Development and Experimental Research on the perfo

2022-07-27
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Development and experimental research of new agitator performance test platform

development and experimental research of new agitator performance test platform

December 15, 2018

mixing and mixing operation is one of the most widely used process unit operations, and is widely used in chemical, petrochemical, medical, papermaking, coating, metallurgy, wastewater treatment and other industries [1]. Mechanical mixing equipment plays a key role in paint and synthetic resin for paint. Unsatisfactory mixing effect will lead to explosion and polymerization in the kettle, which will seriously affect the quality of polymer. Therefore, the research on mixing technology has become very important for Chinese coatings

at present, there are few experimental platforms used to study the performance of agitators, and there are some problems, which are specifically reflected in:

(1) the positioning accuracy of the mixing shaft is low and the flexibility is poor. It can not be guaranteed that the agitator is on the central axis during each experiment. The vertical position of the mixing shaft is relatively fixed, and the height of the agitator cannot be adjusted in the vertical direction according to the change of the mixing kettle

(2) the test condition is simple, and the mixing performance test of the agitator cannot be carried out in the medium with corrosion and certain pressure

(3) the test process is cumbersome, and the viscosity and density of the slurry can not be detected in real time

(4) the heads of agitator are mostly flat bottom heads, while the elliptical heads are widely used in industry

(5) the kettle body is made of all glass, which is not easy to seal and fragile, bringing many unnecessary risks to the test

(6) the diameter of the kettle is small, and the volume of the kettle body is quite different from that of the actual industrial stirring kettle, resulting in a large deviation in the application amplification. Based on the actual needs, this research overcomes the shortcomings of the previous test platform, and develops a new agitator performance test platform with strong comprehensive performance and easy operation. And use fluent "he found 6 The numerical simulation of three kinds of conventional blade mixing power is carried out. The experimental and CFD simulation results show that the experimental platform has stable performance, simple operation and good accuracy

1 structural characteristics 1 1 Introduction to agitator performance test platform

the agitator performance test platform is mainly composed of kettle body, mixing transmission device, mixing shaft lifting support, control cabinet and other components. Its supporting test software can monitor all performance parameters of the agitator in real time. The technical platform can be used for paddles, containers and mixing shafts of different specifications to measure the mixing time, mixing efficiency, mixing power and other performance indicators. The main structure of the test platform is shown in Figure 1

main structure diagram of mixer performance test platform

1 2. Figure 2 shows the physical diagram of the test platform

physical drawing of mixer performance test platform

the kettle body is installed on the base of the test platform and fixed with the base by bolts, which can ensure sufficient rigidity during mixing; Different from the traditional stirring experimental device, this device uses a transparent cylinder in the middle of the kettle body, and its upper and lower parts are connected with stainless steel flat flanges and elliptical heads. In the design, grooves on the metal surface are used and bolts are used to compress, which can achieve a certain pressure; Under normal pressure, the cylinder of the test platform is made of plexiglass with a thickness of 15 mm. According to the requirements of the mixing medium and working conditions, the kettle can be replaced with a cylinder made of tempered glass. The advantage of the transparent container is that it is convenient to observe the flow field in the kettle during the experiment, and to observe the flow field and velocity field of the liquid in the barrel by using particle image velocimetry (PIV) and digital particle image velocimetry (DPIV) [2]; According to the needs of the test, the agitators supporting the kettle bodies of different specifications can also be easily replaced. The upper head of the kettle body is a flat head, which is composed of nested sealing plates of different specifications. While ensuring partial sealing, it is also convenient to replace different mixing shafts and blades. For the first time, the lower head of the kettle body adopts the standard elliptical head widely used in industry in the testing machine, which is convenient for the simulation of amplification technology. At the same time, this head can effectively eliminate the dead zone that is not easy to reach during mixing operation [3]

1. 3 control system

control cabinet is composed of test computer, relevant test instruments and operation console. The actual power of different agitators at different speeds is transmitted to the hp-jca intelligent electronic monitoring station through the frequency converter, and the electrical signal of the temperature sensor is also transmitted to the electronic monitoring station, and then transmitted back to the software interface through the 485 to 232 module. The mixing speed is input on the software interface. Various equations related to agitators are nested in the software. Through the software submenu, you can select custom blades, input the size parameters of the blades, select and input the corresponding parameters of various agitators and the test data related to the stirred liquid, and then you can get the theoretical mixing power and mixing efficiency of different agitators

