不同表面張力水溶液之高速雙液滴碰撞

Abstract

不 同 表 面 張 力 水 溶 液 之 高 速 雙 液 滴 碰 撞

周秉忠 指導教授：潘國隆博士

國立台灣大學機械工程學研究所

摘要 本文針對不同的溶液下所產生的液滴進行正向對撞，進而觀察其碰撞之現象，並且建立一套產生液滴之實驗設備，以及建立一套可觀測液滴撞擊現象的觀測設備，經由改變溶液的性質(表面張力)以及液滴大小與速度，並且藉由攝影所擷取的瞬間影像來了解液滴對撞之現象。實驗著重於二部份，第一，利用液滴產生器以及氣壓缸產生一穩定的低速以及高速液滴，並且能夠改變其成型的粒徑大小以及速度，第二，產生穩定液滴之後，進而使其對撞，對撞面必須為正向，且此二液滴的粒徑大小必須一樣，之後再觀察其現象。期望能夠提供液滴碰撞現象明確而且充分的資料。 過去前人對於液滴碰撞的研究雖然多，然而在之前的研究當中，其所探討之區域主要在較低韋伯數之區域，因此，本實驗主要在於能夠產生高速(高韋伯數)之液滴並且將其正向對撞。而本實驗的控制參數為液滴的性質(表面張力)、液滴大小與速度、噴嘴孔徑的大小、訊號產生器之電壓以及頻率、氣壓缸的壓力大小、馬達之轉速。

本實驗主要探討三個部份：一為在低速(低韋伯數)之下，液滴撞擊之現象觀察與討論；二為在高速(高韋伯數)之下，液滴撞擊之現象觀察與討論；三為更換不同的溶液，將表面張力改變，進而觀察其液滴撞擊的現象，而最後將實驗所得到之數據整理完整，之後再加以分析與比較其之間的差異。

關鍵字：液滴碰撞、液滴產生器、高速液滴、表面張力、韋伯數、訊號產生器

High-Speed Binary Water Droplet Collision with Different Surface Tension Ping-Chung Chou Advisor：Kuo-Long Pan, Ph.D. Department of Mechanical Engineering National Taiwan University

Abstract This study aims at droplet generation with different water solution to achieve a head-on collision and to observe the phenomenon under head-on collision. The set of devices for droplet generation and for observation of droplet collision are elaborated, through changing the parameters of solution (such as surface tension, size and velocity of droplets) and collecting the instant image by a high-speed camera to get more understanding of droplet collision phenomenon. In this experimental study, the most attention is given to two aspects. The first one is to generate a stable droplet with low and high speed respectively by using a droplet generator and a gas cylinder. At this stage we can control the size and velocity of a droplet. The second stage of experiment is to provide the droplet with head-on collision, whereby the size of two droplets must be almost the same, and then we observe the phenomenon. We expect to provide explicit and full data for droplet collision phenomena on this experiment. In spite of numerous researches on droplet collision, most of the research investigated into low Weber number of droplet. Therefore, this experiment is mainly focused on how to generate a high-speed (high Weber number) droplet and to make the droplet always keep head-on collision. The variables in this experiment include the droplet surface tension, the size and the velocity of droplet, the diameter of nozzle, the voltage and the frequency of signal generator, the pressure of gas cylinder, and the rotational speed of motor tested. The conclusions of this experiment consist of three parts. In the first part, we observe and discuss the collision of low velocity (low Weber number). The second is to describe the experimental results of high velocity (high Weber number) droplet collision. The third is to observe and discuss the phenomena of droplet collision under different surface tensions.

Keywords: droplet collision, droplet generator, high-speed droplet, surface tension, Weber number, signal generator.