Design And Optimization Of Melt Cooler For Continuous Polymer Foaming Process Based On Thermal Boundary Layer

Polymer is a new kind of lightweight material,and the foaming of polymer not only makes it realize further lightweight,but also brings a variety of functions,such as heat insulation,buffering and shockproof,sound insulation and noise reduction,which has incomparable advantages over other materials.Polymer extrusion foaming is an important process technology for this lightweight functional material.The key of the extrusion foaming process is to reduce the temperature of polymer melt to a suitable processing temperature window and to get enough melt strength to achieve foaming structure.In this paper,a new type of melt cooling structure is studied to replace the traditional tandem melt cooling extruder,which lays the foundation for the technical upgrading of extrusion foaming process,low energy consumption,short process and high efficiency of extrusion foaming.Firstly,numerical simulation of heat transfer performance of conventional shell and tube heat exchanger is carried out,and a dual fluid-solid coupling CFD model including heat transfer oil,polymer melt and metal is established.The relevant properties of polymer melt are considered in the calculation process,and the simulation results are verified by experiments,which shows that the model is reliable.The model is used to analyze and calculate the new designed core-hole melt cooler.The structure has more complex liquid channel and heat transfer boundary.The simulation results are also consistent with the experiment,which shows that the finite element model can satisfy the heat transfer process analysis and calculation of complex structure.In order to lay a theoretical foundation for the design of industrial melt coolers with large output,it is necessary to obtain an optimized core-hole type heat transfer structure,in which the core-hole diameter plays an important role in the melt cooling,temperature distribution,melt pressure drop and other aspects.In this paper,response surface analysis design method is used to optimize the core-hole structure,calculate and determine the core size and hole number,in order to obtain the maximum cooling range and the minimum pressure drop under the required flow.The key to the optimization of the core-hole structure is to determine the distribution of the thermal boundary layer of the melt in the flow passage.Based on a series of simulation results,an empirical mathematical model for the calculation of the thermal boundary layer of the core-hole melt cooler is derived in this paper.The model is based on the Reynolds number,Prandtl number,dynamic viscosity and flow axial position of the fluid,which can be used to calculate and determine the thickness of the thermal boundary layer of the melt at any position in the runner with different processes and materials.The establishment of boundary layer calculation method lays a theoretical foundation for the design of melt cooler structure suitable for different production and different polymer materials.