This work investigates the growth and detachment of chemically formed micro-bubbles on micro-textured catalyst using a high-speed digital camera and simulation results. Three bubble growth stages were identified for single bubbles grown on circular type Pt catalyst. The first stage was inertia-controlled and the bubble diameter was directly proportional to time, and pertained when the bubble size was smaller than the Pt catalyst; in the second and third stages, gas was generated at a constant rate and the bubble diameter was varied as the cube root of time. However, in the third stage, the bubble growth rate is slightly lower than in the second stage, suggesting saturation. The calculation based on a mathematical model at constant gas generation rate is highly consistent with experimental results. The basic single bubble growth phenomenon was then adopted as a comparison to the bubble growth phenomena on textured catalyst structures. Experimental results revealed that a discontinuous mesh catalyst can effectively shorten the bubble detachment time when the substructures are thoroughly separated and the bubbles are larger than their initial size (*5 lm), while the concentric circular pattern does not. This study provides an insight into the growth and detachment phenomena of chemically formed micro-bubbles on catalyst of different textures, which is useful to the design of reactors for fuel cell systems.
High brightness light-emitting diode (HB-LED) has now become one of the most popular lighting device in our daily life. As the LED industry becomes prosperous, techniques for improving production efficiency become more and more important. In this paper, a system integration method was proposed and successfully realized to implement an automatic measurements and grading (AMG) system for the LED dies after the wafer has been scribed and broken. It can be used to greatly improve the speed, efficiency and accuracy in the testing process. This suggested approach combines machine vision, optical measurement instruments, and mechanical technology to create an affordable, flexible, and highly efficient LED measurement and grading system. System architecture and details on each subsystem were described and performance was evaluated. The average speed of measurement is 3.5 LED dies per second based on repeated testings and evaluations. The experimental results demonstrate the effectiveness and robustness of the proposed system. We hope the results presented in this paper can help the LED manufacturer to make more informed decisions on the design or purchase of the AMG machine.
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