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12INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 1 ISSUE 7 UIF-2022: 8.2 | ISSN: 2181-3337
RESEARCH OF THERMAL PROCESSES IN DRYERS APPLIED IN TECHNOLOGICAL PROCESSES Abdukarimov Bekzod Abobakirovich
docent , Department of Civil engineering construction, faculty of Construction Fergana
polytechnic institute Mirzayev Sardorali Abdullajonovich
Assistant, Department of Electronics and Instrumentation, Faculty of Computerized Design
Systems, Fergana Polytechnic Institute https://doi.org/10.5281/zenodo.7255161
Abstract. The article deals with the study of energy-saving technologies, which has become relevant today. It also addresses the issue of achieving efficient results with solar air heaters, which have been developed in a new way, that use solar energy to reduce the amount of energy used in technologies used to dry agricultural products.
Keywords: Energy, temperature, solar collector, light, absorber, work efficiency, heat exchange.
ИССЛЕДОВАНИЕ ТЕПЛОВЫХ ПРОЦЕССОВ В СУШИЛКАХ, ПРИМЕНЯЕМЫХ
В ТЕХНОЛОГИЧЕСКИХ ПРОЦЕССАХ
Аннотация. В статье речь идет об изучении энергосберегающих технологий, ставших актуальными на сегодняшний день. В нем также рассматривается вопрос достижения эффективных результатов с солнечными воздухонагревателями, которые были разработаны по-новому и используют солнечную энергию для сокращения количества энергии, используемой в технологиях, используемых для сушки сельскохозяйственных продуктов.
Ключевые слова: Энергия, температура, солнечный коллектор, свет, поглотитель, эффективность работы, теплообмен.
INTRODUCTION
If the collection, transportation, storage and processing of agricultural products are organized from a scientific point of view, based on the achievements of science and technology and best practices in this field, the amount of product waste will be significantly reduced. This includes providing 20% or more of the population with additional agricultural products, as well as training qualified specialists in the development of transportation, storage and processing technologies. [1]
There are a number of technologies for drying agricultural products that are mainly based on available energy, including high electricity consumption.
Many researchers and scientists are conducting scientific research on finding solutions to the problems of the introduction of advanced technologies and equipment that are efficient and economical from electric energy and energy resources.
Currently, as a result of scientific research carried out, the implementation of technologies for rational use of renewable energies is being implemented in practice. In particular, solar air heating collars using solar energy are also in the sentence. [2]
MATERIALS AND METHODS
The principle of operation of efficient solar air heaters used for drying agricultural products has been studied.
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In the course of the research work, a solar air heater with a rectangular flat surface duct was studied. Rectangular ribs were installed perpendicular to the air flow of the collector in a staggered manner. The aim of the study was to increase the heat dissipation of a solar air collector by generating a turbulent flow using rectangular fins between the sun absorbing absorber and the lower wood layer. For this, a solar collector was developed with a length of 1.6 m and a width of 0.8 m (Fig. 1). The distance between the transparent surface of the 10 mm collector and the absorber is 25 mm. [3] RESULTS
Two types of absorbers are used in the collector: a black painted aluminum absorber and a fine glass absorber. The rectangular ribs used in the collector serve to increase the heat transfer of the absorber, but the main disadvantage of the device is considered to be the insufficient flow of the turbulence process on the surface of air ducts with a flat surface.
Figure 1.
Schematic view of the collector with fins
In the following research work, which was analyzed, the heat transfer properties of a solar air heater which W-shaped fins artificially installed was experimentally studied. The device has a size of 1500x200x25 mm. (Figure 2)
The absorption plate consists of 1 mm thick galvanized material. The maximum height of the W-shaped ribs is 75 mm. For the study, various geometric W-shaped twenty ribs were tested. In the process of testing, only rough surfaces were used. In addition, for the purpose of comparison, the smooth channel was tested under similar conditions. [4]
The Nusselt number and friction correlations are derived from the airflow parameters for the boot and smooth ducts. With an increase in the Reynolds and Nusselt numbers, they come to the conclusion that the coefficient of air friction decreases [18]. Rugged solar air heaters perform better compared to smooth duct type heaters. It was proved that when using an artificial air duct, the number of copies and the coefficient of friction can be increased by a maximum of 2.16 and 2.75 times compared to a smooth channel, but the main disadvantage of the device is that the air ducts are generally located along the absorption surface. In this case, the heat transfer process occurs only along the outer surface of the air duct. [5]
Figure 2.
