Experimental investigation of heat transfer enhancement in a grooved channel

Forced convection cooling of a parallel plate channel populated with heated blocks is encountered in a large number of important engineering applications, such as industrial heat exchangers, biomedical devices, cooling of microelectronic components, etc. In the grooved channel formed in this way, two main flow regions can be recognized: (i) the bulk flow over the heated blocks in the main channel and (ii) the weak recirculating vortex flow in the groove between adjacent heated blocks. In laminar, steady-state conditions, warm fluid is trapped in the slow recirculating flow in the groove, heated by both upstream and downstream blocks, with diffusion being the dominant heat transfer mechanism through the shear layer between the groove region and main channel flow. This situation impedes the overall heat transport along one heated block and groove periodicity unit. Heat transfer in the reference geometry, the asymmetrically heated parallel plate channel, was compared with that for the basic grooved channel, and the same geometry enhanced by cylinders and vanes placed above the downstream edge of each heated block.; Oscillating temperature fields in the investigated channel geometries were visualized with holographic interferometry, an ideal tool for gaining quantitative insight into the fast changing temperature distributions. Reynolds numbers were varied in the range Re = 200 ÷ 6500, corresponding to flow velocities from 0.76 m/s ÷ 2.36 m/s. Heat transfer in the grooved channels with cylinders and with vanes showed an increase by a factor of 1.2 ÷ 1.8 and 1.5 ÷ 3.5, respectively, when compared to data obtained for the basic grooved channel; however, the accompanying pressure drop penalties also increased significantly. Measurements of the ratio of Nusselt number gain to friction factor gain indicated that the grooved channel with cylinders does not offer any reduction in pressure drop for the requisite heat removal to the basic grooved channel. Based on the same criterion, the performance of the grooved channel with vanes exceeded that of the basic grooved channel for Re ≤ 400.