Abstract: Cooling system is essential in the production process of extruded plastic pipe, which determines the length of production line and product quality. This study simulates the transient heat transfer of spray cooling based on ANSYS. The result shows that for the convective heat transfer coefficient less than 180 W·m^-2·K^-1, the time for cooling to 47℃ changes obviously with the convective heat transfer coefficient, while it does not change much for higher convective heat transfer coefficient. Then we simulate the spray nozzle based on FLUENT software, investigating the effect of entrance velocity and nozzle height on distribution of convective heat transfer coefficient. We have found that with other parameters constant, the total convective heat transfer coefficient increases with entrance velocity (within 6-15 m·s^-1), and the heat transfer coefficient of stagnation point increases from 217 W·m^-2·K^-1 to 386 W·m^-2·K^-1. Wall convective heat transfer coefficient increases as the nozzle height decreases (within 68-128 mm), and heat transfer coefficient of stagnation point increases from 227 W·m^-2·K^-1 to 311 W·m^-2·K^-1. Finally we put forward a proposal on global optimization for spray cooling baths based on above study.

Key words: extruded plastic pipe, spray cooling, nozzle, transient, convection, heat transfer, numerical simulation, global optimization

摘要： 冷却系统是塑料挤出管道生产工艺中的关键设备，其冷却的均匀性和效率直接影响管道产品的质量及生产速度。首先基于ANSYS对喷淋冷却瞬态传热进行模拟，结果表明：对流传热系数小于180 W·m^-2·K^-1时，冷却至目标温度（47℃）所需的时间随传热系数的变化明显；传热系数大于180 W·m^-2·K^-1时，冷却至目标温度所需的时间随传热系数的变化不大。然后基于FLUENT软件对喷淋喷嘴进行模拟，研究了喷淋入口速度、喷嘴高度对喷淋传热系数的影响，结果表明：随着喷淋入口速度的增加（6～15 m·s^-1的范围内），总体对流传热系数增大，驻点处的传热系数由217 W·m^-2·K^-1增加到386 W·m^-2·K^-1；随喷淋高度的减小（68～128 mm范围内），壁面传热系数呈增加趋势，驻点处传热系数由227 W·m^-2·K^-1增加到311 W·m^-2·K^-1。基于以上研究，为真空定径喷淋冷却水槽的整体优化提出合理建议。

关键词: 挤出塑料管, 喷淋冷却, 喷嘴, 瞬态, 对流, 换热, 数值模拟, 整体优化