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RESEARCH OF CONVECTIVE HEAT TRANSFER IN SOLAR AIR HEATERS Abdukarimov B.A.1, Tokhirov ЬН.2 Email: [email protected]
1Abdukarimov Bekzod Abobakirovich - Doctoral Candidate;
2Tokhirov Islomzhon Hakimjon ugli - Assistant, DEPARTMENT OF DRAWING GEOMETRY AND ENGINEERING GRAPHICS, FACULTY OF CIVIL ENGINEERING, FERGANA POLYTECHNIC INSTITUTE, FERGANA, REPUBLIC OF UZBEKISTAN
Abstract: in this article - the introduction of advanced technologies and equipment that can efficiently and economically use energy, as well as the use of solar energy to generate and maintain heat and explores the heat transfer process of flat solar air heaters, mainly the behavior of the air flow in the working chamber of the device, convective heat transfer, the law of convective heat transfer, convective heat transfer rate, kinematic viscosity, as well as air pressure and pressure analyzed for density variations.
Keywords: air heater, convection, heat transfer, mode of action, laminar, turbulent, temperature, pressure, density.
ИССЛЕДОВАНИЕ КОНВЕКТИВНОЙ ПЕРЕДАЧИ ТЕПЛА В СОЛНЕЧНЫХ ВОЗДУШНЫХ ОБОГРЕВАХ Абдукаримов Б.А.1, Тохиров И.Х.2
1Абдукаримов Бекзод Абобакирович - докторант;
2Тохиров Исломжон Хакимжон угли - ассистент, кафедра чертежной геометрии и инженерной графики, строительный факультет, Ферганский политехнический институт, г. Фергана, Республика Узбекистан
Аннотация: в данной статье описывается внедрение передовых технологий и оборудования, которые могут эффективно и экономно использовать энергоресурсы, а также использование солнечной энергии для получения и поддержания тепла и исследуется процесс теплообмена плоских солнечных воздухонагревателей, в основном поведение воздушного потока в рабочей камере устройства, конвективный теплообмен, закон конвективного теплообмена, скорость конвективного теплообмена, кинематическая вязкость, а также давление и давление воздуха проанализированы на вариации плотности. Ключевые слова: воздухонагреватель, конвекция, теплообмен, режим действия, ламинарный, турбулентный, температура, давление, плотность.
UDC 214.74
Today, many researchers and scientists conduct research on the introduction of advanced technologies and equipment that can efficiently and rationally use energy and fuel and energy resources in the heating system. It is known that today the scale of the use of fossil fuels and energy in the industrial sector is declining sharply, so the use of renewable energy sources will preserve existing natural resources and the environmental situation [1].
Today, there are a number of types of solar heaters, such as flat solar heaters, which are widely used.
Optimizing solar thermal heaters can improve performance. The heat exchanger in the working chamber of the solar chamber is mainly a convective heat exchange, which leads to an increase in temperature due to overheating of the heated surface [4].
The optimization of solar thermal heaters can improve performance. The heat exchanger in the solar cell heater is generally a convective heat exchange and increases the temperature of the air as a result of friction on the heated surface [5].
im
Fig. 1. The flow of air in the working chamber of the solar air heater: 1 - outlet of air, 2 - surface of device, 3 - glass, 4 - absorber, 5 - inlet of air, 6 - convection element, 7 - Air movement within of the pipe, 8 - Air movement on the outside of the pipe
Convective heat transfer is the process of heat transfer when gas or liquid macroscopes move from one place to another. Convection is expressed in the irregular movement of particles of the liquid, liquid and gaseous layers. Therefore, when particles move easily, can occurs the convection. Convective heat exchange due to the combined effects of convective and molecular heat transfer is called convective heat transfer. In other words, convective heat transfer is carried out at the same time by two methods: convection and heat transfer. Convective heat exchange between the moving environment and its other (solid, liquid, or gas) boundary surface is called heat transfer.
The main purpose of the convective heat theory is to determine the amount of heat flowing through a washing solid. The final heat flux always moves towards the temperature drop.
The main task of the convective heat transfer theory is to determine the amount of heat flowing through the stream. The final heat flux always moves towards the temperature drop. Newton's law is used to calculate heat transfer in practice.
Q = aF (tc - tdev) -t (1)
This equation is called Newton's convective heat transfer law. According to this law, the amount of heat transferred from a gas to a wall or a wall to a gas is proportional to the surface F involved in heat transfer, temperature ts - tdev, and heat exchange time t. Where tdev is the surface temperature of the wall; ts is the temperature of the air passing through the wall surface. The coefficient of proportionality considering the concrete conditions of heat exchange between gas and solid is called a the heat transfer coefficient. [4]
Convective heat exchange due to the combined effects of convective and molecular heat transfer is called convective heat transfer. Newton's law:
Q = aF (ts-t dev) (2) Where a heat transfer coefficient W/(m2 grad) ts and tdev, temperature of the surface and wall
The Nusselt number describes the heat transfer along the solid and the gas:
a ■ £n Nu =-0 (3)
X
where: %- is a specific linear dimension 10 - heat transfer coefficient of the gas passing through
the surface of the solid.
Number of Reynolds characterizes the ratio of inertia and viscosity forces:
®o ■ ^ 0 Re = —-1 (4)
V
where: V - the kinematic viscosity of the air, a0 - specific air velocity,
Number of Peckle characterize the rate of heat dissipation through convection and heat transfer.
co0 ■ 10
Fe = —-0 (5)
a
where: a - Temperature transfer coefficient of air:
a = X/cp (6)
Number of Euler characterizes the ratio of pressure forces and inertial forces:
P
EU = -Y (7)
PVo
Air turbulent movement in the pipe:
NU=0,018 Re 0,8 (8)
Heat exchange in pipes in turbulent motion:
Nu = 0,021 Rec °'8- Prc 0,48
Pr
V Р1ДВ
0,25 st (9)
Where: where: St - is an adjustment that takes into account the ratio of the length of pipe £ to its diameter d. [3]
4 F
ЙЭКВ = — (10)
Where: F- surface of transverse cross section, m2; V-perimeter, m.
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. 22-31 pages.
2. Duffe J. andBeckman W. Solar Engineering of Thermal Processes. New York: Wiley, 1991.
3. Нащокин В.В. Техническая термодинамика и теплопередача. Москва. «Высшая школа». 60-69 с., 1975.
4. Abdukarimov B.A., Abbosov Yo.S., Umurzakova M.A. Евразийский Союз Ученых (ЕСУ) Ежемесячный научный журнал. № 2 (59), 2019 "Approximate model of heat exchange and solar energy efficiency in a flat solar air heater under conditions of natural convection".
5. [Electronic Resource]. URL.http://www.uzbekenergo.uz/uz/activities/alternative-energy-ources/ (date of the access: 10.01.2019).
