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Ibragimov Umidjon Hikmatullaevich, doctoral student of the department of Thermal Engineering Karshi engineering-economic institute E-mail: ibragimov_u@rambler.ru Khamraev Sardor Ilhomovich, assistant of the department of Thermal Engineering Karshi engineering-economic institute, Shamuratova Sohiba Mustafakulovna, assistant of the department of Thermal Engineering Karshi engineering-economic institute,
STUDY OF HYDRAULIC RESISTANCE IN HEAT EXCHANGER TUBES WITH LOCAL TURBULATORS
Abstract: This article presents the main results of an experimental study in the tubes of a heat exchanger with localized tourists.
Keywords: intensification, turbulizer, local turbulator, hollow, hydraulic resistance.
In order to intensify heat transfer and drastically reduce the formation of deposits on heat-exchanging surfaces, the authors of this article propose to install local turbulators (LT) in heat exchanger tubes (Fig. 1) [1]. The use of these types of
turbulizers not only intensifies the process of heat exchange and reduces the rate of sediment, but also leads to an increase in the hydraulic resistance of the apparatus.
Figure 1. Scheme and general view of the experimental tube with local turbulators: 1 - elastic stainless wire; 2 - turbulators made of hollow; 3 - tube heat exchanger; 4 - direction of movement of raw water
The main elements are thin elastic stainless wire 1 of a free configuration (Fig. 1) and turbulators made of hollow with different geometric configurations 2, and fixed at a certain distance in the wire. One end of the wire 1 is attached to the input of the tube 3, and the other end of the wire remains free. The diameter of the wire is 0.2 ... 0.8 mm. The flow of water 4, washing the uneven surfaces of the hollow, pushes the wire away, and the wire vibrates. Due to vibration, the entire flow is turbulent.
Elements of local turbulizers - polymer hollow, the wire passes through the center of these bodies. Hollow cores can be installed in various combinations. Depending on the density of the coolant, various materials with an appropriate specific weight can be used as wires, for example, steel, polymer, etc.
The geometric shape of the hollow (element LT) can be made of various configurations. The criteria for the optimal choice of the shape of the elements are the Reynolds num-
ber and the hydraulic resistance coefficient of the apparatus channel. It follows that it is necessary to strive to obtain good turbulization of the water flow with the smallest relative increment of the hydraulic resistance of the channel. Developed seven typical designs of local turbulizers [2, p. 229-231].
An experimental stand was developed for laboratory research [3, p. 79-80], where hydrodynamics ofwater flow was studied at different flow conditions.
The main element of the experimental stand is an experimental tube made of transparent glass. Its internal diameter and length were respectively D = 20 mm, l = 1200 mm. LT is a wire free configuration. The hollow can be installed in various combinations. In this case, one end of the wire was attached at the entrance to the tube, and the other end remained free.
The installation works in the following order: water enters the installation through a pipeline from the tank. To regulate
STUDY OF HYDRAULIC RESISTANCE IN HEAT EXCHANGER TUBES WITH LOCAL TURBULATORS
the flow of water installed valve. The flow rate itself is determined by the indication of a calibrated rotameter.
For a visual study of fluid flow regimes and the behavior of local turbulizers, the main part of the installation, the tube was made of glass. To supply the dye from the tank and measure the pressure loss in the tube were provided fittings. Head losses were measured using a U - shaped pressure gauge. To ensure the flow of fluid over the entire cross section of the glass tube, a hydraulic shutter was installed at the exit of the stand.
The results of studies of the hydrodynamics of water flow in a tube using the developed LTs have shown that the main factor influencing the process is the geometric shape, the type of material of the core, the attachment step. A visual observa-
tion showed that the energy of the oncoming flow of water imparts an oscillatory motion to all elements of the LT, at 1000 < Re [4, p. 56-58].
Based on the conducted experiment on the hydraulic resistance in the tubes of the heat exchanger with the local tabulators, generalized dependences were obtained. Generalizing dependencies are obtained on the basis of the DArcy formula and are valid within 1000 < Re < 10000. The results obtained by the empirical dependences are presented in Table 1. The data on the coefficients of hydraulic resistance are summarized with an accuracy of ± 3% in the range Re = 1000-10000. Depending on the design of local turbulators, the hydraulic resistance coefficient increases from 2 to 3 times [5; p. 144-146].
