Non Isothermal Flow Dynamics and Viscous Heat Generation in Polymer Melt Extrusion
Non-isothermal viscous dissipation drives core melt temperature spikes that cause extrudate defects if die land geometry is not scaled to shear rates.
Pressure Drop Calculation
Meaning
Analytical methods for determining the loss of force in a flowing fluid provide the necessary data for sizing pumps and extrusion equipment. A pressure drop calculation accounts for the viscosity of the material, the geometry of the flow path and the speed of the movement. It identifies the amount of energy required to push the fluid through a die or a filter.
Flow Resistance
Friction between the fluid and the walls of the channel creates a resistance that opposes the direction of travel. Performing a pressure drop calculation helps determine if a specific pump has the capability to handle the workload. If the resistance is too high, the motor may overheat or the flow rate will fall below the target.
Model Accuracy
Using the correct mathematical model is necessary because polymers do not behave like simple liquids. A pressure drop calculation for a non-Newtonian fluid must incorporate the shear-thinning effects that occur at high velocities. Incorrect assumptions about the viscosity lead to errors in the predicted power consumption.
Energy Demand
The total cost of operation is directly linked to the amount of force needed to maintain the flow. High values in a pressure drop calculation suggest that the process could be made more efficient by widening the channels or increasing the temperature. Reducing the pressure requirement lowers the stress on the seals and bearings of the machine.