Heat transfer to viscoplastic materials flowing axially through concentric annuli

Heat transfer in the entrance-region laminar axial flow of viscoplastic materials inside concentric annular spaces is analyzed. The material is assumed to behave as a generalized Newtonian liquid, with a modified Herschel–Bulkley viscosity function. The governing equations are solved numerically via a finite volume method. Two different thermal boundary conditions at the inner wall are considered, namely, uniform wall heat flux and uniform wall temperature. The outer wall is considered to be adiabatic. The effect of yield stress and power-law exponent on the Nusselt number is investigated. It is shown that the entrance length decreases as the material behavior departs from Newtonian. Also, it is observed that the effect of rheological parameters on the inner-wall Nusselt number is rather small.