Abstract
The piped hydraulic transportation of tube-contained raw material is a new low-carbon and environmental protection technique for transporting materials. The velocity characteristics of the spiral flow in the pipe with different numbers of guide bars installed on the surface of the piped vehicle body during piped hydraulic transportation of tube-contained raw material were studied by the theoretical analysis and model test. In the test, the numbers of guide bars placed on the surface of the piped vehicle body was respectively 3, 4, 5, and 6, and the studied sections were the section of the piped vehicle body and its rear section, and the flow discharge was 40 m3/h. The results showed that as the number of guide bars increased, the axial velocity of the section of the piped vehicle body increased gradually, while the axial velocity of the rear section of the piped vehicle reduced first and then increased. The section circumferential and radial flow velocity of the piped vehicle body and its rear section both increased first and then reduced. When the number of guide bars installed on the surface of the piped vehicle body was 4, the section circumferential flow velocity of the piped vehicle body and its rear section reached the maximum value, and their distributions were relatively uniform. The results offer theoretical basis so that we can optimize the structure of the piped vehicle and further popularize the piped hydraulic transportation technique of tube-contained raw material.
Keywords: Flow velocity characteristics, guide bars, spiral flow, piped vehicle, hydraulic transportation
Introduction
As logistics activities develops rapidly, modern logistics industry has become a new product of global economic development.1,2 As the “artery system” of the national economy, the logistics revolution has laid a necessary material foundation for the effective operation of natural economic elements and the rational adjustment of social industry distribution.3,4 This is also the driving force for countries around the world to gradually focus on the construction of logistics infrastructure and the development of new delivery system. After considerable development, the comprehensive transportation system including aviation, waterway, railway, highway, and pipeline has been integrated. However, the current transportation mode is mainly based on the consumption of high-carbon energy and the emission of carbon dioxide, which seriously restricts the development of green logistics industry.5,6
Pipe hydraulic transportation technology is an important part of modern pipe transportation technology. The traditional pipeline hydraulic transportation technology represented by slurry, mold, and capsule has played a well role in easing the pressure of national transportation and promoting the development of national economy.7,8 However, there are some defects, such as large power demand, serious waste water consumption, difficult pipeline maintenance, obvious wear and corrosion of pipeline, high cost of bulk material transportation, complex material processing technology, etc. 9 To a great extent, these problems restrict the rapid and efficient development of pipeline hydraulic transportation technology.
In order to effectively supplement the pipeline hydraulic transportation technology and improve the predicament of the existing pipeline transportation system, Professor Xihuan Sun proposed the green energy-saving piped hydraulic transportation of tube-contained raw material with “piped vehicle” as the transportation carrier in 2007. The piped vehicle mainly relied on the differential pressure power of flow in the pipeline to realize diversified material transportation.10,11 After that, many scholars had conducted research on its transportation characteristics. Zhang et al.12–14 studied the influence of fluid-solid coupling on the internal flow field in the pipeline in the piped hydraulic transportation of tube-contained raw material. By establishing the coupling model, the instantaneous velocity of piped vehicle with different length-diameter ratios and the pulsation pressure of flow in the pipe were analyzed. Zhang et al., 15 Wu et al. 16 studied the characteristics of concentric annular gap flow during the movement of piped vehicle with different diameters, and the results showed that the axial flow velocity increased at first and then reduced from the outer wall of the piped vehicle to the inner wall of the pipe. Li et al.17,18 studied the movement characteristics of the piped vehicles under different length-diameter ratios, different flow discharges and different transport loads conditions, and analyzed the transportation energy consumption during the transportation of materials by the piped vehicle. In a word, the current studies on the piped hydraulic transportation of tube-contained raw material mainly focuses on the pressure and velocity characteristics of the flow in the pipeline and the moving speed of the piped vehicle during the transportation of materials by the piped vehicle without the guide bars. However, these researching findings don’t offer enough information concerning the transportation characteristics during the transportation of materials by the piped vehicle with the guide bars. The spiral flow with a certain length is formed in the pipeline when transporting materials by the piped vehicle with the guide bars. This is a new spiral flow phenomenon, but the velocity characteristics of the spiral flow have not been addressed. Therefore, in this paper, the velocity characteristics of the spiral flow of the section of the piped vehicle body and its rear section during the transportation of materials by the piped vehicle with the guide bars were investigated based on the Particle dynamic analyzer (PDA) velocity measurement technology.
