空间热控蒸发器流动沸腾传热特性研究

发布时间：2018-10-19 16:42

【摘要】：热控系统,是保证航天器内温度稳定,各仪器设备稳定工作的重要组成部分。随着航天技术的不断发展,航天器的热控环境愈加恶劣。一方面,在辐射散热效率低的航天器热控系统中,需要使用蒸发器作为消耗性热沉来进行热量排散；另一方面,在低温的环境中,又需要对关键设施进行加热控温。在任何蒸发换热器的结构设计之中,管内两相流流动沸腾传热,都是首要的考虑因素之一。本文从26篇文献中,收集了2783个环形流流型下的流动沸腾换热系数实验数据,建立了环形流流动沸腾换热数据库。该数据库包含七种不同工质,覆盖水力直径范围0.5-14.0mm,质量流速范围50-1290kg/m2s,全液雷诺数范围240～55119,热力学干度范围0.013～0.985,热流密度范围3.0-240.0kW/m2,液相普朗特数范围1.26～5.85,对比压力0.01-0.77。此外,本文总结了19种现有流动沸腾换热系数预测方法,使用所建立数据库对其进行了精度评估,发现大部分现有的方法,并不能对数据库内数据给出令人满意的预测精度。因此,本文基于Cioncolini-Thome环形流湍流模型,提出了一个新的换热关联式,用于环形流流型下的流动沸腾换热系数计算；新关联式的预测精度明显高于所有现有模型,其MAE和MRE分别为13.7%和0.4%,预测误差不超过±15%、±30%和±50%的数据比例分别为66.5%、89.0%和96.9%；同时,新的关联式适用性强,对于不同工质和管道尺寸的换热系数均能给出精度较高的预测。另一方面,本文还针对Q型槽道管内表面结构对流动沸腾传热特性的影响,设计并搭建了两相流流动沸腾传热实验平台,对槽道管内流动沸腾换热特性,以及重力方向对其传热特性的影响,进行了实验研究。研究表明,管道内表面的槽道结构,能够明显强化核态沸腾换热的能力,提高传热性能：在水平流动及竖直上升流动中,槽道管内流动沸腾换热系数约为光滑圆管的1.5-3倍,在竖直下降流动中,最高可以达到光滑圆管8倍左右。然而,不同流动方向的流动沸腾换热特性明显不同,说明在实验参数范围内,管内槽道群结构并不能影响到两相流流型,保证液体工质对槽道的润湿,也不能起到消除重力影响的作用。此外,本文还针对低温环境下航天器的加热控温,制备了一系居里温度符合电子设备热控要求的PTC材料,并从理论和实验两个方面,研究了利用PTC材料进行自适应控温的适用条件和热控特性。
[Abstract]:Thermal control system is an important part to ensure the stability of spacecraft temperature and equipment. With the development of spaceflight technology, the thermal control environment of spacecraft becomes worse and worse. On the one hand, in the spacecraft thermal control system with low radiative heat dissipation efficiency, the evaporator is used as the expendable heat sink for heat emission; on the other hand, in the low temperature environment, the key facilities need to be heated to control the temperature. In the structural design of any evaporative heat exchanger, the boiling heat transfer of two-phase flow in the tube is one of the most important factors. In this paper, the experimental data of flow boiling heat transfer coefficient under 2783 annular flow patterns were collected from 26 literatures, and a database of annular flow boiling heat transfer was established. The database contains seven different working fluids, covering the hydraulic diameter range of 0.5-14.0mm, the mass flow rate range of 50-1290kg / m ~ 2 s, the whole liquid Reynolds number range 240 ~ 55119, the thermodynamic dryness range 0.013 ~ 0.985, the heat flux range 3.0-240.0kW / m ~ (2), the liquid phase Plantt number range 1.265.85, and the relative pressure 0.01-0.77. In addition, 19 existing prediction methods of flow boiling heat transfer coefficient are summarized in this paper. The accuracy of these methods is evaluated by using the established database. It is found that most of the existing methods can not give satisfactory prediction accuracy for the data in the database. Therefore, based on the Cioncolini-Thome annular flow turbulence model, a new heat transfer correlation is proposed, which can be used to calculate the boiling heat transfer coefficient of the annular flow, and the prediction accuracy of the new correlation is obviously higher than that of all the existing models. The MAE and MRE are 13. 7% and 0. 4, respectively. The ratio of prediction error to 卤15, 卤30% and 卤50% is 66.589% and 96.9%, respectively. At the same time, the new correlation has strong applicability, and the heat transfer coefficient of different working fluids and pipe sizes can be predicted with high accuracy. On the other hand, aiming at the influence of the surface structure of Q channel tube on the flow boiling heat transfer characteristics, the experimental platform of two phase flow boiling heat transfer is designed and built, and the flow boiling heat transfer characteristics in the channel tube are analyzed. The influence of the direction of gravity on the heat transfer characteristics is studied experimentally. The results show that the channel structure on the inner surface of the pipe can obviously enhance the heat transfer ability of nucleate boiling and improve the heat transfer performance. In horizontal flow and vertical upward flow, the boiling heat transfer coefficient of the flow in the channel is about 1.5-3 times that of the smooth tube. In vertical descending flow, the maximum is about 8 times of smooth circular tube. However, the flow boiling heat transfer characteristics in different flow directions are obviously different, which indicates that in the range of experimental parameters, the structure of the channel group in the tube can not affect the two-phase flow pattern and ensure the wettability of the liquid working fluid to the channel. Nor can it play a role in eliminating the effects of gravity. In addition, a series of PTC materials with Curie temperature in accordance with the thermal control requirements of electronic equipment have been prepared for spacecraft heating and temperature control in low temperature environment. The suitable conditions and thermal control characteristics of adaptive temperature control using PTC materials are studied.
【学位授予单位】：中国科学技术大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：V444.36

【参考文献】