Heat-transfer enhancement by adaptive reorientation of flow fields

Scope is enhancement of scalar transport (heat, chemical species) in engineered flow systems by reorientations of a laminar base flow. Practical applications include mixing in inline heat exchangers by downstream reorientation of baffles, stirring in bio-reactors by cyclic repositioning of impellers, and subsurface chemicals distribution for in situ minerals mining by unsteady pumping schemes. Conventional reorientation schemes consist of a periodic reorientation (in space or time) of the flow designed to accomplish efficient fluid mixing. However, whether this approach indeed yields optimal scalar transport for significant diffusion and/or chemical reactions is unclear. The present study explores an alternative approach: adaptive reorientation of the flow by interval-wise selection of the reorientation that is predicted to yield optimal scalar transport for a future time horizon. Key enabler for fast predictions is a compact model based on the spectral decomposition of the scalar evolution in the base
flow. The adaptive reorientation scheme is investigated for a representative problem: enhanced heating of a cold fluid in a 2D circular domain by an unsteady flow driven by step-wise activation of moving boundary segments. This reveals that the adaptive reorientation scheme can substantially accelerate
the heating compared to conventional time-periodic reorientation designed for efficient mixing and thus demonstrates its potential for attaining optimal scalar transport in reoriented flows.