Geometrical optimization of heat sinks with square, cylindrical and plate fins for heat transfer increase is numerically analyzed in transition regime external flow. The relations between the thermal characteristics of fins and boundary conditions such as free-stream velocity are investigated. Experimental studies are performed by using manufacturable fins to validate the numerical model. Heat transfer correlations are derived in order to determine average heat transfer coefficients over a certain range of both Reynolds number and non-dimensional geometric parameters like spanwise and streamwise spacings. Confidence level of the experimental work is demonstrated by uncertainty analysis. Cylindrical fins are observed to be approximately 4.5% superior to ones with square and plate profiles in terms of maximum base plate temperature.