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Revista Ciencias Técnicas Agropecuarias

On-line version ISSN 2071-0054

Rev Cie Téc Agr vol.29 no.1 San José de las Lajas Jan.-Mar. 2020  Epub Mar 01, 2020

 

ORIGINAL ARTICLE

Design and Simulation of a Solar Dryer for Botanical Seeds of Grass and Forage

Ing. Yoel Rodríguez GagoI  * 

Dr.C. Yanoy Morejón MesaII 

I Instituto de Ciencia Animal (ICA), San José de las Lajas, Mayabeque, Cuba.

II Universidad Agraria de La Habana, Facultad de Ciencias Técnicas, San José de las Lajas, Mayabeque, Cuba.

ABSTRACT

The present investigation is oriented towards the design of a solar dryer for botanical seeds of pastures and forages. For the fulfillment of the proposed objective, the theoretical-methodological bases referred to the subject were established. It was evident that the proposed theoretical foundations allowed carrying out the design and simulation of a prototype for the solar drying of botanical seeds of pastures and forages. With the use of the Solidworks software (2018 version), the prototype design was carried out and with the Flow Simulation tool, the analysis of fluid kinetics and temperatures was carried out, reaching air velocity values of 0,25 m/s and temperatures of 8 ℃ above room temperature in the drying chamber. On the other hand, with the Simulation tool, a finite element study was carried out to evaluate the structural strength of the prototype, using the von Mises maximum tension criterion, which demonstrated its strength and stability.

Keywords: solar drying; grass seed

INTRODUCTION

The sun is an important source of free and inexhaustible energy for Earth planet. Currently, new technologies have been developed to use solar energy in the generation of electricity and heat. These approaches have already been tested and are widely practiced worldwide as renewable alternatives to conventional technologies. Almost four million exaJoules (1EJ = 1018J) of solar energy arrive on earth annually. Despite this enormous potential and increased awareness, the contribution of solar energy to the world's energy supply remains insignificant. Another important perspective regarding solar research is associated with the current momentum towards reducing global carbon emissions, which has been a global environmental, social and economic problem in recent years. Therefore, the adoption of solar technologies would significantly mitigate the problems associated with energy security, climate change and unemployment (Kabiret al., 2018).

The need for sustainability, food security and for decoupling agricultural production prices from the fluctuating prices of fossil fuels has driven the search for sustainable and adequate processing of agricultural products. A method widely practiced by farmers in developing countries since ancient times is sun drying for the preservation of food, seeds and agricultural crops, but this method has inherent limitations such as: large post-harvest losses caused by drying inadequate; fungal attacks; invasion of insects, birds and rodents; and, unexpected rain and other meteorological phenomena. The limitations described above result in minimum quality standards. In addition, conventional drying methods require longer drying periods, large open areas in which the product can be exposed to the drying process and a large number of working hours. However, artificial drying has proven to be more efficient than other drying methods, which cannot be completely controlled (García-Valladares et al., 2019).

Although there have been many research papers on solar drying technology that have been published in recent years (Sahuet al., 2016; Sonthikun et al., 2016; Roche et al., 2017; Teixeira-da Silva and Malpica-Pérez, 2016; Gavhale et al., 2015); the situation remains unchanged, with solar dryers available. The development of solar drying technology follows two lines: (a) simple and economical dryers with low power capacity, low efficiency and a short service life; or (b) more expensive systems, with a correspondingly higher power and efficiency capacity, and a longer service life, but with a more limited availability. Most of the solar dryer designs currently available are mainly used in different subsistence crops or in small-scale industrialized production. Few studies have focused on the research and development of high capacity solar drying systems (more than 200 kg)

The use of thermo solar technologies in agricultural production is then an economic alternative for small and medium producers to improve their productive capacities, when compared to traditional dehydration methods, allowing them to achieve sustainable development by producing minimal environmental impacts (Milani and Carvallo, 2013). In recent years, the development of applications for the use of alternative energy has aroused interest in the analysis of forms of efficient and adequate use of renewable energy sources. That has motivated the development of drying systems for agricultural products using solar thermal energy.

