Journal of University of Shanghai for Science and Technology 4 kinds of design schemes for solid-liquid two-phase flow pipeline transportation. Among them, a and 2b are non-pressure self-flow conveying modes, which are characterized by relying on the natural pressure difference and the gravity of the slurry itself to realize the transportation without the need of power equipment, so the utility model has the advantages of low energy consumption and low cost. However, since this conveying method requires that the terrain condition must have sufficient self-flowing slope, it is rarely used in practice, and for the pre-mixing pressure conveying mode of the indoor loop tube, it avoids the above disadvantages, and the effect is proved to be good by actual use.
The key to the use of pressure delivery is the choice of pumping equipment, including the slurry pump and its associated power. There are a wide variety of pumps currently used for slurry transport, such as centrifugal pumps, reciprocating pumps and isolating pumps. It can be seen that when the delivery pressure is lower than 4.47 MPa (45.6 kgf/cm2), the centrifugal slurry pump is preferred. According to this principle, and through the hydraulic calculation of the system piping and accessory resistance, the 50ZD centrifugal slurry pump produced by Shijiazhuang Pump Factory was selected. The main technical parameters are motor power corpse = 11kW rated flow 0 = 45m3 / h. Rated head ugly = 21m rated efficiency = 55*% Maximum mass fraction of solid-liquid mixture w = 1.2 Two-phase flow of the mixing and cleaning system. The water tank provided in the cleaning pipeline system has two functions, namely for water debugging. The vertical workbench is 2m high and 0.75m wide. It is vertically arranged with 3 pipes, 2 risers and 1 down pipe. The ascending pipe adopts a parallel pipeline structure, wherein one ascending pipe is used as a main system pipeline, and an electromagnetic flowmeter is installed. Another riser tube design has two roles: when acting. This not only prevents the particles from fouling the pressure measuring holes, but also avoids the phenomenon that the particles enter the pressure gauge when there is a bubble at the top of the tube.
A pressure pipe of 50 mm in length is welded to the pressure measuring hole and connected to the pressure gauge. In order to prevent solid particles from entering the meter, a special isolation device is required for the pressure transmission section between the pressure guiding tube and the meter. Some people have used the isolated tank as the pressure transmitting device, but the device has a slow response speed and low measurement accuracy. It is not ideal for testing two-phase flow pipes with large pressure fluctuations. In practice, the author used the CECC type capacitive remote differential pressure transmitter produced by Shanghai Guanghua Instrument Factory with an accuracy of 0.5. The transmitter uses a closed capillary pressure transmission system, and the capillary tube (filled with silicone oil) is installed on the pressure guiding tube through the remote sealing flange through the diaphragm. When the pressure is measured, the slurry is separated by the diaphragm, avoiding the head and the head. direct contact. This kind of instrument has the characteristics of fast response, high precision and good stability. Because of its electrical signal (4~20mADC), it is easy to connect with computer to form an automatic data acquisition and processing system, which greatly improves) and collects data. Conduct preliminary processing. It consists of two parts: hardware and software.
The hardware includes PC586 microcomputer, printer, DC stabilized power supply, data acquisition card and terminal block. Among them, the data acquisition card selects Advantech's PCL-818LS type card, the main technical parameters: 12-bit A/D resolution, 8 differential analog signal input, 40K/s sampling rate; terminal board selects PCLD-8115 Connected to the data acquisition card via a DB-37 cable, the PCLD-8115 provides onboard passive signal processing components (resistors and capacitors) for easy low-pass filtering, voltage attenuation and 420mA current/voltage conversion.
The data acquisition system runs the main interface 6.0 language application software developed under the Windows98 environment. It includes four modules: system setting, data display, program control and file management. The menu operation mode between modules is convenient and flexible. The system setting module completes the configuration required for the software and hardware connection, and sets the measurement parameters (such as variable name, value range, acquisition time, and sensor calibration formula) of each channel of the acquisition board; the program control module controls the program according to the test flow. It can collect, record and display with the operator's requirements, and can change the working condition at any time by using the interface control keys; the data display module can display various dynamic graphics of the data in real time on the screen in three ways (current, voltage and customization). Number; the file management module is used to generate data report documents and can send printer output as needed.
2 The main function of the experimental platform Because of the comprehensive consideration of many factors in the design, the experimental platform can not only study the flow structure and mechanism of solid-liquid two-phase flow in pipeline transportation, but also simulate the actual work of industrial pipeline transportation materials. condition. The main functions of the test bench include the following.
