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Uzbekov Mirsoli Odiljanovich, Fergana Polytechnic Institute Senior Researcher, the Faculty of Energy Abbasov Yorkin Sodikovich, Fergana Polytechnic Institute Doctor, of Technical Sciences, the Faculty of Construction Omonillayev Boburjon Ilxomjon o'g'li, Student, the Faculty of Energy E-mail: [email protected]
THEORETICAL ANALYSIS OF THE CHARACTERISTICS OF THE AIR FLOW WHEN FLOWING METAL SHAVINGS IN THE SOLAR AIR HEATERS
Abstract: The article is devoted to the determination of the thermal and hydraulic characteristics of the airflow when flowing of metal shavings used as an absorber of a solar air heater. The thickness of the pulse loss for the angular distance n, the thickness of the displacement, the thickness of the boundary layer, the local frictional stress on the surface of the metal shavings are calculated.
Keywords: energy, renewable energy, solar energy, useful heat, solar air heater.
Given that in recent years, the development of Among solar installations that convert solar radiation
the industry has led to a decrease in fuel and energy into useful heat, due to the simplicity of design, ease of
resources and the deterioration of the environmental operation and high efficiency, solar air heaters (SAH)
situation throughout the world, there is a great demand are widely used for drying agricultural products and air
for the use of renewable energy sources (RES) [1]. conditioning systems [2].
Figure 1. Dependence of efficiency on the mass airflow of the solar air heater with the absorber of metal shavings
tages of such solar collectors is a small area of contact of air with heated surfaces.
For example, in [5, 6], small metal shavings were used to heat the air flow. In addition, despite many experimental and theoretical studies [7], the thermal and hydraulic characteristics of the airflow remain uncharted when flowing over metal shavings.
In work [8], a high efficiency of a solar air heater was obtained: the body, a transparent coating, a V-shaped beam absorber, a metal mesh, an absorber of metal shavings, a tube for supply and removal of the coolant.
Experimental studies have shown that the transverse flow of metal shavings by air occurs analogously to the airflow of a cylinder (see Figure 2).
m
¿it***"
Figure 2. Visualization of the flow of airflow of metal shavings
Consequently, to calculate the thermal and hydraulic Using experimental data [8] on the flow ofmetal shav-
characteristics of the airflow in when flowing flow of metal ings (See Table № . 1). shavings, we use the methods ofboundary-layer theory [9].
Table 1. - Experimental data of a solar air heater with an absorber from metal shavings
№ G ,kg / s t oC V C t', oC t", oC
1 2 3 4 5
1 0.0025 92 37 90
2 0.0033 91 37 88
3 0.0061 86 37 83
4 0.009 84 37 81
5 0.015 73 37 68
6 0.0233 63 37 58
7 0.0284 60 37 56
8 0.0323 57 37 53
9 0.0387 55 37 51
At present, in many countries, in institutions such as the Indian Institute of Technology of Delhli, National Institute of Hamirpur, Tamkang University, University of Tanta, Universiti Kabangsaan Malaysia, Alternate Hydro Energy Centre, Xi'an jiaotong University, Shanghai jiao Tong University, King Mongkuts University of Technology Thonburi is conducting an active study to improve the efficiency of SIH indicators. A great contribution was made by such scientists as Beckmann, Duffy, Kazajan, Olimpiev, Avezov R. R. Avezova N. R. E. S. Abbasov, Garg H. P., Saini J. S., Sopian K., Umurza-kova M.A [3].
In works [4] numerous designs of SAH consisting of absorbers by various materials are considered. Disadvan-
1 2 3 4 5
10 0.0438 53 37 50
11 0.0493 52 37 49
Thermophysical parameters of the airflow were determined by the following procedure t' +1"
— = ^ (1)
ta - the airflow temperature was determined as the mean air temperature at the inlet t' and the outlet t".
In addition, the temperature in the boundary layer on the shaving tv was determined from the formula
^ = ty (2)
Where tsh - is the shaving temperature.
Assume that the velocity of the potential flow varies according to the theoretical law
U = 2u0 sinp (3)
Taking into account the fact that the flow past the shaving is gradient, we use the Karman-Pollausen method developed for the hydrodynamic boundary layer.
1) Determine the value of the Reynolds criterion ud
Red =
v
(4)
The physical constants here and below are selected from the book [9] on the temperature of the incoming air.
2) We compare the obtained value of the Reynolds criterion with the critical
Red < Redup = (24-3)-105 (5)
Consequently, the boundary layer to the separation
n
point and at the angular distance "4 is laminar.
