Evaluating Conformal Cooling Circuit Hydraulics to Reduce Machine Cycle Time
Turbulent flow inside conformal cooling circuits requires managing additive channel roughness and diameter to prevent pump choking and inflated cycle times.
Nusselt Number
Meaning
Dimensionless ratio of convective to conductive heat transfer across a boundary in a flowing fluid. This value, known as the Nusselt number, characterizes how effectively heat is carried away from or into a polymer melt during extrusion and moulding processes. Higher values indicate that convective mixing dominates the heat transfer, which is typical for highly turbulent flows or agitated melts.
In polymer processing, where the melt is highly viscous, conductive heat transfer usually dominates, leading to relatively low values for this parameter.
Convective Heat
Evaluation of heat transfer rates depends on the thermal conductivity of the polymer, the flow velocity, and the geometry of the flow channel. A higher value suggests that the fluid motion significantly enhances heat exchange compared to a stagnant melt.
Extrusion Processing
Polymer melt inside an extruder barrel requires precise thermal management to prevent premature curing or degradation of the resin. The value of the parameter helps engineers design the cooling jackets of the barrel to maintain a uniform temperature profile throughout the extrusion run.
Cooling Efficiency
Plastic cooling in the injection mould or during film blowing relies on efficient heat removal to achieve target cycle times. When convective heat transfer is optimized, the cooled part can be ejected sooner without warping or distorting. Processors use heat transfer simulation tools to design conformal cooling channels that maximize the heat extraction rate from the solidifying polymer.