螺棱间隙对单螺杆食品挤压膨化机熔体输送影响数值模拟

采用POLYFLOW软件对单螺杆挤压膨化机中食品熔体的三维等温流场进行数值模拟,结合粒子示踪技术,探索不同螺棱间隙(0.4,0.8,1.2mm)对食品熔体流场和混合性能的影响。研究表明:随着螺棱间隙的减小,螺棱顶端的剪切速率增大,食品熔体平均黏度变小,螺杆的轴向输送能力变差;随着螺棱间隙的增大,食品熔体的停留时间先增后减,分散混合能力变差。当螺棱间隙增至1.2mm时,物料停留时间反而比间隙值为0.4 mm时长,说明螺棱间隙过大,食品物料的停留时间将难以控制,同时对各物料组分的混合效果也较差。螺棱间隙对熔体流场和混合特性均有一定的影响,螺棱间隙为0.8mm时,既能保证对熔体的输送能力,又能保证良好的流场分布和混合效果,为比较理想的螺棱间隙。

Numerical simulation on effect of tip-clearance between screw flight and

The three-dimensional isothermal flow fields of single screws with different values of tip-clearance (0.4, 0.8, 1.2 mm)were simulated by POLYFLOW software. Combined with the particle tracing technique, the effect of different tip- clearance on the flow field and mixing ability of the food melt was also explored. The results show that: the shear rate near the top of the screw flight increases, the average viscosity of food melt decreases, and the conveying capacity of the screw weakens with the decrease of the tip-clearance. On the contrary, with the increase of the tip-clearance, the residence time of the food melt increases first, then decreases subsequently, and the dispersion mixing effect becomes poorer. When the tip-clearance increases to value of 1.2 mm, the residence time of the food melt is even longer than the one with the value of 0.4 mm. It also shows that if the tip-clearance is too large, the residence time of the food material might become hard to be controlled and the mixing effect of these food material components would also become worse. As a result, the tip-clearance between screw and barrel could significantly influence both the flow field and mixing characteristics of food materials, when the tip-clearance is 0.8 mm, it can not only ensure the transport capacity to the food melt, but also behave the good flow field distribution and mixing effect. Therefore, it is the optimal tip-clearance value deduced by the numerical simulation.