There are different types of solar dryers, which are classified as direct, indirect solar dryers and a hybrid of both, according to the way heat is transferred. According to the way in which solar energy is used and the circulation of air within them, they are classified in dryer systems with active and passive solar energy, which are dryers with natural or forced circulation (Roche et al., 2017).

Therefore, the objective of this work is to design an indirect solar dryer with forced air circulation for drying botanical seeds of pastures and forages, which in turn protects the seeds from environmental conditions and contamination that may damage their quality

METHODS

In some publications, a simple classification of solar dryers based on the mode of use of solar energy is proposed. Another classification criterion is according to the energy source that activates them. It is said that a dryer is hybrid when it can be activated by more than one power source. Another classification refers to the productive scale (Laborde and Williams, 2016).

The developed solar dehydration technologies are aimed at economic solutions, such as support for small and medium producers, compatible with the environment, seeking energy efficiency and using easily accessible materials. The models are developed according to the needs of the producers, according to the volume of production, availability of connection to the electricity grid, the seasonality of the crops and the drying conditions of the products. The technologies basically consist of active indirect solar drying systems, that is, they are systems where the products do not receive direct sunlight and operate by forced convection. In general, they have a solar air collector, a drying chamber and a fan (Espinoza, 2016).

The following aspects will be taken into account to design the dryer chamber:

  1. Analysis of the bibliography, that provided the following information:

    1. Three geometries (horizontal, inclined and conical) are the most used in drying chambers, in fixed bed dryers and three methods of product support (fixed trays, mobile trays, fixed bed).

    2. The density of the product.

    3. The recommended airflow.

  2. The dimensions of the product bed, for a given load.

  3. Simulation of the behavior of the air inside the drying chamber, using the SolidWorks 2018 software for the geometry obtained, considering: a) 2D and 3D, b) constant temperature and speed at the exit, c) The drying chamber is isolated, d) The properties of the air are constant, e) The product is considered as porous medium.

  4. The behavior of the velocity field inside the 2D drying chamber.

  5. The speeds obtained are analyzed to verify if the air is distributed in uniform way in the product bed.

To carry out the study of the dynamics of computational fluid CFD by its acronym in English, the following steps were followed: Resolution process through CFD; creating the 3D model; defining the type of problem; defining the type of fluid; defining boundary conditions; defining and generating the mesh; setting the calculation parameters; calculating. Obtaining and analyzing the results.

Drying Chamber Design Considerations

To obtain the dimensions of the drying chamber, the following parameters are considered:

  • 1.- The capacity of the product bed;

V=Wρ (1)

where: V: volume in m3; W: product weight in kg; ρ: volumetric density in kg / m3

h=65·Aπ (2)

where: h: product bed height in m, A: cross-sectional area in m2.

  • 4.- Regarding the air flow inside a fixed bed drying chamber, several authors recommend a flow between 0,12 and 0,25 m3/ s / m2, where m3 / s represents the flow of air and m2 the cross-sectional area, (FARONI et al., 1993);

  • 5- Must allow the humid air to escape avoiding the condensation of water;

  • 6- The temperature and air flow must be distributed homogeneously;

  • 7- The design must be ergonomic, resistant and of easy construction with materials that minimize heat losses.

The proper selection of the materials that will be part of the prototype is essential for its correct operation and durability over time. For this, certain criteria that are shown below must be taken into account (table 1):

TABLE 1 Criteria for material selection 

Criterion Description
Resistance Capacity of the material to resist failures by bending, compression or cutting.
Cost Material acquisition cost
Corrosion resistance Capacity of the material to resist corrosion without additives
Availability Supply of material in the national market
Conductivity coefficient Heat conduction resistance
Installation Ease of installing the material in the equipment
Durability Capacity of the material not to lose its properties

For the determination of the area of the collector, it is precise to take into consideration that it is directly proportional to the energy demand to perform the dehydration process and inversely proportional to the incident solar radiation and efficiency. Equation 1 allows establishing the required area of the collector (MONTERO et al., 2010)

Ac=QuI ×n (3)

Qu=ma·cpaT2·T1 (4)

where: Ac: Collector area, m2; Qu: Useful heat, kW; I: Global solar radiation (5 kWh / m2 day); n: Efficiency (80%).

