剪切射流在受限空间卷吸特性研究

Study on the entrainment features of shear jet in confined space

脉冲袋式除尘器在反吹清灰过程中,其喷吹机构在瞬间放出压缩空气从而形成高速射流,卷吸数倍的二次空气高速射入滤袋,使滤袋急剧膨胀,依靠冲击振动和反吹气流而清灰。如果反吹风清灰设计不合理,反吹风量和二次诱导风总量不够,则达不到清灰效果;如果反吹风量过大会增加压缩机负担,浪费能源。研究剪切射流在受限空间的卷吸特性,即在一次相同风量下,计算单射流、剪切射流(等喷吹管长)、中伸剪切流、中缩剪切流4种形式射流下被卷吸的二次诱导风量,并测得这4种形式射流下受限空间滤袋的表面速度和表面压力。结果表明,在相同质量流量压缩空气的前提下,剪切射流可比单射流卷吸更多的空气进入滤袋,其中中伸剪切射流卷吸量最多,其卷吸率为8.174。中伸剪切流能够卷吸更多空气的同时增大了滤袋内部的压力,但滤袋边壁返流的气流速度增加不大,因此中伸式脉冲喷口在袋式除尘器中的清灰作用更显著。

The present paper intends to introduce our study on the entrainment features of shear jet in a confined space by taking the pulse-backing cleaning process of bag-type dust-collector as our case study sample. As is known, a pulse injection device can release compressed air to form a high-speed jet instantaneously so as to en- train secondary air into the dust-collector bag and make it expand quickly. Since the dust-collection totally relies on the impact vibra- tion and reverse blowing airflow, it is impossible to get the dust cleaning effect if we do not adopt a design of reasonable injection sys- tem without supplying great-enough air volume. On the contrary, it is likely to increase the compressor load and energy waste with excessivecounter blowing air. Therefore, we are trying to explore the entrain- ment features of shear jet in a confined space in this paper, trying to simulate the induced secondary air volume of four jet forms, that is, to work out the forms of the single jet, the shear jet, the central jut- ting shear flow and the central shrinkage shear flow. We would like to make it possible to work out the four jet forms＇ speed and pressure on the internal surface of filter bag, whose space is naturally confined. In proceeding with our study, we have done a contrast analysis of the four different jet forms, gaining the following conclusion： under the premise of the same mass flow of the compressed air, shear jet tends to entrain more air into the filter bag than the single jet, and the cen- tral jutting shear flow would like to induce the greatest volume air of the four jet forms, whose mass rate of entrainment is equal to 8.174. Moreover, the central jutting shear flow can induce more air and in- crease the filter bag＇ s internal pressure, but the reflux air tends to have greater velocity in little. It is natural that the central jutting shear flow would like to enjoy a better dust collecting effect in the machine. Thus, it can be seen that through the simulation of the shear jet in the confined space, we have gained a clearer and deeper understanding of the dust-collecting process, which can in turn pro- vide us a significant guidance for optimizing the design of the bag type dust collector.