Investigation On Flow And Heat Transfer With Phase Change Of Polymer In A Die Channel

Nowadays pelleting under water is the best technology of polymer pelleting in the world. Performance of pelleting die is one of key factors to performance of extruder. However, advanced die with good performance is monopolized by few foreign companies. Dies applied in large petrochemical plants in our country were imported at long time, which restricts the development of ethane industry. Large die with independence intellectual property rights has importance significance for breaking technology monopolization and blockage.Investigation of behavior of flow and heat transfer of polymer in pelleting die is to reveal the law of flow and heat transfer of polymer in a die channel. It has important science and real signification for establishing theory of structure design and optimization of the die, performance evaluation and operating adjustment.Based on the above reasons, in the present work process of flow and heat transfer of polymer in a die channel is studied. The research contents are following: (1) Mathematical model of flow and heat transfer of polymer in a die channel was established, including consideration of non-Newton rheology of polymer. Mathematical model was solved on the platform of FLUENT. Status parameters of flow and heat transfer such as velocity, temperature, pressure and solidification fraction of polymer under operating condition were obtained.(2) Influence of different thermal oil channel on the flow and heat transfer of polymer in a die channel was studied.(3) Influences of different operating parameters such as inlet flow rate of polymer, inlet temperature of polymer, temperature of cooling water, flow rate of thermal oil on the flow and heat transfer of polymer in a die channel were studied.(4) Influence of thermal conductivity of pelletizing layer on the flow and heat transfer of polymer in a die channel was studied.(5) Influence of non-Newton rheology of polymer on the flow and heat transfer of polymer in a die channel was studied.Based on the research, some conclusions could be drawn:(1) Liquid fraction of polymer and pressure loss of polymer are closely relative to the temperature of the die. Liquid fraction of polymer increases with the increasing of the temperature of the die, and pressure loss of polymer decreases with the increasing of the temperature of the die. (2) Structure of thermal oil channel, boundary conditions, and thermal conductivity of the pelletizing layer affect the temperature of the die. The temperature of the die increases with the increasing of the flow area of the thermal oil channel, inlet temperature of polymer, flow rates of polymer and the thermal oil, but it decreases with the increasing of the thermal conductivity of the pelletizing layer.(3) Non-Newton rheology of polymer lightly affects the temperature of the die, but notably affects the phase change of solidification and pressure loss of polymer. Liquid fraction of polymer decreases with the increases of power-law index and consistency index, which results in the increase of the pressure loss of polymer.According to the above investigations, essence of flow and heat transfer of polymer in a die channel was revealed. Influences of key factors on flow and heat transfer of polymer in a die channel were summarized and analyzed. The present work somewhat establishes theory of large twin-screw extruder made in China and provides somewhat available search of structure design and optimization of the die, performance evaluation and operating adjustment.