The engineering question
Reynolds number links velocity, hydraulic diameter and kinematic viscosity. In ordinary internal-flow screening, low values are laminar, 2,000–4,000 transitional, and values above 4,000 generally turbulent; passage geometry and roughness still matter. SmartFlow presents 4,000–8,000 as a mold-cooling reference range and notes diminishing benefit above established turbulence. Lower temperature or glycol normally changes viscosity, so water-only assumptions must not be reused. Use measured flow, temperature and supplier properties.
Use the record, not a universal rule
Keep coolant condition, instrument basis, mold geometry and production state with each result. A calculator narrows the next check; it does not replace flow measurement, a pump curve, mold trial or supplier documentation.
Related tools
Reynolds Number · Required Flow · Circuit Balance · Cooling & Thermal Control hub
Sources
SmartFlow practical mold cooling · SmartFlow flow regulators.