橫向風(fēng)條件下射流擴散火焰形態(tài)與燃燒特性研究
發(fā)布時間：2018-08-31 11:36
【摘要】：外界流場作用下射流火的動力學(xué)行為特征,一直是燃燒學(xué)及火災(zāi)學(xué)基礎(chǔ)研究的重要對象�？諝饬鲃语L(fēng)場會對射流擴散火焰形態(tài)、燃燒特征等產(chǎn)生重要影響,其研究結(jié)果對于提高工業(yè)鍋爐的燃燒效率、減少油田或化工廠廢氣燃燒污染物的排放、降低早期火災(zāi)探測的誤報與漏報率等有重要意義。本文首先從唯象學(xué)角度,針對橫向風(fēng)條件下射流火,綜合考慮浮力、剪切力、慣性力對湍流射流擴散火焰的耦合作用,建立橫向和垂直方向的動量方程并求解得到火焰傾角公式,進一步利用火焰理查德森數(shù)對公式進行簡化,建立了包含浮力-過渡-動量三種不同主控模式的全局火焰傾角模型。其次,自主研制了小尺寸風(fēng)洞平臺,以丙烷為燃料,針對橫向風(fēng)條件下3mm(動量主控)與8mm(浮力主控-過渡)兩種不同噴嘴直徑的射流擴散火焰形態(tài)與燃燒特性,開展了實驗研究。燃料射流出口雷諾數(shù)(Re)310～3305,弗洛德數(shù)(Fr)0.351～756,風(fēng)速范圍0.5～4.0m/s,射流-橫向風(fēng)動量通量比(RM)0.077～13.188,熱釋放速率范圍0.698～2.790kW。實驗利用圖像分析確定火焰長度、傾角等形態(tài)參量,基于比色測溫法反演計算火焰溫度及碳黑體積分數(shù)分布,利用可見火焰度與化學(xué)當量比火焰長度的關(guān)系確定火焰煙點狀態(tài)。研究結(jié)果表明,隨著RM值逐漸增大,火焰依次呈現(xiàn)三種典型形態(tài)。當RM值較小時,火焰主要存在于噴嘴出口平面以下,且集中于噴嘴背風(fēng)側(cè)的負壓區(qū),稱為下洗現(xiàn)象;隨著RM值的增大,火焰呈現(xiàn)出三區(qū)域結(jié)構(gòu),第一個區(qū)域指下洗區(qū)域,第三個區(qū)域指對稱分布的狹長、亮黃色火焰。這兩個區(qū)域中間的連接區(qū)為第二個區(qū)域;RM值繼續(xù)增大,下洗區(qū)域逐漸減小并消失,呈現(xiàn)兩區(qū)域結(jié)構(gòu)�；鹧骈L度隨著橫向風(fēng)速的增大或者RM值的減小,先稍微增大后減小。無量綱火焰長度與射流Fr的關(guān)系為LF =18.8Fr0.239�；诒疚闹械膶嶒灲Y(jié)果,給出了火焰長度轉(zhuǎn)捩點的臨界風(fēng)速與RM值。對于給定噴嘴直徑,臨界RM值趨向于定值。根據(jù)火焰傾角實驗結(jié)果及理論分析,基于RM與Fr,提出了三種不同的傾角主控模式,確定了全局火焰傾角理論公式的適用范圍:橫向風(fēng)/浮力主控模式(RM0.01,Fr＜0.1),過渡模式(0.01RM10,0.1Fr103),和射流/動量主控模式(RM10,103Fr105)�；鹧鏈囟群吞己隗w積分數(shù)總體隨著橫向風(fēng)速的增大或者RM值的減小逐漸降低�；鹧孑椛浞謹�(shù)隨橫向風(fēng)速的增大,8mm直徑工況先稍微增大后降低;3 mm直徑工況則是逐漸減小。最后,給出了橫向風(fēng)條件下,火焰達到煙點狀態(tài)的臨界風(fēng)速與RM值。隨著燃料流量的增大(射流Fr增大),臨界風(fēng)速與RM值都有增大的趨勢。臨界RM值與射流Fr.的關(guān)系為RM=0.170Fr0 345。煙點火焰長度與Fr的關(guān)系為LFsp=13.8Fr0.279。煙點條件下,8mm直徑工況火焰為典型的三區(qū)域結(jié)構(gòu),而3mm工況火焰為典型的兩區(qū)域結(jié)構(gòu)。在實驗范圍內(nèi),當燃料流量大于某臨界值后,無量綱火焰長度的煙點值與最大值之比趨于定值,且3 mm直徑比值大于8 mm直徑。煙點火焰輻射分數(shù)隨著燃料流量的增大(射流Fr增大),8 mm直徑逐漸上升,而3mm先升后降;并且8mm工況遠大于3mm。兩種噴嘴直徑之所以出現(xiàn)不同的趨勢,主要是因為不同RM值造成了不同的火焰流場和火焰碳黑運動軌跡。煙點火焰輻射分數(shù)與無量綱火焰長度之比與RM值的擬合結(jié)果為8 mm工況:XR,sp/LFsp=0.047RM-5.56×10-4,3mm 工況:XR,sp/LF,sp=—3.034RM+5.42×10-4。
[Abstract]:The dynamic behavior of jet fire under the action of external flow field has always been an important object in the basic research of combustion and fire science.The air flow wind field has an important influence on the shape and combustion characteristics of jet diffusion flame.The results of the study can improve the combustion efficiency of industrial boilers and reduce the pollutants in the combustion of waste gases from oilfields or chemical plants. It is very important to reduce the false alarm and missed alarm rate of early fire detection. Firstly, from the phenomenological point of view, considering the coupling effect of buoyancy, shear force and inertia force on turbulent jet diffusion flame, the momentum equations in transverse and vertical directions are established and the flame inclination formula is solved. Then, a small-scale wind tunnel platform with propane as fuel was developed independently, aiming at the two different nozzle diameters of 3mm (momentum control) and 8mm (buoyancy control-transition) under lateral wind conditions. Reynolds number (Re) 310 ~ 3305, Froude number (Fr) 0.351 ~ 756, wind speed range 0.5 ~ 4.0 m/s, jet-transverse wind momentum flux ratio (RM) 0.077 ~ 13.188, heat release rate range 0.698 ~ 2.790 kW. The flame length and inclination isomorphism were determined by image analysis. The flame temperature and the volume fraction of carbon black were calculated based on the colorimetric method. The smoke state was determined by the relationship between the visible flame and the chemical equivalent flame length. With the increase of RM value, the flame presents a three-zone structure, the first zone refers to the downwash zone, and the third zone refers to the symmetrically distributed narrow, bright yellow flame. The relationship between dimensionless flame length and jet Fr is LF=18.8Fr 0.239. Based on the experimental results, the critical wind speed and RM value at the transition point of flame length are given. According to the experimental results and theoretical analysis of flame dip angle, three different main control modes of flame dip angle are proposed based on RM and Fr, and the applicable ranges of the theoretical formulas of global flame dip angle are determined: transverse wind/buoyancy control mode (RM0.01, Fr < 0.1), transition mode (0.01RM10, 0.1Fr103), and jet/momentum control mode (RM10, 103Fr105). (3) Flame temperature and carbon black volume fraction decrease gradually with the increase of transverse wind speed or the decrease of RM value. Flame radiation fraction increases slightly at first and then decreases with the increase of transverse wind speed. At last, the