Abstract In the present work, a novel heat transfer device, radial heat pipe (RHP) has been investigated due to lower flow resistance. Mathematical and computational fluid dynamics (CFD) models have been developed to investigate their thermal performance and two phases flow process inside RHP. The steady-state theoretical model of RHP has been employed to investigate the influence of various filling ratio range of (0–60%) of water and three different values of heat input (3267 W, 4004 W and 4817 W) on the thermal performance of a RHP at different operating conditions. CFD simulations further demonstrate that present built VOF model could effectively reproduce phases-change fluid flow and heat transfer inside RHP. Phenomena such as nucleation boiling, coalescence of bubbles, formation of the liquid film were observed in the heat pipe. Moreover, numerical modelling results were well validated by the experimental tests for various conditions, and maximum deviation falls within 10%.