CO_2-オイル混合物の水平平滑および内面らせん溝付管内の管内沸騰熱伝達

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Experiments on flow pattern, heat transfer and pressure drop of flow boiling of pure CO2 and CO2-oil mixtures in horizontal smooth and micro-fin tubes have been carried out. The smooth tube is a stainless steel tube with an inner diameter of 3.76 mm. The micro-fin tube is a copper tube with a mean inner diameter of 3.75 mm. Experiments were carried out at mass velocities from 100 to 500 kg⁄(m2·s), saturation temperature of 10 °C, and the circulation ratio of lubricating oil (PAG) is from 0 to 1.0 mass%. Flow pattern observations mainly showed the slug and wavy flow for the smooth tube, but the annular flow for the micro-fin tube. As compared with flow patterns in case of pure CO2, an increase in frequency of slug occurrence in slug flow region, and a decrease in liquid amount at the top of the tube in annular flow region were observed in case of CO2-oil mixtures. For pure CO2, the flow boiling heat transfer was dominated by nucleate boiling at low vapor quality region, and the heat transfer coefficients for the micro-fin tube were higher than those of the smooth tube. For CO2-oil mixtures, the flow boiling heat transfer was dominated by convective evaporation especially at high vapor quality region. In addition, the heat transfer coefficient decreased remarkably when the oil circulation ratio was larger than 0.1 mass%. For pressure drop characteristics, in case of pure CO2, the homogeneous model agreed with the experimental results within ± 30 % for the smooth tube. The pressure drops of the micro-fin tube were 0˜70 % higher than those predicted with the homogeneous model. Furthermore, the pressure drops increased at the high oil circulation ratio and high vapor quality conditions. The increases in the pressure drops were considered due to the increase in the thickness of the oil film and the decrease in the effective flow cross-sectional area.
社団法人日本伝熱学会の論文
2009-07-01

CO_2-オイル混合物の水平平滑および内面らせん溝付管内の管内沸騰熱伝達

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