Cooling holes are playing critical roles in the impingement-effusion cooling system. The present experimental investigation have studied the effects of the hole diameters on the cooling efficiency and discharge coefficient. The main flow was heated up via combustion, with a maximum outlet temperature 850K. Cooling air, on the other hand, is supplied by an MAM-200 compressor. Temperature distribution on the hot side of the effusion plate is measured by a thermal infrared imaging camera calibrated by 5 thermocouples embedded in the tested plate. A filter is used to minimize the radiation from the hot gas.
Cooling holes, both the effusion holes and impingement holes are designed in staggered arrangement; and the number of effusion holes is almost equal to the impingement holes. The inclination angle of the effusion holes in the streamwise direction is 20 degree with respect to the liner surface. The pressure drop across the cooling system ranges from 3% to 5% of the total pressure of the inlet flow. Temperature distributions are measured with an infrared thermal imaging system. The length of the holes is kept to be constant. Three various effusion hole diameters/length ratio 0.3, 0.35, 0.43, with impingement hole diameters/length ratio 0.4, 0.47 and 0.6 correspondingly, have been tested and compared. The experimental results indicate that with the increasing of cooling hole diameters, discharge coefficient is also increased. Nevertheless, cooling efficiency reached its maximum with the effusion hole diameter/length ratio 0.35.