Vapor-liquid flows in industrial scale downcomers are tested. Liquid backmixing and circular flow in downcomer are tested with the fluoro-tracer agent and the hot water tracer technique in a 1900mm and a 1200mm diameter simulator,respectively. The downcomer chocking liquid-load is determined in a rectangle simulator, with dimentions of 800mm x 600mm. The results shows severe liquid backmixing in the downcomer, with significant circular flows in the middle of downcomer. Recommendations on tray downcomer designs are also presented in this paper.

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