Figs. 6 and 9 x-axis are not clear as well. Further, authors are using unit “quintal”. Why not kg or tones? In the text authors write units in centimeters and meters. Uniform this. In lines 72 and 168 authors write “a) Drying technology….” Where is the “b)”? What is the point of this “a)”? From line 138 to line 178 there are many equations with explanation of used variables. It is written too messy; need to be edited to be clearer. Line 391 sentence: “Error! Reference source not found. 8”; what is this??? Authors used 6 mm polycarbonate plates; why not glass plates instead? What is the total cost of constructing such system? Did authors thought about “scale up” of the presented hybrid system?

Response to the reviewer:

Title has been corrected

Figure 3. Difference between the internal temperature and the ambient temperature vs. irradiation (a) drying chamber (b) solar collector.

Both components have been analyzed separately Fig. 4 a and b. in Figure4 and Figure 5.

Line 349-352: Figure 4 shows the results obtained with the dryer chamber at different days under environmental conditions. The colors in the graph represent different measurement days. We can see that the solar dryer started at ambient temperature, between 25°C to 30°C and reached the design temperature of 50°C with 450 W/m²

Previous fig. 6 now Fi.7 Operation of the solar dryer and the aerothermal system.

Previous Fig. 9 now Fig 10:  Hybrid dryer work, using solar energy and an auxiliary system (electrical resistance).
The units in kg and cm have been unified. It should be noted that the term "quintal" is commonly used in the agricultural sector of the country (1 quintal = 100 pounds).

All suggested changes have been made.

The 0.6 cm is the thickness of the polycarbonate plate

 

General comment 2

In the Result section authors mentioned that operating temperature in the laboratory was 27 °C and the outside temperature was 24 – 25°C. Why in the laboratory temperature wasn’t 18 – 25°C, which is usually a room temperature? Is there problem with air conditioning system? In terms of repeatability of the experiment conditions anywhere in the World it is important to have some variable which can be considered as basic and constant such is the laboratory temperature. 

Response to the reviewer:

Due to the small area of ​​the laboratory and the number of 1000 W lamps that were used during the tests, the laboratory reached a temperature of 27 ° C, although the conditioned air was on. In addition, the tests were carried out in the hottest months of the year December to March, at that time the environmental temperatures of the city of Guayaquil were 36 ° C with a humidity of 85%. It should be noted that the tests were performed on the ESPOL Campus

 

Specific comment 1

On Fig 2 authors showed reached average temperatures vs radiation. In the text above authors stated that temperature stabilization time is from 40 to 60 minutes. It would be very helpful to show incorporated, if possible, in Fig 2 Temperature vs Time or Radiation vs Time.

By viewing the whole paper it can be noticed that there isn’t any table present. Authors are advised to create at least two or more tables in which data can be more logical and clearer presented. For example, from line 93 to line 100 these data can be showed more easily in the table form. Results explaining the efficiency of the hybrid dryer can be showed in table form as well.

Response to the reviewer:

Fig 2. Radiation, temperature vs. time have been included.

Table 1. Estimate of electricity and industrial LPG consumption.

 

 

Specific comment 2

Overall, taking the whole idea into account and the results presented in this paper, authors are suggested (encouraged) to incorporate more meteorological data (temperature, humidity, rainy days, pressure,…) from area in which experiment was performed (average data through the year). This will bring more useful data. Likewise, authors didn’t mention what is the average initial humidity of product that needs to be reduced to 20-25%. This seems to be a crucial data to someone who is investigating the drying process and constructing the hybrid drying system.

Response to the reviewer:

During our technical field inspection, dryers were used to dry cereals such as rice, wheat, corn were analyzed.

Line 97-99. In economic terms it is estimated that drying 450 kg of product with about 40% initial moisture content to 10% moisture content after 8 hours consumes  250 kWh electric ($25 dollars) and between 45 kg and 90 kg of gas ($12 dollars).

 

Line 293-298

Ecuador has two seasons: the rainy and humid season from December to May and the dry season from June to November where the annual total rainfall is approximately 1506.5 mm (INAMHI). The province coast, during the dry season (June – November) there are average temperatures from 21.65°C to 30.8°C with a humidity of 45 to 60%. While in the rainy season (December – May) the average temperatures is 30.65°C with a humidity of 70 to 99%. From the above, it is necessary to mention that the experimental tests were carried out from March to June.

 

Author Response File: Author Response.docx