The experimental study on the flow pattern of two-phase flow pipelines is divided into single-phase flow such as clean water, and the flow pattern has laminar flow and turbulent flow. For the solid-liquid two-phase flow in the tube, the flow pattern is also based on the relative position and relative content between the two phases. The relative speed and the like are divided into various complex flow patterns. The experiment is carried out in the plexiglass observation tube section of the test pipeline, and the two-phase flow model in the flow rate from high to low is determined by visual observation or by means of high-speed photography and photoelectric image analysis device, and each transient condition during the transition of the flow pattern is determined. Parameters.
Experimental study on the resistance characteristics of two-phase flow pipelines is an important part of pipeline hydraulic transport. It is directly related to the selection and operation energy consumption of power equipment. Through the measurement of the friction loss along the different conveying modes (horizontal, inclined and vertical), different materials and different pipelines, the variation law of the resistance characteristics of the two-phase flow pipeline is found, and the engineering design parameters of the slurry pipeline are determined. And the way of operation provides a reasonable basis.
Experimental study on the optimal transport flow rate of two-phase flow pipelines Transport flow rate is one of the key parameters in pipeline hydraulic transport, which is related to the safety and economy of pipeline operation. The experiment observes the flow state of the slurry through a transparent plexiglass tube, and determines the lower limit of the safe operation of the pipeline by using the flow velocity at the bottom of the tube when rolling or sliding the bed as the critical flow rate; on this basis, considering the solid transport volume per unit The lowest energy consumption is used to establish a hydraulic model of the optimal transport flow rate of the pipeline.
Dynamic experimental study on the maximum laying slope of two-phase flow pipelines Two-phase flow medium will produce solid-liquid layer separation when the pipeline is stopped, and solid matter will precipitate at the bottom of the pipeline. If the slope of the pipeline exceeds a certain value, it may cause the solid sediment to block the pipeline when the pipeline accident stops, which makes it difficult to start the recovery and even cannot be transported. This problem does not exist with single-phase flow media delivery pipes. This limited slope value is currently obtained mainly through the static angle of repose experiment of the pipeline. To be closer to reality, the author further perfected this by using the two-phase flow pipeline test bench to simulate the tilting tube stop pump restart experiment under dynamic conditions. verification. For industrial conveying pipelines, the maximum laying slope is generally 9.09%. The designed bench of the author has an adjustable slope of 16*, which fully meets the actual requirements.
Experimental study on stopping the pump in the two-phase flow pipeline after restarting the pump for a period of time, to see if the slurry can be floated again after sedimentation in the pipeline, determine the starting flow rate; and simultaneously measure the resistance change of the pipeline at the start-up The law provides a basis for designing the system to resume normal operation after it stops.
In addition to the above basic functions, based on the existing devices, according to different test objects and experimental requirements, through the transformation of the experimental system, experimental research on some expansion projects can also be carried out, such as: a. Two-phase flow pipe velocity distribution Experiment with concentration distribution b. Experimental study on resistance loss of local pipe fittings (bent pipe, reducer pipe and valve, etc.); C. Experimental study on water hammering problem of two-phase flow pipe; d. Experimental study on two-phase flow pipe abrasion.
3 Practical application At present, pipeline experiments of solid materials such as PVC pellets, quartz sand and fly ash have been carried out on the experimental bench.
A photograph of the particle flow pattern taken when the material (particle size 4 = 3.36 mm, solid density æ¡ = 1220 kg/m3). It can be seen from the figure that with the flow rate from high to low, four distinct flow patterns can be observed: uniform suspension flow, non-uniform suspension flow, stratified layer flow accompanied by particle sliding, rolling and jumping, and static deposition. Layer flow.
The flow pattern of PVC particles flowing along a 50 mm diameter pipe in water is a measure of the force gradient (ie head loss per unit length) in a horizontal 50 mm diameter and inclined pipe. The experiment was mainly carried out for uniform and non-uniform suspension flow zones (ie, under solid-free deposition conditions), which is in line with industrial practical applications.
It can be seen from the figure that the resistance characteristics of the tube flow change greatly after the solid particles are added to the clean water.
Friction loss when transporting quartz sand in horizontal and inclined pipelines 4 Conclusion Pipeline hydraulic transport of solid materials is an emerging technical field. The hydraulic principle of pipeline transportation, the structure of pipeline system and the test method of conveying parameters are different from the general ones. The clean water pipeline needs to be researched and analyzed by experiments. Therefore, it is very important to design a feasible experimental pipeline system. In this paper, a solid-liquid two-phase flow pipeline transport test bench was designed and constructed for the characteristics of hydraulic transport of granular material pipelines, and the power supply slurry system, mixing and cleaning system, rock slope experimental system, vertical experimental system and test of the experimental bench. The system and so on were separately studied and designed. The actual use proves that the test bench is reasonable in design, complete in function, accurate and reliable in testing, and can be used to simulate various working conditions of industrial pipelines.
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