本文選題：磁性粉末 + 噴嘴��； 參考：《福州大學(xué)》2014年博士論文

【摘要】：霧化法已經(jīng)發(fā)展成為生產(chǎn)粉末材料最重要的方法,但對該方法的研究大多仍停留在經(jīng)驗層次尚未形成一套完整的理論。本文采用計算流體力學(xué)方法,對具有代表性的十一種霧化器的霧化流場進(jìn)行數(shù)值模擬研究,并通過磁性粉末的制備進(jìn)行實驗驗證。本文比較了十一種霧化器的霧化能力；研究了Laval噴嘴結(jié)構(gòu)參數(shù)和工藝參數(shù)的優(yōu)化值；建立了霧化壓力P與冷卻速度V、冷卻時間t三者的定量關(guān)系式。得到以下研究成果：根據(jù)眾多噴嘴的內(nèi)在特點對其進(jìn)行分類,再采用離散相模型(DPM)計算出全部噴嘴的的壓力、速度和溫度場。在此基礎(chǔ)上,通過分析研究得出：在所研究的十一種噴嘴的范圍內(nèi),霧化機(jī)理可分為四類。其中,上噴霧化和水平霧化各為一類,其他類型則根據(jù)壓力云圖曲率的正負(fù)值分為兩類。通過進(jìn)一步分析各種流場以考察霧化過程的穩(wěn)定性和破碎效果；分析激波及速度大小以考察霧化器的破碎能力,結(jié)果表明Laval型噴嘴霧化能力最強(qiáng)。利用DPM模型對Laval型噴嘴結(jié)構(gòu)幾何參數(shù)進(jìn)行優(yōu)化。綜合考慮霧化過程的穩(wěn)定性、破碎效果及馬赫碟對霧化過程的影響,在指定磁粉作為金屬熔體條件下,研究結(jié)果表明,噴嘴的最佳結(jié)構(gòu)參數(shù)應(yīng)定為噴射夾角為45°,導(dǎo)流管直徑為6mm,導(dǎo)流管突出高度為6mm,開口形狀為弧凹形,氣體通路要求平滑,最佳間隙為0.2 mm。結(jié)構(gòu)參數(shù)對流場影響大小的次序依次是導(dǎo)流管突出高度間隙大小開口形狀噴射角氣體通路平滑度導(dǎo)流管直徑。經(jīng)過優(yōu)化的噴嘴在相同條件下,磁粉實驗產(chǎn)品的形貌較優(yōu)化前的D50有明顯地細(xì)化,D50達(dá)到14.5μm。利用DPM模型對Laval型噴嘴的霧化工藝參數(shù)進(jìn)行優(yōu)化。結(jié)果表明最佳工藝條件為：壓力在35-70atm間選擇,根據(jù)霧化介質(zhì)的不同,同時結(jié)合考慮流場突變的影響,即開渦-閉渦突變,選擇不同的數(shù)值；關(guān)于過熱度的影響,綜合考慮熔體氧化和數(shù)值分析的結(jié)果,建議控制在150-250K之間；氣體種類的影響結(jié)果表明,氦氣具有較突出的優(yōu)勢；熔體則應(yīng)盡可能選擇低熔點、低粘度的材料。工藝參數(shù)對流場影響大小的次序依次是霧化壓力過熱度氣體種類熔體性質(zhì)。針對上述的Laval霧化噴嘴,建立了霧化壓力P與冷卻速度V、冷卻時間t三者的定量關(guān)系式,分別為V=57.543P0.5194、V=1.28t-1和t=0.0222P-0.5194。結(jié)合其他公式,可直接對產(chǎn)品的粒度在理論上作出預(yù)測。本文還使用了更先進(jìn)的LES模型和VOF模型模擬霧化過程。VOF模型清楚地再現(xiàn)了霧化的破碎過程。在本模擬條件下,馬赫碟的位置隨著氣路間隙的縮小離噴嘴出口的距離呈現(xiàn)出先變遠(yuǎn)后近的規(guī)律。三種模型的模擬結(jié)果都沒發(fā)現(xiàn)二次破碎,這是由于速度衰減及熔體溫度下降導(dǎo)致需要更高的韋伯?dāng)?shù)。
[Abstract]:Atomization method has been developed as the most important method to produce powder materials, but most of the research on this method is still at the level of experience, which has not yet formed a complete theory. In this paper, the numerical simulation of atomization flow field of 11 typical nebulizers is carried out by means of computational fluid dynamics, and the experimental results are verified by the preparation of magnetic powder. In this paper, the atomization capability of 11 atomizers is compared, the optimum values of structure parameters and process parameters of Laval nozzles are studied, and the quantitative relationship between atomization pressure P and cooling rate V, cooling time t is established. The following results are obtained: according to the inherent characteristics of many nozzles, the pressure, velocity and temperature fields of all nozzles are calculated by using the discrete phase model (DPMM). On this basis, the atomization mechanism can be divided into four categories in the range of 11 kinds of nozzles studied. The upper spray and horizontal atomization are classified into two categories, the others are divided into two categories according to the positive and negative values of the curvature of the pressure cloud image. Through further analysis of various flow fields to investigate the stability and crushing effect of atomizing process and the shock wave and velocity to investigate the crushing ability of atomizer, the results show that the atomization ability of Laval nozzle is the strongest. The geometric parameters of Laval nozzle are optimized by DPM model. Considering the stability of atomization process, the effect of crushing and the influence of Mach disc on atomization process, the results show that the magnetic powder is selected as the melt of metal. The optimum structure parameters of the nozzle should be 45 擄angle, 6mm diameter, 6mm projecting height, arc concave shape, smooth gas path and 0.2 mm clearance. The order of the influence of the flow field on the structure parameters is in the order of the diameter of the smooth gas path of the nozzle with the opening of the gap between the projecting height of the tube and the opening of the jet angle. Under the same conditions, the morphology of the magnetic powder experimental product was obviously finer than that of D50 before optimization, and the D50 was up to 14.5 渭 m. The atomization process parameters of Laval nozzle were optimized by DPM model. The results show that the optimum process conditions are as follows: the pressure is selected between 35-70atm, according to the different atomization medium, and considering the effect of the sudden change of the flow field, that is, the open vortex and the closed vortex catastrophe, the different values are selected, and the influence of superheat degree is also discussed. Considering the results of melt oxidation and numerical analysis, it is suggested that it should be controlled between 150 and 250K, and the effect of gas types shows that helium has outstanding advantages, and the melt should choose materials with low melting point and low viscosity as far as possible. The order of the influence of process parameters on the flow field is the melt properties of atomized pressure superheat gas. In view of the above Laval atomization nozzle, the quantitative relationship between atomization pressure P and cooling rate V, cooling time t is established, which are V _ (57.543) P _ (0.5194) V _ (1.28) t ~ (-1) and t _ (0.0222) P _ (0.5194) respectively. Combined with other formulas, the particle size of the product can be directly predicted in theory. More advanced LES model and VOF model are used to simulate the atomization process. Under this simulation condition, the position of Mach disc changes first and then approaches with the decrease of the gap between the gas path and the nozzle outlet. The simulation results of the three models show no secondary breakage, which is due to the decrease of velocity and melt temperature, which leads to a higher Weber number.
【學(xué)位授予單位】：福州大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2014
【分類號】：TB44;TG14

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