This paper presents and discusses the flow and heat transfer performance of a parallel/ counter flow heat exchanger, when the heat transfer surface is provided with dimples on one or both sides (cold fluid side and hot fluid side). Evaluation of the performance is based here on experimental and numerical data obtained for a typical such exchanger. The Results consist of low characteristics (mainly pressure distributions) and heat transfer characteristics (Nusselt number distributions) comparison against the non-dimpled case (smooth surface) was held. Cases with various dimples depths (d/D= 02, 03 and 0.4) and arrangements (in line and staggered) were tested over a range of Reynolds number (50 to 3000). The numerical solution was obtained by a "FLUENT" computing package that takes into account the K-? turbulence model. Results show the existence of a centrally-located vortex pair and a vortex pairs near the spanwise edges of each dimple, augmenting the local magnitudes of eddy diffusivity of momentum and eddy diffusivity of heat. Advection of reattachment and recirculation of the flow from locations within the dimple cavities, as well as strong instantaneous secondary flows and mixing within the vortex pairs, are apparent. For Nusselt numbers, such augmentations are present near the downstream edges of dimple rims, both slightly within ach depression and on the flat surface nearby each dimple. Also, the staggered arrangement and the dimples placed on the two sides of the plate give good enhancement of heat transfer of this plate. It is found that the dimpled surfaces augment surface heat transfer levels without substantially increasing pressure drop penalties. This is due to the geometry of the dimple do not include significant amount drag. Also, the results show that local Nusselt number augmentation increase as dimple depths increases. These are attributed to :(1) increases in the strengths and intensity of vortices and associated secondary flows ejected from the dimples, as well as (2) increases in the magnitudes of the three dimension of the turbulent transport. It is found that the overall heat transfer rates that are 2.5 times greater for the dimpled surface compared to a smooth surface and the pressure drop penalties in the range of l.5-2.0 over smooth surfaces