CC BY
60
Section 4. Technical sciences
Yorkin Sodikovich Abbasov, Fergana Polytechnic Institute Doctor of Technical Sciences, the Faculty of Construction E-mail: [email protected] Mirsoli Odiljanovich Uzbekov, Fergana Polytechnic Institute Senior Researcher, the Faculty of Construction
Studies efficiency solar air collector
Abstract: The article presents an analysis of the existing solar air collectors. A description of the design and the results of experimental studies on the effectiveness of the solar air collector with an absorber of
from metal shavings.
Keywords: mankind, ecology, energy crisis, alternative energy sources, solar radiation, solar air collectors, efficiency.
For almost the entire history of mankind, the population increased very slowly because of the large dependence of man from nature, frequent wars, epidemics, hunger. Population growth in the 18TH-19th centuries became extremely gather momentum and accelerated sharply in the first half of the 20th century. The growth rate ofpopu-lation is associated with an enormous leap in development and discoveries in the field of basic sciences, medicine, and materials science. As a result of modern life has become much more convenient and easier, which causes an increase in the birth rate and life expectancy of the person.
As ofJanuary 1, 2016 years Earth's population totaled almost 7.3 billion. Predictable number of the world's population stood at 1.01.2016 at 7 295 889 256 people, thus having increased for 1 year at 78 million inhabitants or 1.08 percent.
Main and the obligatory condition of existence man and mankind as a whole, is the consumption of energy and energy resources, the existence of available for energy consumption has always been required to meet human needs.
However, global growth in energy consumption in addition to the positive effect of such a rapid energy development and population growth exists and the negative impact of progress:
- environmental pollution;
- depletion of mineral reserves and others.
The International Energy Agency and the World Energy Council predicts a 400 percent increase in energy consumption in the world by 2050, which will lead to further climate change [1, 9 -11].
One way to deter this threat is greater use of renewable energy sources (RES) [1, 8-10].
Among the renewables, solar radiation on the scale of the resources, environmental friendliness and omnipresence is the most promising energy source for heat and cold [2, 25-26].
According to the data of 2011, more than 180 mil-lion.m2 solar collectors are used in the world, which provide different heat consumers. The most common of these technologies in China (59%), in second place — Europe (14%). 186 large are firms producing solar collectors in 41 countries [3, 9-10].
One of the first decisions made when choosing a solar power system is the choice of the working fluid for the type of heat transfer. The heat transfer can be considered as liquids and gases. Currently prevailing heat transfer fluids: water, antifreeze, aqueous solutions of ethylene — and propylene glycol, oil. The only gas became widespread as a coolant is the air [1,11-12].
When choosing a set of coolant is necessary to consider various factors (Table 1). If we analyze all the
Section 4. Technical sciences
factors, the air-type collectors are usually cheaper than the identical liquid, but generally have a lower level of the coolant temperature and efficiency. However, the scope of the air collectors (due to temperature stratification in the battery or due to the fact that air is taken from out-
Table 1. - Comparison
side or from the premises) located near the low value of reduced temperature and high efficiency, while the water collectors have to be used at higher values of the reduced temperature and consequently, at lower efficiency [5, 17-19].
of air and water systems
Factor Air system Water system
The possibility of corrosion Potentially low probability Potentially high probability
Influence of leaks Negligible, if they are small Significant damage to the system
The problems associated with phase transitions coolant (freezing, boiling) - Potentially high probability; needed protection
Pipelines, canals An air duct of larger cross section (higher cost) Pipes with relatively small cross sections (the lower value)
The cost of the pump (fan) relatively high relatively low
Tank capacity — Battery More than in water systems Less than air systems
collector weight Relatively lightweight design Relatively heavy construction
Fabrication and installation It does not require high accuracy Requires high precision (tightness)
For air heating buildings and drying agricultural products have received widespread solar air collectors, which are ways of moving the absorber air is relatively divided into two types: convective (contact) and matrix (transposition) [6, 15-16]. In the first — air flow washes impervious surface absorber, heated by solar radiation, and in the second — there is filtration of air movement through the structure of the absorber.
According to an overview of the world market of solar heating, performed Franz Mautner and Werner Weiss
from the institute AEE INTEC (Austria) under the «Solar heating and cooling,» the International Energy Agency (May 2013), at the end of 2011 in the world operated by air solar total area 2,213,434 m 2, including the majority (71%, 15 68549 m 2) — without glazed collectors. Glazed collectors constitute for 29% (644,885 m 2). The following table shows the distribution of air solar collector in volumes of more than 100 thousand m 2 installations by country.
Table 2. — Air air solar collector area of the countries of the world [4].
Countries don't vitrified vitrified Total, m 2 Countries don't vitrified vitrified Total, m 2
Australia 264000 6600 270600 Japan — 475199 475199
Austria - 1078 1078 Mexico - 7664 7664
Canada 334426 11781 346207 Norway — 1019 1019
Denmark 3133 17280 20413 Switzerland 876000 — 87600
Germany - 32256 32256 United Kingdom 14000 — 14000
Hungary 1440 1152 2692 USA 75000 75185 150185
India — 15667 15667 Total 1568549 644885 2213434
Israel 550 - 550
As a result of structural analysis USED solar air collectors currently in practice [1; 3; 6; 8; 9] may be developed which are the most effective collector matrix type air because of the greater area of contact with the absorber and the greater the value of convection coefficient heat absorber in the air.
In recent decades, much research conducted to improve the efficiency of solar air collectors. To improve the efficiency of the solar air collectors heat must be effectively
transferred from the absorber to around his air [3, 1-2], reducing radiation and reduce overall heat loss coefficient of absorber in the surrounding environment [1, 13-15].
