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微重力池沸腾传热与单气泡热动力学特征研究
Alternative TitleStudy on Pool Boiling Heat Transfer and the Thermal Dynamical Characteristics of Single Bubble in Microgravity
吴克
Thesis Advisor赵建福
2019-11-27
Degree Grantor中国科学院大学
Place of Conferral北京
Subtype博士
Degree Discipline流体力学
Keyword微重力 沸腾 临界热流密度 单气泡池沸腾 气泡热动力学 实践十号卫星
Abstract

  沸腾现象由于利用了相变潜热而具有很高的传热效率,在日常生活和众多工程实践中有着十分广泛和重要的应用,对于沸腾传热机理的研究一直受到学术界的重视。

  在地面常重力环境下,浮力作用往往主导着沸腾现象,掩盖了与沸腾传热直接相关的加热面附近的细观流动与传热过程。利用微重力环境抑制浮力作用,增大气泡生长过程中的时间和空间尺度,有助于对沸腾现象中局部、瞬态过程进行细致研究,揭示沸腾传热的真正机理。

  本文利用实践十号(SJ-10)返回式科学实验卫星开展了微重力环境池沸腾传热实验研究,具体内容和取得的成果如下:

  首先,参与了空间实验用“沸腾气泡箱”装置的研制和集成式组合加热器的开发。“沸腾气泡箱”装置采用局部脉冲过热来激发产生“种子”气泡,实现对气泡生成的精确时-空定位,并使其在背部主加热器的加热作用下持续生长;加热面表面10路局部温度传感器以及加热基板背面的主加热器测量沸腾过程中的加热面局部温度与基板下表面平均温度,进而反演加热固壁内导热性能。完成了温度、压力、集成式组合加热器等的标定及“沸腾气泡箱”装置的地面环境测试,验证了装置的可靠性。

  其次,利用正样飞行件实验装置开展了地面常重力池沸腾传热的对比实验研究。提出了集成式组合加热器温度传感器的同步标定方法,实现了对局部温度和主加热器温度测量的准确标定。利用温度循环试验数据,计算了地面对比实验中不凝气体的含量。数据分析表明,地面常重力实验中单相自然对流传热特征与经典模型预测一致,核态沸腾起始时存在明显的温度过冲现象,核态池沸腾传热曲线符合Rohsenow关联式的预测。

  第三,完成了SJ-10卫星微重力池沸腾空间实验与数据分析。改进了集成式组合加热器同步标定方法,解决了空间实验中集成式组合加热器过热-再冷引发的标定难题。空间实验中,沸腾起始时加热面温度和气泡行为的特殊变化,表明加热面上气泡运动和聚集形式对沸腾传热的影响。核态沸腾传热实验结果的天地对比,揭示了过冷度、重力等对传热效率的影响。空间实验中沸腾现象在很低热流密度下即发生向过渡沸腾和/或膜态沸腾的转变,微重力临界热流大大降低。

  最后,利用局部脉冲过热方法,在空间飞行实验中成功激发并完成了单气泡池沸腾实验。对图像数据的分析揭示了微重力下气泡生长的动力学特征;加热表面局部温度分布的变化,揭示了单气泡生长过程中加热面温度的时空演化特征,以及三相接触线与加热表面干斑的动态演化过程。此外,根据微液层内部导热的平衡关系,反演确定了生长气泡底部初始微液层的厚度。这些成果为进一步揭示气泡热动力学行为与传热性能间的关联机制提供了良好的基础信息。

Other Abstract

  Boiling phenomenon has a very high heat transfer efficiency due to the use of the latent heat of phase change. It has a very wide and important application in daily life and many industry practices, so that the research on boiling heat transfer mechanism has been paid much attention by academia.

  Under the terrestrial normal gravity environment on the ground, buoyancy force often dominates the boiling phenomenon, masking the mesoscopic flow and heat transfer process near the heating surface, which are directly related to boiling heat transfer. In microgravity environment, the buoyancy force is suppressed, so the spatial and temporal scale of bubble growth process are increased, which will help to study the local and transient processes in boiling phenomenon and reveal the true mechanism of boiling heat transfer.

  In this paper, the pool boiling heat transfer experiment was carried out in microgravity environment by using the returnable scientific experimental satellite SJ-10. The contents and achievements of this paper are as follows:

  First of all, I participated in the development of the space experimental device “SOBER-SJ10” and the development of integrated micro-heater. The experimental device used local pulsed overheating to excite the “seed” bubbles, so that bubble generation could be positioned in precise location and time. The bubble will continue to grow under the heating of the main heater on the backside of the integrated micro-heater. The local temperature on top and the average temperature on back side of the heater were measured by the 10 local temperature sensors and the main heater respectively, so that the heat conduction in the heating solid wall could be inverted. The calibration of the temperature, pressure, integrated micro-heater, and the ground environmental test of the "SOBER-SJ10" device were completed to verify the reliability of the device.

  Secondly, a comparative experimental study on the pool boiling heat transfer in ground normal gravity was carried out using flight module of the experimental facility. A syn-calibration method was used to calibrate the temperature of local temperature sensors and the main heater. Non-condensable gas concentration in each ground experiment was estimated by using data from the thermal test. The data analysis shows that the single-phase natural convection in normal gravity experiment is consistent with the prediction of the classical model. There is obvious temperature overshoot at the beginning of the nucleate boiling, and the nucleate pool boiling curve is consistent with the prediction of Rohsenow’s correlation.

  Thirdly, the on-orbit experiment aboard the SJ-10 satellite was successfully carried out, and data analysis of the microgravity pool boiling experiments was completed. The syn-calibration method of integrated combined heater was improved to solve the calibration problem caused by overheat and fast-cooling of integrated micro-heater in space experiments. In space experiments, the special variation of the surface temperature and bubble behavior at the onset of boiling indicates that the bubble motion and aggregation form on the heating surface influence the boiling heat transfer process. The comparison of the results of nucleate boiling heat transfer process in space and ground experiments reveals the effects of subcooling and gravity on heat transfer efficiency. In the space experiments, the transition to transition boiling or to film boiling occurs at a very low heat flux density, and the critical heat flux is greatly reduced in microgravity.

  Finally, using the local pulse superheating method, the single bubble pool boiling experiments were successfully carried out in the on-orbit flight experiment. The analysis of image data reveals the dynamical characteristics of bubble growth under microgravity. The variation and distribution of local temperature on the heating surface reveals characteristics of the spatial-temporal evolution of the surface temperature, as well as the dynamical evolution of three-phase contact line and the dry spot on heating surface, during the single bubble growth. In addition, according to the equilibrium relationship of heat conduction inside the micro-layer, the initial thickness of the micro-layer at the bottom of the growth bubble was evaluated. These results provide good and basic information for further revealing the mechanism between the bubble thermal dynamical behavior and heat transfer performance.

Call NumberPhd2019-035
Language中文
Document Type学位论文
Identifierhttp://dspace.imech.ac.cn/handle/311007/80725
Collection国家微重力实验室
Recommended Citation
GB/T 7714
吴克. 微重力池沸腾传热与单气泡热动力学特征研究[D]. 北京. 中国科学院大学,2019.
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