Experimental design
Piped vehicle
The piped vehicle was mainly made up of barrel, brace, and guide bars. In this study, the piped vehicle’s length L was 15 cm, and the piped vehicle’s diameter D was 7 cm. There were three cylindrical braces of 120° interval angle at both ends of the barrel to make the barrel’s axis and the pipe’s axis always coincident, thus reducing the friction between the barrel and the inner wall of the pipe, extending the service life of the pipe and ensuring the safety and stability of the piped vehicle. The guide bars were stalled on the outer wall of the piped vehicle and made by the mold. The length, height, and thickness of the guide bars were 15 cm, 1 cm, and 0.3 cm, respectively, and their torsion angle was 15°. The numbers of guide bars placed on the surface of the piped vehicle body P was respectively 3, 4, 5 and 6. The structural schematic diagram of the piped vehicle can be seen in Figure 1.
Figure 1.
Schematic diagram of the piped vehicle.
Experimental system and section arrangement
The test system19,20 was mainly made up of the centrifugal pump of the water supply device, the test pipeline, the delivery device, and receiving device of the piped vehicle, the turbine flow meter for measuring the flow discharge and the PDA for measuring the spiral flow velocity in the pipeline. PDA is an instrument based on Doppler effect, which uses high coherence and high energy of laser to measure fluid velocity. The principle is to obtain the velocity of the tracer particle by using the Doppler frequency of the scattered light of the moving particle and the Doppler signal of the tracer particle of the laser beam. Since the tracer particles and the fluid have good following fluidity, the measured velocity of the tracer particles is the flow velocity. Therefore, PDA can collect the instantaneous velocity value of the measuring point in real time through the change of signal frequency. The schematic diagram of the test device can be seen in Figure 2. During the experiment, water was pumped out of the underground reservoir by a centrifugal pump and flowed into the plexiglass pipe through the steel pipe. The piped vehicle was put into the test pipe from the delivery device and was secured by the brake device. Adjusted flow discharge through the gate valve to the flow discharge required by the test. After the flow was stable, we removed the braking device, released the piped vehicle, and measured the spiral flow velocity in the pipeline when the piped vehicle moved in the test section. Eventually, the piped vehicle ran into the receiving device from the pipe outlet, and the water flowed into the underground reservoir through the outlet pool, thus forming a circulation system. The test pipe was a plexiglass pipe with an inner diameter of 100 mm and a thickness of 5 mm and the flow discharge in the pipe was 40 m3/h.
Figure 2.
Test device: (a) schematic diagram. 1. Centrifugal pump, 2. Regulating valve, 3. Turbine flow meter, 4. The delivery device of the piped vehicle, 5. Brake device, 6. Computer, 7. Flow velocity receiving device, 8. The photoelectric sensor, 9. PDA, 10. Rectangular water jacket, 11. Capsule, 12. The water supply device and the receiving device of the piped vehicle, and (b) physical diagram. 1. Rectangular water jacket, 2. Probes of PDA, 3. Coordinate frame, 4. Horizontal pipe, 5. Data acquisition system for flow velocity, 6. Computer, 7. The delivery device of the piped vehicle.
In this study, the velocity characteristics of the spiral flow of the section of the piped vehicle body and its rear section in the pipe with different numbers of guide bars installed on the surface of the piped vehicle body were studied. Therefore, along the flow direction, five test sections were arranged in the annular gap area of the piped vehicle body, and three test sections were arranged in the rear area of the piped vehicle. The layout of the test section was shown in Figure 3.
Figure 3.
The layout of the test section.
