淀粉在旋转气流干燥器中的热量传递

Heat Transfer in Swirl Pneumatic Flash Dryer for Starch

在旋转气流干燥器中,取一物料环作微元体,根据热平衡原理,建立了计算热介质与颗粒固体间的给热系数数学表达式。由气、固两相在旋转运动中的相对滑移关联式,进行了努塞尔准数Nu、空塔气速表征的雷诺数Re、气固质量比B的关联。在作者开发的φ150mm实验设备中,用淀粉进行传热的正交实验研究,得到了颗粒尺寸、颗粒湿含量、给热系数随干燥管高度的分布曲线。用非线性回归方法得到的关联式为: Nu=-0.937+0.133Re^(0.622)-0.042Re^(-1.285)B^(-0.790) 122≤Re≤189 0.0170≤B≤0.

A mathematic formula for calculating heat transfer coefficient in swirl pneumatic flash dryer has been derived basing on the heat balance principle of a differential unit, which is a ring of swirl mass current in the dryer. The experimental relationship of Nusselt number Nu, Reynold number Re and the ratio of gas and solid loading B has also been correlated. Experiments have been performed according to orthogonalizing experimental process in a small scale swirl flash installation(Φ150mm)using corn starch as experimental material. The plots of particle size and moisture content of starch as well as the heat transfer coefficient between starch particles and hot air stream versus the height of dryer have been obtained. The data obtained have been regressed nonlinearly with electron brain and a regression equation is established asNu=-0.937+0.133Re^(0.662)-0.042Re^(-1.285)B^(-0.790)Heat transfer in the swirl pneumatic flash dryer is very uniform andthe heat transfer coefficient is greater than that in the straight flash dryer. It is affected significantly by temperature.