The most favorable placement of the solar radiation capture surfaces will be that which, depending on the application to which the system is destined, captures as much energy as possible. For the sizing of the sensors of the thermal photo systems, it is proposed that the ideal is to tilt them over the horizontal, the latitude of the place plus 100. In this way, the maximum performance in winter will be obtained. (Ekechukwu and Norton, 1999)

β=δ (5)

where the declination angle δ is given by:

δ=23,45·sin360284+n365 (6)

where: β: inclination angle; L: latitude of the place.

To design the drying chamber it is necessary to establish the conditions of its internal structure, where the seed will be deposited on a fixed bed. Initially, determine the volume of the seed to be processed. Equation 6 allows setting the volume of the drying chamber

Vtp=Mtρap (7)

where: Vtp: Total volume of product to be processed; Mt: Total mass of the product to be processed; ρap: Bulk density of the product to be processed.

The relationship between the cross-sectional area and the height of the product is (Faroni et al., 1993).

h=65Aπ (8)

The cross-sectional area of the drying chamber must have the following relationship (FAO, 1996):

L= 1.5 a. (9)

For the airflow inside a fixed bed drying chamber, FAO recommends a flow between 0.12 and 0.25 m3 / s m2. (Dalpasquale et al., 1991).

In order to avoid crushing and consider an adequate space between each tray, the volume of the internal chamber is 0,054 m3. The dimensions of the internal chamber of the drying chamber are 0,52 m wide, 0,315 m high and 0,33 m deep.

RESULTS AND DISCUSSION

For the determination of the movement kinetics of the fluid (hot air) and the thermal behavior inside the dryer and the seed layer, the incident solar radiation on the thermal system or installation was considered as initial data. For that, it was necessary to determine the optimal location of the solar collector in the installation, in order to obtain the highest possible thermal efficiency. Considering that Cuba is located in the northern hemisphere with respect to the equator, the surface of the collector must be oriented towards the south. Therefore, by means of the expression for the winter season (β = | ∅ | +100), it was determined that the optimal angle of inclination between the surface of the collector and the horizontal should be 32 °, based on the geographical latitude of the Institute of Animal Science (ICA) which has a value of 22 °.

Taking into account the considerations and the proposed methodology. The following results were obtained:

The mesh of the computational domain and the boundary conditions applied to the model are shown in Figure 1, where the mesh refinement can be seen. From a level of refinement equal to 3, a total of 32 684 cells were obtained, of which 12 426 cells correspond to the fluid, 6 248 cells to the solid and 14 010 to partial cells of solid and fluid.

FIGURE 1 Boundary conditions and computational domain meshing. 

The volumetric air flow that moves the air extractor was made to influence the dryer outlet (red arrows) in the normal direction to the X-Z plane with a value equal to 5 m s-1. At the entrance, the total pressure is declared having as reference the atmospheric pressure (green arrows). In the simulation of the prototype, the components that have been declared as porous media and perforated mesh have been deactivated. Through the simulation, 333 iterations were carried out to solve the convergence criterion for the engineering goals declared in the software in a time of 1051 s, obtaining a satisfactory level of convergence of the appropriate results. Figure 2 shows the distribution of the temperatures obtained inside the dryer, for a cross section in the YZ plane. A homogeneous temperature in the drying chamber section, that exceeded the ambient temperature by 12 ℃, was achieved, with an average temperature of 32 ℃. That favors the drying of the seeds since the temperature does not exceed 45 ℃, the maximum recommended temperature for the safe drying of seeds.

