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系統識別號 U0026-0812200910191091
論文名稱(中文) 超微噴嘴長寬比對噴霧特性之影響
論文名稱(英文) Effects of Large Aspect ratio on Atomization Performance of a Micro-nozzle
校院名稱 成功大學
系所名稱(中) 航空太空工程學系碩博士班
系所名稱(英) Department of Aeronautics & Astronautics
學年度 90
學期 2
出版年 91
研究生(中文) 陳義豐
研究生(英文) Yi-Feng Chen
電子信箱 p4689111@sparc1.cc.ncku.edu.tw
學號 p4689111
學位類別 碩士
語文別 中文
論文頁數 111頁
口試委員 指導教授-王覺寬
口試委員-徐明生
口試委員-張克勤
中文關鍵字 超微噴嘴  噴霧平均粒徑  單束噴流  出口長寬比 
英文關鍵字 micro-nozzle  aspect ratio  single stream  SMD 
學科別分類
中文摘要 摘要

本研究主要探討超微噴嘴出口長寬比對於噴霧流場霧化特性與噴流動態演變過程之影響,實驗在常溫常壓下進行,以水為工作流體,霧化壓力在5至11atm 之範圍內,孔徑為水力直徑dH=66.67μm,孔口長寬比為1:5。視流觀察顯示噴霧流場皆成單束流之噴霧形態,以閃頻儀觀察可發現噴嘴出口形成一小範圍之液面狀流場分佈。實驗結果亦顯示,於不同長寬比下,對噴嘴之質流率、出口流速取其比值,顯示隨著霧化壓力增加,因所受之壓損漸趨一定值,故其比值亦漸趨於一定值。此超微噴嘴之質流率屬於一種微增量之控制範圍,其流量之微量控制可降低至約0.013g/sec-atm,適合微引擎之應用,亦可適用於需要微流量之控制器。隨著霧化壓力的提升,有助於增加工作流體有效動量之比率。增加長寬比卻使得整體的能量轉換率降低,尤其在高霧化壓力下僅30%左右。在高霧化壓力下其壓損比值趨於一定,顯示在高壓時可獲得較高之能量轉換率。根據量測之結果發現,在霧化壓力5atm、7atm及9atm時,噴霧流場之粒子概率的分佈在軸向位置隨著越往下游,大液滴(100μm以上)比例有漸少的趨勢。PDPA量測之數據顯示在軸心位置之粒子密度及體積流通率為緊鄰其外之剪流層的2.3倍以上,此為一種單束流之特性。當噴嘴出口之長寬比為1:2時,霧化SMD隨軸向愈往下游位置呈遞增趨勢,其液滴軸向速度隨軸向變化遞減較快;但當噴嘴出口之長寬比為1:5時,霧化SMD在軸向位置之變化呈較一致之情況,其液滴軸向速度隨軸向變化呈緩降之趨勢。而液滴之徑向速度分佈多集中在軸心附近處,此亦可知是單束噴流之影響。此單束噴流現象至流場下游位置Z=5cm時,在軸心R=0mm位置所呈現之大小粒子皆為等速之現象,與傳統之噴霧流場有所不同,此亦是單束噴霧之特徵現象。在此噴霧剪流層內,80μm粒子之速度梯度為150μm大粒子的四倍多,亦即80μm粒子在剪流層內與氣相流之動量傳遞強過150μm大粒子三倍以上。亦可得知當長寬比為1:5時其單束噴霧流場內剪流層之速度梯度較一般噴霧流場高二個數量級之變化,代表單束噴霧流場存在顯著的狹窄剪力層特性。不同大小之粒子在單束流之剪力層區域軸向速度之擾動量為往外圍減緩,而不同大小之粒子在單束流之剪力層區域徑向速度之擾動變化量極大,這與粒子和氣相空氣間之動能傳遞有關。流場中粒子交互之碰撞作用以塑性結合為主要機制,對於外圍剪流層之粒子速度隨著軸向位置變化而有降低的情形,其緣故為在較長的粒子運動時間後,氣液兩相動量交換之結果。



