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An optical measurement system was developed to investigate gas-liquid two-phase flow characteristics in a circular microchannel of 100 μm diameter. By using multiple optical fibers and infrared photodiodes, void fraction and gas plug and liquid plug lengths, and their velocities were measured successfully. The probes responded to the passage of gas and liquid phases through the microchannel adequately so that the time-average void fraction could be obtained from the time fraction for each phase. Also, by cross-correlating the signals from two neighboring probes, the interface velocity representing gas plug velocity or ring-film propagation velocity depending on the flow pattern could be computed. Within the ranges of superficial gas and liquid velocities covered in the experiments (jL = 0.2∼0.4 m/s and jG = 0 ∼ 5 m/s), the gas plug length was found to increase with the increasing superficial gas velocity, but the liquid plug length was found to decrease sharply as the superficial gas velocity was increased, so that the total length of the gas-liquid plug unit decreased with the superficial gas velocity.

An optical measurement system was developed to investigate gas-liquid two-phase flow characteristics in a circular microchannel of 100 μm diameter. By using multiple optical fibers and infrared photodiodes, void fraction, gas and liquid plug lengths, and their velocities were measured successfully. The probes responded to the passage of gas and liquid phases through the microchannel adequately so that the time-average void fraction could be obtained from the time fraction for each phase. Also, by cross-correlating the signals from two neighboring probes, the interface velocity representing gas plug velocity or ring-film propagation velocity depending on the flow pattern could be computed. Within the ranges of superficial gas and liquid velocities covered in the experiments (j L=0.2∼0.4 m/s and j G = 0∼5 m/s), the gas plug length was found to increase with the increasing superficial gas velocity, but the liquid plug length was found to decrease sharply as the superficial gas velocity was increased; thus, the total length of the gas-liquid plug unit decreased with the superficial gas velocity.

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The effect of lubricants on deep drawability was studied for two types of zinc-coated steel sheets on a high-speed deep-drawing machine. The drawability of galvannealed steel sheet, GA, at low speeds is significantly improved by friction modifiers, due to reduction in frictional forces around the die radius. I n contrast to the results for GA, double layered steel, GAE, which has an Fe-rich alloy coating on the top, and is superior to GA in terms of drawability, is insensitive to changes in the additives. This is mainly because the hardness of the upper coating layer of GAE decreases frictional resistance through a decline in the boundary contact area. Abstract Keywordsdeep drawing, alloy-coated steel, double layered steel, zinccoated steel, friction modifiers, viscositySince the mid 1970s, various types of zinc-coated steel have been developed for automotive bodies in place of cold rolled steel to improve corrosion resistance. The main corrosionresistant materials used are hot-dip galvannealed steels, whose coating weight has increased from 20 g/m2 t o 60 g/m2 in accordance with the requirement for a high level of anticorrosion. Recently, double layered steel with an electrogalvanised Fe-rich alloy coating has been used for the outer panels of automobiles owing to excellent spot weldability and paintability. As the coating weight has increased, however, zinc-coated steels have been liable to exhibit fracture during the drawing process because of insufficient lubricity between the coating layer and the tool when conventional rust preventive oils are In order to improve the drawability of zinc-coated steels, rust preventive oils with high lubricity are required.

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