| Summary: | 碩士 === 國立虎尾科技大學 === 機械與機電工程研究所 === 100 === The thesis analyze the on-focus and off-focus images to examine the influence of the gradations of off focus (S) on the original equivalent diameter (Dx), the diameter of the interior spot (d1), the distance (b) between the center of the droplet (CDx) and the center of the interior spot (Cd1), and the distance (L1) between the left edge of the droplet image and Cd1, and the distance (L2) between the right edge of the droplet image and Cd1. The most important findings are summarized as follows:
1. The original equivalent diameter (Dx), the spot diameter of (d1), the distances L1 and L2 increase with the the gradations of off focus (S) (ex. 50 % increases in S leading to increases of Dx, d1, L1, and L2 by 20.5%, 420%, 12% and 67%, respectively.
2. The distance (b) between CDx and Cd1 remains alomost constant (< ±2%) and seems to be independent of the increase of the gradations of off focus (S) up to 100 %.
The distance (b) was used to estimate the real droplet diameter (Chen 2011). The thesis, therefore, suggests the ratio α (L1/ b) as an index of off focus and examine the influence of the gradation of off focus (S) on the ratio α and the real droplet diameter (D).
The experimental results suggest :
(1) the gradation S linearly increases with the ratio α by 1.7% per mm, and is defined as
S =[(αn－α0)/ α0]/0.017.
(2) the ratio α is symmetrical in positive and negative values of the gradation S.
The experimental results confirm that the gradation S the drifting distance (Ldn) due to air drag, which is defined as
Ldn = [(αn－α0)/ α0]/0.017 and the initial droplet shift S2.
where：αn is L1n/ bn of an arbitrary image;
α0 (L1o/ b) is 2.46, the base value obtained at the on-focus positions.
The thesis finally carried out an series of experiments to test the practicability of above findings. The results confirm that the above relationships can correctly estimate real droplet diameter and the gradation of off focus (S) according to the original diameter (Dx), the distances b, L1 and the ratio α for droplet diameter larger than 200 μm, and gradation (S)less than ±10mm. As a result, the above findings are of practicability since a camera lens used to shot images of 200 μm droplets is usually associated with a short focal length with a narrow depth of focus less than ±5mm.
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