To achieve these goals, the authors' are proposing variant design solar air collector with absorber convection-matrix type.
The main technical indicators of the solar air collector is showed in Figure 1. Solar air heater is made from durable and lightweight two-chambered plastic frame
from lambri (1) that allows to exploit by the collector without insulation, reducing its weight and increasing mobility. First absorber (3) represents the profiled sheeting with a thickness of 1 mm, total area 0.7 m 2, painted with Matt black light from the side the sun, underneath the absorber (2) mounted 3 partitions, to increase the length of the path of air through the collector, over the profile sheet set second absorber (4) from metal shavings (made by steel metal NH 78t) with a diameter of 0.5 to
0.7 cm, thickness 1^2 mm, total area of 0.725, painted bluish light. As a transparent insolation (5) used glass with thickness 4 mm.
The basic idea of the design of such a solar collector, that the use of metal shavings as absorber of the solar heater, allows you to maximize the heat exchanging surface heating and air contact area with the absorber and absorbers of from a profile sheet and of metal shavings intensify heat that increases efficiency.
1 — insulation;
2 — partitions;
3 — absorber of from profiled sheet;
4 — absorber of from metal shavings;
5 — transparent insulation;
T1 .. ,T5 — point temperature measurement
Figure 1. Air Solar Collector scheme. Table 3. - The dimensions of the designed constructions:
№ The name of the Value № The name of the Value
1 The length of the collector (channels) L2, m 1.45 7 The thickness of the channel h2, m 0.01
2 The length of the collector, L1, m 1.5 8 The thickness of the channel h3, m 0.01
3 The width of the manifold (channel) b, m 0.5 9 The thickness of the channel h4, m 0.015
4 The width of the manifold, b, m 0.6 10 Absorber area AU 1 m 2 0.7
5 The height of the collector (channels) h1, m 0, 072 11 Area of heating surface 2, m 2 0, 725
6 Area of heating surface 2, m 2 0,7 12 Unit weight, kg 20
Solar radiation falling on the collector, passing through a transparent coating, part is absorbed by the absorber of metal shavings, the remainder absorbed the second absorber, which heated up. Air is fed into the solar air collector heater using a fan is blown through the inlet tube (Figure 1), air enters the space between
the bottom of the absorber and the collector (I). The heated air passing the lower openings enters the space between the absorbers (II), where intensify heating air. The air then enters the space between the absorber and the transparent insulation (III), after the air goes through the exit tube.
Figure 2. The dependence of the efficiency of the collector from the heating absorbers for with / without absorber of METAL SHAVINGS
Section 4. Technical sciences
Experimental studies on the thermal characteristics of a solar collector were carried out in field conditions and in the following order: For a fixed value of the angle of inclination of the 45 to measure the in collector
temperature used chromel — copel thermocouple connected to the TRACE MODE software, through TRM 138 — measuring system, air flow rate was varied by changing the fan speed.
Figure 3. The dependence of the temperature characteristics of the measured points of FROM the efficiency of air heaters
Coefficient of efficiency solar air collector, which is the ratio of the amount of usable energy obtained air in the collector, to the amount of energy coming from solar radiation at the surface of the absorber solar air collector, based on dependencies:
where Qtg — the amount of usable energy, W; Q — the amount of energy coming from solar radiation at the surface of the absorber, W; G — coolant mass flow rate, kg/s; C — specific heat capacity, J/(kg K); T^
T i„Put — output, input air temperature, °C; Ac — the area
n =
Q
Q,
G ■ c.
■ (T -T )
v outp inp '
p ■ Q ■ cp
■ (T - T )
v outp inp '
A ■ H
A ■ H
of a collector, m 2; Ht — parish of total solar radiation at the surface of the collector, w/m 2; p — density, kg/m 3; Q — volumetric flow rate, m3/s.
1
0,9
0,8
0,7
c 0,6
t 41 0,5
0,4
0,3
0,2
0,1
0
0,87 0,91
0,75 0,79 0,8
0,71
0,61
0,2V
0,2
9 11,88 21,96 32,4 54 83,88 102,24116,28139,32157,68177,48
G, Kg/s
Figure 4. The dependence of the efficiency of heater from the air flow
Test results for the year May 5, 2016 in total solar Tinput = 37 ° C, the amount of energy coming from solar radiation on inclined surface Ht = 0.9 kW/m 2, diffuse radiation at the surface of the absorber Q^ = 0.6525. radiation S = 0, 1 kW/m 2, at an ambient temperature
Table 4.
(G) flow rate, kg/s o AT = T - T out in Qu^ W Efficiency,% t* °C t3, °C t„, °C
0.0025 53 0.1331 0.204 71 85 92
0.0033 51 0.1631 0.2592 67 84 91
0.0061 46 0.4321 0.4321 65 78 86
0.009 44 0.3379 0.6099 61 76 84
0.015 31 0.4673 0.7132 53 65 73
0.0233 21 0.4917 0.706 49 57 63
0.0284 19 0.5137 0.787 44 51 60
0.0323 16 0.599 0.796 42 48 57
0.0387 14 0.5445 0.83 41 46 55
0.0438 13 0.5722 0.87 40 44 53
0.0493 12 0.5945 0.91 39 44 52
Conclusions: 4. Proved an experimental use metal shaving as the
1. Produced a literary analysis of the existing solar absorber will reduce the cost of air solar collectors.
air collectors 5. Proposed options for increasing the area of the
2. Experimentally proved high efficiency of the col- heating surface heat transfer agent using metal shavings lector. as an absorber.
3. Analysis of the results of experimental studies 6. The results can be used by developers when de-showing the high efficiency of the use of metal shav- signing solar air systems.
ings in the air collector systems.
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