英文摘要 ABSTRACT

This research is to investigate the effects of large aspect ratio of the nozzle on atomization performance and the droplet evolution in the spray jet of a micro-nozzle. All experiments are measured under room temperature and atmosphere pressure. Working pressure is 5atm to 11atm. The orifice hydraulic diameter is 66.67μm and the aspect ratio is 1:5. Flow visualization with stroboscope shows that the liquid film is formed near the nozzle. Results also show that the ratios of mass flow rate and exit-velocity are almost constant at different aspect ratios when pressure is increased. It also shows that the mass flow rate as low as 0.013g/sec-atm is achieved with this nozzle. It can be used in the micro-engine or micro-flow applications. The energy conversion rate is decreased when the aspect ratio is increased i.e., only 30% conversion in high pressure range. The pressure drop is almost constant under high working pressure. Hence the energy conversion rate increases in the high-pressure range. Measurements show that the proportion of droplets-probability with diameter more than 100μm tends to decrease in the downstream. Measurements by PDPA further show that the number density and volume flux in the core region is 2.3 times more than that in the shear layer region. Hence, it can be considered as a single stream spray jet. The mean drop size tends to increase and the reduction of the axial velocity of the droplets in the down stream is more significant when the aspect ratio is 1:2. On the other hand, the mean drop size is almost constant and the axial velocity of the droplets decreases slowly in the down stream when the aspect ratio is 1:5. The radial velocity distribution of droplets concentrates in the vicinity of core region due to the single stream effects. It is also found that the velocities of droplets from 4μm to 176μm are all the same value in the core region when operating at Pt=7atm. A shear layer is measured at Z=5cm, resulting in an extreme high velocity gradient(ΔU/ΔR)in this particular flow field . It is believed that the momentum transport is very high in this case because its velocity gradient is two orders of magnitude higher than the conventional spray flow. Data measured by PDPA also indicates that droplet coalescence takes place in the down stream because the droplet velocity decreases in the down stream due to the momentum transfer in the two phase flow.



