臺灣博碩士論文加值系統

冷凍空調設備需要長時間的運作，所以效能、效率、壽命、噪音都是評比一台設備好壞的指標性項目，本研究以此論點進行探討，利用套裝模擬軟體進行輔助設計，期望先從理論進行理解並建構出一套高效率的模擬方法；最後有系統性的研究離心式壓縮機的幾何模型參數與其影響，期望在此堅實的設計能量下，以設計出符合需求的高性能改良產品。本研究使用FLUENT進行CFD數值模擬，NIST標準資料庫是最具權威的冷媒資料來源，研究中發現在選用NIST冷媒標準資料庫之材料進行模擬時，其收斂難度、格點需求皆相當高且其收斂時間相當長，若直接使用此方法進行研究，勢必無法有效率的研究與設計；所以使用數學家Soave所提出的SRK數學方程，並利用冷媒大廠Solvay於網路上釋出的冷媒測試資料進行冷媒資料的建構，經模擬嘗試與比對顯示，此方法所建構的冷媒資料較NIST冷媒資料庫之冷媒資料收斂時間少四倍且收斂穩定，而計算出的數值與NIST資料相比僅有1%差別，證明此方法能應用在快速設計與研究上。為了確認後續研究數值之可信度，在此將SRK資料計算出的數值代入NIST標準資料庫內進行二次收斂，此方法相較於單純使用NIST資料庫進行收斂亦節省了兩倍左右的時間。
利用上述方法模擬後針對壓縮機流場的物理現象進行探討，發現在高負載操作點時葉輪具有超音速現象，利用一連串的模擬驗證此現象，包括不同紊流模組與溫度影響探討，確認超音速現象的模擬結果後；接著分析壓縮機的流場現象，再藉由出口靜壓與靜壓效率來訂定改善目標進行後續改良。首先，從葉輪開始針對扇葉數量、Meridional Contour變化、入口、出口角度等進行參數改良，接著針對外殼的截面設計、尺寸選用、舌部改變與增壓器直徑等參數進行研究，雖然重新設計的外殼與原始的設計差異不大，但是此建立完整的模擬參數設計結果，可為後續設計做為參考。最後，從流場與數據結果呈現，新葉輪在低負載時較於原始設計靜壓效率上多5 %，整體靜壓效率提升至74.8%，出風的均勻度也明顯優於原始設計；而在高負載方面，通過出口速度流場與馬赫數的比較也具有相當大的改善，顯現出改善方向的成功。綜合歸納上述成果，本文透過一系列的模擬驗證並進行離心式冷媒壓縮機的參數改良，所建立完整的研究成果與快速模擬方法不僅能做為後續相關研究開發之參考，更能縮短工程師開發週期。

Due to the longtime operation characteristics, the static pressure, noise, efficiency, and life time become the crucial evaluation indices for selecting the proper refrigeration and air-conditioning equipment. And the demand on designing a high-efficiency compressor motivates this thesis aiming to establishing an effective and reliable simulation scheme for accelerating the compressor design. Incorporated with the commercial CFD codes Fluent, a new two-step calculation procedure is proposed here to speed up the lengthy convergence procedure encountered in utilizing the built-in NIST (National Institute of Standards and Technology) database. Note that the database in NIST is recognized as the most accepted property source for the coolant HFC-134a. Nevertheless, using NIST data leads to the time-consuming, high-grid-quality and hard-to-converging problem, which enables the comprehensive parametric study on the high-speed compressor using HFC-134a almost impossible to carry out within a reasonable time interval. To solve this difficulty, this work firstly chooses the famous Soave-Redlich-Kwong (SRK) equation to execute the simulation associated with compressor to obtain the first-order calculation spending 1/4 CPU time of that needed in the regular simulation. Thereafter, with the first result as the initial condition, the final tune-up simulation is performed normally in Fluent with NIST database. As a result, not only 1% deviation between the normal and two-step solutions is found, but also more than 50% reduction on CPU time and a better stable convergence are observed in this new approach at the 50%-loading operation point.
Afterward, with this new approach, the performance enhancement on centrifugal compressor is executed numerically in two parts aiming at the impeller and the housing in sequence. At first, with the aids of CFD visualization on the corresponding flow phenomenon, variations on meridional contour, number, and inlet/outlet angle of the blade are analyzed systematically to identify the appropriate parameter setting on this compressor rotor. Later, the cross-section of spiral housing, the cut-off clearance, and the diameter of diffuser are adjusted for finding out the proper settings to yield a superior compressor design. Accordingly, at the 60%-loading operation, the optimized impeller design yields a 74.8% static efficiency, which is 5% higher than the original design’s. Also, no significant changes on the maximum static pressure and the volume flow rate are observed over the entire operating range. On the other hand, at medium- to high-loading conditions, the velocity distribution at the fan discharge becomes more uniform, which may result in a noise reduction usually. In conclusion, this research successfully establishes a systematic and reliable simulation scheme to improve the aerodynamic performance of a high-speed centrifugal compressor. Also, the new two-step calculation procedure enables the design process to complete in a realistic time for meeting the engineer’s practical need.

目錄
致謝 I
摘要 II
目錄 VI
圖索引 VIII
表索引 XI
符號索引 XII
第一章 緒論 1
1.1前言 1
1.2文獻回顧 2
1.3研究流程 6
第二章 磁浮式離心式壓縮機簡介與研究目的 11
2.1冷凍循環及冷媒性質 12
2.2冰水主機的種類 14
第三章 離心式壓縮機之物理和數值模型 20
3.1離心式壓縮機模型介紹 20
3.2離心式壓縮機設計 25
3.3網格規劃 30
3.4邊界條件設定 35
第四章 數值方法 37
4.1統御方程式 38
4.2數值計算方法 41
4.2.1離散化方程式 41
4.2.2壓力與速度耦合的處理 43
4.2.3 Soave-Redlich-Kwong 狀態方程 45
4.3數值求解流程 46
第五章原始模型之模擬分析 49
5.1 Soave-Redlich-Kwong方程冷媒與NIST冷媒模擬之比較 51
5.2不同規範模擬測試 57
5.3 空氣模擬可行性測試 63
5.4不同數值方法模擬比較與分析 65
5.5 實驗測試與模擬數值之比較 75
第六章模型之模擬分析與改善 77
6.1原始壓縮機模型之流場探討 78
6.2扇葉數 87
6.3扇葉曲線與角度改良 89
6.4外殼設計 98
6.5 改善後模型與原始設計之比較與分析 108
6.5.1外殼改變之性能比較與分析 108
6.5.2葉輪改善之性能比較與分析 111
第七章結論與建議 118
7.1結論 118
7.2建議 120
參考文獻 123

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