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標題: | 片堆對駐波型熱聲效應影響及複動式合成噴流特性之研究 The study of the stack effect on thermoacoustic and the feature of double-acting synthetic jet |
作者: | Shu-Shen Hsu 許書申 |
指導教授: | 王安邦 |
關鍵字: | 駐波型熱聲系統,片堆長度/位置,最小啟動功率,熱聲功率,複動式合成噴流,體積效率, Standing-wave thermoacoustic system,stack length/position,minimum onset power,thermoacoustic power,double-acting synthetic jet,volumetric efficiency, |
出版年 : | 2015 |
學位: | 博士 |
摘要: | 論文分成兩大部份,第一大部份探討片堆幾何設計參數與共振管角度對熱聲效應及啟動值之影響,第二部份為複動式與傳統合成噴流特性之比較研究。
在第一部份熱聲引擎的探討中,先前文獻多專注在討論片堆截面幾何尺寸或管長影響,缺少片堆位置與長度的討論,此外,雖有探討不同氣體或不同共振管角度在熱聲啟動後之溫差、聲壓之影響,但都未對臨界啟動熱聲值探討。故本論文分別探討無因次片堆長度(ls*)、無因次片堆位置(Xs*)、共振管角度(θ)對溫差(ΔT)及溫度梯度(▽T)、聲壓(PA)、效率(η)之間的關係,並探討熱聲系統最小啟動功率(PWmin)與ls*、θ間之關聯性。在熱聲熱泵部份,探討ls*、Xs*、開口率、熱傳導係數對ΔT、▽T之影響。 本文在駐波型熱聲引擎系統ls*與Xs*的研究中,對ls*、Xs*、ΔT、▽T、PA、η進行系統性分析,建立熱聲效率之ls*-Xs*分佈圖,並找到最大效率位置在Xs* = 0.25、ls* = 0.086。在ls*與θ對臨界啟動熱聲影響之研究中,發現PWmin主要為提供補償熱傳導與自然熱對流所造成的熱損失。熱聲啟動前,片堆短,所產生溫度梯度大,故熱聲較易啟動,熱傳導與自然對流之比例約為2:3;反之片堆長,所產生溫度梯度小,熱聲較難啟動,熱傳導與自然對流之比例降為1:4以下。熱聲啟動後,短片堆之空氣可作功面積小,故增加輸入功率時之聲壓上升速率較慢;長片堆則反之,增加輸入功率時之聲壓上升速率較快。在共振管角度研究中,以開口朝上,片堆熱端下冷端上之設置(θ = 90°),因熱浮力往上有助於突破空氣阻力故最易啟動。至於片堆使用低熱傳導係數玻璃,以降低熱傳導損失,在熱聲引擎證實可有效降低PWmin 13%,而由熱聲功率PWacoustic和無因次單位片堆長度之聲壓參數關係,發現不同熱聲系統間具有相似性;而在熱聲熱泵的研究中,除了建立毛細玻璃片堆與陶瓷片堆溫度差之ls*-Xs*分佈圖,找出最大溫差,發現在短毛細管玻璃片堆,其最大溫度梯度,為陶瓷片堆的1.7倍,但開口率影響不大;而在長毛細管玻璃片堆時,開口率高之片堆則有較大的溫差(可再提升13%)。 在第二部份複動式合成噴流(DAHSJ)與傳統合成噴流(SASJ)特性之研究中,以水為工作流體,利用染劑顯影,清楚呈現DAHSJ腔體間流體交換與渦漩形成過程。由PIV量測流場之結果比較,DAHSJ具有非零質量流的特性,故在冷卻之應用時,可補充新鮮之冷流體,降低噴流溫度,提高散熱效果。此外DAHSJ渦漩強度超過SASJ的2倍。噴流寬度不到SASJ的一半,故可加強噴流與發熱元件間流體混合以強化散熱。而由數值模擬(林祺峰,2007)與實驗之進一步比較分析,發現移除原本DAHSJ中央噴流之擋牆時,中央噴流會在側邊流道引致阻擋渦漩之產生,此可減少在中央腔室要噴出之混合流體被吸入側邊流道,由此大幅提升淨流量(> 6倍),與體積效率(>3倍)。而移除複動式合成噴流產生器之流體二極體後,體積效率可再提升。 This dissertation includes two parts: the effect of the stack geometry design parameters, the spatial angle on the thermoacoutstic system and its onset value were studied in the first part; the feature of the double-acting and single-acting synthetic jet waere investigated in the second part. In the first part, most of the previous works only focus on the effect of the stack’s cross-section and the resonator’s tube length without the discussion of the stack’s position and its length. Besides, although the effect of the different gas and the spatial angle on the temperature difference, pressure after onset has been studied, there is no discussion about the critical onset of thermoacoustic. In this dissertation, the relation between the dimensionless stack length (ls*), the dimensionless stack position (Xs*) and the spatial angle (θ) on the temperature difference (ΔT), temperature gradient (▽T), pressure (PA) and efficiency (η) in thermoacoustic system were investigated. Meanwhile, the relation between the minimum onset power (PWmin) of the thermoacoustic engine and the ls*,θwere also studied. In the part of the thermoacoustic heat pump, the effect of ls*, Xs*, opening ratio, thermal conductivity on ΔT, ▽T were studied. In this dissertation, the effect of the ls* and Xs* in the standing-wave thermoacoustic engine on ls*, Xs*, ΔT, ▽T, PA, η were investigated systematically. The contour map of thermoacoustic engine efficiency on ls*-Xs* were build. The maximum efficiency is located at Xs* = 