Experiment results and analysis
Velocity characteristics of spiral flow in the annular gap section of piped vehicle body
Axial velocity
Figure 4 showed the annular gap section axial flow velocity distribution of piped vehicle body with different numbers of guide bars installed on the surface of the piped vehicle body. As we can see from Figure 4:
Figure 4.
The annular gap section axial flow velocity distribution of piped vehicle body with different numbers of guide bars: (a) section 1, (b) section 2, (c) section 3, (d) section 4, (e) section 5, and (f) average axial velocity distribution of each section.
The contour map of the axial flow velocity in the annular gap area of the piped vehicle body showed a change from dense to sparse in the flow direction, indicating that the gradient of the axial flow velocity gradually reduced in the direction of the piped vehicle body. That was because the sudden contraction of the entrance section of the piped vehicle caused the flow velocity in the pipeline to increase suddenly. After flowing over a distance, the axial flow velocity in the pipeline gradually recovered and tended to be stable, resulting in the gradual reduce of the axial flow velocity gradient along the section of the piped vehicle body.
It can also be seen from the contour map of five sections of the piped vehicle body that the contour map of Section 1 was in disorder, and the axial flow velocity was also larger than the other four sections. The contour density of Section 2-Section 5 was relatively uniform, which showed that the axial flow velocity distribution of the section had gradually become gentle, and the separation between the high-speed flow area and the low-speed flow area was gradually obvious.
As the number of guide bars increased, the axial flow velocity of the section of the piped vehicle body showed a slowly increasing trend. The main reason was that when the number of guide bars increased, the disturbance of guide bars to the annular gap flow would be more severe. Moreover, the increase of the number of guide bars reduced the area of annular gap between the piped vehicle body and the inner wall of pipeline, resulting in a slight increase in the axial velocity.
Circumferential velocity
Figure 5 showed the circumferential flow velocity distribution of the annular gap section of piped vehicle body with different numbers of guide bars installed on the surface of the piped vehicle body. As we can be see from Figure 5:
Figure 5.
Circumferential flow velocity distribution of the annular gap section of piped vehicle body with different numbers of guide bars: (a) section 1, (b) section 2, (c) section 3, (d) section 4, (e) section 5, and (f) average circumferential velocity distribution of each section.
The section circumferential flow velocity of the piped vehicle body reduced first and then increased. The reason was that when the water ran around the piped vehicle, the area of the cross section of the water would shrink sharply. In addition, the guide bars can also promote the flow circumferential velocity. Because the influence of section contraction on Section 1 and Section 2 was greater than that of the guide bars, the circumferential flow velocity of Section 2 would reduce slightly with the redistribution of flow velocity along the section. After that, when the water flowed through Section 3-Section 5, the influence of the guide bars on the circumferential flow velocity was dominant, and the circumferential flow velocity gradually increased along the section.
As the number of guide bars increased, the circumferential flow velocity of the section of the piped vehicle body increased at first and then reduced. When the number of guide bars P = 4, the circumferential flow velocity reached the maximum, and the contour map distribution of the circumferential flow velocity was relatively gentle. Under this condition, the promoting effect of guide bars on circumferential flow velocity was the largest.
The contour map of the circumferential flow velocity in the annular gap area of the piped vehicle body showed a change from dense to sparse along the flow direction, showing that the gradient of the circumferential flow velocity gradually reduced in the direction of the piped vehicle body.
Radial velocity
Figure 6 showed the radial flow velocity distribution of the annular gap section of piped vehicle body with different numbers of guide bars installed on the surface of the piped vehicle body. As can be seen from Figure 6:
Figure 6.
Radial flow velocity distribution of the annular gap Section of piped vehicle body with different numbers of guide bars: (a) section 1, (b) section 2, (c) section 3, (d) section 4, (e) section 5, and (f) average radial velocity distribution of each section.
