本文選題：稠密氣固同軸射流 + 間壁效應(yīng)�。� 參考：《華東理工大學(xué)》2017年博士論文

【摘要】：本文以單噴嘴水冷壁式粉煤加壓氣化技術(shù)為研究背景,以解決同軸噴嘴因嚴(yán)重磨蝕而影響使用壽命及安全生產(chǎn)為研究目標(biāo),對(duì)稠密氣固兩相同軸射流中的顆粒流動(dòng)特性進(jìn)行了詳細(xì)而深入的研究。發(fā)現(xiàn)了同軸噴嘴端部的顆粒逆向卷吸現(xiàn)象是導(dǎo)致了噴嘴的磨蝕主要原因,并分析噴嘴間壁厚度對(duì)同軸射流遠(yuǎn)場顆粒彌散的影響。具體內(nèi)容歸納如下:1.利用高速攝像儀配合高倍變焦鏡頭,觀測了噴嘴端部的顆粒局部流動(dòng)特性。發(fā)現(xiàn)了由于噴嘴壁面厚度而產(chǎn)生間壁效應(yīng),引起了同軸氣體強(qiáng)烈的回流作用,從而誘導(dǎo)了顆粒逆向卷吸現(xiàn)象的出現(xiàn)并導(dǎo)致噴嘴的磨蝕。通過處理與分析實(shí)驗(yàn)圖像,揭示了顆粒逆向卷吸隨環(huán)隙氣速、間壁厚度、顆粒質(zhì)量流率和顆粒粒徑的變化規(guī)律。發(fā)現(xiàn)了顆粒逆向卷吸的臨界環(huán)隙氣速隨顆粒質(zhì)量流率的增加呈線性增加,得到了顆粒流卷吸長度和逆向彌散角的經(jīng)驗(yàn)關(guān)系式。此外,通過數(shù)值模擬計(jì)算獲得了間壁效應(yīng)中的回流氣體流場特性,并呈現(xiàn)了高氣速下被卷吸顆粒的流動(dòng)軌跡。根據(jù)氣固兩相流理論和修正曳力模型,建立了被卷吸顆粒的運(yùn)動(dòng)模型,得到了顆粒回流速度,為解決噴嘴磨蝕提供了理論分析。2.研究了間壁效應(yīng)對(duì)稠密氣固兩相同軸射流中顆粒彌散特性的影響。發(fā)現(xiàn)了間壁效應(yīng)會(huì)增加同軸環(huán)隙氣體射流的渦層厚度,顯著削弱對(duì)中心顆粒流的剪切作用,進(jìn)而抑制顆粒彌散。分析了噴嘴間壁厚度對(duì)顆粒波狀彌散中的擾動(dòng)波長、振幅和彌散角等特征量的影響。利用不穩(wěn)定性理論揭示了擾動(dòng)波長與修正渦層厚度呈線性關(guān)系,獲得了波動(dòng)振幅隨修正渦層厚度的變化規(guī)律。3.考察了稠密氣固兩相同軸交叉射流的顆粒流動(dòng)特性。發(fā)現(xiàn)了由于同軸交叉氣體射流的"擠壓"作用,射流近場的中心顆粒流發(fā)生收縮現(xiàn)象。通過觀測顆粒射流近場中的局部流動(dòng)特性,得到了顆粒流最小直徑和收縮長度都隨環(huán)隙氣速和交叉角的增加而減小。提出了顆粒流最小直徑和收縮長度與交叉角、環(huán)隙氣速和顆粒質(zhì)量流率之間的數(shù)學(xué)模型。引入交叉角因子來分析同軸交叉射流對(duì)顆粒射流彌散長度的影響,修正了交叉射流中的彌散長度關(guān)系式。揭示了顆粒射流彌散角與環(huán)隙氣速和交叉角呈非線性關(guān)系,提出了交叉角對(duì)顆粒彌散的影響是由徑向擠壓擾動(dòng)和軸向剪切不穩(wěn)定共同決定的。此外,還發(fā)現(xiàn)了同軸交叉射流中的間壁效應(yīng)誘導(dǎo)顆粒逆向卷吸現(xiàn)象更靠近噴嘴壁面,加劇了噴嘴的磨蝕,并利用交叉角因子修正了顆粒流卷吸長度。
[Abstract]:In this paper, the research background is single nozzle water-cooled wall type pulverized coal pressurized gasification technology. The purpose of this paper is to solve the problem of coaxial nozzle affecting service life and safety production because of serious abrasion. The particle flow characteristics in dense gas-solid two-phase coaxial jet are studied in detail. It is found that the reverse entrainment of the particles at the end of the coaxial nozzle is the main cause of the erosion of the nozzle, and the influence of the thickness of the wall between the nozzles on the dispersion of the particles in the far field of the coaxial jet is analyzed. The details are summarized as follows: 1. The local flow characteristics of particles at the nozzle end were observed by using high speed camera and high power zoom lens. It is found that the interwall effect is produced because of the wall thickness of the nozzle, which leads to the strong reflux of coaxial gas, which induces the appearance of particle reverse entrainment and leads to the erosion of the nozzle. By processing and analyzing the experimental images, the variation of particle entrainment with annular gas velocity, interwall thickness, particle mass flow rate and particle size was revealed. It is found that the critical annular gas velocity of particle reverse entrainment increases linearly with the increase of particle mass flow rate, and the empirical relationship between particle entrainment length and reverse dispersion angle is obtained. In addition, the characteristics of the reflux gas flow field in the interwall effect are obtained by numerical simulation, and the flow path of the entrained-particle at high gas velocity is presented. According to the theory of gas-solid two-phase flow and the modified drag force model, the motion model of entrained-particle is established, and the velocity of particle reflux is obtained, which provides theoretical analysis for solving the erosion of nozzle. The effect of interwall effect on particle dispersion in dense gas-solid two-phase coaxial jet was studied. It is found that the wall effect will increase the thickness of the vortex layer of the coaxial annular gas jet, weaken the shear effect on the central particle flow, and then restrain the particle dispersion. The influence of the thickness of the internozzle wall on the characteristic quantities such as the disturbance wavelength, amplitude and dispersion angle in the particle wave dispersion is analyzed. By using the instability theory, the linear relationship between the perturbation wavelength and the thickness of the modified vortex layer is revealed, and the variation of the amplitude of the wave with the thickness of the modified vortex layer is obtained. The particle flow characteristics of dense gas-solid two phase coaxial cross jet were investigated. It is found that the central particle flow in the near field of the coaxial cross gas jet shrinks due to its "squeezing" effect. By observing the local flow characteristics in the near field of particle jet, it is obtained that the minimum diameter and shrinkage length of particle flow decrease with the increase of annular gas velocity and cross angle. A mathematical model of the minimum diameter of particle flow, shrinkage length and cross angle, annular gas velocity and particle mass flow rate is presented. The cross angle factor is introduced to analyze the influence of coaxial cross jet on the dispersion length of particle jet, and the relation of dispersion length in cross jet is modified. The nonlinear relationship between particle jet dispersion angle and annular gas velocity and cross angle is revealed. The influence of cross angle on particle dispersion is determined by radial extrusion disturbance and axial shear instability. In addition, it is found that the interwall effect of coaxial cross jet induces the reverse entrainment of particles closer to the nozzle wall, which intensifies the erosion of the nozzle, and modifies the particle flow entrainment length by using the cross angle factor.
【學(xué)位授予單位】：華東理工大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：TQ541

【相似文獻(xiàn)】

相關(guān)期刊論文 前1條

1 ;百葉窗r干，

本文編號(hào)：1973577