Scheme of air duct
INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 1 ISSUE 7 UIF-2022: 8.2 | ISSN: 2181-3337
e
Static and dynamic position of triangular duct flat solar air heater:
A model of a flat solar air heater with a triangular duct was developed. The length of the device is l = 800 mm, the width is a = 400 mm, and the height is h=62 mm. The working chamber of this solar heater has triangular metal ducts. The length of each duct is l=150 mm. The distance between the two bases of the air duct is l=60 mm, the height of the channel is h=60 mm. On each side of the base of the air ducts, two rows of geometric-shaped inner boots are given, the depth of which is h=2 mm and the width is a=15 mm. The geometric shape imparted to the air ducts of the collector is in the position of the inner batik relative to the outer surface of the duct, and vice versa on the inner surface. [6]
The device works in two different ways.
- Spraying air
- Absorbing air
Inlet and outlet pipes are used along the diagonal of the device for air spraying.
As for the absorption of air, each duct is used in its own separate order from the incoming air ducts.
The location of the ducts is in the form of chess and completely covers the entire air flow passing through the common working chamber surface.
Figure 3.
Scheme of solar air heater with triangular air duct
In tubular solar air heaters, mainly convective heat exchange takes place. On the opposite surface of the solar heater tube, a boundary layer is formed, the thickness of which increases in the direction of flow. At some points, a separation of the boundary layer from the surface is observed, and two symmetric bends appear behind the pipe. [7-8]
When using these collectors when drying agricultural products, some key indicators of the device and the dried product are taken into account.
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Dried (i.e., due to adiabatic evaporation of moisture contained in the dried product) and humidified desiccant is discharged into the environment through the upper part of the drying chamber at a temperature t2 and relative humidity
The formula for determining the heat capacity transmitted to the bottom of the drying chamber using a drying agent is Qp
QP = Gcp(t1 - t0) (1)
Typically, the useful heat output of a solar collector is determined by the formula below.
opttfpad kpr(J-f
(2)
Here:
G and cp - the drying agent consumption and specific heat capacity, respectively; ~qtp -the efficiency of the heat collector of the solar collector; qopt - the optical usefulness of the heat collector optical surface of the solar collector; qpaa - the current density of the total solar radiation transmitted to the frontal surface of the collector; kpr - the unit of total heat lost on the front light-receiving surface of the collector; - the average temperature of the heat carriers (along the length of the collector) in the heat-conducting channels of the heat-receiving surface located in the drying agent of the solar collector; - the area of the radiant frontal surface of the solar collector.
Figure 5.
General scheme of the drying device of agricultural products
1-solar air collector; 2-sunlight; 3-pipe to send heated air to the working chamber; 4-drying chambers; 5-air inlet pipes to the collector
The heat capacity generated in the solar collector, in turn, is spent on the evaporation of moisture contained in the dried product in the drying chamber (Qpoi), in addition, is spent on replacing the heat lost through the separating elements (walls) of the drying chamber (Qtp) and (Qsb) with the release and rejected heat power using a drying agent.
QP = Qpoi + Qtp + Qsb (3)
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This value
Qpoi, QtP, Qsb (4)
is determined by the formula, which is part of the following formula: Qpoi = Gvpr (5)
(6)
QtP=IlklFl(tk-t0)
Qsb = GCp(t2 - t0),
(7)
Here: Gvp- the constant flow of moisture evaporating from the dried product; r - the latent heat; kt and Ft - the heat exchange surface and heat loss coefficients, respectively. tk - the average temperature of the drying agent (according to the height of the drying chamber) in the drying chamber; t2 - the temperature of the drying agent used (at the exit of the drying chamber). [9]
Depending on the direction of movement of the drying agents of solar collectors of the type under consideration, it is recommended to increase the temperature (from t0 to tt) and decrease (from to t0). In this regard, depending on the length of the average solar air heater and the height of the drying chamber, the temperature of the drying agent (iy) depends on the following formula (2) and (t1) on the interaction of this formula (6).
U -t
tk =
ti-t2 Inl1
(8) (9)
The thermal efficiency of the solar collector (^c) and the drying chamber performance can be found in the generally accepted equations:
QP
Vc =
Qpal
Vk
_ Qpad
= QP
(10) (11)
Here Qpad - the total solar radiation flux transmitted along the front light receiver surface of the collector:
Qpad = QpadFfr (12)
We put the Qpoi indicator determined by (4) and draw the result using the following equation:
Vk = l
QtpQsb QP
(13)
The total thermal efficiency of the considered type of drying device is determined using the equation:
Qpoi
V =
Qpad
(14)
Based on the procedure, we can consider the overall thermal efficiency of the drying device as the thermal performance produced by the solar collector and the drying chamber.
