The local heat/masstransfercharacteristics on an innersurfaceoftheeffusion platein an impingement/effusion cooling system have been investigated. Two perforated plates are installed in parallel position to simulate the impingement/effusioncooling system.Theexperimentshavebeenconductedforthreedifferentholearrangements, staggered, square, and hexagonal, with various gap distances of 1, 2, 4, and 6 times the effusion hole diameter. The Reynolds number based on the effusion hole diameter is e xed at 1 £ £10 4 . A naphthalene sublimation method is used to determine the local heat/mass transfer coefe cients on the effusion plate. For all of the tested cases, high transfer regions are formed near the stagnation points and at the midline region of the adjacent impinging jets due to secondary vortices and e ow acceleration to the effusion holes. The heat/mass transfer coefe cient in the whole region increases with decreasing gap distance. The staggered hole arrangement shows the highest average heat transfer coefe cient due to the largest area ratio of the effusion to the injection hole; however, the heat/mass transferon theeffusionplateismoreuniform forthesquareand hexagonalholearrangementsbecausethenumber of injection holes is increased. Nomenclature Ae = total hole area of effusion plate Ai = total hole area of injection plate D = effusion hole diameter d = injection hole diameter H = gap distance between injection and effusion plates hm = local mass transfer coefe cient Knaph = mass diffusion coefe cient of naphthalene vapor in air ND = number of effusion holes Nd = number of injection holes Nu = Nusselt number based on effusion hole diameter P = pitch of array holes Pr = Prandtl number ReD = Reynolds number based on effusion hole diameter and the average velocity in the hole Red = Reynolds number based on injection hole diameter and the average velocity in the hole Sc = Schmidt number Sh = Sherwood number based on effusion hole diameter, Eq. (2) Sh = average Sherwood number x;z = distance from the center of a hole (Fig. 2)