An Experimental study was conducted on heat transfer characteristics in the developing region of a flat channel with a combination of a dimpled surface and a protruded surface for relatively low Reynolds numbers of Re = 1000 - 5000. Detailed local heat transfer characteristics were measured by the naphthalene sublimation method. Attention was directed to the influence of the distance between the dimpled surface and the protruded surface opposing it on the local heat transfer characteristics. The depth/height of the dimple/protrusion δ was fixed at 2.2mm and the distance between two surfaces H was changed as 1.36δ, 2.27δ and 4.54δ. The influence of the protruded surface on the local heat transfer on the dimpled surface appeared in the transitional Reynolds number range of Re = 2500 - 3000 for H = 1.36δ and 2.27δ, but it was not observed for H = 4.54δ. The influence of the dimpled surface on the local heat transfer on the protruded surface was observed mainly on its flat area only in the channel of H= 1.36δ.
