New Simple Formula for Estimation of Pressure Drop of Polymer Melt Flow in A Converging Channel

Pressure drop estimation in the polymer processing is important from practical point of view. Although there are rigorous modeling method such as finite elements method, but a simple formula is valuable in the envelope back calculations. Applying the momentum balance in the spherical coordinates to a converging flow (such as nozzle part of injection molding or extrusion processes) a simple formula is derived. The shear thinning Ostwald-De waele rheological behavior is selected for the polymer melt. The pressure drop due to the normal stresses and the velocity changes in the flow direction are contributed in the formula. This new formula is examined for the flow of polystyrene and polypropylene melt in two different converging zone and different temperatures. The comparison of experimental and calculated results show that the formula is excellent for an amorphous polymer such as PS and is good for a semicrystalline polymer such as PP.

Keywords:

Converging channel , Pressure drop , Polymer melt , Momentum transport , Power law