critical wind speed and RM of flame reaching smoke point under transverse wind condition are given. The relationship between the critical RM value and the jet Fr. is RM = 0.170Fr 0 345. The relationship between the flame length and Fr is LFsp = 13.8Fr 0.279. Under the smoke point condition, the flame with 8mm diameter is a typical three-zone structure, while the flame with 3mm diameter is a typical two-zone structure. In the experimental range, when the fuel flow rate is greater than a certain critical value, the ratio of smoke point value to maximum value of dimensionless flame length tends to be fixed, and the ratio of 3 mm diameter is greater than 8 mm diameter. The main reason why the two nozzles have different diameters is that different RM values result in different flame flow field and flame carbon black trajectory. Fou
【學(xué)位授予單位】：中國科學(xué)技術(shù)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：TK16;X932
本文編號：2214866
[Abstract]:The dynamic behavior of jet fire under the action of external flow field has always been an important object in the basic research of combustion and fire science.The air flow wind field has an important influence on the shape and combustion characteristics of jet diffusion flame.The results of the study can improve the combustion efficiency of industrial boilers and reduce the pollutants in the combustion of waste gases from oilfields or chemical plants. It is very important to reduce the false alarm and missed alarm rate of early fire detection. Firstly, from the phenomenological point of view, considering the coupling effect of buoyancy, shear force and inertia force on turbulent jet diffusion flame, the momentum equations in transverse and vertical directions are established and the flame inclination formula is solved. Then, a small-scale wind tunnel platform with propane as fuel was developed independently, aiming at the two different nozzle diameters of 3mm (momentum control) and 8mm (buoyancy control-transition) under lateral wind conditions. Reynolds number (Re) 310 ~ 3305, Froude number (Fr) 0.351 ~ 756, wind speed range 0.5 ~ 4.0 m/s, jet-transverse wind momentum flux ratio (RM) 0.077 ~ 13.188, heat release rate range 0.698 ~ 2.790 kW. The flame length and inclination isomorphism were determined by image analysis. The flame temperature and the volume fraction of carbon black were calculated based on the colorimetric method. The smoke state was determined by the relationship between the visible flame and the chemical equivalent flame length. With the increase of RM value, the flame presents a three-zone structure, the first zone refers to the downwash zone, and the third zone refers to the symmetrically distributed narrow, bright yellow flame. The relationship between dimensionless flame length and jet Fr is LF=18.8Fr 0.239. Based on the experimental results, the critical wind speed and RM value at the transition point of flame length are given. According to the experimental results and theoretical analysis of flame dip angle, three different main control modes of flame dip angle are proposed based on RM and Fr, and the applicable ranges of the theoretical formulas of global flame dip angle are determined: transverse wind/buoyancy control mode (RM0.01, Fr < 0.1), transition mode (0.01RM10, 0.1Fr103), and jet/momentum control mode (RM10, 103Fr105). (3) Flame temperature and carbon black volume fraction decrease gradually with the increase of transverse wind speed or the decrease of RM value. Flame radiation fraction increases slightly at first and then decreases with the increase of transverse wind speed. At last, the critical wind speed and RM of flame reaching smoke point under transverse wind condition are given. The relationship between the critical RM value and the jet Fr. is RM = 0.170Fr 0 345. The relationship between the flame length and Fr is LFsp = 13.8Fr 0.279. Under the smoke point condition, the flame with 8mm diameter is a typical three-zone structure, while the flame with 3mm diameter is a typical two-zone structure. In the experimental range, when the fuel flow rate is greater than a certain critical value, the ratio of smoke point value to maximum value of dimensionless flame length tends to be fixed, and the ratio of 3 mm diameter is greater than 8 mm diameter. The main reason why the two nozzles have different diameters is that different RM values result in different flame flow field and flame carbon black trajectory. Fou
【學(xué)位授予單位】：中國科學(xué)技術(shù)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：TK16;X932
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