Development of an optimal mechanism for a solar-air collector for drying thermolabile products

The article presents theoretical and experimental studies about the alternative construction of energy-efficient solar air collector that generates heat based on alternative energy sources for the drying process of agricultural products. In particular, the geographical latitude of the place (φ), the angle of elevation of the sun to the horizon (h°), the angle of deviation of the sun (δ), and τ the interrelationships between the sun’s hour angles (τ) were studied. The patterns of changes in the wet air and dry air parameters entering the solar air collector were analyzed. The mechanism of efficient use of the heat generated in the solar air collector was developed. The kinetics of the process of drying spices at low temperature was studied.B NNBB. 1


Introduction
At present, comprehensive reforms are being carried out on the issues of developing the complex processing system of agricultural products and increasing the export potential of our Republic.
In particular, the laws of heat energy generation are based on the rational use of solar energy heat, which is an alternative energy source, in the product processing system, the trajectory of the sun's movement from the east pole to the west pole, and the change in the angle of the sun's spectrum falling on the earth's surface.Issues of developing a new design of a solar-air collector, which converts solar energy into thermal energy, and the theoretical basis of the mechanism of efficient use of solar energy are reflected in this article.
At this point, it should be noted that the annual technical potential of sulfur energy in our Republic is 290 mln. is equal to the amount of conventional fuel per ton, which is 4 times more than the total amount of primary energy resources used for domestic needs of our country during the year.In total, the potential of solar energy is 5000 times greater than that of the Earth, and 1,500 times greater than that of hydropower [1,2].
It is known that the power of solar radiation on the Earth's surface is 1.78‧1017 W, which is equivalent to 5.4‧1024 J of energy per year.This is 10 times higher than the global reserves of fossil fuels, which are estimated at 6.9‧1023 J, or 1000 times higher than the global energy consumption projected by the end of the century, equal to 15.3‧1020 J. Consequently, the use of even 0.1% of the total the energy potential of solar radiation will make it possible to fully satisfy the energy needs of humanity until the end of the 21st century [3-5, 7, 8].
It is desirable to develop an optimal design of the solar-air collector for the drying system by analyzing the laws of heat generated under the influence of sunlight falling on the earth's surface according to the seasons of the year [6,9].
It is known that the intensity of sunlight depends on the angle of its incidence on the earth's surface, and the amount of radiated energy changes during the day.Also, the amount of heat generated in the solar-air collector depends on the temperature of the external environment and metrological changes between regions [8].
The main task of the research work is to justify the laws of distribution of the solar spectrum in the region and to make appropriate decisions in the development of the optimal design of the solar-air collector that generates heat with the help of irradiated solar energy.
In order to solve the problems set as a task in the research work, the theoretical basis of the laws of energy generation according to the trajectory of the sun, the angles of incidence of the sun in relation to the horizon in time units were developed [8].

Theoretical basis
The change in the temperature of the surface of the solar-air collector and the heating agent coming out of the collector depends on the change of the angle of elevation of the sun relative to the horizon per unit of time.A number of studies have been conducted to substantiate this law.
It is known that the amount of heat generated on the surface of the solar-air collector changes due to the changes in the angle of incidence of the sunlight falling on the earth's surface during the years, months, seasons, and minutes.If sunlight  falls on the earth's surface at a certain angle, then the trajectory of the radiant energy falling on the earth's surface from 9:00 a.m. to 5:00 p.m. takes a spherical shape (figure 1).Sunlight falls at a distance OA=r, and radiated energy generates energy on the surface of the earth in the direction OD, OE, OC, OA.Accordingly, the amount of energy falling on the earth's surface is equal to Q, the amount of energy falling in the form of parallel rays is equal to S, and the sum of energies D spreading from the atmosphere layer [8,9] .
where: h is the elevation angle of the sun relative to the horizon.The relationship between geographical latitude (), sun declination angle (), and sun hour angles () was determined by spherical trigonometry formulas.
Analyzes show that these quantities depend on the change in the angle of elevation of the sun relative to the horizon.Radius OA = r Angles B and C of the spherical triangle ABC on the sphere with, as well as sides B and C, are less than 900 relative to the ground.Therefore, the amount of energy generated is high because the angle of incidence of sunlight is sharp, less than 900 [8][9][10].
If we make an attempt from the point A to the sides AB and AC and form the sections AD and AE, then the trigonometric equation will have the following form [8,10].
Equating the quantities in this equation, we create the following equation: the expressions in parentheses  2 are equal to and (A), then  = , We reduce this equation to the following form, By interchanging the places of the multipliers, we form the following equation, The location points of the ray directed to the surface by the angle of elevation of the sun relative to the horizon form an astronomical triangle (figure 2).The obtained results show that the arc lengths of the sides of the triangle formed by the points of sunlight falling on the surface  = ,  = 90 0 − ,  = 90 0 − are.
The angle at the pole is ZPM =  when establishing PZM =90 −A will be equal.Then, using expression (7) to calculate the elevation angle of the sun, we get the following, But, = sin(90 0 − ℎ 0 ) = ℎ 0 since it forms, the expression takes the following form, By means of this expression, during the months of June and July from 10:00 a.m. to 5:00 p.m., the change of the height angle of the irradiated solar energy falling on the earth's surface with respect to the horizon was analyzed ℎ 0 .It was based on the fact that the change of the angle value depends on the geographical latitude, the angle of the sun's deviation, and the angle of change of the sun relative to the surface per unit of time [8].

