Effects of hole arrangements on local heat/mass transfer for impingement/effusion cooling with small hole spacing

The present study investigates the local heat (mass) transfer characteristics of flow through perforated plates. Two parallel perforated plates were placed, relative to each other in either staggered, in line, or shifted in one direction. Hole length to diameter ratio of 1.5, hole pitch to diameter ratio of 3.0, and distance between the perforated plates of 1-3 hole diameters are used at hole Reynolds numbers of 3000 to 14,000. For flows through the staggered layers and the layers shifted in one direction, the mass transfer rates on the surface of the effusion plate increase approximately 50% from impingement cooling alone and are about three to four times that with effusion cooling alone (single layer). The high transfer rate is induced by strong secondary vortices formed between two adjacent impinging jets and flow transition so that heat/mass transfer c oefficient in the midway region is as high as stagnation heat/mass transfer coefficient. The mass transfer coefficient for the in-line arrangement is approximately 100% higher on the target surface than that of the single layer case. In overall, the staggered hole arrangement shows better performance than other cases.