渦漩式霧化裝置之理論分析、模擬暨實驗探討

Theoretical Analysis, Simulation and Experimental Investigation of Swirl Atomizers

朱佳建(Chia-Chien Chu)

指導教授 ： 周賢福

國立臺灣大學/工學院/機械工程學研究所/博士(2008年)

https://doi.org/10.6342/NTU.2008.00737

摘要

本文主要區分為三大部份。第一部份為以之前相關研究為基礎，使用理論分析方式預測渦漩式霧化裝置之液膜厚度、速度分佈、噴霧角度、粒徑尺寸等相關參數。首先，流體假設為不可壓縮牛頓流體，流場為穩態且軸對稱，於渦漩腔內以質能守恆推導求得邊界層成長及液膜厚度關係式。於噴嘴外則使用Squire之液膜分析模式，求得液膜轉變成液帶再斷裂為液珠後重要特性參數之關係式。包含噴霧角度及粒徑尺寸等參數，皆可表示為噴嘴尺寸、驅動壓力及流體密度之外顯函數。
第二部份則使用數值模擬軟體FLUENT，使用兩相流設定，搭配 之紊流模式及壁面函數，模擬圓柱式與平板式噴霧裝置之流場，並求得流量、噴霧角度與噴嘴尺寸及驅動壓力之關係曲線圖。與第一部份之理論分析結果相比較，可以了解數值模擬軟體於預測流量、噴霧角度上的準確程度。
本文第三部份則為實測驗證，求得流量與驅動壓力之關係、流量與噴嘴尺寸之關係、噴霧角度及粒徑與噴嘴尺寸之關係、噴霧粒徑與驅動壓力之關係。實驗所得結果，再與理論分析之結果相比較，了解並驗證理論分析得到之趨勢正確性。最後，基於上述之理論、模擬與實驗結果，提出渦漩式霧化裝置效率之最佳化策略，達到針對驅動壓力、噴嘴尺寸等變數之調整，而達到增加噴霧角度、縮小噴霧粒徑之顯著效果。

關鍵字

渦漩式 ； 霧化裝置 ； 液膜厚度 ； 粒徑

並列摘要

In this study, theoretical analyses have been performed to investigate the effects of atomizer construction and controlled pressure difference of swirl atomizers. The analysis of fluid field in the swirl chamber is governed by mass/energy conservation rules; in the region outside the nozzle, the analysis of oscillation of liquid sheet is based on Squire`s expression for the amplitude growth rate. With some physical assumptions of control volume, initial values and model correlation, analytical results make it possible to predict film thickness, velocity distribution, spray cone angle and droplet size directly. The distribution of velocity profile and boundary layer thickness in the swirl chamber has been established with the aid of MATLAB.
From the theoretical analysis, the equations for the droplet size, velocity components, the boundary layer thickness and the spray cone angle were deduced based on the fundamental governing equations. The purpose of the second stage is to establish a feasible model in FLUENT for the prediction of certain characteristics of swirl atomizers. The control variables in the simulations are pressure difference, nozzle geometries and the dependent variables are volume flow rate, spray cone angle and the resulting discharge coefficient.
The purpose of the final stage of this study is to further compare the experimental result with the theoretical one already gained by a satisfactory embodiment of series of experiments. The aim is to corroborate the analytical results of the influence of atomizer construction and controlled pressure difference on typical swirl chambers. The results provide the droplet diameter as a function of pressure difference, swirl atomizer geometry, flow rate and spray cone angle. The experimental outputs also show good confirmation of theoretical results and can also be used for further optimization on existing swirl chambers. Based on the results obtained, an optimization methodology on characteristics of swirl atomizers is proposed with the adjustment of individual design parameter and the matching flow number.

並列關鍵字

Swirl atomizer ； droplet ； spray cone angle

參考文獻

[2] N. Dombrowski and D. Hasson: The Flow Characteristics of Swirl (Centrifugal) Spray Pressure Nozzles with Low Viscosity Liquids, AIChE Journal, Vol. 15, Issue 4, 604-611 (1969).

[3] J. Ballester and C. Dopazo: Discharge Coefficient and Spray angle Measurements for Small Size Pressure-Swirl, Atomization and Sprays, Vol. 4, 351-367 (1994).

[4] A. Datta, S. K. Som: Numerical Prediction of Air Core Diameter, Coefficient of Discharge and Spray Cone Angle of a Swirl Spray Pressure Nozzle, International Journal of Heat and Fluid Flow, Vol. 21, 412-419 (2000).

[5] J. L. York, H. E. Stubbs, and M. R. Tek: The Mechanism of Disintegration of Liquid Sheets, Transactions of The ASME, Vol. 75, 1279-1286 (1953).

[6] N. Dombrowski and P.C. Hopper: The Effect of Ambient Density on Drop Formation in Sprays, Chemical Engineering Science, Vol. 17, 291-305 (1962).