Momentum and heat transfer from spherical sections in Bingham plastic fluids

• Blunter the particle shape, lower is the critical Reynolds for the flow separation • Shapes of the spherical segments strongly modify the drag coefficient. • Nusselt number increases with the decreasing α due to negligible fluid inertia Extensive numerical results on the momentum and heat transfer from several isothermal segments of a sphere submerged in Bingham plastic fluids are presented here. These results embrace wide ranges of particle shapes (30° ≤ α ≤ 150°, where 2α is the angle subtended by the section removed from the sphere) with its flat surface oriented towards to the free stream and of the relevant kinematic parameters, Reynolds number (0.1-150) and Prandtl number (0.1-100) and the rheological parameters (0 ≤ Bn ≤ 100). Included here are also the results for the limiting Newtonian fluid behaviour ( Bn = 0). Detailed kinematics of the flow is discussed in terms of streamline, velocity and isothermal contours and the apparent yield surfaces delineating the yielded and unyielded subdomains present in the flow field. The gross macroscopic behaviour is captured in terms of the hydrodynamic drag coefficient and Nusselt number as functions of Reynolds number, Bingham number and Prandtl number for six cut-sections of the sphere. The Nusselt number bears a positive relationship with both the Reynolds and Prandtl numbers whereas the influence of Bingham number is modulated by the degree of bluntness of the spherical segment, i.e., the value of α. The paper is concluded by presenting predictive correlations for estimating the value of drag coefficient and Nusselt number in a new application and by performing comparisons with limited experimental data.