Comparative evaluation of three heat transfer enhancement strategies in a grooved channel

Results of a comparative evaluation of three heat transfer enhancement stra tegies for forced convection cooling of a parallel plate channel populated with heated blocks, representing electronic components mounted on printed c ircuit boards, are reported. Heat transfer in the reference geometry, the a symmetrically heated parallel plate channel, is compared with that for the basic grooved channel, and the same geometry enhanced by cylinders and vane s placed above the downstream edge of each heated block. In addition to con ventional heat transfer and pressure drop measurements, holographic interfe rometry combined with high-speed cinematography was used to visualize the u nsteady temperature fields in the self-sustained oscillatory flow. The loca tions of increased heat transfer within one channel periodicity depend on t he enhancement technique applied, and were identified by analyzing the unst eady temperature distributions visualized by holographic interferometry. Th is approach allowed gaining insight into the mechanisms responsible for hea t transfer enhancement. Experiments were conducted at moderate flow velocit ies in the laminar, transitional and turbulent flow regimes. Reynolds numbe rs were varied in the range Re = 200-6500, corresponding to flow velocities from 0.076 to 2.36 m/s. Flow oscillations were first observed between Re = 1050 and 1320 for the basic grooved channel, and around Re = 350 and 450 f or the grooved channels equipped with cylinders and vanes, respectively. At Reynolds numbers above the onset of oscillations and in the transitional f low regime, heat transfer rates in the investigated grooved channels exceed ed the performance of the reference geometry, the asymmetrically heated par allel plate channel. Heat transfer in the grooved channels enhanced with cy linders and vanes showed an increase by a factor of 1.2-1.8 and 1.5-3.5, re spectively, when compared to data obtained for the basic grooved channel; h owever, the accompanying pressure drop penalties also increased significant ly.