3) We determine the thickness of the momentum
n
loss for the angular distance ~ by the formula
(Q2 _ 0,47
v _ U6
x
Ju 5dx _
0,47
(2u0 sinç)'
but the distance along the arc ofthe circle x = R = R ■ (R is the radius of the metal shavings), therefore
n
(O2 _ 0,47(2u0)5
(2u0 )(sinp) o
0,41R] . 5
=-6 \sm Vdç
(2u0sinç) 0o
4
jsin5pd (Rç) =
(7)
We calculate the integral
n n n
4 4 4
Jsin5yd = Jsin5yd (sinyd) = - Jsin 4yd (cosy) =
(8)
= I (1 - cos V)2 d (cosy) = 2,67 -10-2
Then
Location
(O2 0,47R
v (2u0 sinç)
0,47 R
O = J—--r-V
i (2u0 sinç)
(9)
(10)
4) We determine the second form of the Karman -Polgaouzon parameter by the formula
(Q2 U _ (S")2 d(2u0sing) _
v dx v d (Rg) (n)
(SY 2u0
cosç
-J(2W0 smy)5 dx (6) T0 (E) =
vR
5) We select from [9] the second form of the parameter f (K), f2 (K) and the first form parameter. After integration, we have
2 = 1; f (K) = 2,508; f2 (K) = 0,252.
6) Determine the thickness of displacement according to equation
=5". f (K) = r- f (K), m (12)
7) Determine the local frictional stress on the surface according to equation
^Ufi (K) _ ^(2uosinv)fi (K)
-, n/m [ (13)
o o
8) We determine the thickness of the boundary layer from equations
H * = S = -3-—= 3- — = 0,2917 (14) S 10 120 10 120
and
* 5
o = —;r, m H
(15)
0
0
71
v
Table 2.- Results of calculations
u010-4 Red (°2 10-4 v S 10-4 K 10-4 f (K) 10-4 r0 (E 10-2 S 10-4
440 293 100 3.88 124.43 9.73 0.0852 33.3
570 380 77 3.41 124.12 8.55 0.1256 29.3
1070 710 41 2.49 124.06 6.24 0.3230 21.4
1580 1580 28 2.05 124.89 5.14 0.5794 17.6
2630 1750 16 1.59 124.88 3.98 1.2436 13.6
4090 2720 10.8 1.27 124.92 3.19 2.4213 10.9
4980 3320 10.6 1.26 124.95 3.16 2.9716 10.8
5670 3780 7.8 1.08 124.91 2.71 3.9472 9.3
6790 4520 6.5 0.988 124.81 2.48 5.1670 8.5
7680 5120 5.75 0.929 124.88 2.33 6.2155 8
8650 5770 5.11 0.875 125 2.19 7.4325 7.5
Table 3.- Results of calculations
n 0 0.1 0.2 0.3 0.5 0.7 0.9 1
0 0.2105 0.4026 0.5712 0.823 0.9572 0.9982 1
(p(v)
-1-1-1-1-1-1-1-1-1-
0,2 0,4 0,6 0,8 1,0 t]
Figure 3. Dimensionless velocity profile
i-i—'—---—■—i—■—i—■—i— Kpr,
D 1(KO ZK-Z WOO <1000 50W HBO
Figure 4. Dependence of the pulse loss thickness on the Reynolds number
Figure 5. Dependence of the thickness of the boundary layer on the Reynolds number
9) Construction of a dimensionless velocity profile. Define a series of values of n and calculate the value of f (n) by the formula
v{n) = i + (i-n)3
1
(16)
-n-1-n
V 6
Conclusions:
1. The visualization of the transverse flow of metal shavings by the airflow is performed.
2. A model for the flow of metal shavings in the Reynolds number range was developed at which the high efficiency of SAH was observed.
3. Dependences of the thickness of the pulse loss and the thickness of the layer losses on the Reynolds numbers are obtained.
References:
1. Uzbekov M. O. Shermatov B. A. XXXVII International scientific and practical conference "European research: innovation in science, education and technology" February 7-8,- 2018. London, United Kingdom.- P. 21-26.
2. Uzbekov M. O., Nasretdinova F. N. International Scientific Review No. 1(43) / International Scientific Review of the Problems and Prospects of Modern Science and Education: XLI International Scientific and Practical Conference (Boston, USA - 30 January,- 2018).
3. URL: https://www.scopus.com/term/analyzer.uri
4. Raupov A. H., Tyukhov I. I. Differences of air solar collectors on the construction of heatabsorbing panels heat-return channels. Innovations in Agriculture,- 2015.- No. 2 (12).
5. Patent utility model SU1599627. F24 J 3/02, published - 1979.
6. Patent utility model SU No. 1474394, F24 J 2/281979.
7. Uzbekov M. O. and others. Efficiency of heat exchange of a solar air collector with a light-absorbing surface made of stainless steel shavings International Journal ofAdvanced Research in Science, Engineering and Technology.-Volume 5, Issue 2, February - 2018.
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