臺灣博碩士論文加值系統

本研究進行一個渦捲式熱交換器之模擬分析，主要探討兩流體間管壁中沿渦線方向之熱傳導對熱交換器之熱傳性能之影響。此熱交換器之幾何結構由四條渦捲線於同一中心點出發，分別組成管壁與冷熱流道，其中冷熱流道中之流體考慮為逆向流，而冷熱流體之比爾數為相同，同時管壁最外層之半圈與位於中心處冷熱流體間之隔板假設為絕熱之情形，經能量平衡公式之推導與數值方法之解析，並利用電腦計算出流道中流體之無因次出口溫度，即可獲得熱交換器之熱效率。分析之結果顯示，在一個固定之熱傳單位數(NTU)下，當冷熱流體之比爾數值逐漸減小時，或無因次化管壁厚度增加時，亦即管壁之熱傳導增加時，熱效率會隨之減小。在NTU小於10以下，此研究所獲得之熱效率與不考慮渦線方向熱傳導所獲得之熱效率經比較後發現，熱效率之下降值會隨著NTU之增加而變大，在 為0.01、0.1與1.0時且 值為0.01， 之最大值分別為0.015、0.095與0.22。

The effect of spiral-direction heat conduction in solid wall on the heat transfer performance of a spiral heat exchanger was numerically analysed. The heat exchanger is composed of four spirals which form two solid walls, hot-flow channel and cold-flow channel. In the analysis, the flows were considered to be counter-current. The Biot number of the cold flow was the same as that of the hot flow. The outer-most half turns of the walls and the partition between the hot flow and cold flow in the center were assumed to be insulated. The result shows that, at a fixed NTU value, the heat transfer effectiveness decreases with the Biot number of the cold flow and hot flow value, and it decrease with an increase of the ratio of wall value. At NTU 10, the present acquired data were compared to those solved using a model without considering the solid heat conduction effect. The result shows that, the degradation of the heat transfer effectiveness value tends to increase with the NTU value. At the Biot number of the cold flow and hot flow value of 0.01, the maximum degradation of the heat transfer effectiveness values for the ratio of wall values of 0.01, 0.1 and 1 are 0.015, 0.095 and 0.22 respectively.

致 謝---- i
摘 要---- ii
ABSTRACT- iii
目 錄---- iv
表目錄--- vii
圖目錄--- viii
符號說明- xi
第一章 緒論------- 1
1.1 前言- 1
1.2 相關研究------ 2
1.3 研究目的------ 7
第二章 渦捲式熱交換器之能量平衡----- 8
2.1 在一極座標下曲線之長度- 8
2.2阿基米德渦捲線之長度---- 9
2.2.1 管壁內圈之長度------ 9
2.2.2 管壁外圈之長度------ 13
2.3 渦捲式熱交換器之幾何分析-------- 17
2.3.1 渦捲式熱交換器之管壁熱傳面積-- 17
2.3.2 渦捲式熱交換器之管道熱傳面積-- 18
2.4 管壁之能量平衡--21
2.4.1 熱流道於內側之隔板(虛線)------ 21
2.4.2 熱流道於外側之隔板(實線)------ 23
2.5流道之能量平衡--26
2.5.1 熱流道之能量平衡----- 26
2.5.2 冷流道之能量平衡------27
2.6 無因次化參數-- 29
2.6.1 管壁能量平衡公式之無因次化---- 30
2.6.2 流道中流體之能量平衡方程式之無因次化--- 32
2.7 熱效率與熱效率下降值-- 36
2.7.1熱效率------- 36
2.7.2 熱效率下降值--37
第三章 數值分析--- 38
3.1管壁能量方程式之有限差分法------- 38
3.1.1管壁之內側為熱流道時(如圖2.6中之虛線)--- 38
3.1.2管壁之外側為熱流道時(如圖2.6中之實線)--- 42
3.2 流道能量方程式之有限差分法------46
3.2.1熱流體之熱容率小於冷流體之熱容率------46
3.2.2熱流體之熱容率大於冷流體之熱容率------48
3.3 電腦模擬程式-- 50
3.4 模擬之格點誤差 --51
3.5 模擬之結果---- 52
3.5.1比爾數與管壁厚度比對熱效率之影響------52
3.5.2熱效率之下降量-----53
3.5.3流體與管壁之溫度分佈(較小NTU值情況)----56
3.5.4流體與管壁之溫度分佈(較大NTU值情況)----57
第四章 結論-----60
參考文獻-----62

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