以流場可視化與數值模擬探討熔融沉積成形 3D列印機內之微粒汙染問題

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研究生：	林政毅 Cheng-Yi Lin
論文名稱：	以流場可視化與數值模擬探討熔融沉積成形 3D列印機內之微粒汙染問題 Investigation of Particulate Pollutant in a FDM 3D Printer by Flow Visualization and Numerical Simulation
指導教授：	田維欣 Wei-Hsin Tien
口試委員:	鄭逸琳 Yih-Lin Cheng 黃智永 Chih-Yung Huang 溫琮毅 Tsrong-Yi Wen
學位類別：	碩士 Master
系所名稱：	工程學院 - 機械工程系 Department of Mechanical Engineering
論文出版年：	2018
畢業學年度：	106
語文別：	英文
論文頁數：	115
中文關鍵詞：	3D列印、超微細微粒、揮發性有機化合物、視流法、計算流體力學
外文關鍵詞：	3D Printing, Ultra Fine Particles, Volatile Organic Compounds/VOC, Flow Visualization, Computational Fluid Dynamics
相關次數：	點閱：310 下載：16
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在眾多3D列印技術之中，由於其低成本與較小的機台尺寸，熔融沉積成形FDM (Fused Deposition Modeling)較其他類型的3D列印機台來的更受歡迎。而近來的研究顯示使用熔融層積成形技術之3D列印機會在列印過程中釋出大量的超微細微粒(UFP)及揮發性有機物(VOCs)，造成室內空氣污染與健康風險。主要原因是FDM型的列印機所使用的熱塑性線材在列印過程需要較高的工作溫度，噴頭加熱至工作溫度230℃與加熱底板110℃時產生的熱裂解則是排放汙染的主要原因。許多現有的研究都集中在討論列印機排放至外部環境的汙染問題，而忽略了列印機內部的微粒擴散問題。因此本研究利用流場可視化技術與數值模擬來了解列印機內的流場分布情形。在流場可視化實驗中，使用一原尺寸之透明壓克力FDM型3D列印機模型並裝備實機內之零件如加熱板與噴頭模組。以油霧作為循跡微粒，並經由雷射光頁照射後可用以觀測內部的流場，並了解超細微粒在列印過程中跟隨內部空氣的流動與散布。本研究使用的CFD分析軟體為ANSYS FLUENT，透過噴頭與加熱底板分別設定為230℃、110℃及散熱風扇設定其P-Q curve的邊界條件，以進行內部的流場計算模擬，最後利用流場可視化技術的實驗結果對模擬結果進行分析比對驗證。研究結果發現，與前人文獻相較下，在兩個步進馬達中央加裝一塊鋁塊減少了內部循環的向後流區域。而由於主要微粒汙染產生在噴頭附近，在風扇散熱喉管的同時，因噴頭模組結構的下方縫隙所造成的向下噴流會造成微粒的擴散，鰭片所產生的側向噴流也會從側邊帶走噴頭下方的汙染物，並且加快整體內部的空氣循環。這些結果亦顯示將上半部的冷卻風扇區域與下半部列印區域做有效隔絕，同時對下方區域獨立收集汙染物的效果較有幫助，可以有效避免強制對流所造成的汙染物散布問題。最後，改變加熱底板高度之實驗結果發現，加熱片位置較高時(Y=190mm)由於向下噴流撞擊加熱片會增快側向流動，會造成比加熱片位置較低時(Y=30mm)更快的從側邊帶走噴頭下方的汙染物。

