Shear viscosity, fluid inertia and extension viscosity also contribute to this juncture loss. The juncture loss model is derived from flow experiments to characterize the pressure drop. The juncture loss model can be used to improve the predictions of pressure and flow balance in the feed system.
It was found experimentally that the results of the extra pressure losses at various temperatures and shear rates can be collapsed onto a single master curve (for a given generic grade of material), by plotting the extra pressure loss versus the wall shear stress.
The following correlation, originally developed by Munstedt, is used to relate the extra pressure loss to the wall shear stress in the capillary data analysis. 97
If juncture loss data is not available for the material that you selected, you can evaluate whether juncture loss is significant to your application by running Fill analyses with and without juncture loss coefficients. For this purpose, you can use typical values for the juncture loss coefficients, and enter these into the material data. There is an inverse relationship between the coefficients, so as increases, decreases. values range from 0.00001 to 10 (typically 0.0001), while values range from 2.5 to 1 (typically 2). If analysis results show that juncture loss is significant to your application, it is strongly recommended that you have the material characterized by Autodesk Moldflow Plastics Labs for juncture loss coefficients.