摘要
为了探究Soret效应对具有自由表面的圆柱形浅液池内双组分溶液热对流过程的影响,通过实验观察了质量分数为50%的正癸烷/正己烷混合溶液在不同深宽比的液池内流动失稳后的自由表面耗散结构及液池内的温度波动.结果表明,双组分溶液流动失稳的临界热毛细Reynolds数小于纯工质的值,且其随液层深宽比的变化规律与纯工质相同.当深宽比小于0.0848时,流动失稳后在自由表面观察到热流体波,监测点处温度波动主频随热毛细Reynolds数增大而增加;当深宽比大于0.0848时,随热毛细Reynolds数的增大,流动失稳后自由表面依次呈现轮辐状、花苞状、分离-合并-分离交替变化的条纹状结构.
In this paper, a series of experiments are conducted to understand the influence of Soret effect on thermal convection of binary mixture in a cylindrical pool with a free surface. The cylindrical pool is filled with the n-decane/n-hexane mixture with an n-decane initial mass fraction of 50%. The cylindrical pool and the disk on the free surface are kept at constant temperatures of Th and Tc （Th 〉 Tc）, respectively. Temperature fluctuation pattern on the free surface is obtained by the schlieren method. Various temperature oscillatory patterns on the free surface are observed when the thermal convection of the n-decane/n-hexane mixture destabilizes at different aspect ratios. Results show that the critical thermal capillary Reynolds number of the incipience of the three-dimensional oscillatory flow in the n-decane/n- hexane mixture is smaller than that in the n-hexane fluid, and the variation tendency with the aspect ratio in the n-decane/n-hexane mixture is the same as that in the n-hexane fluid. The solute-capillary force caused by Soret effect plays an important role of the thermal convection in the n-decane/n-hexane mixture. Because the solute-capillary force has the same direction as the thermocapillary force, the thermal convection in the n-decane/n-hexane mixture becomes more instable and the critical thermocapillary Reynolds number is smaller than that in the n-hexane fluid. In the n- decane/n-hexane mixture, when the aspect ratio increases from 0.0217 to 0.0392, the critical thermal capillary Reynolds number decreases from 7.2× 10^4 to 5.0 × 10^4. With the increase of the aspect ratio, the effect of the buoyancy is enhanced, and the critical thermocapillary Reynolds number decreases. When the aspect ratio increases from 0.0392 to 0.0434, the cold plume which facilitates destabilizing the thermal convection cannot be obviously enhanced. There is little effect of the cold plume on the fluid near the bottom. Therefore, the critical thermal capillary Reynolds number increases from 5.0 × 10^4 to 6.4 × 10^4 in this range. In the deep pool, the critical thermal capillary Reynolds number is almost a constant value. When the aspect ratio is smaller than 0.0848, the three-dimensional oscillatory flow occurs and the hydrothermal waves are observed. After the three-dimensional oscillatory flow appears, two groups of the hydrothermal waves with opposite propagating directions coexist in the pool. With the increase of the thermal capillary Reynolds number, the honeycomb-like patterns appear on the free surface, which are similar to the B^nard cells. In addition, the non-dimensional fundamental oscillation frequency increases with the thermal capillary Reynolds number. When the aspect ratio is bigger than 0.0848, spoke pattern, rosebud-like pattern and thin-longitudinal stripes will appear sequentially with the increase of thermocapillary Reynolds number. Furthermore, the number of the rosebud-like patterns decreases, while the area on the free surface in the pool occupied by the rosebud-like pattern increases with the increase of the thermal capillary Reynolds number.
出处
《物理学报》
SCIE
EI
CAS
CSCD
北大核心
2015年第22期306-313,共8页
Acta Physica Sinica
基金
国家自然科学基金(批准号:51176209)资助的课题~~
关键词
Soret效应
双组分溶液
热对流
实验研究
Soret effect, binary mixture, thermal convection, experimental study