As the number of guide bars increased, the radial flow velocity of the section of the piped vehicle body increased at first and then reduced. When the number of guide bars P = 4, the radial flow velocity reached the maximum, and the contour map distribution of the radial flow velocity was relatively gentle. Overall, the radial flow velocity of the section of the piped vehicle body varied from −0.2 m/s to 0.3 m/s, with an average value of about 0.05 m/s, which was far less than the axial flow velocity of the same section and about 30% less than the circumferential flow velocity of the same section.
The number of measuring points in the radial flow velocity direction away from the center of the pipe was obviously more than that in the radial flow velocity direction away from the center of the pipe. That was, there were more measuring points with positive radial flow velocity, indicating that the radial flow in the annular gap area of the piped vehicle had a general movement trend deviating from the center of pipe.
Velocity characteristics of spiral flow in rear section of piped vehicle
Axial velocity
Figure 7 showed the rear section axial flow velocity distribution of the piped vehicle with different numbers of guide bars installed on the surface of the piped vehicle body. As can be seen from Figure 7:
Figure 7.
The rear section axial flow velocity distribution of piped vehicle with different numbers of guide bars: (a) section 6, (b) section 7, (c) section 8, and (d) average axial velocity distribution of each section.
The existence of the piped vehicle destroyed the concentric distribution of the original axial flow velocity in the pipeline. The axial flow velocity of the nearest Section 6 of the rear of the piped vehicle had a large fluctuation range, and the overall distribution of axial flow velocity was also relatively disordered. The main reason was that when the annular gap spiral flow flowed into full pipe area from the annular gap area, the spiral flow diffused to the whole pipe, and the streamline expanded, resulting in eddy current, which greatly influenced on the axial flow velocity distribution of Section 6. When the water flowed through Section 7 and Section 8, the flow pattern had reached a more uniform distribution after a distance of redistribution, and only the axial velocity fluctuation near the pipe wall was larger. Overall, the rear section axial flow velocity of the piped vehicle reduced gradually and tended to be stable.
As the number of guide bars increased, the rear section axial flow velocity of the piped vehicle reduced at first and then increased. When the number of guide bars P = 4, the rear section axial flow velocity of the piped vehicle reached the minimum value.
Circumferential velocity
Figure 8 showed the rear section circumferential flow velocity distribution of the piped vehicle with different numbers of guide bars installed on the surface of the piped vehicle body. As we can see from Figure 8:
Figure 8.
The rear section circumferential flow velocity distribution of piped vehicle with different numbers of guide bars: (a) section 6, (b) section 7, (c) section 8, and (d) average circumferential velocity distribution of each section.
The rear section circumferential velocity of the piped vehicle showed a gradually decreasing trend from the center of the pipe to the pipe wall, and its maximum value was close to the center of the pipe, while its minimum value was close to the pipe wall.
As the numbers of guide bars increased, the rear section circumferential flow velocity of the piped vehicle increased first and then reduced. When the number of guide bars P = 4, the circumferential flow velocity reached the maximum.
Radial velocity
Figure 9 showed the rear section radial flow velocity distribution of the piped vehicle with different numbers of guide bars installed on the surface of the piped vehicle body. As we can see from Figure 9:
Figure 9.
The rear section radial flow velocity distribution of piped vehicle with different numbers of guide bars: (a) section 6, (b) section 7, (c) section 8, and (d) average radial velocity distribution of each section.
The absolute value of the rear section radial velocity of the piped vehicle away from the center of the pipe was larger than that of pointing to the center of the pipe. With the distribution of the spiral flow velocity along the pipeline, the radial flow velocity gradually reduced and tended to be stable.
Similar to the section of the piped vehicle body, the number of measuring points in the radial flow velocity direction of the rear section of the piped vehicle away from the center of the pipe was also obviously more than that in the radial flow velocity direction away from the center of the pipe. That is, there are many measuring points with the radial velocity in the positive direction, which indicated that the radial flow of the rear section of the piped vehicle also had a general movement trend deviating from the center of the pipe.
The rear section radial flow velocity of the piped vehicle varied between −0.4 m/s and 0.3 m/s. As the numbers of guide bars increased, the rear section radial flow velocity of the piped vehicle increased at first and then reduced. When the number of guide bars P = 4, the radial flow velocity reached the maximum.