2 working principle and characteristics 2 1 technical characteristics

see Table 1 for the technical parameters of the mixer performance test platform

technical parameters of mixer performance test platform

2 2 working principle

the lifting system of the test platform is composed of a transmission device and a base, and is powered by two motors. The speed regulating motor realizes the required mixing speed through Siemens 6se6440-2ud17-5aa1 frequency converter, and its power is also transmitted to the software through the frequency converter. The other motor uses the hydraulic principle to realize the lifting and lowering of the mixing shaft

blades are important components of the mixing system. This test platform is equipped with paddle, open turbine, disc turbine, propulsion and other blades. With this design, on the one hand, it is convenient to replace the paddles and lift the mixing shaft to the upper part of the kettle body, which can facilitate the replacement of paddles of different specifications and models. On the other hand, when replacing the mixing container, it can ensure that the mixing shaft is on the same central axis, and according to the change of the kettle body, the paddles can stay at any position in the vertical direction of the kettle body. Mixing time is usually measured by fading method [4], conductivity method [5] and temperature difference method [6]. Considering the accuracy and simple operation, this test platform uses the temperature difference method to measure the mixing time. The software of the test platform realizes the real-time detection and transmission of the three-point temperature through three temperature sensors placed in different positions. 3D printing material business opportunities: the global plastic sales have reached 310million US dollars. Hp-jca intelligent electronic monitoring station processes and transmits the electrical signals from the temperature sensors to the software. Based on the intelligent control of the test system, the designer has developed a supporting visual software system. During the test process, the time used to meet the mixing requirements is automatically recorded by the software, and the temperature time image is drawn synchronously, which can directly reflect the mixing process and mixing effect

3 experimental test and analysis 3 1 measurement of mixing time

seven kinds of traditional blades, such as paddle, open turbine and disc turbine, are tested on this test platform. Add the aqueous solution at a certain temperature to the 70% volume scale, then lower the mixing paddle to the appropriate height, add the 90 ℃ aqueous solution with a certain proportion of volume, and input different mixing speeds to measure the mixing time. Figure 3 shows the test results at the speeds of 2 R/s, 3 R/s and 4 R/s

measurement results of mixing time of each agitator

it can be seen from the test results that this performance test platform accurately and intuitively reflects the correlation between mixing speed and mixing effect (mixing time), that is, within a certain speed range, increasing the speed can significantly reduce the mixing time. At low speed, the mixing time of paddle type is relatively long, and that of turbine six straight blades type is the shortest. With the increase of rotating speed, the liquid turbulence intensifies, and the mixing time of various agitators decreases significantly, and is getting closer and closer

3. 2 measurement of mixing power

mixing power is an important characteristic of the blade. The theoretical mixing power is calculated according to formula (1) [7]:

μ Is the viscosity value of the measured liquid; N is the set stirring speed value; ρ Is the liquid density; D is the diameter of the kettle body; H is the liquid depth. The power of the above seven blades was tested in aqueous solution. The rotating speeds of the bunched cable combustor were 2 R/s, 3 R/s and 4 R/s respectively. The measured results are shown in Figure 4

measurement results of mixing power of each agitator

it can be seen from Figure 4 that the actual power consumed by each agitator increases significantly with the increase of rotating speed. Among them, the power consumed by paddle agitator is relatively low, and the power consumed by disk six straight blades and turbine six straight blades is larger. At the same rotating speed, the power consumed by the paddle type folded blade propeller is about 2/7 of that of the turbine six straight blade propeller and the disk six straight blade propeller. Use the finite element software fluent6 3 simulate the power of three kinds of agitators [8-9]. Figure 5 shows the comparison between measured power and simulated power. Compare the two results in order to facilitate measurement, we can know that the platform can accurately measure the actual power consumed by the agitator. The error percentage between actual power and theoretical power is within 10%. Through the test results of 7 kinds of blades, it can be seen that the error of the experimental data is very small when tested in aqueous solution. With the increase of solution viscosity, the power error of some blades increased slightly during the experiment. The reason is that, on the one hand, with the increase of viscosity, the power consumed by mixing also increases correspondingly, which increases the mechanical loss of reducer and coupling; On the other hand, there is a certain manufacturing error in the test blade. With the increase of viscosity, the power error caused by it becomes more and more obvious

comparison between measured power and simulated power of agitator

4 conclusion the experimental platform adopts fully automatic hydraulic lifting system, open transparent mixing tank, intelligent variable frequency speed regulation system and visual operation interface. Compared with the traditional mixing experimental device, the labor intensity of the operator is greatly reduced, and it is more convenient to clean the mixing tank and replace the blades. At the same time, the positioning accuracy of the blades is greatly improved. The design of the open transparent mixing tank and the visual control program more intuitively reflect the mixing process in the tank, and also provide a platform for the application of the latest particle image velocimetry (PIV). The experimental and numerical simulation results show that the experimental device has high precision, which provides a reliable basis for the teaching of mixing performance and the development and optimization of new blades in the coating industry

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