Detailed measurement of heat transfer and flow characteristics in rectangular duct with rib turbulators mounted on the bottom surface

The present work is an experimental study to investigate the heat transfer and flow characteristics in the entrance region of a rectangular channel with a single and two solid square ribs mounted on the bottom surface of the channel. Hot wire anemometry (HWA) and resistance thermometry (RTD) have been utilized for the velocity and temperature measurements in the flow-field. Liquid crystal thermography (LCT) has been employed to map the surface temperature profiles and evaluation of the heat transfer coefficient. The effectiveness of one-rib and two-ribs is studied from flow modulation and heat transfer enhancement point of view. The Reynolds number (based on the hydraulic diameter of the channel) is set equal to 2.09 x 10(4). The rib pitch-to-height ratio set during the experiment is equal to 10. The Nusselt number variation on the bottom surface for the no-rib case is similar to what is observed from the law of the wall. The Nusselt number augmentation results from transient LCT closely follows the energy balance check. The turbulent boundary layer well past the ribs for both one-rib and two-rib case is different from that of the plane surface as evident from the higher Nusselt number observed in the far-field region. The stagnation region around the second rib is not as significant as that around the first rib. There is some degree. of correlation between the velocity fluctuation and temperature fluctuation, the former being significant in the core of the shear layer while later is significant close to the wall. Overall, the thermal boundary layer, the hydrodynamic boundary layer, flow visualization and the Nusselt number results are observed to correlate with each other very well.