0.25、ls* = 0.086. In the study of the effect of ls*,θ on the critical onset of the thermoacoustic engine, the minimum onset power input PWmin was to compensate the heat loss of thermal conduction and thermal convection. Before the onset, short stack has larger temperature gradient, so it is easy to startup. The heat loss ratio of the conduction and convection is 2:3. While long stack has smaller temperature gradient, it is hard to startup. The heat loss ratio of the conduction and convection is reduced to under 1:4. After onset, the short stack has less working area between the air and the stack, so the sound pressure increase slowly along with the power input. While the long stack has larger working area in between. In the study of resonator’s spatial angle, the easiest startup system setup is open end up with the hot side up and cold side down ( θ = 90°) on the stack because the thermal buoyance can help the air break through the resistance. The glass stack with low thermal conductivity was build and tested. It can lower the minimum onset power 13% because of less heat loss of thermal conduction. The data curve can be merged based on the relation between thermal acoustic power PWacoustic and the unit length sound pressure. It shows that the similarity between different setup. In the study of thermoacoustic heat pump, the ls*-Xs* temperature difference contour map of the glass stack and the ceramic stack was build and found the maximum. The low thermal conductivity capillary glass tube stack can have 1.7 times higher temperature gradient than the ceramic stack in short stack. The high opening ratio glass tube stack can increase the temperature difference 13% in longer stack. In the second part, the study of the double-acting synthetic jet (DAHSJ) and the single-acting synthetic jet (SASJ), the water was used as the working fluid. By the method of fluorescent dye visualization technique, the fluid exchange between the cavities and the formation of the vortex were clearly displayed. Comparing with the SASJ by PIV method, the DAHSJ has the feature of non-zero-net-mass-flux, so the fresh cold fluid can be supplied to cooling down the jet temperature, then the cooling ability can be improved. Besides, DAHSJ has 2 times more stronger vortex and half times less jet width than SASJ, so it can enhance the fluids mixing between the jet and the heating devices to improve the cooling. Finally, DAHSJ was modified and simplified the vertical wall of the central jet by numerical simulation (C.-F. Lin, 2007) to improve the volumetric efficiency and comparing with experiment. The results show that the blockage vortex forms at the side channel while the fluid pumps out from the central jet, which can prevent and reduced the central jet fluid sucking back into the side channle. By this way, it can enhance the net flow (more than 6 times) and the volumetric efficiency (more than 3 times). After removing 12 fluid diodes around the DAHSJ device, the volumetric efficiency can be enhanced more. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/52111 |
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顯示於系所單位: | 應用力學研究所 |
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