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ТЕХНИЧЕСКИЕ НАУКИ
OPTIMIZATION OF OPERATING PARAMETERS OF FLAT SOLAR AIR HEATERS
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Abdukarimov B.A. , Abbosov Yo.S. , Mullayev I.I. Email: [email protected]
1Abdukarimov Bekzod Abobakirovich - Doctorate;
2Abbosov Yorqin Sodikovich - Associate Professor of Technical Sciences;
3Mullayev Ikromjon Isroiljon ogli - Doctorate, DEPARTMENT OF CONSTRUCTION OF ENGINEERING COMMUNICATIONS, FACULTY OF CIVIL ENGINEERING, FERGANA POLYTECHNIC INSTITUTE, FERGANA, REPUBLIC OF UZBEKISTAN
Abstract: this article mostly in a separate order discusses the efficiency of solar air heaters, the efficiency and their optical useful ratio, by optimizing the design of flat air heaters and studying their operating parameters. In addition, to install in the working chamber of a horizontal solar air heater elements that increase the efficiency, also to establish these special elements that will help create the desired rotational movement for more efficient horizontal solar air heat.
Keywords: solar heaters, air, collector, energy, heating, heat transfer, absorber, temperature.
ОПТИМИЗАЦИЯ РАБОЧИХ ПАРАМЕТРОВ ПЛОСКОГО СОЛНЕЧНОГО ВОЗДУШНОГО ОБОГРЕВАТЕЛЯ Абдукаримов Б.А.1, Аббосов Ё.С.2, Муллаев И.И.3
1Абдукаримов Бекзод Абобакирович - докторант;
2Аббосов Ёркин Содикович - доктор технических наук, профессор;
3Муллаев Икромжон Исроилжон угли - докторант, кафедра строительства инженерных коммуникаций, строительный факультет, Ферганский политехнический институт, г. Фергана, Республика Узбекистан
Аннотация: в данной статье обсуждается эффективность солнечных воздухонагревателей, коэффициент полезного действия и их оптический полезный коэффициент, путем оптимизации конструкции плоских воздухонагревателей и изучения их рабочих параметров. Кроме того рекомендуется установить в рабочей камере горизонтального солнечного воздухоногревателя элементы, повышающие коэффиццент полезного действия, также установить перечисленные специальные элементы, которые помогут создать нужное вращательное движение для большей эффективности горизонтального солнечного воздухонагревателя. Ключевые слова: солнечные нагреватели, воздух, коллектор, энергия, нагрев, теплообмен, абсорбер, температура.
UDC 214.74
Today, many researchers and scientists are conducting research to solve the problem of introducing advanced technologies and equipment that will effectively and efficiently use energy and fuel and energy resources in the heat supply system. It is known that today natural fuel and energy resources used on an industrial scale are sharply reduced, so the use of renewable energy sources can save existing natural resources and the ecological situation at the existing level [4].
In our country, about 20% of the world's total primary energy production is consumed, but the cost of fossil fuels is growing rapidly, environmental problems associated with environmental pollution are worsened using fuel plants, especially with increasing consumption of low-grade solid fuels. In connection with these problems, it is becoming increasingly necessary to use non-conventional energy resources, primarily solar, wind, geothermal energy, along with the introduction of energy-saving technologies. There are quite ample opportunities to use solar installations for individual consumers, especially in rural areas. Scaling up the use of solar installations will not only provide significant energy savings, but also help mitigate the environmental situation [1].
The thermal analysis for predicting the performance of different types of solar air collectors has been presented by many investigators. The mean difference between them lies in the estimated heat transfer coefficients and in the numerical solving procedures. In order to simplify the problem, numerous investigations have been carried out by considering that the plates are maintained at the main temperatures However, in solar air heaters, these temperatures vary along their length. Therefore, for accurate thermal simulations, we use a discrete approach which consists of dividing the collector into several differential elements in the air flow direction [2]. The solar energy system modeled in the present work is shown in Figs. (1) structure of the solar air heaters.
