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Computer Aid Design and Experiments on Double Pipe Heat Exchangers Subject to Ultra-Supercritical Steam
|Authors: ||Tsung-Yuan Huang|
|Contributors: ||NTOU:Department of Mechanical and Mechatronic Engineering|
Heat Exchanger;Ultra-Supercritical;Wall Thickness of Pipes;Overall Heat Transfer Coefficient
|Issue Date: ||2013-10-07T03:02:36Z
|Abstract: ||溫度壓力的提高可以有效提升發電效率，目前應用之溫度壓力範圍已經達到超超臨界狀態。本文旨在探討超臨界水熱物理特性，尤其對於臨界點在超超臨界狀態之效應。首先在高溫高壓狀態下，設備遇到的難題是輸送管件能否承受此嚴苛之運轉條件，因此本研究針對傳熱管壁厚度做安全性分析，過程必需符合國家標準規範CNS內容，依使用溫度範圍及壓力分別計算SUS316L及Inconel-718兩種材料所需符合規範安全係數的管壁厚度，計算過程以電腦EXCEL程式編纂，可供不同使用條件下安全厚度的運算。 本研究主要針對台電綜合研究所建置之超超臨界狀態蒸氣沖蝕實驗設備，系統中之所有熱交換器進行設計及分析。設計最高壓力400大氣壓，最高溫度760℃，熱交換器選擇套管式，熱傳計算採用對數平均溫差法（LMTD），主要在求得總括熱傳係數(Uo)，據以估算傳熱管長度。總括熱傳係數之理論值與實際值比較，在300kg/hr的實驗中，其誤差約為5%，但在180kg/hr的實驗中誤差卻大幅增加為50%，推測其原因為在低質量流速下導致雷諾數下降或內外套管偏心造成部份縫隙縮小而形成層流，進而熱傳變差。 在超臨界狀態下因無明顯相變化，鍋爐採用無汽水鼓之貫流式鍋爐。貫流式鍋爐缺點為容易產生過熱燒毀。本文亦對於此問題探討新技術，將鍋爐膛管採用内螺纹管使流體旋轉產生離心力，將較輕之氣泡移向管中央，使乾涸現象延後發生，有效降低管壁溫度。|
The increase in the temperature and pressure can effectively enhance the efficiency of power generation. The current operating range of steam has reached the ultra-supercritical state. The thermal physical properties subject to high temperatures and pressures of steam have been investigated in this thesis, especially at the critical point. To achieve the goal, the safety wall thickness of a pipe at a specified pressure and temperature was calculated according to the specification of CNS. The detailed procedure was written in an EXCEL code and it can be executed in a personal computer. The data base includes SUS-316L and Inconel-718 which facilitates the information of physical property during the calculation. Based on a designate pressure of 400 atm and the maximum temperature up to 760 ℃, an experimental device has been established by TPRI to study the effect of erosion. The thermal behavior of all the heat exchangers in this loop was investigated in this work. LMTD method has been used to estimate the heat transfer area in the design of double pipe heat exchangers. The experiments were also conducted. The deviation between theory and data is about 5% in a flow rate of 300kg/hr, whereas it increases to 50% in a test of 180kg/hr. It is doubted that the reason was due to low mass flow rate in which Reynolds number falls into the laminar flow regime maybe the eccentric allocation in double pipes. Usually, once-through type boilers have been used in a supercritical power plant. The heating pipes in is type of boiler is subject to the risk of dryout and burnout. A new generation of super-critical boiler bore pipe uses the rifled tube, internally rifled tube allows fluid rotation to produce centrifugal force, the bubble is moved toward the centerline of the tube. Hence the dryout phenomenon can effectively delay.
|Appears in Collections:||[機械與機電工程學系] 博碩士論文|
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