低壓噴油嘴設計與微機電製程研發

Low Pressure Atomizer Design and UV-LIGA Micro Fabrication

陳琮瑜(Tsung-Yu Chen)

指導教授 ： 楊鏡堂

國立清華大學/工學院/動力機械工程學系/博士(2008年)

https://doi.org/10.6843/NTHU.2008.00115

摘要

本文主旨在於使用UV-LIGA製程製作霧化噴嘴，探討微型噴嘴在微尺度下的幾何限制，提供一種設計準則，並由套裝數值模擬軟體CFD-RC分析提供噴嘴內部流場的物理機制，分析空氣柱的成因與噴嘴幾何形狀的關係，最後以都卜勒粒徑分析儀(Phase Doppler Particle Anemometer, PDPA)實際量測霧化後的粒徑，瞭解噴嘴幾何形狀對霧化影響。
在發展微機電製程中，對於次毫米等級的製作上向來有較難的限制，因其尺度處在於傳統製造與微米結構之間，對於傳統製程的更精密製作和微機電製程的向上堆疊能力都受到嚴格的考驗，本文使用SU-8當作噴嘴母模，其在光罩的設計上與在軟烤顯影等步驟對於溫度的敏感度有嚴苛的限制，使得需要掌握精確的時間控制才能達到準確的製作，本文成功達到1200 ?m雙層光阻堆疊製作。
壓力渦漩式噴嘴在傳統毫米等級的設計上可由一些參考工具書上得到正確的設計原則，然而邁入更小尺度的設計，其幾何尺度限制卻須備受考量，利用數值模擬我們可以得到更多的物理機制以瞭解幾何設計對壓力渦漩式噴嘴霧化的重要性。
本文由數值分析以及實際量測噴嘴外部流場之粒徑與速度分佈，發現掌握幾何尺度最重要的參數是進液流道與釋流孔面積比值，此值是影響空氣柱形成的主要原因，比值超過4，不能形成空氣柱，最後霧化效果由PDPA量測出的粒徑明顯較大，且由垂直速度分佈場發現，其噴射方式已由壓力渦漩式轉化為平孔噴射，本文建議此比值設計在1.2~2.5之間，能得到較佳的霧化。最後量測NAG1噴嘴，其平均霧化噴嘴粒徑SMD值達到105 ?m，這比目前台灣機車用噴射噴嘴的霧化效果還佳（380 ?m）。

關鍵字

粒徑量測儀 ； 微噴嘴 ； 微機電製程 ； 霧化

並列摘要

We manufacture miniature atomizers by UV-LIGA, and investigate the influence of geometry scale of atomizer on atomization. With CFD simulation study, the air core generation and flow phenomenon within atomizers were understood. Meanwhile, the SMD of atomized droplet was measured by PDPA (Phase Doppler Particle Anemometer). It was found that SMD size of atomized droplet was inversely proportional to air core diameter.
Sub-millimeter scale is a transient zone between traditional and MEMS manufacturing. The reasons lie on the precision of traditional fabrication and formation of thick photo-resist. In the traditional fabrication, the drill with its diameter less than 200 ?m gets easily shaking, and is hard to drill a concentric circle. Moreover, it can’t manufacture high aspect ratio geometry. This work successfully manufactures micro atomizer with discharge orifice diameter less than 200 ?m.
Compared simulation data with experimental data, we organize an important parameter, contraction ratio, the ratio of inlet area to outlet area. It affects the air core generating within the atomizer. When contraction ratio is higher than 4, the air core can’t be formed. The data from PDPA also evident it generates coarse droplets even vertical velocity of center droplets is higher than those in the outer field. The spray model has transferred from swirl motion to jet motion. We recommend to design contraction ratio between 1.2~2.5 for reaching good atomization.
Atomizer named NAG1 has Sauter mean diameter (SMD) of 105 ?m, and it is the best among the designed atomizer in the presented work. And it is superior to those nozzles used in the motorcycles (380 ?m).

並列關鍵字

micro-atomizers ； MEMS fabrication ； atomization ； phase-Doppler particle anemometry ； LIGA

參考文獻

劉中和, 曾培元, 郭光平, 朱裕瑞, 2001, “微尺度壓力渦漩式霧化器之紊性流場計算,” 中國航空太空學會學刊, Vol. 33, No. 1, pp. 53-58.

王覺寬, 徐明生, 王承光, 林富祈, 1997, “氣助式及氣衝式平面噴嘴中霧化空氣量對噴霧特性之影響,” 中國航空太空學會學刊, Vol. 29, No. 2, pp. 185-193.

Bachalo, W. D., 1994, “Injection, Dispersion, and Combustion of Liquid Fuels,” The 25th International Symposium on Combustion, The Combustion Institute, Pittsburgh, pp. 325-331.

Baik, S., Kang, S., Blanchard, J., and Corradini, M., 2000, “Development of Micro-Diesel Injector Nozzles via MEMS Technology and Effects on Spray Characteristics,” The Eighth International Conference on Liquid Atomization and Spray Systems, Pasadena, CA, USA, July 2000.

Chen, S. K., Lefebvre, A. H., and Rollbuhler, J., 1992, “Factors Influencing the Effective Spray Cone Angle of Pressure-Swirl Atomizers,” Journal of Engineering for Gas Turbines and Power, Vol. 114, January, pp. 97-109.