Abstract
This study proposed a nonintrusive and cost-efficient technique to measure the thickness of a thin water film/rivulet based on the grayscale index. This technique uses millions of probes and only needs a digital camera, fill lights, and pigment. For water colored with diluted pigment, the grayscale index of the water captured by a digital camera depends on the water thickness. This relationship can be utilized to measure the water thickness through digital image processing. In the present study, the relationship between the grayscale index and water thickness was theoretically and experimentally investigated. Theoretical derivation revealed that when the product of water thickness and the color density approaches to 0, the grayscale index is inversely proportional to the thickness. The experimental results show that under the color density of 0.05%, the grayscale index is inversely proportional to the thickness of water film when the thickness is less than 6 mm. This linear relationship was utilized to measure the distribution and profile of a water rivulet flowing on the lower surface of a cable model.
Highlights
Water thickness measurement is important in the fields of aircraft icing [1], rain-wind induced cable vibration [2,3,4,5,6], fluid mechanics [7,8,9,10], galloping of cables with ice accretion, etc
Several nonintrusive techniques have been developed to measure the thickness distribution of water film/rivulets, including structured light techniques (e.g., [1,11,12,13,14]), ultrasonic techniques [3,15,16], stereoscopic imaging techniques [17,18], density-based techniques (e.g., [19,20]), and laser-induced fluorescence imaging technique (e.g., [21,22,23,24])
Cobelli et al [11] and Salvi et al [13] described the principle of a structured light technique, which is an optical profilometric technique and mainly consists of a projector and a digital camera
Summary
Water thickness measurement is important in the fields of aircraft icing [1], rain-wind induced cable vibration [2,3,4,5,6], fluid mechanics [7,8,9,10], galloping of cables with ice accretion, etc. Zhang et al [1] developed a digital image projection system to measure water film and rivulet flows on airfoil surfaces. Laser-induced fluorescence techniques are widely used in flow visualizations When these techniques are combined with a charge-coupled device camera, the new system is referred to as a laser-induced fluorescence imaging technique system and is able to measure the thickness of water film/rivulets or the liquid-gas free boundary. Special lights (e.g., laser or ultraviolet) and special fluorescent material are required to induce the shine of fluorescence Under these circumstances, this study proposed a digital imaging method to measure the thickness of water film/rivulets based on the grayscale index. InFidgiugrieta2l (ibm)acgoensf.irTmhse tlhinaetatrhreelnaotinodnismheipnsinionEaqluarteioan S(1c (0q)Tw)il/lBbHe exlipneerairmlyenintaclrleyavseaslidwaitehdthane dwtahteer ptahriacmkneetesrssw, bh0eanntdheb1w, watiellrbfielmcailsibtrhaitne.d through experiments
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