The piped hydraulic transportation of tube-contained raw material is a transporting technique in which the pressurized flow acting on the piped vehicle pushes the piped vehicle to move forward. As the carrier of conveying materials, the structure parameters of piped vehicle directly affect the flow pattern in the pipe. When the piped vehicle’s diameter, the piped vehicle’s length and the guide bar’s structural parameters change, the flow velocity characteristics in the pipe will be affected. In this paper, the velocity characteristics of spiral flow in pipeline with different numbers of guide bars installed on the surface of the piped vehicle body under unchanged structural parameters of the piped vehicle and the guide bar were experimentally investigated.
Conclusion
As the number of guide bars increased, the axial flow velocity of piped vehicle body section increased slowly, while the axial flow velocity of its rear section reduced first and then increased. The section axial flow velocity gradient of the piped vehicle body reduced gradually along the flow direction, while the rear section axial velocity of the piped vehicle reduced gradually and tended to be stable along the flow direction.
As the number of guide bars increased, the circumferential flow velocities of the section of the piped vehicle body and the rear section of the piped vehicle increased at first and then reduced. The sectional circumferential flow velocity of the piped vehicle body reduced at first and then increased, and the gradient of the circumferential velocity reduced gradually in the direction of piped vehicle body, while the rear section circumferential velocity of the piped vehicle reduced gradually from the center of the pipe to the pipe wall.
As the number of guide bars increased, the radial flow velocities of the section of the piped vehicle body and the rear section of the piped vehicle increased at first and then reduced, and both deviated from the center of the pipe.
Described the research condition in this paper, when the flow in the pipe was constant and the number of guide bars installed on the surface of the piped vehicle body P = 4, the circumferential flow velocities of the section of the piped vehicle body and the rear section of the piped vehicle reached the maximum value and their distributions were relatively uniform. In this case, the guide bars had the greatest promoting effect on the circumferential velocity.
Author biographies
Li Yongye, Associate professor, College of Water Resources Science and Engineering, Taiyuan University of Technology, People’s Republic of China. Theory and experiment of engineering hydraulics and the pipeline hydraulic transportation have been mainly studied. More than 50 academic papers, 6 national invention patents and 3 monographs have been published. Email: liyongye@tyut.edu.cn
Gao Yuan, Postgraduate student, Degree in Hydraulics and River Dynamics, College of Water Resources Science and Engineering, Taiyuan University of Technology, People’s Republic of China. Theory and experiment of engineering hydraulics and the pipeline hydraulic transportation have been mainly studied. 5 academic papers and 1 national invention patents have been published. Email: gaoyuan@tyut.edu.cn
Zhang Tao, Postgraduate student, Degree in Hydraulics and River Dynamics, College of Water Resources Science and Engineering, Taiyuan University of Technology, People’s Republic of China. Theory and experiment of engineering hydraulics and the pipeline hydraulic transportation have been mainly studied. 2 academic papers and 1 national invention patents have been published. Email: gaoyuan@tyut.edu.cn
Xihuan Sun, Professor, College of Water Resources Science and Engineering, Taiyuan University of Technology, People’s Republic of China. Theory and experiment of engineering hydraulics and the pipeline hydraulic transportation have been mainly studied. More than 90 academic papers have been published. The editorial board of journal of hydrodynamics have been served. Email: sunxihuan@tyut.edu.cn
Xuelan Zhang, the lecturer, College of Water Resources Science and Engineering, Taiyuan University of Technology, People’s Republic of China. Theory and experiment of engineering hydraulics and the pipeline hydraulic transportation have been mainly studied. More than 20 academic papers, 3 national invention patents and 1 monographs have been published. Email: zhangxuelan@tyut.edu.cn
Footnotes
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding: The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research is supported by both the National Natural Science Foundation of China (51179116, 51109155) and the Natural Science Foundation of Shanxi Province (201701D221137).
ORCID iD: Yongye Li 
https://orcid.org/0000-0002-6241-2313
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