Results and discussion
The level of heat generation on the surface of the collector of the radiated energy generated during the movement direction of the sun during the day was studied.Accordingly, the construction of the energysaving solar air collector, which moves in proportion to the change of the angle of incidence of the irradiated solar energy on the surface, and generates heat for the drying system, was developed (figure 3).Clean atmospheric air enters the solar collector 1 through holes 2 and is heated to a temperature of 62-65°C using a device for receiving and absorbing sunlight 3 installed along the length of the collector.
To supply heated air regularly (through pipe 7) to the drying chamber, fan 6 is used.With sensor 5, they are used to adjust the collector according to the angle of maximum incidence of sunlight.The drying chamber is not indicated in the picture.A pair of gears 10 and a servomotor rotate the collector towards solar radiation.To adjust the angle of inclination of the collector and the direction of its movement, the corresponding signals from sensors 5 are sent to the servomotor 11 and the adjusting device 8.The guide plate 4, installed at an angle of 65°, serves to transfer air heated in the solar collector to the fan 6.
The structure of the solar collector, length 1.7 meter, width 0.77 meter, is made of stainless steel sheet.The longitudinal surfaces of the metal sheet are equal to each other, and form small surfaces in the form of ribs with an angle of 45-47°.
The collector structure has a mechanism for maximum reception of sunlight falling on the earth's surface at different angles from 10:00 a.m. to 5:00 p.m.
Also, for maximum sunlight reception, the design is equipped with a system for automatically adjusting the rotation of the collector to the optimal angle along the path of the sun from the east to the west pole.
A number of experiments were carried out, the patterns of changes in temperature and relative humidity of atmospheric air on the surface, at the initial and final points of the solar collector were studied during the first ten days of July (from 10:00 a.m. to 5:00 p.m.).Clean atmospheric air enters the solar collector 1 through holes 2 and is heated to a temperature of 62-65°C using a device for receiving and absorbing sunlight 3 installed along the length of the collector.
To regularly supply heated air (through pipe 7) to the drying chamber, fan 6 is used.With sensor 5, they are used to adjust the collector according to the angle of maximum incidence of sunlight.The drying chamber is not indicated in the picture.A pair of gears 10 and a servomotor rotate the collector towards solar radiation.To adjust the angle of inclination of the collector and the direction of its movement, the corresponding signals from sensors 5 are sent to the servomotor 11 and the adjusting device 8.The guide plate 4, installed at an angle of 65°, serves to transfer air heated in the solar collector to the fan 6.
The structure of the solar collector, length 1.7 meter, width 0.77 meter, is made of stainless steel sheet.The longitudinal surfaces of the metal sheet are equal to each other, and form small surfaces in the form of ribs with an angle of 45-47°.
The collector structure has a mechanism for maximum reception of sunlight falling on the earth's surface at different angles from 10:00 am to 5:00 pm.
Also, for maximum sunlight reception, the design is equipped with a system for automatically adjusting the rotation of the collector to the optimal angle along the path of the sun from the east to the west pole.
A number of experiments were carried out, the patterns of changes in temperature and relative humidity of atmospheric air on the surface, at the initial and final points of the solar collector were studied during the first ten days of July (from 10 a.m. to 5 p.m.). Figure 3. Solar-air collector 1-solar-air collector; 2-hole for air intake; 3-device for receiving sunlight; 4-plate air deflector; 5-tilt sensors and direction of movement of the collector; 6-fan; 7air exhaust pipe; 8 -device for adjusting the angle of inclination of the collector; 9 -bed; 1 0 -a pair of gears; 11servomotor.
• operating time from 10:00 a.m. to 12:00, the parameters of the heated air at the outlet of the solar-air collector are t = 580C ; φ=22%; • operating time from 13:00 p.m. to 17:00 p.m., the parameters of the heated air at the outlet of the solar-air collector are t = 64,50 C, φ =15%.
Results were also obtained on changes in atmospheric air at the inlet and outlet of the solar collector, based on experiments conducted in the first ten days of July 2023.From 10:00 a.m. to 17:00 p.m., the results of changes in the degree of heating and relative humidity of the atmospheric air were as follows: • when the collector is located at an angle of 39 -43.5° relative to the sunlight falling on the surface of the earth, the initial temperature of the atmospheric air entering the air intake pipe of the collector in the period from 10:00 a.m. to 12:00 hours was 28-310C, relative humidity 53%, absolute humidity -15.2%, dew point temperature -18°C.At the same time, the temperature of the atmospheric air leaving the collector was 58°C, and the relative humidity was 22%; • in the afternoon (between 13:00 p.m. and 17:00 p.m.) the temperature of the atmospheric air entering the collector is 38-41.5°C,relative humidity 39%, absolute humidity dew point temperature 23°C.The temperature of the atmospheric air at the outlet of the collector was 64.5°C, the relative humidity was 15%.All data were determined using appropriate measurement instruments [8].Based on the above parameters, the process of drying herbs was studied.To ensure uniform release of moisture from the products, mesh racks with a total area of 3 m2 are installed in the drying chamber.To ensure maximum coolant passage and accelerate the release of moisture, 1м² 2-4 kg of products are placed on top.The free area between products is 30-35% relative to the total surface [8,9].
The drying process of spicy products was carried out in the following mode: • the temperature of the thermal agent heated by the solar collector is 64.5°C, the relative humidity of the atmospheric air is 20%.In this case, the specific load of herbs per unit area of the mesh hearth was 2 kg/m2 (figure 4).As can be seen from the graph, if the solar-air collector with respect to the incident sunlight (39 -43.5°) if placed in a corner, from 10:00 a.m. to 12:00 hot air temperature coming out of the collector up to   = 58 0 C, from 13:00 p.m. to 17:00 p.m. until   = 64.5 0 С forming and drying time of the product   = 4 ÷ 4.5 ℎ the clock is running (curve 1).If the solar air collector is relative to the incident sunlight (500) and placed at an angle higher than that, from 10:00 a.m. to 12:00 hot air temperature up to   = 38 − 40 0 C , from 1300 p.m. 17:00 p.m. until   = 60 − 62 0 C time to dry the product to equilibrium moisture   = 5.5 ÷ 6.0 ℎ the hour lasts (curve 2).Accordingly, in accelerating the drying process of spice plants, compared to the sunlight of the solar air collector (39 -43.5°) it is desirable to install at an angle and place 1.8-2.2kg of product on 1m2 of surface [8,10].
Thus, the drying rate determines one of the most important technological parameters -the intensity of moisture evaporation from the material m, which is expressed by the amount of moisture evaporated from a unit surface of the material F per unit time.