FIGURE 2 Distribution of temperatures inside the dryer. 

FIGURE 3 Relative pressure behavior (considering the seed layer) 

FIGURE 4 Relative pressure behavior (without considering the layer of seeds). 

When analyzing the behavior of the relative pressure, shown in Figures 3, it is observed that in the specific case of the variant that considers the porous medium, the minimum pressures are reached in the region of the extractor, specifically at the exit of the extractor with a value -72,70 Pa and the maximum pressures are reached in the region of the drying chamber, specifically in the solar collector, having a value of -0,48 Pa. This evidenced that a pressure drop of 72,22 Pa occurred. However, as it can be seen in Figure 4, (the variant that does not consider the porous medium), the minimum pressures are also reached in the extractor region, at the outlet of the extractor with a value of -48,23 Pa and maximum pressures are reached in the region of the drying chamber and the collector, having a value of -0,58Pa. It evidencing in this way that a pressure drop of 47,56 Pa occurred.

FIGURE 5 Relative pressure behavior (without considering the seed layer). 

In order to know the behavior of the prototype, a series of simulations were carried out for each month of the year with the meteorological data of the last 12 months prior to the study, considering the meteorological variables of minimum average temperature and relative humidity for each month (Table 2). In these simulations the variables of maximum temperatures inside the dryer were determined taking into account the seed bed inside it (Tmax with MP), without the seed bed inside the dryer (Tmax without MP) and the average temperature in the seed bed (Tmed). These data are shown in the table below.

With the annual meteorological variables of Cuba, a simulation of the solar dryer operation was carried out for each month of the year following the CFD resolution method described above. Twenty-four simulation studies were performed. For each month of the year the behavior of the temperatures inside the dryer were measured taking into account the volume of seeds and without it. The months where the highest temperatures were reached within the designed prototype, without the seed layer were July and August reaching values of 43 ℃ as maximum temperature. The highest temperatures reached inside the dryer, considering in the study the volume of seeds, were in August and September, with maximum values of 45 ℃ and 46 ℃, respectively.

When analyzing the temperatures of the fluid that circulates through the volume of seeds in the drying chamber, it was found that during the months of August and September, temperatures of 32 ℃ were reached for both months, achieving a temperature increase of 8 ℃ with respect to the ambient temperature set in the CFD analysis. For the months with the lowest average minimum temperature (December, January, February), a temperature increase similar to the warmer months is achieved, with an increase of up to 9 ℃.

TABLE 2 Monthly and internal ambient temperature data of the dryer 

Year Month Tmin Tmax HR, % Tmax without MP Tmax with MP Tmed seed bed
2018 J 24 31 78 40,27 46,23 32,79
F 22 30 78 39,47 44,49 30,89
M 20 28 75 37,28 41,74 28,76
A 18 27 74 34,92 39,65 26,71
2019 M 18 26 75 35,06 39,29 26,49
J 18 26 73 35,5 40,01 27,1
J 19 28 71 35,79 41,41 27,02
A 20 29 71 36,51 42,13 28,77
S 21 30 74 37,62 44,01 28,96
O 23 31 76 41,11 44,59 30,79
M 24 32 75 43,6 44,35 31,61
D 24 32 76 43,3 45,06 32,25

In general, after analyzing the behavior of temperatures within the designed prototype, it is valid to note that they do not exceed the maximum temperature of 45 ℃, recommended for drying seeds.

Another result obtained was the behavior simulation of the temperatures reached by the materials of the prototype component parts and the temperature of the fluid inside the dryer in general and in the drying chamber in particular for 8 hours of work (Table 3). This simulation was carried out for environmental conditions with an average minimum temperature of 17 oC, an average relative humidity of 70% and a solar radiation of 4,2 kW. These average values are ones of the lowest that could exist during the months of the year where it would be more complex to achieve an increase in temperatures in a solar dryer.

