| With the development of Western China,more and more tunnels are built in the mountains.When the tunnel passes through limestone and karst areas,calcium carbonate crystals are easily formed on the wall of the drainage pipe of the tunnel.As time goes by,the accumulation of calcium carbonate crystals will eventually block the pipe,seriously affect the service life of the tunnel structure,cause various traffic safety accidents,and cause huge human and financial resources loss.Therefore,in view of the problem that the tunnel drainage pipe in this area is easy to be blocked by crystallization,through the analysis of the crystallization mechanism of the crystal,combined with the idea of the electric field treatment of scale in the industry,three kinds of electric field anti crystallization test devices are designed:steel plastic composite pipe alternating electric field,common PVC pipe alternating electric field and steel plastic composite pipe circumferential alternating electric field.The scale removal effect of the three devices is analyzed after determining the best electric field device,the flow test and the application of the device to the 1:10 tunnel model and field test are carried out for more in-depth experimental analysis,and then the adsorption energy between the carbonate crystal and the PVC polymer of the drainage pipe is studied by combining the molecular dynamics simulation software,so as to finally solve the problem of crystal plugging of the tunnel drainage pipe in limestone and karst areas question.The main results are as follow:(1)Ca2+ and CO32-in calcium carbonate solution move toward the positive and negative poles of the electric field respectively under the action of alternating electric field,separating the calcium carbonate crystal.The polarity of water solution will also be enhanced under the action of electric field,and strong polar water molecules will wrap the anions and cations,so that the anions and cations will not contact the wall directly.When the positive and negative electrodes of electric field change,the anions and cations in the solution will move backwards.Because Ca2+ and CO32-are enclosed by polar water molecules,new CaCO3 crystals will also be enclosed by polar water molecules and suspended in the solution after the collision.In liquid to avoid direct contact with the pipe wall and eventually flush out of the pipe with water;(2)Comparing the three kinds of electric field effect devices with the ordinary tube,we can know that the amount of crystallization inside the pipe after the electric field treatment is significantly less than that of the ordinary tube,and the treatment effect is different due to the different voltage intensity.Among them,when the voltage is 6V,the electric field of steel-plastic composite tube has the best anti-crystallization effect,and the anti-scaling rate is 25%.The SEM scanning of this test is also intuitive.It can be seen that the size of the crystal is smaller,the form of cohesion is looser,and the crystal is easier to break and peel off to drain the pipe after the treatment of the electric field;(3)Different flow rates found in the tests of three voltage and three flow rates after determining the best electric field effect device will lead to different cross sections of the solution through the electric field line and different number of ions affected.Even if the cross section of the electric field line is large each time when the flow rate is large,the more CaCO3 crystals in the solution adhere to the wall,but the more ions affected by the electric field the larger the amount,the more CaCO3 crystals suspended in the solution and more readily discharged with the water flow.From the analysis of the test results,it can be seen that when using 6V steel-plastic composite pipe alternating electric field at high flow rate of 192ml/s or 76.9ml/s,the crystallization amount of the inner wall of the pipeline is the least;when using 12V steel-plastic composite pipe alternating electric field at low flow rate of 34.7ml/s,the crystallization amount of the inner wall of the pipeline is the least;(4)The 1:10 tunnel model and field test can also verify the scientificity of the indoor test process.The lower flow rate in the tunnel model belongs to the low flow rate test of the flow test model.From the test results,the scale inhibition rate at 6V voltage is 12%,at 9V voltage is 16%,and at 12V voltage is 31%.Therefore,it can be concluded that 12V voltage has the best anti-scaling effect under low flow conditions,while field test can fully show that it is not easy to have residual crystals in the pipeline under high flow conditions and that the crystal morphology and structure type in calcium carbonate solution can be changed under the action of electric field;(5)The results of molecular dynamics simulation show that the adsorption energy between CaCO3 crystal and PVC tube wall decreases significantly after the effect of adding alternating electric field.The minimum adsorption energy is when the electric field strength is 100V/m,which indicates that this electric field intensity has the best descaling effect without considering the effect of flow water. |
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