Table 1. - The values of the coefficients of hydraulic resistance
№ View of the turbulizer The equation
1. Smooth tube 4 = 136,25/Re1,15
2. Disk 4 = 9,07/Re0,73
3. Square 4= 44,38/Re0,87
4. Rectangular 4 = 108,64/Re0,98
5. Oval 4 = 58,02/Re0,93
6. Taper 4 = 43,08/Re0,88
7. Rhombic 4 = 1045/Re1,23
Based on the obtained empirical dependencies for oval turbulizers, a hydraulic calculation of heat exchangers with local turbulators was performed. The results of the hydraulic calculation of heat exchangers with oval turbulators show that the required power of the pump for pumping the heating coolant increases and is 417 W.
The use of oval turbulizers in the tubes of a heat exchanger increases the hydraulic resistance (due to the increase in internal local resistances) by almost 8-10%.
To study the influence of the geometric shape and configuration on the hydraulic resistance inside the pipes, an experimental study of the hydrodynamics of pipes with local turbulators was carried out. Experimental studies were carried out on an experimental installation IT-84. Experimental studies were conducted in the following range of basic parameters: water flow, G = 15 + 210 kg / hour; coolant inlet temperature tj = 230 C ; internal diameter of heat exchange tubes, dB=0,016 mm. According to the results of the experiments, tables of experimental data were formed and graphs of hydraulic resistance and Reynolds numbers along the length of the tube with local turbulators were plotted. During the experiment in the first series, the geometrical parameters and configuration of the turbulator are assumed to be constant and only the pitch and design of the local turbulator change. Ex-
perimental results obtained on the basis of experimental studies are valid within 1000 < Re < 10000.
The effect of the geometric shape of local disk turbulizers on the hydraulic resistance in pipes with the same ranges of the main parameters was also experimentally investigated. Geometrical parameters of a local disk turbulizer: disc diameter, d = 8 + 12 mm; disk width, b = 2 +10 mm; turbulent step, s = 40 100 mm. Experimental results obtained on the basis of experimental studies are valid within 1000 < Re < 10000. [6, 156-158].
The authors concluded that using the developed design of local turbulizers under certain conditions, it is possible to achieve an increase in the turbulence of the fluid flow in the tubes of heat exchangers with a relatively small increase in the hydraulic resistance of the channel by about 25-40%.
Analysis of the published works shows that there is a prospect of using this design of local turbulizers in order to intensify the heat exchange process and reduce the rate of formation of deposits, because the oscillatory motion of local turbulizers creates in the tube volume moving vortex flows. In addition, this design of local turbulators is simple to manufacture, low-cost and does not require replacement of existing equipment.
References:
1. The patent for the invention on the topic "Turbulizing device of the heat exchange tube." Babahodzhaev R. P., Mukhid-dinov D. N., Tokhtokhunov K. A., Khojaev B. A., Ibragimov U. Kh., Yusupov B. V., Khuzhanov R. A. Registered in the state register of inventions of the Republic of Uzbekistan,- Tashkent, 28.05.2012 y.
2. Ibragimov U. Kh. Intensifiers like a local turbulizer // Young scientist.- Kazan. Publishing house Young scientist, 2016.-No. 8 (112).- P. 229-231.
3. Ibragimov U. Kh., Pulatova D. M., Islamov R., Tsoi K. Experimental stand for the study of hydrodynamics of turbulized water flow // Bulletin of Tashkent State Technical University.- Tashkent, 2010.- No. 3.- P. 79-80.
4. Ibragimov U. Kh., Babakhodzhaev R. P., Uzakov G. N., Khamrayev T. Y., Boymurodova Kh. U. Experimental study of hydrodynamics in heat exchanger tubes using local turbulizers // Young scientist.- Kazan. Publishing house Young scientist, 2013.- No. 3 (50).- P. 56-58.
5. Ibragimov U. Kh., Shomuratova S. M., Ruzikulov G. Generalization of experimental data on hydraulic resistance in tubes of heat exchangers with local turbulizers // Young scientist.- Kazan. Publishing house Young scientist, 2013.- No. 10(57).-P. 144-146.
6. Ibragimov U. Kh. Experimental study of the influence of the geometric shape of local disk turbulizers on the hydraulic resistance in pipes // Young scientist.- Kazan. Publishing house Young scientist, 2016.- No. 9 (113).- P. 156-158.
