New technology for automatic cleaning of dirt and fluid dynamic spiral in pipe

(1 Graduate School of Central South University, Changsha, Hunan 410078, China 2 Institute of Mechanical Cleaning, Hunan University of Technology, Zhuzhou 412008, China) The nozzle bearing block-rushing force wheel strengthens the cleaning dynamic torque of the rotating plastic spiral. The test results show that the effect of automatic cleaning of the dirt in the heat transfer tube is good; it can be industrially applied at a lower flow rate; the heat transfer enhancement range is 52 6% higher than the steel wire spiral; and the resistance of the equipment is not large.

Fund Project: Hunan Natural Science Foundation Project (02Y2070) 1975-), female, Dongyang, Zhejiang, graduate student of Central South University, associate professor of Hunan University of Technology, engaged in research on automatic cleaning of heat transfer equipment.

The spiral wire cleaning technology inside the heat transfer tube was first seen in the German invention patent of 1974. The external power drive is transmitted to the screw shaft of each heat transfer tube through the gear. The precision requirement is high and the reliability is low, as shown. Subsequently, the invention patent of the former Soviet Union in 1985, the transmission of power between the gear shaft and the spiral shaft through the flexible shaft, the reliability is higher than the former, and the cost is also increased, as shown. Domestic research on the reciprocating spiral driven by external power to achieve descaling11, the structure is too complicated, low reliability, and poor cleaning uniformity, difficult to accept for engineering.

France's French refining and general distribution company invented the spiral lateral vibration descaling technology 121 induced by fluid flow in the pipe. Domestic research has also been carried out. 131 Plastic spirals are axially fixed at the inlet end of the heat transfer tubes. There is a large gap between the outer diameter of the spiral and the inner wall of the tube, which can rotate freely. The fluid in the tube pushes the spin line to cause it to rotate. A certain elastic and flexible spiral continuously hits the inner wall of the pipe, and sweeps the dirt to achieve the purpose of automatic descaling and anti-scaling on-line. At the same time, due to the guiding action of the plastic spiral on the fluid in the tube, the axial flow in the near wall area is changed to a spiral flow, and the spiral of the rotation is disturbed to the residual boundary layer of the near wall, so that the convection heat transfer in the tube can be strengthen.

2 dirt cleaning ability Whether the cleaning ability of this self-rotating plastic spiral can meet the actual production needs, a simulation test of the automatic cleaning effect is carried out. Artificially simulated dirt is cement and lime mixed in a certain proportion. The inner diameter of the carbon steel pipe used for the test is 32mm and the length is 2 000mm; the diameter of the plastic spiral is 40mm, which is more than 10 times the cross-sectional area of ​​the 12mm diameter steel wire. The outer diameter of the spiral wire is 27mm and the pitch is 35mm and 40. After 133h continuous cleaning test, The carbon steel pipe was taken apart and cut longitudinally. The observation result was that the small piece of dirt in the heat transfer tube with the pitch of 35mm plastic spiral became smooth and the dirt was cleaned; the plastic spiral with a pitch of 40mm was cleaned at a faster speed than the former. Slightly slower. Since the artificial simulated dirt is much harder than the actual dirt, the three plastic spirals have a sufficiently strong automatic cleaning function.

3 The rotation torque of the plastic spiral is strengthened by replacing the steel spiral with a thick plastic spiral. As the axial force is significantly increased, the frictional resistance of the spiral rotation increases, and most of the heat transfer equipment The flow rate in the tube is low, and the self-rotation torque appears weak, which is often insufficient to overcome the resistance torque and rotate reliably.

To this end, it is necessary to study the reinforcement of the plastic spiral cleaning torque. The solution is to design the nozzle housing of the fixed plastic spiral as a pre-swirl structure, and install a power wheel at the head of the spiral. The structural principle is as shown. After passing through the pre-swirl bearing housing, the fluid is converted into a rapid swirling flow, which directly pushes the force wheel, so that the plastic spiral obtains a relatively large additional dynamic torque, which is superimposed with the rotation torque of the plastic spiral itself, and the total value of the dynamic torque. Significantly increased to enable reliable automatic cleaning at lower flow rates.

