Experiments and simulations on flow and heat transfer behavior of Therminol 55 liquid phase heat transfer fluid have been conducted in a ribbed tube with outer and inner diameters of 25.0 and 20.0 mm, pitch and rib height of 12.0 and 1.0 mm respectively. Experimental results show that the increase in heat transfer rate of the ribbed tube has a mean value of 2.24 times in the turbulent flow and in a range of 33 -5.2 times in the laminar flow over the smooth tube at the test range. The measured average friction factor of the ribbed tube is in a range of 2.2-2.6 times over the smooth tube. The numerical results show that the heat transfer rate of the windward face wall is 1.34 times in excess of the heat transfer rate of the leeward face wall of ribs, which enhances heat transfer compared with smooth tube. In addition, correlations of the Nusselt number and friction factor in terms of Reynolds number and Prandtl number are determined, based on the curve fitting of the experimental data. (C) 2016 Elsevier Ltd. All rights reserved.