WANG Shuai^1，2，JIN Hanyu¹，LIU Jiang^1，2，WANG Jiaxing^1，3

1. School of Energy Science and Engineering， Harbin Institute of Technology， Harbin 150001，China；2. Zhengzhou Research Institute of Harbin Institute of Technology， Zhengzhou 450001， China；3. Yantai Longyuan Power Technology Co. ， Ltd. ， Yantai 264006， China

Abstract

Objective The study aims to investigate the heat and mass transfer characteristics of fluidized bed drying under pulsating airflow and to regulate the drying process of non-spherical wet particles.

Methods Numerical simulations were conducted to study the fluidized bed drying process of non-spherical wet particles. The computational fluid dynamics-discrete element method (CFD-DEM) was employed to characterize the gas-particle flow and mass/heat transfer behaviors. To achieve an accurate characterization of non-spherical wet particles, a flow-heat/mass transfer model was developed considering the variations in inter-particle liquid bridge forces. In this model, the equivalent radius at the contact position was used in place of the particle radius when calculating liquid bridge forces. Liquid migration during particle collisions was also incorporated, along with the influence of liquid bridges on heat transfer and variations in gas-phase water vapor concentration during drying. The evolution of heat and mass transfer for non-spherical wet particles in a spouted bed dryer was studied， and the influence of sinusoidal and rectangular wave-shaped pulsating airflows on fluidized bed drying behavior was analyzed.

Results and Discussion The proposed model was validated against experimental data. The results showed that, as drying progressed, the liquid content of particles gradually decreased and particle agglomeration weakened. Compared to non-pulsating airflow, pulsating airflow significantly increased the drying rate, resulting in a smaller drying dead zone. Under rectangular wave-shaped pulsating airflow, particles in the annular region were difficult to fluidize, leading to a larger dead zone compared to sinusoidal waveform. The total pressure drop under the rectangular wave-shaped pulsating airflow was lower than that under sinusoidal wave-shaped pulsating airflow. As drying continued, more particles participated in fluidization under sinusoidal wave-shaped pulsating airflow, whereas the rectangular wave-shaped pulsating airflow showed no significant improvement in fluidization. Compared to sinusoidal wave-shaped pulsating airflow, rectangular wave-shaped pulsating airflow exhibited a slower particle heating rate, and in the later stage of drying, a larger standard deviation of particle temperature in the bed indicated relatively weaker and more heterogeneous heat transfer between gas and particles. In contrast, sinusoidal wave-shaped pulsating airflow demonstrated higher heat transfer efficiency, with a more uniform temporal and spatial distribution of gas-particle heat transfer. Rectangular wave-shaped pulsation exhibited lower heat transfer via liquid bridges and wet particle contact. Notably, dry particle contact conduction emerged earlier in the spouted bed under rectangular wave-shaped pulsating airflow, indicating premature complete drying of some non-spherical wet particles. The drying rate and its standard deviation evolved differently over time under pulsating airflows of different waveforms. Specifically, the drying rate under rectangular wave-shaped pulsating airflow declined earlier due to insufficient gas-particle contact for certain particles in the later drying stage, which reduced the overall drying rate in the bed.

WANG Shuai, JIN Hanyu, LIU Jiang, et al. Fluidized drying characteristics of non-spherical wet particles under pulsating airflows［J］. China Powder Science and Technology，2025，31（6）：1−9.