Condensation heat transfer enhancement mechanism for vertical upflows by the phase separation concept at small gravity  

作　　者：Qicheng Chen Dongliang Sun 

机构地区：[1]School of Energy and Power Engineering, Northeast Dianli University [2]School of Mechanical Engineering, Beijing Institute of Petrochemical Technology

出　　处：《Science Bulletin》2015年第20期1759-1767,共9页科学通报（英文版）

基　　金：supported by the National Natural Science Foundation of China(51476054 and 51506026);the Program for New Century Excellent Talents in University(NCET-13-0792)

摘　　要：In the field of aerospace, minimum and seal of equipments cause the increase in the thermal loading sharply. Due to the lack of driving force, the performance of conventional condenser deteriorates greatly under the small gravity environment, which leads to reduction in the service life of equipments. In this study, a passive condenser, developed on basis of the phase separation concept,is utilized to improve the performance of the condensation heat transfer under the small gravity environment. As a result of the limitation of experiments, the mechanisms of heat transfer enhancement of the phase separation condenser tube are revealed through numerical simulation based on the volume-of-fluid(VOF) method. The following conclusions could be obtained:(1) A novel phase distribution of ‘‘gas near the tube wall and liquid in the tube core'' is formed. The thin liquid film is indeed created after the flow pattern modulation by inserting mesh cylinder.(2)The condensation quantity for single bubble in the annular region increases about 16 times greater than that in the bare tube region in the case of Jl= 0.0574 m/s and Jg= 0.0229 m/s.(3) Gas volume fraction affects the parameters of liquid film thickness, bubble length and liquid bridge length. The increase in the gas volume fraction results in the decrease in the evaluation index from21.56 to 12.82. The evaluation index is defined as the ratio of the condensation quantities per unit tube length of the annular region and the bare tube region.In the field of aerospace, minimum and seal of equipments cause the increase in the thermal loading sharply. Due to the lack of driving force, the performance of conventional condenser deteriorates greatly under the small gravity environment, which leads to reduction in the service life of equipments. In this study, a passive con- denser, developed on basis of the phase separation concept, is utilized to improve the performance of the condensation heat transfer under the small gravity environment. As a result of the limitation of experiments, the mechanisms of heat transfer enhancement of the phase separation con- denser tube are revealed through numerical simulation based on the volume-of-fluid （VOF） method. The follow- ing conclusions could be obtained： （1） A novel phase dis- tribution of ＂gas near the tube wall and liquid in the tube core＂ is formed. The thin liquid film is indeed created after the flow pattern modulation by inserting mesh cylinder. （2） The condensation quantity for single bubble in the annular region increases about 16 times greater than that in the bare tube region in the case of Jl = 0.0574 m/s and Jg =0.0229 m/s. （3） Gas volume fraction affects the parameters of liquid film thickness, bubble length and liquid bridge length. The increase in the gas volume frac- tion results in the decrease in the evaluation index from 21.56 to 12.82. The evaluation index is defined as the ratio of the condensation quantities per unit tube length of the annular region and the bare tube region.

关 键 词：Condensation heat transfer PHASESEPARATION Small gravity Liquid film thickness 

分 类 号：V444.3[航空宇航科学与技术—飞行器设计]