Protruded or dimpled-arc absorbers help in accelerating the heat transfer through the rectangular air flow channels while keeping the friction factor at lowest possible value. In the present study, the effective efficiency distribution for protruded/dimpled-arc absorbers in a solar thermal collector is studied taking into account the thermal energy gain and the required pumping power for air flow as simultaneous considerations. The mathematical model used for computation has been validated and the effective efficiency characteristics have been presented as a function of flow Reynolds number. Further, the optimization of process parameters has been carried out and the design procedure for selection of optimal set of design parameters for desired value of temperature rise is discussed. The investigation concludes that the relative height and pitch affect the effective reattachment of the distributed flow whereas the arc angle due to presence of vortex legs generation by dimple/protrusion affects laminar sub-layer and thereby the performance attributes. Highest effective efficiency of 72% for protruded-arc absorber for protrusion height ratio of 0.36, protrusion pitch ratio of 12 and arc angle of 60 degrees has been achieved while maximum of 69.7% for dimpled-arc absorber is achieved on dimple height ratio of 0.3, dimple pitch ratio of 10 and arc angle of 60 degrees. (C) 2019 Elsevier Ltd. All rights reserved.