Local Heat/Mass Transfer With Various Rib Arrangements in Impingement/Effusion Cooling System With Crossflow

The present study has been conducted to investigate the effect of rib arrangements on flow and heat/mass transfer characteristics for an impingement/effusion cooling system with initial crossflow. Two perforated plates of square hole array are placed in parallel and staggered arrangements with a gap distance of $2d$ and the crossflow passes between the injection and effusion plates. Both the injection and effusion hole diameters $d$ are 10 mm and Reynolds number based on the hole diameter and hole-to-hole pitch are fixed at 10,000 and $6d,$ respectively. Square ribs of various rib arrangements and attack angles are installed on the effusion plate. With the initial crossflow, locally low transfer regions are formed and the level of heat transfer rate become lower as flow rate of the crossflow increases because wall jets are swept and the stagnation regions are affected by crossflow. With rib turbulators, the flow and heat transfer patterns are changed because the ribs protect near-wall flows including wall jets and generate secondary flow in a duct. For $M⩾1.0,$ the overall heat transfer is promoted when ribs are installed on the effusion surface, and higher values are obtained with smaller pitch of ribs. But, the attack angle of the rib has little influence on the average heat/mass transfer. For low blowing ratio of $M=0.5,$ the ribs have adverse effects on heat/mass transfer. Pressure drop between the inlet and exit of the channel increases up to 20% of total loss when ribs are installed while it is only 5% of total pressure loss across the perforated plates without ribs.