【摘要】：在能源短缺與環(huán)境污染問(wèn)題日益突出的今天,如何提高能源利用率、減輕生產(chǎn)生活領(lǐng)域的污染成為關(guān)系到我國(guó)經(jīng)濟(jì)發(fā)展與人民生活水平的關(guān)鍵課題。在水泥、鋼鐵等高耗能行業(yè)中,工業(yè)余熱的高效利用方法具有重要的研究?jī)r(jià)值。將閃蒸引入高耗能行業(yè)余熱發(fā)電系統(tǒng)是進(jìn)一步提高工業(yè)余熱利用效率、減輕生產(chǎn)熱污染的有效手段。余熱利用程度與閃蒸方式、參數(shù)水平、閃蒸效率等因素密切相關(guān)。因此,對(duì)閃蒸機(jī)理與特性進(jìn)行分析與研究具有重要意義。本文圍繞在余熱回收領(lǐng)域有重要應(yīng)用價(jià)值的高參數(shù)水噴霧閃蒸過(guò)程展開(kāi)全面研究,進(jìn)行了有深度的理論分析與數(shù)值模擬,開(kāi)展了廣泛參數(shù)的實(shí)驗(yàn)研究,掌握了高參數(shù)水噴霧閃蒸過(guò)程的基本規(guī)律與特性。在此基礎(chǔ)上,從霧化噴嘴的角度提出了較好的優(yōu)化方案。首先,本文運(yùn)用歐拉-拉格朗日法思想,建立噴霧閃蒸數(shù)學(xué)模型。在歐拉坐標(biāo)系下求解蒸汽的流動(dòng)與傳熱特性,在拉格朗日坐標(biāo)系下求解噴霧液滴的運(yùn)動(dòng)與閃蒸。其中,液滴閃蒸過(guò)程因其機(jī)理特殊性而無(wú)法使用常規(guī)蒸發(fā)模型預(yù)測(cè)。本文從閃蒸蒸發(fā)機(jī)理特殊性出發(fā),建立新的過(guò)熱液滴閃蒸數(shù)學(xué)模型,描述閃蒸過(guò)程中液滴質(zhì)量、直徑與溫度的變化規(guī)律。采用數(shù)值方法求解噴霧閃蒸數(shù)學(xué)模型,編寫用戶自定義函數(shù),對(duì)CFD軟件進(jìn)行二次開(kāi)發(fā),實(shí)現(xiàn)了噴霧閃蒸過(guò)程全尺寸三維數(shù)值模擬。通過(guò)計(jì)算得出閃蒸罐內(nèi)部噴霧場(chǎng)與流場(chǎng)的發(fā)展過(guò)程及穩(wěn)態(tài)特性。結(jié)果表明,噴霧在發(fā)展初期具有較高過(guò)熱度,蒸發(fā)劇烈,引發(fā)噴嘴出口附近蒸汽高速流動(dòng),液滴溫度和直徑隨蒸發(fā)而迅速減小。隨著噴霧的繼續(xù)發(fā)展,蒸發(fā)劇烈程度明顯減緩,同時(shí)液滴初始動(dòng)量影響力減弱,噴霧徑向擴(kuò)展趨勢(shì)減小。噴霧場(chǎng)與流場(chǎng)共同發(fā)展至穩(wěn)定狀態(tài)后,中心軸線附近液滴速度較高,噴霧外緣液滴速度較低。蒸汽流場(chǎng)出現(xiàn)對(duì)稱的大尺度旋渦。對(duì)噴霧閃蒸特性進(jìn)行參數(shù)敏感性分析,探究噴霧錐角、液滴粒徑大小、噴射方向、初始速度和閃蒸壓力對(duì)閃蒸特性的影響。結(jié)果表明,噴霧錐角的增大可以提高噴霧的覆蓋程度,并使閃蒸進(jìn)行的充分程度稍有提高。液滴粒徑的減小雖使噴霧寬度降低,但顯著提高閃蒸速度,噴嘴出口附近蒸汽流速也顯著增加。流體向上噴射時(shí)無(wú)法充分利用閃蒸罐內(nèi)部空間,且存在蒸發(fā)不完全和蒸汽帶水的可能性,在實(shí)際應(yīng)用中并不推薦。噴霧初始速度的減小能夠延長(zhǎng)液滴在閃蒸罐內(nèi)停留時(shí)間,使閃蒸進(jìn)行的更加充分。閃蒸壓力的提高意味著流體過(guò)熱度的減小,閃蒸強(qiáng)度明顯降低,噴霧寬度也因曳力的增大而降低。在均勻噴霧閃蒸過(guò)程數(shù)值研究基礎(chǔ)上,建立了非均勻噴霧閃蒸模型,對(duì)液滴尺寸分布符合Rosin-Rammler函數(shù)的噴霧閃蒸過(guò)程進(jìn)行求解。發(fā)現(xiàn)粒徑較小的液滴群集中分布于軸線附近,粒徑較大的液滴群徑向覆蓋范圍較廣。噴霧溫度在軸向上呈現(xiàn)頂部高、底部低的特點(diǎn),在徑向上呈現(xiàn)中心低、外緣高的特點(diǎn)。噴霧液滴速度變化幅度大于均勻噴霧,粒徑較小的液滴群速度變化較大。噴嘴出口附近蒸汽流速與湍流強(qiáng)度顯著提高。蒸汽流場(chǎng)出現(xiàn)了尺度不同、方向相反的雙旋渦�；谝怨I(yè)余熱為熱源的大型噴霧閃蒸實(shí)驗(yàn)臺(tái),開(kāi)展噴霧閃蒸實(shí)驗(yàn)研究。鑒于目前閃蒸實(shí)驗(yàn)參數(shù)普遍較低的現(xiàn)狀,在實(shí)驗(yàn)中提高參數(shù)水平,將初始水溫提高至100℃以上,將過(guò)熱度范圍擴(kuò)大至30～46℃,將閃蒸罐運(yùn)行壓力保持為正壓,拓展了閃蒸的實(shí)驗(yàn)研究范圍。實(shí)驗(yàn)結(jié)果表明,閃蒸蒸發(fā)量隨初始溫度的提高而增大,隨閃蒸壓力的提高而減小。流體噴射方向向下時(shí)蒸發(fā)量更高,蒸汽帶水更少。噴嘴尺寸對(duì)閃蒸的影響體現(xiàn)在霧化效果與液體停留時(shí)間兩個(gè)相反的方面,需根據(jù)閃蒸空間大小與噴嘴特性選擇合適的噴嘴。過(guò)熱度是閃蒸的驅(qū)動(dòng)力,經(jīng)擬合得出過(guò)熱度與閃蒸效率的經(jīng)驗(yàn)公式。提出以無(wú)量綱的Jakob數(shù)作為閃蒸過(guò)程的特征數(shù),分析不同實(shí)驗(yàn)條件下Jakob數(shù)與閃蒸效率的關(guān)系,對(duì)實(shí)驗(yàn)數(shù)據(jù)進(jìn)行無(wú)量綱化多元回歸分析,提出Jakob數(shù)、無(wú)量綱壓力與閃蒸效率的經(jīng)驗(yàn)公式。在對(duì)噴霧閃蒸進(jìn)行全面分析的基礎(chǔ)上,考慮到噴嘴內(nèi)部發(fā)生相變的可能性及其對(duì)噴霧特性和噴霧閃蒸的影響,進(jìn)一步將噴嘴內(nèi)部納入研究范圍。將多相流模型與降壓相變模型相結(jié)合,對(duì)實(shí)驗(yàn)用含雙S形葉片的噴嘴內(nèi)部流動(dòng)與閃蒸進(jìn)行數(shù)值模擬。在此基礎(chǔ)上提出一種改進(jìn)的噴嘴結(jié)構(gòu),增設(shè)一組S形葉片,并將葉片兩端與噴嘴內(nèi)壁的幾何關(guān)系由相切改為垂直。分析表明,改進(jìn)的結(jié)構(gòu)在促進(jìn)閃蒸、減輕積垢與增大通流能力方面具備優(yōu)勢(shì)。
[Abstract]:With the increasingly prominent energy shortage and environmental pollution, how to improve the utilization of energy and to reduce the pollution in the field of production life has become a key subject of the economic development and people's living standard in our country. In the high energy consumption industry, such as cement, steel, etc., the efficient utilization method of industrial waste heat has important research value. The high-energy-consumption industry waste heat power generation system is introduced into the high-energy-consumption industry, so that the utilization efficiency of the industrial waste heat can be further improved, and the effective means for reducing the production heat