Fig. 1. View of a flat solar air heater with a metal element: 1 - outlet of air, 2 - surface of device, 3 - glass, 4 - absorber, 5 - inlet of air, 6 - convection element
Solar air heater performance improves through the installation of a special convective carrier element on the flat part of the device. The air temperature rises to a high temperature as a result of the greater part of the air striking the convective actuating member.
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Fig. 2. Flat solar air heater In working process
In the collector of a solar collector, the stimulating element is similar to chess, which, in turn, is rapidly increasing. Figure 1 shows the awakening element.
Fig. 3. Structure of element creates rotational motion
The special element of the rotational motion has a length of 120 mm, a height of 25 mm and a width of 30 mm.
It is important to note the processes of heat transfer and aerodynamic resistance by installing a special element that forms air inclusions installed in the working solar cell of a solar air heater.
Heat transfer in horizontal solar air heaters occurs not only under the action of forced convection, but also under the influence of free convection movement. Since the heaters are usually installed vertically or obliquely under the windows, in this case it is necessary to take into account the development of a free convective layer along the vertically located absorber.
The modern theory of heat transfer with free convection is a theory of a boundary layer whose movement occurs along a plate under the action of lifting forces arising due to the difference in density between liquid and gas layers at different temperatures. In the
literature, these forces are called floating forces. The buoyancy of the medium is especially pronounced when the density gradient of the medium increases and, accordingly, the value of the Richardson criterion increases.
* i = o (fe) (1)
Here, A p — is the difference between the densities of the liquid or gas at points separated by the characteristic distance h, which is measured in the vertical direction, and u is the flow velocity. If the Richardson number is zero, the influence of free forces disappears. From the formula of the Richardson criterion it corresponds that it increases if the ratio ^ increases. It
should be said that in a flat solar air heater there is a combined action of forced and free convection, which is called mixed convection.
The equations describing free convection in horizontal-laminar flows are a particular form of the general equations of fluid motion and heat transfer. If you direct the X coordinate in the vertical direction, then the equation of motion for the boundary layer has the form:
iudu , du\ dp , d ( du\
p{— + vi;) = —Tx + Ty{^) — pa (2)
The continuity equation has the form
(;rx(pu) + ry(pv) ) = 0 (3)
The energy equation has the form:
_ (udT , dT \ d (T,dT\
p cp(~+vi;) = ry(Ki;) (4)
The main task of the theory of convective heat transfer is to determine the amount of heat passing through the surface of a solid to be washed. In the general case, stationary convective heat transfer can be covered by the following system of differential equations.
The heat transfer flux through the laminar boundary layer of air through the elementary surface of the heat exchange surface is transmitted by heat transfer and is characterized by the following Fourier laws:
dQ = -Xd-ds (5) an
By Newton's Law dQ=aAtds If we equalize the right side of the equation, we get the following:
dt , . x dt
-X~ = -aAt yoki a = —-—- (6)
dn At dn
(5) It is a differential equation of convective heat transfer. This equation describes the process of heat transfer to solids and liquids and indicates the temperature gradient and temperature distribution in the air to find the heat transfer coefficient. [3]
Conclusions: To increase the efficiency of solar air heaters, a special stimulating element is installed in the working chamber, creating a rotational motion and experimental studies are needed.
References / Список литературы
1. Safarov N.M., Alinazarov A.Kh. "Use of clean energy sources". Tashkent, 2014. 11-16 p.
2. Duffe J. and Beckman W. Solar Engineering of Thermal Processes. New York: Wiley, 1991.
3. MadaliyevE.O'. Heat Engineering. Fergana (2012). 150-168 page.
4. [Electronic Resource]. URL. http://www.uzbekenergo.uz/uz/activities/alternative-energy-ources/ (date of the access: 10.01.2019).
