Local heat and mass transfer measurements for multi-layered impingement/effusion cooling: Effects of pin spacing on the impingement and effusion plate

Practical implementation of transpiration cooling system can be realized by multi-layered impingement/effusion cooling system which is composed of two or more layers with pins. Due to restrictions of very low height in multi-layered impingement/effusion cooling, heat transfer characteristics are affected by pin space to diameter. In this paper, the effects of pin space to diameter ratio, sp/d, are investigated on all internal surfaces including impingement plate and pin surfaces. Local heat/mass transfer measured using a naphthalene sublimation method. The ratio of height to diameter ratio, h/d, is fixed at 0.25, and Reynolds number based on the hole diameter is 3000. As a results, heat transfer characteristics on effusion plate are similar to narrow impingement jet cooling without pins, in the case of sp/d = 6.0. Local Sherwood number distributions are affected by biased location of pins at sp/d = 2 and 1.5. Pins block the flow channel, and make flow area narrower. The secondary peak moved outwards in the radial direction, 18%, and Sherwood number of the secondary peak was enhanced by 6%. Comparing the heat/mass transfer of all of the cases, and considering pumping power, increasing pins (decreasing sp/d) resulted in superior performance. Comparison factor of sp/d = 2.0 and sp/d = 1.5 was on the 2.2.