超声场强化污泥对流干燥热湿耦合迁移过程的数值模拟

Numerical Simulation of Coupled Heat and Moisture Transfer in Convection Drying Process of Sludge Enhanced by Ultrasonic Field

为理论上有效预测超声作用对污泥对流干燥过程的影响,基于非平衡热力学理论,建立了超声场作用下污泥对流干燥热湿耦合迁移过程的数学模型.对不同声能密度作用下污泥内部温度及湿度场分布进行数值模拟.结果表明,超声作用可以有效加速污泥内部的湿迁移过程,但超声强化效果随污泥厚度增大而逐渐减弱.此外,超声热效应使污泥温度有所升高,但污泥内部的温度梯度却略有降低,因此,污泥内部由温度梯度引起的湿分扩散并未因超声波作用而得到强化.

For effectively predicting the effect of ultrasound on moisture migration in convection drying process of sludge in theory, a mathematical model for coupled heat and moisture transfer process in convection drying of sludge under the effect ultrasonic field was established based on the theory of nonequilibrium thermodynamics. The numerical simulation for the effects of ultrasonic energy density on temperature and moisture content distribution in sludge drying process was studied. The simulation results showed that, ultrasonic irradiation effectively accelerated the moisture migration process in sludge, but the ultrasonic effects on sludge drying rate decreased gradually with the increase of sludge thickness. Furthermore, ultrasonic heating effect generated the increase of sludge temperature, but temperature gradient in sludge became slightly lower. Therefore, the moisture diffusion caused by the temperature gradient in sludge couldn＇t be enhanced by ultrasonic effect.