Conclusion
Based on the conducted theoretical and experimental studies, an optimal construction of the mechanism of efficient use of solar energy heat, which is considered as an alternative energy source for accelerating the process of drying agricultural products at low temperature, has been developed.Temperature changes on the outer surface of the solar air collector and atmospheric air at the initial and final points within a unit of time under the influence of radiated solar energy are based on the dependence of the angle of incidence of sunlight on the surface.Also, the amount of heat generated in the collector in the first (10:00 a.m.÷ 12:00) and second (13:00 p.m. ÷ 17:00 p.m.) half of the day, the main parameters of humid air were determined.
One of the main factors is the temperature of the heating agent, the speed and the mass of the product falling on the unit surface in order to ensure the moisture content of the product.Based on research, as an optimal mode of accelerating the drying process: -the solar air collector in relation to the incoming sunlight 39÷43.5°installation; -heating agent temperature   = 64.5 0 С organization; -the initial temperature of the air entering the collector 38÷41.5°C;-relative humidity 39%; -absolute humidity 20.5%; -it is desirable that the humidity of hot air from the collector to the outlet is 15%.Based on these optimal parameters, the kinetics of the drying process of spices were studied and the curves describing the process were obtained.

Figure 1 .
Figure 1.Irradiated solar energy formed on the surface of the earth triangle (ABC).

Figure 2 .
Figure 2. Astronomical shape of the sun's rays relative to the earth's surface.