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21Theoretical and Applied Heating Engineering Теоретическая и прикладная теплотехника
DOI: 10.17516/1999-494X-0370 УДК 662.997:66.02
Research of the Hydraulic Resistance Coefficient of Sunny Air Heaters
with Bent Pipes During Turbulent Air Flow
Bekzod A. Abdukarimov and Akmaljon A. Kuchkarov*
Fergana Polytechnic Institute Uzbekistan
Received 15.12.2021, received in revised form 29.01.2022, accepted 06.02.2022
Abstract. This article examines the issues of hydraulic resistance of solar air heaters with concave tubes and reduction of pressure losses, as well as the determination of the air flow in concave tubes installed in the working chamber of the solar air heater and discusses the reduction of the number of common tubes to reduce pressure losses in the solar air heater and the installation of concave pipes to give air a swirling motion to eliminate a sharp decrease in the heat transfer process.
Keywords: solar air heater, pressure, hydraulic resistance, immersion tube, absorber, air, laminar, turbulent, height, dynamic viscosity.
Citation: Abdukarimov, B. A., Kuchkarov A. A. Research of the hydraulic resistance coefficient of sunny air heaters with bent pipes during turbulent air flow. J. Sib. Fed. Univ. Eng. & Technol., 2022, 15(1), 14-23. DOI: 10.17516/1999-494X-0370
© Siberian Federal University. All rights reserved
This work is licensed under a Creative Commons Attribution-Non Commercial 4.0 International License (CC BY-NC 4.0). Corresponding author E-mail address: [email protected], [email protected]
Исследование коэффициента гидравлического сопротивления эдлнечных воздухонагревателей с изогнутыми трубками при турбулентном потоке воздуха
Б. А. Абдукаримов, А. А. Кучкаров
Ферганский политехнический институт Узбекистан, Фергана
Аннотация. В данной статье рассмотрены вопросы гидравлического сопротивления солнечных воздухонагревателей с изогнутыми трубками и снижения потерь давления, а также определения расхода воздуха в трубках, установленных в рабочей камере солнечного воздухонагревателя. Обсуждается уменьшение общего количества трубок для снижения потерь давления в солнечном воздухонагревателе и установка изогнутых трубок для придания воздуху вихревого движения с целью устранения резкого снижения процесса теплопередачи.
Ключевые слова: солнечный воздухонагреватель, давление, гидравлическое сопротивление, погружная трубка, абсорбер, воздух, ламинарный, турбулентный, высота, динамическая вязкость.
Цитирование: Абдукаримов, Б. А. Исследование коэффициента гидравлического сопротивления солнечных воздухонагревателей с изогнутыми трубками при турбулентном потоке воздуха / Б. А. Абдукаримов, А. А. Кучкаров // Журн. Сиб. федер. ун-та. Техника и технологии, 2022, 15(1). С. 14-23. DOI: 10.17516/1999-494Х-0370
Introduction
Today, at this stage of the development of world civilization, the urgent task is the widespread introduction and use of renewable energy sources [1], associated with an excessive increase in energy demand [2], continuous growth of valuable energy [3], as well as a reduction in fuel and energy resources [4] and deterioration environmental conditions around the world [5, 6, 7] In this regard, close attention is paid to the development of new generations of solar energy installations with increased efficiency [8, 7] and minimal economic costs [9].
Scientific research is being conducted in the world aimed at creating energy systems using solar low-potential installations in heat supply systems [10, 11], taking into account the optimization of heat and mass transfer processes [12, 13, 14], necessary for the development of operating [15], technological and design parameters [10], control and management schemes [16.], which provide continuity of hydrodynamic and thermal processes [17, 18, 19]. Improving the efficiency and development of new modern designs of solar installations [20], as well as improving the methodology of their thermal calculations are one of the most important research tasks in this field [21, 22]. At the same time, increasing the efficiency of solar air-heating collectors, based on an improved design of absorbers and intensification of heat transfer processes [23, 24, 25, 26], due to turbulization of the heat carrier flow [27], is relevant for heat supply systems [28].
Among renewable energy sources, solar energy in terms of resources [29], ecological purity [30.31] and ubiquitous prevalence is the most promising energy resource [32]. Among installations operating on renewable energy sources, solar air heating collectors stand out for their simplicity of
design [33] and relatively high efficiency [34].The general direction of work on the creation of air solar collectors is to find ways to reduce heat loss to the environment [35], intensify heat transfer on the absorber [36] and reduce the cost of pumping air through the collector [37, 38] by reducing the hydraulic resistance of the collector.
A model of a solar water heater with a concave tube with low hydraulic resistance (Fig. 1) was developed; the device has a length l = 1200 mm, width = 400 mm, height h = 62 mm. This solar air heater has metal tubes in the working chamber with a small heat capacity and concave shape and is built in a checkerboard pattern. The length of each pipe is l = 150 mm. The average duct distance is l = 60 mm. At the base of the duct, a concave shape is given in two rows, this geometric figure has a depth h = 2 mm and a width = 15 mm. The geometric shape attached to the manifold ducts is internally concave along the outer surface of the channel and vice versa. When using a solar air heater, the inlet and outlet pipes are located at d = 15 mm when using a spray gun.
