The prime objective of present work is to study exp erimentally the heat transfer enhancement through d ifferent circular diametrical dimple surfaces in longitudinal and lateral directi ons. In this paper horizontal rectangular plates of Stainless Steel and Galvanised Iron with different circular diametrical dimples (l ike 11mm , 14mm ) for in-line arrangements were stu died in forced convection with varying laminar external flow condition. The variou s parameters considered for study are Reynolds Numb er, Nusselt number, Prandtl Number, Co-efficient of Friction, Heat transfer coe fficient and heat transfer rate for a constant Pran dtl number (0.698) It has been found that the heat transfer coefficient and heat trate increases for various dimple surfaces as compared to plane surface. It has been also found that the heat transfer coeffici ent and heat transfer rate increases along longitud inal direction as compared to lateral direction. And it is seen that heat transfer rate is maximum for larger diameter (14mm) of dim ple. For circular dimples, heat transfer enhancements (relative to a flat plate) we re observed for Reynolds number range from 350 to 5 50.