Abstract: Heat transfer coefficient and pressure loss measurements were carried out on spheric dimpled test surfaces placed on one wall of a rectangular channel.Three dimpled plates with non-dimensional streamwise space 1.5,1.2,and 0.8,were tested to provide information on the influences of dimple space.Significant local Nusselt number variations were observed at different streamwise and spanwise locations.Comparing the dimpled wall with the smooth wall,globally-averaged Nusselt numbers increase around 45%,friction factors increase around 92%,and globally-averaged thermal performance parameters increase 16%.Decreasing dimple space results in the increase of friction factors,globally-averaged Nusselt numbers and thermal performance parameters.Data also illustrate that the influences of Reynolds number on Nusselt number ratio and friction factor ratio are relatively small.