Numerical Simulations Of Flow And Heat Transfer Of The Polymer And The Thermal Oil In The Die

Pelletizing system under water as a kind of advanced technology is extensively used in the polymer processing involving palletizing, and it is developing toward large-scale and better adaptability, finally achieves the demand of large batch and continual production. The die is an important component of the palletizing process.The fluid flow and heat transfer of the polymer and thermal oil in the die have an important impact on the palletizing performance of the die. Three-dimensional models of heat transfer have been established and numerically solved using a commercial software package, Fluent, in order to obtain distributions of temperature, velocity, pressure, and liquid fraction of the polymer in the die. The influences of the boundary conditions, the thermal conductivity of the pelletizing layer, the structure of the die, and the viscosity of the polymer on the pressure and phase change of the polymer and the temperature distribution in the die have been evaluated. The results show that the temperature of the region close to the palletizing surface is relatively low with a sharp temperature gradient due to the cooling effect of the cool water, while the temperature deeper inside the die is higher, with a lower temperature gradient, as a result of the heating effect of the hot thermal oil and the polymer. A solidification phase change of the polymer occurs near the polymer outlet due to heat loss from the polymer to the water, while deeper inside the hole the polymer remains fluid without solidification, due to heating by the thermal oil.Three-dimensional models of 1/4 die and the thermal oil inside also have been established and numerically solved by Fluent to obtain velocity, pressure distribution of the thermal oil and the temperature in the die. The results show that the uniformity of the flow resistance of the thermal oil in the die leads to the uniformity of the flux of the thermal oil, as a result of the uniform arrangement of the thermal oil channel in the die. Therefore, the uniform temperature distribution of the die near the pelletizing region is improved.Numerical simulation provides a reliable method to optimize the design of the die, the choice of metallic material for the die, and the operating conditions of the polymer pelletizing under water.