論文目次 目 錄
摘要
英文摘要
誌謝
目錄 Ⅰ
表目錄 Ⅲ
圖目錄 Ⅳ
符號說明 Ⅵ
第一章 緒論 1
1-1簡介 1
1-2文獻回顧 2
1-2-1液體碎化過程研究 2
1-2-2霧化流場氣動力分析 4
1-2-3噴霧流場中液滴破裂模式 6
1-2-4影響壓力式渦漩霧化器霧化特性研究 7
1-3研究動機 11
第二章 實驗設備及儀器 12
2-1實驗設備 12
2-2超微噴嘴的設計 13
2-3實驗量測儀器 13
2-3-1相差都卜勒粒子分析儀(PDPA) 13
2-3-2攝影器材、顯微影像系統與影像處理系統 15
2-4主要參數簡介 16
第三章 實驗步驟及方法 19
3-1噴霧流量之測定 19
3-2視流觀測與攝影 19
3-3相差都卜勒粒徑分析儀的量測 19
3-3-1儀器的校正 19
3-3-2霧化器量測條件 21
第四章 結果與討論 22
4-1超微噴嘴噴霧流場的視流觀察 22
4-2不同長寬比之超微噴嘴流量與其衍生之結果 22
4-2-1不同長寬比之超微噴嘴流量-壓力特性曲線 22
4-2-2不同長寬比之出口動壓揚程與壓損揚程的比較 23
4-3超微噴嘴噴霧粒子在空間中之演變過程 25
4-3-1不同霧化壓力下液滴大小在流場中之變化情形 26
4-3-2霧化液滴在流場中動態之演變 28
第五章 結論 38
參考文獻 40
自述 111
著作權聲明 112
表目錄
表一 超微噴嘴質量流率、出口速度、動壓以及壓損
在不同霧化壓力下之特性 44
表二 超微噴嘴與傳統壓力式噴嘴之霧化特性比較 45
圖目錄
圖1-1 三種不同型態的噴嘴 46
圖1-2 平面液膜受低速及高速氣體衝擊破裂機構 47
圖1-3 壓力式霧化器液膜三種破裂模式 48
圖1-4 液膜上下游破裂模式 49
圖1-5 壓力式渦漩霧化器霧化過程 50
圖1-6 單一液滴與空氣交互作用破裂機構 51
圖1-7 壓力式渦漩霧化器噴霧流場結構圖 52
圖1-8 壓力式渦漩霧化器噴霧流場內部結構圖 53
圖1-9 平面噴嘴之氣動力特性圖 54
圖1-10 噴霧流場變化過程圖 55
圖1-11 液滴碰撞相關位置和參數液膜局部破裂圖 56
圖1-12 各類液滴碰撞型式圖 57
圖1-13 1994年,C.K.Chiang之實驗結果圖 58
圖1-14 液滴受高速氣體衝擊破裂機構圖 59
圖2-1 實驗裝置系統圖 60
圖2-2 光學桌與光學量測儀器配置圖 61
圖2-3 超微噴嘴結構圖 62
圖2-4 相差都卜勒粒子分析儀光學系統設置圖 63
圖2-5 超微噴嘴元件及釋流孔顯微攝影圖 64
圖3-1 相差都卜勒粒子分析儀量測位置圖 65
圖4-1 超微噴嘴在不同霧化壓力下噴霧流場照相圖 66
圖4-2 超微噴嘴與傳統噴霧流場之示意圖 67
圖4-3 流量及流速對霧化壓力之關係圖 68
圖4-4 不同長寬比下質流率等之比值對霧化壓力之關係圖 69
圖4-5 出口動壓揚程與壓損揚程對霧化壓力之關係圖 70
圖4-6 不同長寬比下動壓等之比值對霧化壓力之關係圖 71
圖4-7 四種管徑大小之單位長度壓損揚程 72
圖4-8 霧化壓力為5 atm下噴霧流場之粒子概率分布圖 73
圖4-9 霧化壓力為7 atm下噴霧流場之粒子概率分布圖 74
圖4-10 霧化壓力為9 atm下噴霧流場之粒子概率分布圖 75
圖4-11 噴流流場軸向之粒子密度分布圖(霧化壓力Pt=9 atm) 76
圖4-12 噴流流場軸向之體積流通率分布圖(霧化壓力Pt=9 atm) 77
圖4-13 超微噴嘴噴流內部結構之霧化特性圖 78
圖4-14 霧化流場軸向之平均粒徑-霧化壓力關係圖 79
圖4-15 超微噴嘴不同長寬比之SMD-Z axis關係圖(Pt=5 atm) 80
圖4-16 超微噴嘴不同長寬比之SMD-Z axis關係圖(Pt=7 atm) 81
圖4-17 超微噴嘴不同長寬比之SMD-Z axis關係圖(Pt=9 atm) 82
圖4-18 超微噴嘴霧化流場之軸向速度-Z axis關係圖 83
圖4-19 超微噴嘴不同長寬比之軸向速度-Z axis關係圖(Pt=5 atm) 84
圖4-20 超微噴嘴不同長寬比之軸向速度-Z axis關係圖(Pt=7 atm) 85
圖4-21 超微噴嘴不同長寬比之軸向速度-Z axis關係圖(Pt=9 atm) 86
圖4-22 超微噴嘴霧化流場之徑向速度-Z axis關係圖 87
圖4-23 噴流內部結構之粒徑-軸向速度關係圖 88
圖4-24 噴流內部結構之粒徑-徑向速度關係圖 97
圖4-25 單束噴霧流場中剪流層區域之粒子軸向速度分布圖 106
圖4-26 單束噴霧流場中剪流層區域之粒子徑向速度分布圖 107
圖4-27 單束噴霧在剪流層之軸向速度擾動分布圖 108
圖4-28 單束噴霧在剪流層之徑向速度擾動分布圖 109
圖4-29 超微噴嘴霧化流場速度-粒徑相關性圖(Pt=5 atm) 110


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