ABSTRACT An ex-situ visualization experimental system for the proton exchange membrane fuel cell (PEMFC) is developed to study the dynamic characteristics of a droplet in a square flow channel. The extraction of droplet dynamic contact angles based on droplet shape is performed by a customized image processing method. The best double circle fitting is found by comparing different fitting methods for contact angle extraction. The accuracy of double circle fitting is improved by the relationship between droplet shape and data analysis, and it achieves good consistency with manual measurement. The contact angle hysteresis gradually increases to the maximum during droplet evolution until the droplet detaches. With the increase of gas flow rate, the contact angle hysteresis decreases at the instant of detachment, the droplet size and removal time are found to decrease, and the oscillation of the droplet is severer before droplet detachment.
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