In this study, the heat transfer, friction factor and thermal performance factor characteristics of a new solar air heaters (SAHs) with circular type turbulators having different relief angles and distances were performed. Effect of the pitch ratio (PR) and angle ratio (AR) were investigated to improve in heat transfer in SAHs in a range of between 3000 and 7500 Reynolds number under solar radiation heat flux. The experimental results obtained using various turbulators were compared with conventional plain tube. Nusselt numbers were increased with increasing Reynolds number whereas; it was decreased with increasing PR and AR. The friction factor and thermal performance factor was decreased with increasing Reynolds number, PR and AR. It was found that the turbulators arrangement with PR = 2 and AR = 0.125 shown the maximum heat transfer enhancement of 416%, friction factor of 511% than conventional plain tube and the thermal performance factor was obtained as similar to 2.9. In addition, the empirical equations for heat transfer, friction factor and thermal performance factor were derived and compared with the experimental results. The predicted results indicated a good agreement with experimental results within 10% of error. (C) 2015 Energy Institute. Published by Elsevier Ltd. All rights reserved.