Theoretical modeling of the drag reduction influenced by film boiling heat transfer on a spherical body

Drag reduction is a common phenomenon in various fields, such as enhanced heat transfer process of microchannels, or fuel-coolant interaction (FCI) during severe accidents in nuclear power plants. It significantly affects the solidification process of hot particles and the likelihood of occurrence of vapor explosion, as well. In this work, theoretical modeling of the drag reduction influenced by film boiling heat transfer on a spherical body is conducted, and a fitting method is adopted to obtain a semi-empirical model of drag coefficient (CD), which can be described as a function of particle Froude number (Frp), entrainment Reynolds number (Re alpha), and the ratio of steam density to coolant density (rho 0). There seems to be a positive relationship between Re alpha and CD, however, negative relationships occur between Frp and CD, and between rho 0 and CD. Verifications against single effect experiments and an integral experiment under different initial conditions for a hot solid/melts moving downward in the coolant, and several classical correlations of convective heat transfer and drag coefficient under nonisothermal conditions strongly ensure the accuracy of the present physical model. It can be evaluated from the present model that a negative relationship between the drag coefficient and Reynolds number still occurs in turbulent regime, and there is a significant difference of CD under different sphere diameters in turbulent regime, which haven't been recognized and presented by various classical models yet. The present work can guide to solve the issue of drag reduction during FCI or thermal management and provide a new understanding of mass, momentum, and heat transfer under multi-phase flow conditions which may take place in different kinds of chemical reactions, as well.