Mist/Steam Heat Transfer of Multiple Rows of Impinging Jets

Internal mist/steam blade cooling technology is considered the future of high-temperature gas turbine systems that burn hydrogen or synthetic gases. This paper experimentally investigates the mist/steam heat transfer of three rows of circular jet impingement in a confined channel. Fine water droplets with an average diameter of 3-μm are generated by atomizing water through small nozzles under high pressure. The circular jets have a uniform diameter of 8-mm, and the distance between adjacent jets in a row is 3 diameters. Jets in different rows are staggered and the distance between rows is 1.5 diameters. The spacing of nozzle-to-target is 2.8 diameters. Experiments were conducted with Reynolds numbers at 7,500 and 15,000 and heat fluxes ranging from 3,350 to 13,400W/m². The results indicate that the wall temperature significantly decreased because of mist injection. A region of high cooling enhancement is observed and more extensive than those employing one row of circular jets or a slot jet. While the details depend on flow conditions, it is seen that the enhanced region of 3-row jets is about 5 jet diameters at Re = 7,500, q” = 7.54 kW/m², and m_l/m_s = 3.5%, compared to 2 jet diameters for single-row jets. The enhancement becomes negligible after a certain distance downstream. The maximum local cooling enhancement is up to 800% by injecting 3.5% of mist at low heat flux condition and 150% for high heat flux condition. The average cooling enhancement can achieve more than 100% within 2 jet-diameter distance from the stagnation line at Re = 15,000 and m_l/m_s = 1.5%.