Influence of Microstructures on Convective Heat Transfer under Laminar and Turbulent Flow Conditions

Abstract

Microstructures on heat transfer surfaces can enhance heat transfer. This effect appears during the induction period of the crystallization fouling process where often a negative fouling resistance occurs. It is interpreted by the increase in near-wall turbulence due to first crystals growing on the surface resulting in the observed heat transfer enhancement [1]. Man-made microstructures in the same scale may utilize this positive effect in single-phase convective heat transfer. Plain copper plates with systematically and randomly distributed structures of 100 to 500 μm were designed and manufactured. Number, size, design, and allocation of the microstructures were varied. The plates were applied to a heat transfer test rig that allows investigation of Reynolds numbers between 1,000 and 17,000. The heat transfer can be calculated from temperature measurements and compared to smooth surfaces. Microstructures show an increase of heat transfer, described by the Nusselt number, up to 18% in the turbulent regime compared to a smooth plate. In laminar flow, a maximum of the Nusselt number was observed for some geometries. All results are strongly dependent on the design of the probes. These results show the potential for the optimization of microstructured surfaces to maximize heat and, subsequently, mass transfer rates.