pollution are reduced. The degree of waste heat utilization is closely related to the factors such as flash evaporation method, parameter level and flash efficiency. Therefore, it is of great significance to analyze and study the flash mechanism and characteristics. In this paper, a comprehensive study on the high-parameter water spray flash process with important application value in the field of waste heat recovery is carried out. The theoretical analysis and numerical simulation are carried out, and the experimental research on the wide parameters is carried out. The basic law and characteristics of the high-parameter water spray flash evaporation process are mastered. On this basis, a better optimization scheme is put forward from the angle of the atomizing nozzle. First, this paper uses the Euler-Lagrange method to set up a mathematical model of spray flash evaporation. The flow and heat transfer characteristics of the steam are solved in the Euler coordinate system, and the motion and the flash of the spray droplets are solved in the Lagrange coordinate system. in which the liquid drop flash process cannot be predicted using a conventional evaporation model due to its particularity. In this paper, a new mathematical model of the flash evaporation is set up from the particularity of the evaporation mechanism of the flash evaporation, and the change of the quality, diameter and temperature of the liquid drops in the flash evaporation process is described. The numerical method is used to solve the mathematical model of spray flash evaporation, and the user-defined function is written, and the second development of the CFD software is carried out to realize the full-size three-dimensional numerical simulation of the spray flash process. The development process and the steady-state characteristic of the spray field and the flow field inside the flash tank are obtained by calculation. The results show that the spray has a high degree of superheat in the early stage of development, the evaporation is violent, the high-speed flow of the steam near the outlet of the nozzle is induced, and the temperature and the diameter of the liquid drop rapidly decrease with the evaporation. With the continued development of the spray, the degree of evaporation is obviously reduced, and the initial momentum influence of the droplets is reduced, and the spray radial expansion tendency is reduced. When the spray field and the flow field are developed to a stable state, the velocity of the liquid drops near the central axis is higher, and the droplet velocity of the outer edge of the spray is lower. The steam flow field has a symmetric large-scale vortex. The effects of spray cone angle, droplet size, spray direction, initial velocity and flash pressure on the flash characteristics were investigated. The results show that the increase of the spray cone angle can improve the coverage of the spray, and the full extent of the flash evaporation can be improved slightly. Although the size of the droplets is reduced, the spray width is reduced, but the flash speed is significantly increased and the steam flow rate in the vicinity of the nozzle outlet is also significantly increased. when the fluid is injected upward, the inner space of the flash tank cannot be fully utilized, and the possibility of incomplete evaporation and water of the steam is present, and is not recommended in practical application. the reduction in the initial velocity of the spray can extend the residence time of the droplets in the flash tank to make the flash more sufficient. the increase of the