Ali Syed Sadiq, Arsad Agus, Roberts Kenneth L, Asif Mohammad
School of Chemical and Energy Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, Johor Bahru 81310, Johor, Malaysia.
UTM-MPRC Institute for Oil and Gas, School of Chemical and Energy Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, Johor Bahru 81310, Johor, Malaysia.
Nanomaterials (Basel). 2022 Jun 11;12(12):2019. doi: 10.3390/nano12122019.
Bed collapse experiments provide vital information about fluidized bed hydrodynamics. In this study, the region-wise bed collapse dynamics of glass beads, titania (TiO), and hydrophilic nanosilica (SiO) particles with widely different voidages (ε) of 0.38, 0.80, and 0.98, respectively, were carefully investigated. These particles belonged to different Geldart groups and exhibited varied hysteresis phenomena and fluidization indices. The local collapse dynamics in the lower, lower-middle, upper-middle, and upper regions were carefully monitored in addition to the distributor pressure drop to obtain greater insight into the deaeration behavior of the bed. While the collapse dynamics of glass beads revealed high bed homogeneity, the upper middle region controlled the collapse process in the case of titania due to the size-based segregation along the bed height. The segregation behavior was very strong for nanosilica, with the slow settling fine agglomerates in the upper bed regions controlling its collapse dynamics. The collapse time of the upper region was 25 times slower than that of the lower region containing mainly large agglomerates. The spectral analysis confirmed the trend that was observed in the pressure transients. The clear presence of high frequency events at 20 and 40 Hz was observed in the nanosilica due to agglomerate movements. The residual air exiting the plenum was strongly affected by the bed voidage, being lowest for the nanosilica and highest for the glass beads.
床层坍塌实验提供了有关流化床流体动力学的重要信息。在本研究中，分别对空隙率（ε）差异很大，分别为0.38、0.80和0.98的玻璃珠、二氧化钛（TiO）和亲水性纳米二氧化硅（SiO）颗粒的区域床层坍塌动力学进行了仔细研究。这些颗粒属于不同的Geldart组，表现出不同的滞后现象和流化指数。除了分布器压降外，还仔细监测了下部、中下部、中上部和上部区域的局部坍塌动力学，以更深入地了解床层的脱气行为。虽然玻璃珠的坍塌动力学显示出较高的床层均匀性，但由于沿床层高度基于尺寸的偏析，在二氧化钛的情况下，中上部区域控制了坍塌过程。纳米二氧化硅的偏析行为非常强烈，上部床层区域中缓慢沉降的细团聚体控制了其坍塌动力学。上部区域的坍塌时间比主要包含大团聚体的下部区域慢25倍。频谱分析证实了在压力瞬变中观察到的趋势。由于团聚体运动，在纳米二氧化硅中观察到20和40Hz处明显存在高频事件。离开气室的残余空气受到床层空隙率的强烈影响，纳米二氧化硅的残余空气最低，玻璃珠的最高。
