本文選題：多相流 + 懸浮液等離子體噴涂　； 參考：《浙江大學》2016年博士論文

【摘要】：等離子體噴涂是一項重要而復雜的表面處理技術,利用該技術可以生產(chǎn)出高質量的納米結構涂層。等離子體噴涂以微納米粉體作為噴涂材料,以等離子體射流作為加速和熔化粉體的氣體介質。等離子體噴涂過程涉及到許多復雜現(xiàn)象,比如,等離子體射流的產(chǎn)生,顆粒的入射,等離子體流場和顆粒之間質量、動量和熱量的傳遞等。等離子體噴涂的理論研究遠遠落后于該技術的發(fā)展,本文旨在研究微納米顆粒在等離子體湍射流中的動力學和熱力學行為以及流場與顆粒之間的輸運現(xiàn)象;從機理上分析噴涂過程中的各種現(xiàn)象,研究影響噴涂過程的參數(shù)以期對噴涂過程進行優(yōu)化。本文采用歐拉法和拉格朗日法相結合的理論,建立了高溫等離體子射流中微納米顆粒的受力、傳熱和相變的三維計算機模型。首先采用歐拉法求解流場,將等離子體湍射流場假設為多組分、可壓縮、存在化學反應的理想氣體,并用顯式格式求解流場的瞬態(tài)過程。將計算得到的射流場溫度與實驗進行了對比,結果表明兩者吻合良好,誤差在10%以內。在已知流場信息和顆粒初始條件的情況下,采用基于拉格朗日描述的顆粒軌道法追蹤不同顆粒的運動,用一維球形熱傳導模型求解液滴表面的對流傳熱、溶劑的蒸發(fā)和微米顆粒內部的熱傳導,采用微納米顆粒多相流模型模擬多個微納米粒子的受力、運動、霧化和碰撞等過程。利用該三維數(shù)值模型,論文深入研究了單顆粒及多顆粒的動力學行為。首先對等離子體噴涂中的懸浮微納米顆粒進行了詳細的受力分析,比較了單個顆粒主要受到的拖曳力、Saffman力和布朗力的量級,并通過分析Stokes數(shù),驗證了當前流場參數(shù)下顆粒繞過基板邊界層的臨界粒徑。其次,考慮了多顆粒之間的碰撞以及顆粒與流場之間的雙向耦合,定量分析了顆粒入射對流場速度和溫度的影響,比較了微米顆粒群與納米顆粒群之間不同的運動和分布特點,研究了湍流擴散對多顆粒分布的影響。論文對不同工況的噴涂過程進行了參數(shù)化研究。重點分析了輸入功率和氣體組分對流場以及顆粒參數(shù)的影響,研究了噴涂距離和基板尺寸對顆粒沉積效率的影響,比較了霧化入射和粉體入射兩種入射方式對顆粒傳熱過程的影響,研究了入射位置、入射角度、液滴和聚合物尺寸對多顆粒釋放百分數(shù)的影響。確定了有利于等離子體噴涂的工況參數(shù)。本文通過計算觀察到了實驗無法觀測到的單顆粒和多顆粒的運動過程,全面的參數(shù)分析對噴涂過程有重要的理論指導意義。
[Abstract]:Plasma spraying is an important and complex surface treatment technology, which can be used to produce high quality nanostructured coatings. Plasma spray is made of micro and nano powder and plasma jet is the gas medium for accelerating and melting the powder. The plasma spray process involves many complicated phenomena, such as the generation of plasma jet, the incidence of particles, the mass of plasma flow field and particles, the transfer of momentum and heat, etc. The theoretical study of plasma spraying is far behind the development of this technology. The purpose of this paper is to study the kinetic and thermodynamic behavior of microparticles in the plasma turbulent jet and the transport between the flow field and particles. In order to optimize the spraying process, this paper analyzes the various phenomena in the process of spraying and studies the parameters that affect the process of spraying. Based on the theory of Euler method and Lagrangian method, a three-dimensional computer model of the force, heat transfer and phase transition of micro and nanocrystalline particles in high temperature isobaric jet has been established in this paper. The flow field is solved by Euler method. The plasma turbulent jet field is assumed to be a multicomponent compressible ideal gas with chemical reaction and the explicit scheme is used to solve the transient process of the flow field. The calculated temperature of the jet field is compared with the experimental results, the results show that the two agree well, and the error is less than 10%. In the case of known flow field information and particle initial conditions, the particle orbit method based on Lagrangian description is used to track the motion of different particles, and the one-dimensional spherical heat conduction model is used to solve the convection heat transfer on the liquid drop surface. The evaporation of solvent and the heat conduction in micron particles were used to simulate the force motion atomization and collision of multiple microparticles by using the multiphase flow model of micro- and nanocrystalline particles. Using the three-dimensional numerical model, the dynamic behavior of single particle and multi-particle is studied in depth. Firstly, the force of suspended microparticles in plasma spraying is analyzed in detail, and the order of magnitude of Saffman force and Brownian force is compared, and Stokes number is analyzed. The critical particle size of particles bypassing the boundary layer of the substrate is verified under the current flow field parameters. Secondly, considering the collision between particles and the bidirectional coupling between particles and flow field, the effects of velocity and temperature of particle incident flow field are quantitatively analyzed, and the different motion and distribution characteristics between micron particle group and nano-particle group are compared. The effect of turbulent diffusion on the distribution of multi-particles was studied. The parameterization of spray process under different working conditions was studied in this paper. The effects of input power, gas component flow field and particle parameters on the particle deposition efficiency are analyzed. The effects of spray distance and substrate size on particle deposition efficiency are studied. The effects of atomization incidence and powder incidence on the heat transfer process of particles were compared. The effects of incident position, incident angle, droplet size and polymer size on the percentage of multi-particle release were studied. The working conditions of plasma spraying were determined. In this paper, the motion processes of single or multiple particles which can not be observed in experiments are observed by calculation. The comprehensive analysis of parameters is of great theoretical significance to the spray process.
【學位授予單位】：浙江大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：O53;O358

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