Boiling Heat Transfer of Carbon Dioxide in a Horizontal Tubes
Boiling Heat Transfer of Carbon Dioxide in a Horizontal Tubes
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DOI：
10.1115/ht2007-32885
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发表时间：
2005-07
期刊：
影响因子：
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通讯作者：
Takashi Yamada;N. Haraguchi;E. Hihara;Jianfeng Wang
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文献类型：
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作者：
Takashi Yamada;N. Haraguchi;E. Hihara;Jianfeng Wang
在这项研究中，对水平放置的光滑管中二氧化碳的沸腾传热系数进行了实验研究。传热管内径为1、2、4、6mm。实验在蒸发温度为 5°C 和 15°C、热通量为 4.5 至 36 kW/m2、质量通量为 360 至 1440 kg/m2·s 的条件下进行。研究了干燥前区域和干燥后区域的传热系数以及干燥质量。由于CO2的粘度和表面张力较小，干燥发生在0.4至0.7的较小质量下。起始质量随质量通量的增加而降低，并受热通量和管径的影响；预干区热流密度对传热系数的影响非常显着，这与核态沸腾的激活有关。相反，由于临界点附近两相密度比较低，质量通量的影响相对较小。另外，当测试小管时，这种趋势变得更加明显；在干燥后区域，质量速度是传热系数的主导因素。在小质量流量时，传热系数随着质量的增加而减小，而在大质量流量如1440kg/m2·s时，传热系数则随着质量的增加而转为增加。通过提高蒸发温度，干燥前传热系数增加，而干燥起始质量和干燥后传热系数受蒸发温度影响不大。Copyright © 2007 by ASME
In this study, boiling heat transfer coefficients of carbon dioxide in horizontally located smooth tubes were experimentally investigated. The inner diameter of heat transfer tubes was 1, 2, 4, and 6 mm. Experiments were conducted at evaporating temperature of 5 and 15 °C, heat fluxes from 4.5 to 36 kW/m2 , and mass fluxes from 360 to 1440 kg/m2 s. The heat transfer coefficients in the pre-dryout region and post-dryout region were investigated, as well as the dryout quality. Due to the small viscosity and surface tension of CO2 , the dryout occurs at a small quality from 0.4 to 0.7. The inception quality decreases with the increase of mass flux, and is affected by the heat flux and tube diameter; the effects of heat flux on the heat transfer coefficient are much significant in the pre-dryout region, which is related with the activation of nucleate boiling. On the contrary, the effects of mass flux are relatively low due to the low two-phase density ratio near the critical point. In addition, this tendency becomes more significant when the small tube is tested; In the post-dryout region, mass velocity is the dominating factor on heat transfer coefficient. At small mass flux, the heat transfer coefficient decreases with the increase of quality, while at large mass flux such as 1440kg/m2 s, the heat transfer coefficient turns to increasing with the quality. By increasing the evaporating temperature, the pre-dryout heat transfer coefficient increases, while the dryout inception quality and post-dryout heat transfer coefficient are not affected greatly by the evaporating temperature.Copyright © 2007 by ASME