Local heat and mass transfer characteristics for multi-layered impingement/effusion cooling

Multi-layered impingement/effusion cooling is an advanced cooling configuration that combines impingement jet cooling, pin cooling, and effusion cooling. The arrangement of the pins is a critical design factor because of the complex heat transfer in the internal structure. Therefore, it is important to measure the local heat transfer at all internal surfaces as a function of the pin spacing. In this study, a naphthalene sublimation method was employed to measure the details of the heat/mass transfer at the internal surfaces, including the injection plate, effusion plates, and the pins. An staggered array of holes was formed at the injection plate and effusion plates where the ratio of the height to the diameter of the pins, h/d, was fixed at 0.25. The ratio of the pin spacing to the diameter, s_p/d, was varied in the range 1.5≤s_p/d≤6, and the Reynolds number based on the hole diameter was 3000. As a result, a vortex ring formed near the pin, leading to re-impingement flows in the narrow channel. The jet flow impinged strongly on the pin, resulting in a large heat transfer region at each surface. The total average Sherwood number with s_p/d=1.5 was larger than that with s_p/d=6 by a factor of 1.5.