Due to the stratification of sludge particles in the ultrasonic field, the acoustic interaction forces the particles to agglomerate on a plane perpendicular to the direction of ultrasonic propagation. Therefore, the thickness of sludge can significantly influence the characteristics of ultrasound-assisted hot air convective drying municipal sewage sludge. In this paper, the stratified aggregation phenomenon of sludge with different thicknesses was observed in the ultrasonic field using the experimental method. It was found that the stratification of the internal structure of sludge became more obvious with the increase of its thickness. The effects of ultrasound on the drying time and the drying rate of sludge with various thicknesses were studied. Meanwhile, the effective moisture diffusivity (D_eff) was analyzed. The experimental results demonstrated that within a certain range, the larger the sludge thickness, the longer the time length of the first falling rate stage, and the promotion of the drying rate is worse. The situation is opposite at the constant rate stage. Among the sludge with the thicknesses of 5 mm, 10 mm, and 15 mm, the total drying time and energy consumption of the sludge with a thickness of 10 mm decreases the most substantially at different power ultrasound-assisted. The smaller the thickness of sludge is, the less obvious the effect of ultrasound on the effective moisture diffusivity (D_eff), and vice versa.

由于污泥颗粒在超声场中分层，声相互作用迫使颗粒在垂直于超声传播方向的平面上聚集。因此，污泥的厚度会显着影响超声辅助热空气对流干燥市政污水污泥的特性。本文采用实验方法，在超声场中观察到了不同厚度污泥的分层聚集现象。发现随着污泥厚度的增加，污泥内部结构的分层变得更加明显。研究了超声波对不同厚度污泥的干燥时间和干燥速率的影响。同时，有效水分扩散率（D _eff）进行了分析。实验结果表明，在一定范围内，污泥厚度越大，第一个降速阶段的时间长度越长，干燥速度的提升越差。在恒定利率阶段，情况则相反。在厚度为5mm，10mm和15mm的污泥中，在不同功率的超声辅助下，总干燥时间和厚度为10mm的污泥的能耗最大程度地降低。污泥厚度越小，超声波对有效水分扩散率（D _eff）的影响就越不明显，反之亦然。