厌氧发酵液中气泡生成特性的数值研究

为了探究带有屈服应力性质的厌氧发酵液中的气泡生成特性,采用VOF法对带有屈服应力性质的厌氧发酵液中的气泡生成过程进行了数值研究。研究发现:带有屈服应力性质的厌氧发酵液中的气泡生成过程可分为膨胀阶段和脱离阶段。在气泡膨胀阶段,气泡中心的起始纵向速度较大,然后速度下降,并维持在一个较小的速度下膨胀;此时,气泡周围的流体主要沿气泡的外法线方向流动,使气泡加速膨胀,直至膨胀成球状。在气泡脱离阶段,气泡的侧端产生了对称的左右漩涡,促使其顶部继续向外扩张,纵向速度有较明显的增加;同时,气泡的"长颈"开始加速生成,最后与喷嘴脱离。在气泡的生成过程中,屈服区域逐渐变大。对于不同的屈服应力的流体而言,气泡的纵横比随着屈服应力的增大而减小,其生成时间随着屈服应力的增加而增加。文章的研究结果将有助于禽畜粪便厌氧发酵过程的优化设计。

The numerical study of the bubble generation characteristics in anaerobic fermentation slurry

In order to explore the generation characteristics of bubbles in anaerobic fermentation slurry with yield stress property,the generation process of single bubble in anaerobic fermentation slurry was studied numerically using VOF method.The results shows that the period of bubble generation could be divided into two stages:bubble expansion stage and bubble separation stage.And the initial upward velocity is high,then the upward velocity decreases and maintains at a lower value in the bubble expansion stage.At the same time,the fluid around the bubble mainly flows towards the outer normal direction of the bubble surface,which makes the bubble expand to a sphere shape.In the stage of bubble separation,a symmetrical left-right vortex is generated at the bubble sides,which causes the upper part of bubble expands continuously and upward velocity increases significantly.Meanwhile,the"long neck"of the bubble starts to generate,and the bubble separate from the nozzle finally.Moreover,the yield area becomes larger with the generation of the bubble.For the fluids with different yield stress,the aspect ratio of bubbles decreases with the increase of yield stress,and the generation time increases with the increase of yield stress.The simulated results will be helpful to the optimal design of livestock manure anaerobic fermentation process.