Influence of stepped cylindrical turbulence generators on the thermal enhancement factor of a flat plate solar air heater

•Influence of stepped cylindrical turbulence generators on thermal enhancement of a solar air heater is discussed.•Turbulators having cylindrical stepping’s tend to make the flow turbulent near the edges of the step. This is due to flow separation around the stepped generators causing beneficial effect on the heat transfer process.•It is revealed in the study that thermal enhancement factor increases with the number of rows as well as decrement in core diameter increases the thermal enhancement factor.