An experimental investigation of air, mist/air, and steam film cooling on a flat plate with single- and double-row holes

Mist/air cooling, a novel technology proposed to enhance conventional air cooling, has been extensively studied. However, previous experimental studies have been limited to relatively low mainstream temperatures, resulting in incomplete mist evaporation. This study presents the first experimental investigation of mist/air film cooling under high-temperature mainstream conditions up to 460 K, focusing on the effects of blowing ratios (0.5–1.5) and row arrangements (single, in-line, and staggered-row). Comparative analyses are also performed using air-only and steam cooling results to provide a comprehensive evaluation of cooling performance. The results indicate that inline hole film cooling demonstrates improved performance along the centerline, though its effectiveness (η) diminishes between adjacent holes compared to single-row holes. In contrast, the staggered hole arrangement enhances cooling performance and results in more pronounced jet lift-off followed by reattachment to the wall. As the blowing ratio (M) increases, both single-row and inline hole arrangements experience a decrease in η, with mist cooling for single rows being an exception. Conversely, the staggered holes exhibit increased effectiveness. Additionally, both mist and steam cooling outperform conventional air film cooling in terms of η. Specifically, steam cooling increases the area-averaged effectiveness by up to 65.5 % at M = 1.5 with single-row holes, while mist cooling increases the effectiveness by 22.7 % at M = 1.0 for the staggered-row, with minimal water usage (6 % of coolant mass flow).