flash pressure means a reduction in the degree of superheat of the fluid, a significant reduction in the flash strength, and a reduction in the spray width as a result of the increase in the drag force. On the basis of the numerical study of the uniform spray flash process, a non-uniform spray flash model was established to solve the spray flash process of the Roin-Rammler function. It is found that the droplet group with small particle size is distributed in the vicinity of the axis, and the larger diameter of the droplet group has a wide radial coverage. the spray temperature has the characteristics of high top and low bottom in the axial direction, and has the characteristics of low center and high outer edge in the radial direction. and the change of the velocity of the spray liquid drop is larger than that of the uniform spray, and the change of the droplet group speed with small particle diameter is relatively large. the velocity of the steam near the outlet of the nozzle and the turbulence intensity are obviously improved. The steam flow field has a two-vortex with different dimensions and opposite directions. The experiment of spray flash evaporation is carried out on the basis of a large-scale spray flash experiment table based on industrial waste heat as a heat source. In view of the fact that the current flashing experiment parameters are generally low, the parameter level is raised in the experiment, the initial water temperature is raised to above 100 DEG C, the degree of superheat is increased to 30 to 46 DEG C, the operating pressure of the flash tank is kept to a positive pressure, and the experimental research range of the flash evaporation is expanded. The experimental results show that the flash evaporation increases with the increase of the initial temperature and decreases with the increase of the flash pressure. the evaporation capacity is higher when the direction of the fluid injection is downward, and the steam is less in water. The effect of the size of the nozzle on the flash is reflected in the two opposite aspects of the atomization effect and the liquid residence time, and a suitable nozzle is selected according to the flash space size and the nozzle characteristics. The superheat degree is the driving force of the flash evaporation, and the empirical formula of the degree of superheat and the flash efficiency is obtained by fitting. The relationship between the number of Jakob and the flash efficiency under different experimental conditions is analyzed, and the empirical formula of the number of Jakob, the dimensionless pressure and the flash efficiency is presented. On the basis of a comprehensive analysis of the spray flash, the possibility of the phase change inside the nozzle and its influence on the spray characteristics and the spray flash evaporation are taken into account, and the inside of the nozzle is further included in the scope of the study. The multi-phase flow model is combined with the step-down phase-change model, and the internal flow and the flash of the nozzle with the double S-shaped blade are numerically simulated. On this basis, an improved nozzle structure is proposed, a set of S-shaped blades is added, and the geometric relation between the two ends of the blade and the inner wall of the nozzle is changed to be vertical. The analysis shows that the improved structure has the advantages in promoting the flash evaporation, reducing the scale and increasing the flow capacity.
【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：TK124;TK115

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