本文選題：CFD + 閃急沸騰霧化��； 參考：《青島科技大學》2017年碩士論文

【摘要】：氣液噴射器作為一種具有高強度混合效果的流體裝置,近年來在化工、能源、環(huán)保等領(lǐng)域已有廣泛應(yīng)用,其性能好壞關(guān)鍵在于霧化過程中形成的液滴大小及分布情況。閃急沸騰霧化作為一種新型高效噴射霧化裝置,能夠獲得比傳統(tǒng)霧化裝置更加細小和均勻的液滴分布。目前雖然對閃急沸騰霧化的研究較多,但大多數(shù)集中在發(fā)動機的燃油特性的研究中,而在化工領(lǐng)域研究很少。而且由于影響閃急沸騰霧化特性的因素較多,閃急沸騰霧化流場結(jié)構(gòu)復(fù)雜,導(dǎo)致影響霧化特性因素的研究不夠系統(tǒng)全面。本課題主要從噴嘴結(jié)構(gòu)以及操作條件兩方面入手,以改善液體霧化為最終目的,采用計算流體動力學(CFD)模擬的方法,系統(tǒng)地研究噴射壓力、噴嘴結(jié)構(gòu)對噴嘴內(nèi)流型變化的影響規(guī)律,建立了新的流型判定模型;在此基礎(chǔ)上,進一步對噴嘴結(jié)構(gòu)和操作條件對閃急沸騰霧化特性的影響進行了分析,對傳統(tǒng)霧化與閃急沸騰霧化的不同霧化特性和機理進行了比較,獲得了如下結(jié)論:一、建立了利用CFD方法判斷噴嘴內(nèi)流型變化的數(shù)學模型,并利用文獻實驗數(shù)據(jù)對模型進行了驗證。并利用模型研究了噴射壓力、入口倒角半徑與噴嘴直徑的比r/d、噴嘴長度與噴嘴直徑的比L/d對噴嘴內(nèi)流型變化的影響,結(jié)論如下:(1)研究表明,噴射壓力越大,噴嘴內(nèi)更容易產(chǎn)生空穴區(qū)。r/d越大,越不容易產(chǎn)生空穴現(xiàn)象。對已經(jīng)形成柱塞流的噴嘴,通過增大L/d值可以使得噴嘴內(nèi)形成的柱塞流再次轉(zhuǎn)變?yōu)榫植靠昭鳌?2)得到平孔噴嘴內(nèi)流型變化與r/d和L/d之間的關(guān)系,建立了新的流型判斷模型并與目前平孔噴嘴內(nèi)流型判斷經(jīng)驗?zāi)Ｐ瓦M行比較,驗證了其準確性。本文所建立的模型有助于對已有的柱塞流經(jīng)驗判斷公式的修正。二、通過耦合氣泡噴嘴模型和液體蒸發(fā)模型,建立了噴射器閃急沸騰霧化的CFD模型,并對模型可靠性進行了驗證。并基于模型對影響閃急沸騰霧化特性的各因素進行了研究,結(jié)論如下:(1)采用汽化率表示液體過熱度,在其它工況條件一定的前提下,增大噴射液體的汽化率,可以使噴射液體在噴嘴出口處受到氣體的沖擊力增加,從而改善霧化質(zhì)量。(2)僅僅改變表面張力時,隨著液滴表面張力的減小,霧化形成的液滴SMD值減小,液滴分布范圍變小,分布更加均勻。(3)密度對液滴霧化特性的影響與表面張力相反,隨著液滴密度的增大,霧化形成的液滴SMD(索特平均直徑)值減小,分布更加均勻。(4)在本文模擬過程中,粘度在小于0.01 kg/(m·s)時,其變化對霧化特性的影響較小;當粘度大于0.01 kg/(m·s)時,粘度對液滴粒徑產(chǎn)生影響,粘度越大,SMD值越大。其影響效果與表面張力類似,均是對液滴的破碎起到了阻尼作用。三、對傳統(tǒng)霧化與閃急沸騰霧化的特性進行了對比分析。分別在閃急沸騰霧化與傳統(tǒng)霧化保持相同噴射量和相同噴射壓力的情況下,對閃急沸騰霧化與傳統(tǒng)霧化效果進行了比較,結(jié)果表明在相同條件下,閃急沸騰霧化形成的液滴平均粒徑更小,分布更均勻,顯示出閃急沸騰霧化較傳統(tǒng)霧化裝置相比更有優(yōu)勢。
[Abstract]:As a fluid device with high strength mixing effect, gas liquid ejector has been widely used in the fields of chemical, energy and environmental protection in recent years. The key of its performance is the size and distribution of droplets in the process of atomization. Flash boiling atomization can be used as a new type of high efficient spray atomizing device, which can be compared with traditional atomization. The device has more finer and even distribution of droplets. Although there are many researches on flash boiling, most of them are concentrated in the study of the fuel characteristics of the engine, but few in the chemical field. And because there are many factors affecting the atomization characteristics of flash boiling, the structure of the atomization flow field is complex, which leads to the effect of atomization. The study of sex factors is not systematic and comprehensive. This topic mainly starts with the two aspects of the nozzle structure and operating conditions, in order to improve the liquid atomization as the ultimate goal. The method of computational fluid dynamics (CFD) simulation is used to systematically study the effect of the jet pressure and the nozzle structure on the flow pattern in the nozzle, and a new flow pattern determination model is established. On this basis, the influence of the nozzle structure and operating conditions on the atomization characteristics of flash boiling is analyzed. The different atomization characteristics and mechanism of the traditional atomization and flash boiling atomization are compared. The following conclusions are obtained: first, a mathematical model is established to judge the change of inner