TABLE 3 Behavior of solids and fluid temperatures in 8 working hours 

Hour Tinitia oC Temperature of solids ℃ Temperature of fluid ℃
T máx T min Tmáx T cam d. secado
8 17 71,25 15,30 34,26 22,86
9 80,42 18,97 46,08 25,26
10 86,74 20,78 56,95 27,16
11 90,56 22,43 59,20 27,49
12 91,07 23,51 61,64 27,50
13 90,06 22,21 58,81 27,17
14 87,37 21,30 57,80 26,94
15 80,41 19,41 45,66 25,45
16 71,24 17,28 36,81 23,50
Average 83,24 20,13 50,80 25,93

As it can be seen in Table 3, the maximum temperatures reached in the prototype materials reach 91,06 oC at 12 hours with an average of 83,24 oC, obtaining the highest values between 10 and 14 hours. Similarly, with the behavior of the temperature of the fluid both, the maximum and the average in the drying chamber, the highest values were obtained at 12 hours, coinciding with the schedule of higher temperature of the solids with values of 61,64 oC and 27,50 oC, respectively. Also, it could be confirmed that the temperature inside the drying chamber was higher between 10 and 14 hours for an average temperature of 27,25 oC with a daily average for the fluid temperature of 25,93 oC, being 8,93 oC above room temperature. The temperature values reached the highest values at solar noon, which is when solar radiation strikes more perpendicularly on the collector surface.

CONCLUSIONS

  • The thermal modeling and kinetics of the design conceived are activated with the use of the SolidWorks computer system, the porous medium (seed layer for drying) and the evidence of an increase in temperature and a pressure drop, within the proposed installation.

  • For unfavorable conditions of solar radiation and low temperatures during simulation of fluid kinetics, the prototype designed radiation temperatures that exceeded the environment by 8 oC.

  • As for the temperature in the drying bed, the highest values were obtained in the months of July, August and September, with temperature increases of 8 oC throughout the year, which demonstrates the stable operation of the prototype designed.

REFERENCES

DALPASQUALE, V.A.; DE QUEIROZ, D. M; MARQUES, P. J.A. PEREIRA; R. S.: Secado de granos: natural, solar y a bajas temperaturas, [en línea] ser. Tecnología Poscosecha 9, Oficina Regional de la FAO para America Latina y el Caribe ed., Santiago, chile, 1991. Disponible en: http://www.fao.org/3/x5058s/x5058S05.htm#4.%20Secado%20de%20granos%20a%20bajas%20temperaturas [Consulta: 13 de marzo de 2019]. [ Links ]

EKECHUKWU, O.V.; NORTON, B.: ¨Review of solar-energy drying systems II: an overview of solar drying technology¨, Energy Conversion & Management, 40: 615-655, 1999. [ Links ]

ESPINOZA, J.: ¨Innovación en el deshidratado solar¨, [en línea] Ingeniare. Revista chilena de ingeniería, DOI-10.4067/S0718-33052016000500010, 24(Especial): 72-80, agosto de 2016. ISSN-0718-3305. [ Links ]

FARONI, L.R.D.; TEIXEIRA, M.M.; PEREIRA, I.A.M.; PEREIRA, A.L.R.; SILVA, F.A.P.: Manual de manejo poscosecha de granos a nivel rural, [en línea] ser. Pérdidas alimentarias posteriores a la cosecha, Ed. Oficina Regional de la FAO para América latina y El Caribe. Santiago, Chile, pp. 203, Roma, Italia, 1993. Disponible en: http://www24.brinkster.com/alexweir/Links ]

GARCÍA, V. O.; ORTIZ, N.M.; PILATOWSKY, I.; MENCHACA, A.C.: ¨Solar thermal drying plant for agricultural products. Part 1: Direct air heating system¨, [en línea] Renewable Energy, DOI-10.1016/j.renene.2019.10.069, S0960-1481(19)31560-5, October 2019. ISSN-0960-1481, [ Links ]