Among many 3D printing technologies, Fused Deposition Modeling (FDM) is more popular than other types of 3D printers, due to its low cost and small size. Recent studies have shown that fused deposition modeling (FDM) type 3D printers have high emission rates of the ultrafine particles (UFP) and volatile organic compounds (VOCs) in the printing process, which can cause indoor air pollution and health risks. The thermal decomposition of commonly used thermoplastic filament materials, such as ABS and PLA, due to the operating temperatures of nozzle at 230°C and the bottom plate at 110°C is the main source of the emission. Many existing studies are focusing on the pollutants emitted to the external environment but ignored the problem of particle distribution inside the printer. In this study, the flow inside a FDM printer is investigated by flow visualization and numerical simulation. For flow visualization, a 1:1 transparent acrylic printer model is used with exactly the same components such as the heater plate, extruder module installed in real printer models. Using oil mist as tracer particles and illuminating with laser sheet, the internal flow field can be observed in order to understand the distribution of the ultrafine particles during the printing process. ANSYS FLUENT is used for the CFD numerical simulation. The nozzle and heater plate were set to 230°C and 110°C and the flow from of the cooling fan of the extruder module is set by the fan P-Q curve for simulation. The experimental results from flow visualization are compared with the simulations. The results show that the extra aluminum block at the center of the two-step motor reduces the backward recirculating region compare to the previous study. Because the main particle emission is near the nozzle while the fan is cooling the extruder module, the downward jet caused by the gap below the extruder module spreads out the particles. The lateral jets created by the fins also bring the particles to both sides and speed up the overall internal air circulation. These results suggest that it is helpful to separate the cooling fan area from the printing area and collect the pollutants from the printing area, because it can effectively avoid pollutant spreading by forced convection. Lastly, results from changing the heater plate position show that at the upper heater plate position (Y=190mm), the spread of the particles is stronger due to the downward flow impinges on the heater plate which creates faster side flows than the lower heater plate position (Y=30mm).

摘要    i
ENGLISH ABSTRACT    iii
ACKNOWLEDGEMENTS    v
CONTENT    vi
NOMENCLATURES    ix
LIST OF FIGURES    xi
LIST OF TABLES    xv
CHAPTER 1 INTRODUCTION    1
1 Motivation    1
2 Literature Review    3
2.1 3D Printer Emissions    3
2.1.1 3D Printing Types & Filament Selection    3
2.1.2 Fused Deposition Modeling (FDM)    5
2.1.3 Ultrafine Particle Emissions    6
2.1.4 Volatile Organic Compounds    10
2.1.5 Thermal Decomposition Problem    11
2.2 Flow Visualization    13
2.3 Computational Fluid Dynamics (CFD)    14
3 Objective    15
4 Structure of Thesis    17
CHAPTER 2 EXPERIMENTAL AND COMPUTATIONAL METHODS    18
1 Experimental Methods    18
1.1 3D Printer Model    18
1.1.1 1:1 Scale Model    20
1.1.2 Extruder Module    22
1.1.3 Heat Plate    24
1.1.4 Generation of the Flow Tracer:  The Haze Machine    26
1.2 Setup of Flow Visualization Experiments    29
1.2.1 Laser Sheet Generation    30
1.2.2 Particle Generation    33
1.2.3 Camera Parameters    35
1.2.4 Image Processing    36
1.3 Experimental Procedure    37
2 Establishment of the  Simulation Model    39
2.1 Governing Equation    42
2.2 Standard K-Epsilon Model    43
2.3 Finite Volume Method    45
2.4 Model Geometry    45
2.5 Grid Generation    47
2.6 Boundary Conditions    50
2.7 Fan P-Q Curve    52
2.8 Simulation Procedure    54
CHAPTER 3 RESULTS AND DISCUSSION    55
1 Results of Flow Visualization Experiment    57
1.1 The flow on X-Y Plane (Z = 190mm)    57
1.2 the flow on Y-Z Plane (X = 240mm)    66
1.3 Side Flow Velocity next to the Fin in the Experiment    72
2 Results of CFD Simulation    74
2.1 The flow on X-Y Plane (Z = 190mm)    74
2.2 The flow on Y-Z Plane (X = 240mm)    79
2.3 Side Flow Velocity next to the Fin in Simulation    84
3 Discussion    86
3.1 Comparisons between Experiment and Simulation Results    86
3.2 Side Flow Comparison between Simulation and Experiment    87
3.3 The Comparison to Previous Work    90
3.4 The limitation of this study    92
CHAPTER 4 CONCLUSIONS AND FUTURE WORK    94
1 Conclusions    94
2 Future Work    95
BIBLIOGRAPHY    96

                                

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