Application of solar dryers for drying agricultural products and optimization of drying time

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Many agricultural products are grown around the world. Quality collection and storage of these products is very important, it is advisable to use dryers in this regard. However, most of the dryers currently in production are powered by electricity and fuel. Organizing the efficient operation of dryers and saving fuel and energy products is a pressing issue today. Also, according to the data provided today, little research has been done on the effect of the design of the gelo-receiving surface on the increase in air temperature in the dryer. In order to ensure quality drying of products and continuous operation of dryers, recommendations have been developed for the efficient use of solar energy and to increase the F.I.K of the dryer and the effective use of such dryers in production. The advantage of the solar dryer recommended below is that it is energy-efficient, inexpensive and has the ability to dry high-quality and fast-drying varieties of fruits and vegetables with high sugar content, while maintaining the characteristics of the product. Figure 1, 2 shows a schematic of a solar dryer. In this case, normal air from the outside comes to the solar air heater and is heated, then passes to the drying chamber. The product is then dried and the air is released into the atmosphere through a pipe. This Solar Air Heater is designed for sunny days of the year and in our experience we use this equipment mainly for drying agricultural products. The principle of operation of the device in the form of a paralipipet is simple and the productivity is high. It is necessary to ensure that the surface of the equipment is perpendicular to sunlight, i.e. the sunlight falls at an angle to the surface of the equipment. Cold air is directed from the bottom of the equipment and the air is heated upwards. As a result, the air is heated and the air in the air collector transmits its heat. Then, using natural convection, the air slowly begins to move upwards. 4 - When it comes to the drying chamber, the hot air 5 - transmits its heat to the fruits located on the grill. The dryer is equipped with a hot and humid air control unit. This device is installed to improve natural convection. Fig. 1. View of the drying chamber (a), product drying chamber of the solar drying equipment (b): 1 - camera body; 2 - placement of fruits or vegetables; 3 - barriers to uniform air supply; 4 - natural and artificial hot air inlets; 5 - humid air outlet to the atmosphere; 6 - temperature adjustment and control device in the chamber; 7 - source of hot air supply by electricity Fig. 2. appearance of solar air heater (a), natural hot air router of solar dryer equipment (b): 1 - solar air heater housing; 2 - direction of cold air entering the equipment; 3 - insulations used to reduce heat loss; 4 - surface polished ferrous metal; 5 - thermometer; 6 - perforated ferrous metal; 7 - light-transmitting window; 8 - hot air outlet As a result of the experiments, the air temperatures in the solar air collector and the drying chamber were determi-ned, and the results obtained in the experiment were presented in tabular form. Based on the values obtained above, we determine the drying time of the products using the Nusselt, Reynolds, Grasgof and Prandtl criteria. Hence, we calculate the heat transfer process under free convection conditions for the values shown in Table 1 below. q = 3600α(tc - tM) = qMr W/m2. In the formulas - the heat given to the fruit, r - the latent heat of water vapor. In this formula - the heat transfer coefficient, we determine from the formula of free convection: Gr = gβΔtd3/v2; β = 1/T; τ = (1/N)((wн - wкр) - 128wн lg (x)(wн - wp)) time. In the above formula, d is the diameter of the fruit, Δt is the difference between the air and the surface temperature of the fruit. Temperature differences change during the day, due to changes in solar radiation. Table 1 № Air temperature, °С The temperature of the heater, °С The temperature of the drying chamber, °С 1 15-18 40-45 28-30 3 18-22 48-50 30-31 3 20-22 50-52 30-32 4 22-25 50-55 30-35 5 22-27 50-58 32-35 6 24-27 55-58 33-36 7 24-29 52-60 34-38 8 24-30 55-70 40-45 Based on the value of Gr ∙ Pr =, the values of С and n should be selected from Table 2. Table 2 Gr ∙ Pr 0,001-500 500-2 ∙ 107 2 ∙ 107-1 ∙ 1013 C 1,18 0,54 0,135 n 1/8 1/4 1/3 Hence, we continue the computational work for the above values. N = C(G ∙ P)n. We determine the heat transfer coefficient. α = Nu λ/d W/m2 °С. We use the following formula to determine the drying speed of the fruit in a solar dryer. N = qm F ∙ 100/(p0V) %/hour. We calculate the heat given to the fruit - qm. qm = 3600α(tc - tM)/r W/m2. We use the following formula to determine the drying time of the fruit in a solar dryer. Based on the work presented in the article, it can be concluded that the production and implementation of such devices around the world is highly effective. The main reason for this is that many countries are rich in agricultural fruits and vegetables, melons. High-quality collection of products solves the problem of not losing their useful properties and, most importantly, saving energy resources.

About the authors

Rustam Kh. Rakhimov

Institute of Materials Science, SPA “Physics-Sun”, Academy of Science of Uzbekistan

Email: rustam-shsul@yandex.com
Dr. Sci. (Eng.); Head at the Laboratory No. 1 Tashkent, Republic of Uzbekistan

Dilmurod N. Mukhtorov

Fergana Polytechnic Institute

Email: dimajone0909@gmail.com
assistant at the Department of Electrical Engineering, Electrical Mechanics and Electrical Technology Fergana, Republic of Uzbekistan

References

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