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首页> 外文期刊>Heat transfer >Heat Transfer and Flow Characteristics of Flow Boiling of CO_2-Oil Mixtures in Horizontal Smooth and Micro-Fin Tubes
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Heat Transfer and Flow Characteristics of Flow Boiling of CO_2-Oil Mixtures in Horizontal Smooth and Micro-Fin Tubes

机译：水平光滑和微细管中CO_2-油混合物的沸腾传热和流动特性

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摘要

Experiments were carried out on the flow pattern, heat transfer, and pressure drop of flow boiling of pure CO_2 and CO_2-oil mixtures in horizontal smooth and micro-fin tubes. 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. The experiments were carried out at mass velocities from 100 to 500 kg/(m~2·s), saturation temperature of 10 ℃, and the circulation ratio of lubricating oil (PAG) was from 0 to 1.0 mass%. Flow pattern observations mainly showed slug and wavy flow for the smooth tube, but annular flow for the micro-fin tube. Compared with the flow patterns in the case of pure CO_2, an increase in frequency of slug occurrence in the slug flow region, and a decrease in the quantity of liquid at the top of the tube in the annular flow region were observed in the case of CO_2-oil mixtures. With pure CO_2, the flow boiling heat transfer was dominated by nucleate boiling in the low vapor quality region, and the heat transfer coefficients for the micro-fin tube were higher than those of the smooth tube. With CO_2-oil mixtures, the flow boiling heat transfer was dominated by convective evaporation, especially in the high vapor quality region. In addition, the heat transfer coefficient decreased significantly when the oil circulation ratio was larger than 0.1 mass%. For the pressure drop characteristics, in the case of pure CO_2, the homogeneous flow 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 flow model, and the pressure drops increased for the high oil circulation ratio and high vapor quality conditions. The increases in the pressure drops were considered to be due to the increase in the thickness of the oil film and the decrease in the effective flow cross-sectional area.
机译：对水平光滑和微翅片管中纯CO_2和CO_2-油混合物的流型，传热和沸腾压降进行了实验。光滑管是内径为3.76毫米的不锈钢管。微翅片管是平均内径为3.75mm的铜管。在100至500 kg /（m〜2·s）的质量速度，10℃的饱和温度下进行实验，润滑油（PAG）的循环比为0至1.0质量％。流动模式的观察结果主要显示光滑管为团状和波状流动，而微翅片管为环状流动。与纯CO_2情况下的流动模式相比，在环状流动区域中，在团状流动区域中发生团状的频率增加，并且在管顶部的液体量减少。 CO_2-油混合物。对于纯CO_2，在低蒸汽质量区域中，沸腾传热主要由成核沸腾引起，并且微翅片管的传热系数高于光滑管的传热系数。对于CO_2-油混合物，特别是在高蒸气质量区域，对流蒸发主要是流沸腾传热。另外，当油循环率大于0.1质量％时，传热系数显着降低。对于压降特性，在纯CO_2的情况下，均质流模型与光滑管的实验结果在±30％之内一致。微翅片管的压降比均相流模型预测的高0-70％，并且在高油循环比和高蒸汽质量条件下，压降增加。认为压降的增加是由于油膜的厚度增加和有效流截面积的减少。

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