Mold Cooling Baffles

Flat Baffle: Single-Pass U-Turn Flow Separation

A flat baffle blade divides a drilled waterline into two semicircular cross-sections. Coolant travels down the supply side, reverses direction by $180^\circ$ around the blade tip, and flows back up the return side. While cost-effective, this creates a major aerodynamic challenge: as flow reaches the blade tip, the cross-sectional flow area suddenly increases. This causes local fluid deceleration, creating a stagnant zone (dead zone) at the very tip with a low convective heat transfer coefficient ($h$). To mitigate this, a **Radius-Cut Tip** or a $180^\circ$ bevel should be chosen to smooth fluid turning and minimize boundary layer separation. Achieving fully developed turbulent flow ($Re > 10,000$) in flat channels requires a higher entry velocity, typically $\ge 2.0 \text{ m/s}$.

Spiral Baffle: Helical Swirl and Forced Mixing

A spiral baffle consists of a helical screw molded or machined onto a central core, forcing the coolant into a three-dimensional helical flow pattern against the channel wall. The continuous rotational acceleration generates secondary flow vortices (swirl flow) that continuously disrupt the thermal boundary layer. Consequently, the fluid transitions to turbulent heat transfer at much lower velocities ($Re > 4,000$ shows turbulent characteristics), boosting the overall heat transfer coefficient ($h$) by 20% to 40% compared to flat baffles at equivalent flow rates. However, the forced helical path increases flow friction, resulting in a 15% to 25% larger pressure drop ($\Delta P$). Spiral baffles are highly recommended for deep cavities where conventional flat baffles would allow flow stratification.

Critical Fluid Tolerances

Baffle effectiveness depends on three critical tolerances: (1) **Radial Clearance**: The gap between the baffle edge and the channel wall should be held to $0.3 \text{ to } 0.5\text{ mm}$. Exceeding this allows coolant bypass (short-circuiting), bypassing the hot tip. (2) **Tip Clearance**: The distance from the baffle tip to the bottom of the drilled hole must be set between $1.0\text{ to } 1.5 \times$ the channel hydraulic radius to balance flow restriction against stagnant volume. (3) **Flow Rate**: Monitor inlet pressure to ensure the minimum flow rate required for turbulence is maintained across all circuits.