In this paper, the effects of the variations of the coil pitch and coil diameter on ferrofluid flow boiling characteristics inside helical tubes have been investigated using two-fluid model and control volume technique. The effects of the non-uniform magnetic field on the ferrofluid flow boiling inside helical tubes have also been studied. The results indicated showed that decreasing the coil diameter enhances the heat transfer coefficient. This is due to the effect of centrifugal force which is increased by decreasing the coil diameter. Also, the results confirmed the dual role of the centrifugal force on heat transfer (increase) and vapor volume fraction (decrease) and at the same time remarkable increasing of locally void fraction on heated wall and raising possibility of occurrence of CHF. In addition, the improvement of surface wettability which is induced by nanoparticles sedimentation during the boiling process has been considered. Results showed the reduction of the void fraction. The application of a magnetic field at critical regions resulted in the bubble departure diameter and vapor volume fraction generation reduction. Consequently, the critical heat flux is increased
