低压蒸汽滴状冷凝过程中液滴生长特性

研究了低压条件对滴状冷凝过程液滴生长特性的影响。首先,研究了超疏水表面上空气环境和蒸汽环境中附着液滴的接触角,发现蒸汽环境中的接触角比空气环境中的小,而蒸汽压力对接触角没有显著影响。第二,实验研究了冷凝过程中的液滴的生长周期和脱落尺寸,液滴的脱落半径随压力的降低而增大,生长周期也随之延长。第三,实验研究了液滴合并生长速率,并结合理论分析直接冷凝长大的生长速率,直接冷凝生长速率随压力的减小而减小,并随过冷度的减小而下降,而实验范围内合并生长速率不受压力影响。第四,根据滴状冷凝液滴分布的时间序列模型,分析了不同压力下液滴生长的临界尺寸,随着压力的降低,液滴生长方式的临界尺寸增大。

Motion Characteristics of Droplets of Dropwise Condensation in the Vacuum Conditions

The motion characteristics of droplets of dropwise condensation in the vacuum conditions are investigated experimentally.With the contact angles analisising,it is found that contact angles in steam conditions would be smaller than those in the air conditions.High-speed camera is applied to monitor the dynamic growth characteristics of droplet.And it is found that the growth rate of droplets by coalescene according to experiments is the same under different pressures.And the growth rate of droplets grown by direct condensation at different pressure and different subcooling degrees are calculated by the model in the literature.The growth rate of droplets by direct condensation is lower when the pressure or the subcooling degree is decreased.And the distribution of droplets of different generations is investigated at low pressure,and it is found that the ratio of radius of two generations is decreased as the droplet radius increases,and tends to about 1 at different pressures.