Preparations And Properties In Pool Boiling Of Anticorrosion And Antifouling Coatings On Different Metal Substrates For Oilfield Geothermal Water

In the process of geothermal energy utilization in oil field,there are often corrosion and fouling issues for heat exchangers and pipe fittings.Especially foulling issue,which make heat transfer efficiency decrease and energy consumption increase,is a worldwide issue that has not been solved well.The micro-nano coating method is considered as a new technology with great potential for anticorrosion,antifouling and heat transfer enhancement.In this thesis,firstly,for different metal substrates,based on the existing research work,the preparations of micro-nano-coating for anticorrosion and antifouling of associated geothermal water in North China Oilfield were studied.The mechanisms of anticorrosion and antifouling were explored.Secondly,the pool boiling heat transfer and antifouling performances of the titanium-based coating on the vertical heating surface were investigated.The main research contents and results are as follows:For associated geothermal water in North China Oilfield,two kinds of samples coated with titanium dioxide and titanium dioxide-fluorosilane on stainless steel substrates were prepared using liquid deposition method.Together with uncoated stainless steel,the corrosion and fouling behaviors in simulated geothermal water of North China Oilfield were studied.The results show that,the surface of the SS-Ti O₂-FPS composite coating shows good anticorrosion and antifouling properties in simulated geothermal water due to its hydrophobicity.It is a relatively suitable material surface for the geothermal water of North China Oilfield.For the geothermal water of North China oil field,which contain a certain proportion of crude oil(Voil:Vwater=1:15,1:25,1:35,1:45 and 1:55),the crystalline fouling and oil pollution will compete to adhere to the surfaces of different samples,and the crystalline fouling depositing on the surfaces will increase the surface roughness,thus making the surfaces easier to further adhere to oil pollution and crystalline fouling.For the fouling and corrosion issues of copper heat exchanger during the process of geothermal energy utilization,The preparation process of copper-based superhydrophobic micro-nano coating was studied.the optimum preparation conditions obtained under the experimental conditions are as follows:the concentration of octadecanic acid in ethanol solution is 0.02 mol/L,the immersing temperature is 35?,and the immersing time is 120 h.The static contact angle of the superhydrophobic coating formed on the copper substrate can get to 157°,and the contact angle lag is about 4.2°.Ultrasonic aid can greatly shorten the etching time and improve the etching uniformity.Compared with the polished copper substrate,the copper-based superhydrophobic coating has better anticorrosion and antifouling properties.For the fouling issue of titanium heat exchanger in the process of geothermal energy utilization,the anodized preparation process of superhydrophobic coating on titanium substrate with Ti O₂nanotube porous array structure was studied.The optimum preparation process obtained under experimental conditions are as follows:0.14 mol/L Na F and 0.5 mol/L H₃PO₄mixture is as electrolyte,the voltage is 25 V,electrolysis temperature is 50°C.Anodic oxidation process is with ultrasonic assistance for 1h,then the surface is calcined at 500°C for 2 h,and finally modified with fluorosilane hydrophobic.The static contact angle of the final titanium-based superhydrophobic coating can get to 161.8°.The prepared micro-nano-coating has good anti-fouling property compared with the surface of bare titanium and the surface of titanium-based Ti O₂nanotube arrays surface without hydrophobic modification.The heat transfer and antifouling performances of the titanium-based superhydrophobic coating on vertical heating surface in pool boiling were studied using pool boiling device,and compared with the unhydrophobic-modified titanium-based superhydrophilic coating and bare titanium surface.The vertical heating surface is beneficial to eliminate the influence of particle gravity settlement on the experimental results.In low heat flux range,the pool boiling heat transfer performance of the titanium-based superhydrophobic coating is superior to the uncoated bare titanium surface and superhydrophilic Ti-Ti O₂nanotube array surface.The fouling thermal resistance of the prepared superhydrophobic Ti O₂nanotube array coating surface was significantly lower than that of bare titanium and superhydrophilic Ti-Ti O₂nanotube array surface,showing better antifouling property in pool boiling of Ca CO₃solution.For the system of pool core boiling heat transfer device with vertical heating surface,a heat transfer mechanism model for the generation,growth and detachment of individual bubbles on the vertical heating surface was established.And the mathematical model was solved and analyzed by the program written by MATLAB.The results show that Raising the input heat flux can improve the departure frequency of the bubbles,and the higher input heat flux has a higher heat transfer coefficient than the lower input heat flux.The simulation results are in good agreement with the experimental results.Compared with the experimental results of Duan,the results are in good agreement on the shape of the curve.The above research results have important guiding significance to realize the efficient and economical utilization of the associated geothermal energy in oil field,and also have certain reference value for other industries facing the same fouling problem.