Pressure-recovery-driven flow maldistribution in U-shaped cooling manifolds: Mechanisms and control

Flow maldistribution in a single-inlet, closed-end cooling manifold arises from the interaction between pressure recovery in the main header and the distributed hydraulic resistance of the branches. This maldistribution can cause non-uniform transverse cooling of hot-rolled steel strips, thereby affecting product quality and strip-shape stability. This study investigates the underlying flow physics of a U-shaped cooling manifold using an experimentally validated computational fluid dynamics model. Continuous mass extraction through successive branches causes progressive decay of the axial momentum in the main header and a corresponding recovery of static pressure, thereby providing progressively greater hydraulic driving pressure to downstream branches. Near the closed end, however, recirculation and enhanced shear dissipation locally weaken the pressure-recovery process and generate localized spatial variations in terminal branch flow rates. The results further show that the outlet-to-inlet area ratio alone does not uniquely determine the flow-distribution behavior: varying the main-header diameter primarily modifies the axial velocity level and pressure-recovery gradient, whereas varying the throttling-orifice diameter mainly changes branch resistance and discharge capacity. These findings indicate that spatial coordination between header pressure recovery and branch resistance provides a practical physical basis for controlling flow maldistribution. Based on this physical understanding, a segmented orifice-resistance distribution reduces the flow non-uniformity coefficient from 0.828% to 0.756% and the total system pressure drop from 2867.51 to 2310.8 Pa, corresponding to reductions of 8.70% and 19.41%, respectively. The findings provide a physics-informed interpretation and a practical resistance-redistribution strategy for controlling flow maldistribution in closed-end multi-branch cooling manifolds.