Fig. 1. General schematic view of a solar air heater with concave tubes. Here1-air outlet, 2-window, 3-black metal surface (absorber), 4-air duct, 5-channels for air inlet, 6-case
This solar air heater works in two ways:
- Blowing air into the inside of the collector;
- Air intake from the manifold.
During operation by the method of inflating air, diagonal inlet and outlet nozzles of the device are used.
In the case of air intake, each channel uses its own separate channels for air intake.
The channel diagram is a checkerboard shape that covers the entire airflow of the collector through the chamber.
The working chamber of the heater has a concave geometric shape in the air pipes (Fig. 2). air striking these figures forms a vortex motion.
The depth of the concave shape should not exceed h = 2 mm, the diameter of the tube (Fig. 3).
The coefficient of hydraulic resistance in the air pipes of a solar air heater is determined as follows:
Device characteristic
2
Pressure loss analysis on the device
Fig. 2. Circular motion on the concave parts of the air duct
Fig. 3. General view of the air duct
Fig. 4. Schematic view of the steps of a concave air duct
(1)
Here fl is the hydraulic resistance coefficient of a smooth air pipe; Re is the value characterizing the air flow regime, dvn is the diameter of the smaller part of the pipe, Dvn is the largest diameter of the pipeline, t is the number of steps in the pipe (Fig. 4).
The hydraulic resistance coefficient fl of a smooth air tube, as mentioned above, is determined as follows:
.
(2)
Here Re is the value characterizing the air flow regime, p is the dynamic viscosity of air at certain temperatures, and ^ st is the dynamic viscosity of heated surface air. n - the ratio of dynamic volatility to temperature differences is 1/3.
The Reynolds number is determined as follows:
vcL
Re =
(3)
Here is v - speed, d - diameter, v - kinematic viscosity of air. The dynamic viscosity of air is determined by the following:
To+c
fl
o T+C
(4)
Here p is the dynamic viscosity in (Pa) at a given temperature T; ^-control viscosity in (Pa) at some control temperature T0; T-set temperature in Kelvin; T0 control temperature in Kelvin; Sutherland C-constant for the gas whose viscosity is to be determined.
The pressure loss on the device is determined by the following:
Ah = £ £ * —.
^ 2 a
(5)
Here is the total hydraulic resistance coefficient, v is the average velocity, and g is the free fall velocity:
(6)
Theoretical analysis of experimental results
The concave tube solar heater was mainly tested at five different speeds, and at each speed experiment, the main parameters were obtained, including the air speed, the temperature of the heated air from the heater, and the temperature of the absorber and concave tubes (Fig. 5-9, Table 1-5).
Fig. 5. The process of working a solar heater with concave tubes
Table 1. The results were obtained at five different speeds from a concave-tube solar air heater (14.08.2019)
Inlet air Outlet air Time for Outdoor Heated air Absorber Surface temperature oC Tube
speed m/s speed m/s experience temperature oC temperature oC temperature oC
3.86 3.68 73 84 82
5.2 4.78 72 84 81
6.4 5.84 1330-1400 34 71 83 81
7.88 6.23 70 82 80
8.2 6.55 68 81 79
Reynolds (Re)
Fig. 6. Reynolds number versus hydraulic resistance coefficient, 1= f(Re)
Table 2. The dependence of the Reynolds number on the coefficient of hydraulic resistance
Re 5111 6766 8271 9559 9993
\fl 0.036 0.033 0.031 0.03 0.0295
^co 0.2 0.194 0.19 0.187 0.185
0.236 0.227 0.221 0.217 0.214
Fig. 7. Reynolds number versus speed, v=f(Re)
Table 3. Reynolds number versus speed
Re 5111 6766 8271 9559 9993
V m/s 3.77 4.99 6.1 7.05 7.37
0,1
5000 6000 7000 8000 9000 10000 Reynolds (Re)
Fig. 8. Reynolds number versus pressure loss Ah=f(Re)
Table.4 Reynolds number versus pressure loss
Re 5111 6766 8271 9559 9993
Ah m 0.16 0.28 0.41 0.54 0.59
80
£75
E 1
£ 65
60
5000 6000 7000 8000 9000 10000 Reynolds (Re)
Fig. 9. The dependence of the Reynolds number on the temperature jf the heated air, t = f(Re)
Table 5. Reynolds number versus temperature of heated air
Re 5111 6766 8271 9559 9993
t oC 73 72 71 70 68
Conclusion
By replacing common pipes in the working chamber of a solar air heater with pipes with a concave geometric shape, a decrease in the hydraulic resistance coefficient and pressure loss without reducing the heat transfer coefficient of the device was achieved.
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