CYLINDRICAL CROSS-BARS FOR THERMAL PERFORMANCE AUGMENTATION IN AIR CHANNEL

Abstract

Experiments of the heat transfer and pressure drop are performed in a rectangular channel employing eight different arrays of cylindrical cross-bars as inserts. Numerical simulations are also performed to examine the secondary flow caused by the cylinders. The objectives are to investigate the enhancement of the channel-wall heat transfer and pressure drop caused by the local flow, cylinder array geometry, and flow Reynolds number. Two different cylinder diameters of 1.0 mm and 2.0 mm are employed. The diameter of 2.0 mm is used to create four in-line arrays while the diameter of 1.0 mm is used to create four staggered arrays of the cylinders. The cylinder arrays employ different diameter-to-pitch ratios (0.025 to 0.2) and cylinder orientations (45°, 90°) relative to the main flow direction. The flow Reynolds number is varied between 600 and 13,000. Only two array geometries, one in-line and one staggered, with the cylinders oriented at 90° to the flow are modeled for the numerical study. The numerical results show that the local flow accelerates in the gap between the cylinder and channel wall. The vortex shedding downstream of the cylinders interacts with the channel wall. The Nusselt number on the channel wall and the friction factor are measured with and without the cylinders. The ratios of Nusselt numbers and friction factors increase with the Reynolds number when the Reynolds number is less than 3000. The ratios always increase with the diameter-to-pitch ratio.