The test of torque strengthening is divided into two steps. Firstly, the test of the minimum flow rate of the spiral starting rotation and the carbon steel pipe of 38mmX3mmX2000mm pass the tap water. The scheme of not installing the pre-swirl bearing seat and the urging force wheel is of little value because of the self-rotating flow rate. The requirement is higher than m/s. Therefore, the pitch optimization test of the plastic spiral with the swirling bearing housing and the thrust driving force wheel scheme is carried out. The test results are shown in the graph. The plastic spiral has a screw diameter of 28 mm and a pitch of 40.

Starting from the relationship between the rotation speed and the pitch, on the basis of this, the torque characteristic curve test of the plastic spiral and the pre-swirl bearing-clamping force wheel is carried out. The test conditions are that the vertical stainless steel tube has a cooling water of 40 mm X 3 mm inside the tube. The test results are as shown. The rotation torque of the plastic spiral increases as the flow rate increases, and is approximately linear. Within the range of measurement, the average torque of the pre-swirl bearing-pushing force wheel is 2m, and the rotation torque of the plastic spiral is increased by 75%. Therefore, the additional torque of the pre-swirl bearing-pushing force wheel makes 2m 75% of the total dynamic torque of the long plastic spiral rotation. According to the relationship between the rotation torque of the plastic spiral and the flow rate, the pre-swirl bearing-crushing force wheel can make the flow rate requirement of the 2m, 4m long plastic spiral rotation. Reducing 43% and 27% respectively. Bearing-power wheel dynamic torque and plastic spiral dynamic torque 4 self-rotating plastic spiral heat transfer test Plastic spiral has the same heat transfer enhancement function as steel wire spiral, the difference is the cross-sectional diameter ratio of the spiral The wire spiral is much larger and the pitch is larger. To this end, it is necessary to retest the heat transfer enhancement function of the plastic spiral. The test measures the vertical diameter of the plastic spiral with a vertical stainless steel tube of 000 mm. The screw diameter of the plastic spiral is 28 mm, the pitch is 40 mm, and the water is cooled in the tube. The test results are shown. In the range of measurement, the heat transfer coefficient K value is increased by 52 6% on average before the installation of the plastic spiral. The heat transfer enhancement of the steel wire spiral is 3285%16 on average, and the reinforcement range is 60% higher than the latter. Plastic spiral The heat transfer enhancement characteristic curve 5 The resistance test The cross section of the plastic spiral is much larger than the steel wire spiral, and the resistance is too large, and the plastic spiral is subjected to a resistance test in the horizontal heat transfer tube. The test conditions are as follows: the inner diameter of the carbon steel pipe is 35 mm long and the diameter of the 2000 mm plastic spiral is 4 mm, the screw diameter is 28 mm, and the pitch is 29 3540 mm. The measured resistance curve is as shown.

It can be seen that the resistance of the plastic spiral decreases with the increase of the pitch, which is obvious and consistent with the conclusion of the torque optimization. Although the resistance is larger than the wire spiral, the resistance of the equipment is still within the general user's permission. Taking the flow rate of 08m/s as an example, the plastic spiral after the structural optimization has a screw diameter of 28mm and a pitch of 40mm per meter, and the resistance is 1625kPa. Therefore, even the 4-tube process with a length of 6m has a resistance of only 39kPa. 6 Conclusion Plastic spiral The structural optimization of the line is optimized from the point of low starting flow rate, large rotation torque, or from the viewpoint of reducing the resistance.

The automatic cleaning of the plastic spiral has a good effect and can meet the requirements of industrial applications.

The plastic spiral can be applied to the automatic cleaning in the lower flow heat transfer tube after the pre-swirl bearing block-crushing force wheel torque is strengthened.

The plastic spiral heat transfer enhancement range is 52 6%, which is 60% higher than the steel spiral. The equipment resistance of the plastic spiral is within the general user's permission.

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