SUMMARY

Forced convection heat transfer in compact, air-cooled heat exchangers with high-density, high aspect ratio fin channels is typically limited by low channel Reynolds number (Re) that is limited by the volume flow rate of the cooling air. As a result, heat transfer is restricted by the thin thermal boundary layers over the fin surfaces and by limited mixing of the heated air with the cooler core flow. These limitations are commonly overcome by increasing the air volume flow rate, the fin planform dimensions and density, or by passive generators of vortical motions (e.g., vortex generators and dimples) at significant increases in flow losses. Earlier work at Georgia Tech has shown that heat transfer within high aspect ratio rectangular channels can be significantly increased with minimal penalty in flow losses by inducing small-scale vortical motions within the channels using cantilevered thin-film aero-elastically oscillating reeds. The present investigations focus on the formation and advection mechanisms of these small-scale motions and their role in heat transfer enhancement. It is shown that the induced small-scales when the channel flow is laminar result in “turbulent-like” characteristics and when the flow is transitional accelerate the onset of turbulence. Details of the reed motion and the ensuing flow within channel models were investigated using imaging of the reeds and 2-D PIV along with hot wire anemometry. The local and global heat transfer coefficients in the absence and presence of the reeds were computed along with the associated flow losses to determine the efficiency of the heat transfer enhancement and key flow and reed parameters which affect this efficiency were identified. The scaling of the present results was assessed by comparing the reed driven heat transfer and associated losses with corresponding setups in arrays of fin channels. Link to presentation: https://bluejeans.com/455777339