flow pattern of the nozzle by CFD method, and the literature is used in the literature. The model was verified by the experimental data, and the effect of the injection pressure, the radius of the inlet angle and the diameter of the nozzle r/d, the effect of the nozzle length and the diameter of the nozzle on the change of the flow pattern in the nozzle were studied. The conclusions are as follows: (1) the study shows that the larger the injection pressure is, the greater the.R/d in the cavity area is produced in the nozzle, the less easily it is produced. Hole phenomenon. For the nozzle which has formed the plunger flow, the plunger flow formed in the nozzle can be changed to the local cavitation flow by increasing the L/d value. (2) the relationship between the change of the flow pattern of the nozzle and the r/d and the L/d is obtained. A new flow pattern judgment model is established and compared with the current model of the inner flow pattern judgement of the flat nozzle. The model established in this paper helps to correct the empirical formula of the existing plunger flow. Two, by coupling the bubble nozzle model and the liquid evaporation model, the CFD model of the ejector flash boiling atomization is established, and the reliability of the model is verified. The following factors are studied and the conclusions are as follows: (1) using the vaporization rate to express the liquid overheat, increasing the vaporization rate of the jet liquid under the condition of other conditions, can increase the impact force of the jet at the outlet of the nozzle, thus improving the mass of the atomization. (2) only when the surface tension is changed, the surface tension of the droplet is with the surface tension. The droplet SMD value decreases, the droplet distribution range becomes smaller and the distribution is more uniform. (3) the influence of density on the droplet atomization characteristics is opposite to the surface tension. With the increase of the droplet density, the droplet SMD (SOT mean diameter) decreases and the distribution is more uniform. (4) the viscosity of the droplet is less than 0.01 kg/ during the simulation process. When m. S), the change has little influence on the atomization characteristics; when the viscosity is greater than 0.01 kg/ (M. S), the viscosity has an effect on the droplet size, the greater the viscosity and the greater the SMD value. The effect is similar to the surface tension, and all of the droplets are damped. Three, the characteristics of the atomization and flash boiling are compared and analyzed. In the case of flash boiling atomization and traditional atomization keeping the same injection amount and the same injection pressure, the effect of flash boiling atomization and traditional atomization is compared. The results show that under the same conditions, the average particle size of the droplet formed by the flash boiling atomization is smaller and the distribution is more uniform, showing that the flash boiling atomization is more than the traditional atomization device. It's more advantageous than that.
【學位授予單位】：青島科技大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TQ027.32

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本文編號：1929510