(15)
In turn, taking into account the indicators and the following Qp, Qpoi and Qpad, in addition, by putting the values obtained from iy and tk (8) and from (9) we get the following result:
Qn Qnoi
■q = —----— = qcqk
Qpad Qp
1
INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 1 ISSUE 7 UIF-2022: 8.2 | ISSN: 2181-3337
T.kiFi(t1-t2)-t0
v = v
Vi*
kpr Rpad
t!-tQ
L Íi-Í0J
FfrWtp
lopt'
k-,
pr t1-t0
1pad\ In
\ l0 .
Rpad
From the above theoretical analysis, it can be seen that the usefulness of the drying device (n) depends on the heating temperature ( t x) of the drying agent in the solar collector and on the temperature at the outlet of the drying chamber (t2). It is obvious that increasing the temperature of the separated drying agent (t2) when used under normal conditions will reduce the drying efficiency. Because at a temperature of ti=80°C, an increase in t2 to 55°C (during the period of a constant drying rate) occurs up to 90 ° C (at the end of the drying process, n will decrease from 0.41 to 0.25), which is 39%. [10]
The efficiency of the solar air heater. The efficiency of a solar air heater is determined using the following formula:
(17)
here:
I - intensity of falling solar radiation, W/m2 Tu - collector outlet air temperature, °C Tur - outside air temperature, °C U0-10W/m2 (scale coefficient)
DISCUSSION
Figure 6.
The efficiency of the solar air heater (15.08.2019 W00-W30 t=32 oC)
0,60 0,50
¡X
y 0,40
z
I 0,30
i 0,20 W
0,10 0,00
M concave absorber a flat absorber 0,52 0,51
0,49
0,48
0,48
0,41 0,40
0,35
0,35
2,86
3,2 3,4 3,88
VELOCITY OF AIR FLOW
4,2
Figure 7.
The efficiency of the solar air heater (15.08.2019 1100-1130 t=33 oC)
2
INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 1 ISSUE 7 UIF-2022: 8.2 | ISSN: 2181-3337
THE EFFICIENCY OF THE SOLAR AIR HEATER
M concave absorber ——flat absorber
2,86
0,60 0,53 ■- 0,52 0,52 0,50 0,49
0,50 YCN 0,40 I 0,30 IF0,20 w 0,10 0,00 É- '--A'-- --
0,1.3 0,40 0,37 0,37 0,36
3,2 3,4 3,88
VELOCITY OF AIR FLOW
4,2
Figure 8.
The efficiency of the solar air heater (15.08.2019 1200-1230 t=34 oC)
0,70
^ 0,60
U 0,50 z
E0,40
HH 5
u 0,30 Ü 0,20 W 0,10 0,00
THE EFFICIENCY OF THE SOLAR AIR HEATER
M concave absorber a flat absorber 0,64 0,63 0,61 0 60
0,55
2,86
3,2 3,4 3,88
VELOCITY OF AIR FLOW
0,58
4,2
Figure 9.
The efficiency of the solar air heater (15.08.2019 1500-1530 t=33 oC)
THE EFFICIENCY OF THE SOLAR AIR HEATER
0,70
0,60 Y
C0,50 EN 0,40 0,47
HH
CI0,30
l¡ 0,20 E
0,10
0,00
0,58
2,86
■concave absorber * flat absorber 0,56 0,55 0,53
0,46
0,44
0,43
T
3,2 3,4 3,88
VELOCITY OF AIR FLOW
0,52
0,43
f
4,2
Figure 10.
The efficiency of the solar air heater (15.08.2019 1500-15301=31 oC)
THE EFFICIENCY OF THE SOLAR AIR HEATER
concave absorber * flat absorber
0,б0
0,5б
0,55
0,53
0,52
0,50
> 0,50
Z 0,40
§ 0,30
Ц 0,20
W 0,10
0,4б
0,4б 0,43 0,41
0,38
0,00
2,8б
3,2
3,4
3,88
4,2
VELOCITY OF AIR FLOW
The quality of a collector's work also depends on its location. The angle of inclination of the collector must be correctly estimated Its size depends on the latitude of the area [17]. Sunlight falling on the collector should fall at the most right angle possible. In addition, the manifold must be oriented towards the equator. Incorrect orientation leads to a significant (25%) decrease in its effectiveness.
- The geometric shape given to the air duct allows air to whirl and allows the air temperature to rise to the maximum.
- By reducing local resistance, the device works effectively even at low speeds.[10]
Thus, with the help of the solution obtained from (16), it is possible to optimize the
drying rate during the drying period when leaving the solar collector (respectively, when leaving
the drying chamber).
REFERENCES
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CONCLUSION
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