GAVHALE, M.; KAWALE, S.; NAGPURE, R.; MUJBAILE, V.N.; SAWARKAR, N.S.: ¨Design And Development Of Solar Seed Dryer¨, International Journal of Innovative Science, Engineering & Technology, 2(4): 1005-1010, 2015. ISSN-2348-7968. [ Links ]

KABIR, E.; KUMAR, P.; KUMAR, S.; ADELODUN, A.A.; KIM, K.-H.: ¨Solar energy: Potential and future prospects¨, [en línea] Renewable and Sustainable Energy Reviews, DOI-10.1016/j.rser.2017.09.094, 82: 894-900, febrero de 2018. ISSN-1364-0321. [ Links ]

LABORDE, M. A.; WILLIAMS, J. R.: Energía Solar, ser. Publicación Científica N. 10, Ed. Academia Nacional de Ciencias Exactas, Físicas y Naturales, III ed., pp. 161, Buenos Aires, Argentina, 2016. ISBN-978-987-41-1100-5. [ Links ]

MILANI, M.C.M.; CARVALLO, D.A.: Diseño de un secador solar prototipo de placas planas para pruebas en laboratorio, 181pp., Tesis (en opción al título de Ingeniería Mecánica), Universidad Central de Venezuela, Venezuela, 2013. [ Links ]

MONTERO, I.; BLANCO, J.; MIRANDA, T.; ROJAS, S.; CELMA, A.R.: ¨Design, construction and performance testing of a solar dryer for agroindustrial by-products¨, [en línea] Energy Conversion and Management, DOI-10.1016/j.enconman.2010.02.009, 51(7): 1510-1521, 2010. ISSN-0196-8904. [ Links ]

ROCHE, L.D.; HERNÁNDEZ, J.P.; GARCÍA, A.: ¨Conceptual design of pilot scale solar dryer for seaweeds¨, Departamento de Ingeniería Química, Facultad de Química y Farmacia, Universidad Central «Marta Abreu» de Las Villas. Cuba., : 17, 2017. [ Links ]

SAHU, T.K.; GUPTA, D.V.; SINGH, A.K.: ¨A Review on Solar Drying Techniques and Solar Greenhouse Dryer¨, 3, 13: 31-37, 2016. ISSN-320-334X. [ Links ]

SONTHIKUN, S.; CHAIRAT, P.; FARDSIN, K.; KIRIRAT, P.; KUMAR, A.; TEKASAKUL, P.: ¨Computational fluid dynamic analysis of innovative design of solarbiomass hybrid dryer: An experimental validation¨, [en línea]; Renewable Energy, DOI-http://dx.doi.org/10.1016/j.renene.2016.01.095, (92): 185-192, 2016. ISSN-0960-1481. [ Links ]

TEIXEIRA-DA SILVA, J. M.; MALPICA, P.F.A: ¨Desarrollo de un modelo matemático para dimensionar un deshidratador solar directo de cacao¨, Ingeniería Mecánica, 19(1): 30-39, abril de 2016. ISSN-1815-5944. [ Links ]

4The mention of trademarks of specific equipment, instruments or materials is for identification purposes, there being no promotional commitment in relation to them, neither by the authors nor by the publisher.

Received: September 25, 2019; Accepted: December 19, 2019

*Autor para correspondencia: Yoel Rodríguez Gago, e-mail: ygago@ica.co.cu

Yoel Rodríguez Gago, Investigador, Instituto de Ciencia Animal (ICA), San José de las Lajas, Mayabeque, Cuba, e-mail: ygago@ica.co.cu

Yanoy Morejón Mesa, Profesor Auxiliar, Universidad Agraria de La Habana, Facultad de Ciencias Técnicas, Centro de Mecanización Agropecuarias, San José de las Lajas, Mayabeque, Cuba, e-mail: ymm@unah.edu.cu

The authors of this work declare no conflict of interests.

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