Reynolds Number Calculator
Calculate the Reynolds number and determine the flow regime (laminar, transitional, turbulent) of polymer melt in a runner channel or coolant in mold cooling channels. Flow regime affects pressure drop and heat transfer efficiency.
Input Parameters
Results
Fill in the data and click Calculate
ARGUS automatically analyzes the flow regime in all mold channels
The Reynolds number determines the flow regime and heat transfer efficiency — ARGUS monitors these parameters automatically.
How do we calculate the Reynolds number?
The Reynolds number (Re) is a dimensionless index that characterizes the flow regime of a fluid in a channel. Three regimes are distinguished: laminar (Re < 2300), transitional (2300 < Re < 4000) and turbulent (Re > 4000). In injection molding, Re is relevant both for melt flow in runner channels and for coolant flow in mold cooling channels.
The calculator applies the classical Reynolds formula for flow in a circular pipe.
Re — Reynolds number [-]
ρ — fluid density [kg/m³]
v — flow velocity [m/s]
d — channel diameter [m]
η — dynamic viscosity [Pa·s]
For polymer melts viscosity is very high (50–2000 Pa·s), so flow in runner channels is almost always laminar (Re << 2300). For coolant (water: η ≈ 0.001 Pa·s) flow is typically turbulent, which is desirable for efficient heat transfer.
Importance of Turbulence in Cooling
Turbulent coolant flow is critical for effective mold cooling:
Transitional (2300–4000) — unstable, unpredictable
Turbulent (Re > 10000) — efficient heat transfer (3–5× better)
For 10 mm cooling channels, the water flow rate required to achieve Re > 10,000 is approximately 3–4 l/min. Laminar flow in cooling channels reduces heat transfer efficiency by 3–5×, extending cooling time and lowering production output.
Cooling Flow Optimization
To ensure turbulent flow: increase flow velocity (higher pump pressure), reduce channel diameter (while maintaining adequate flow rate), use flow obstacles (baffles, bubblers). Monitoring the Reynolds number for each cooling circuit helps detect channels with inefficient cooling.
ARGUS automatically monitors the coolant flow regime in all channels
See for yourself — book a presentation and explore cooling monitoring in ARGUS.