Complex fluid flow in annular space under the effects of mixed convection and rotating wall of the outer enclosure

This study aims to investigate the roles of pertinent parameters on the mixed convection of complex liquids in annular devices. The investigated area consists of two circular cylinders with fixed and heat walls. Both cylinders are enclosed within a circular room with a cold wall and rotate regularly. The zone between the inner obstacles and the outer space contains complex power-law fluids. This investigation is numerically achieved by using the package ANSYS-CFX, which is based on the finite-volume method. The parameters studied in this study are the arrangement and size of inner tubes (d/D), the rotational speed of outer space, the rheological nature of fluids (n), and the relative concentration of thermal buoyancy force. These pertinent parameters were quantitatively expressed for the following values: d/D (= 0.1, 0.25, and 0.45); Reynolds number (Re = 1 to 20); flow behavior index (n = 0.6, 1 and 1.6); Richardson number (Ri = 0 to 100), respectively. It was found that increasing the thermal buoyancy value and the rotational speed of the outer container increases the rate of heat transfer of the cylinders in the vertical and horizontal arrangement. For example, for shear-thinning fluid (n = 0.6), raising the value of Ri from 0 to 100 increases Nu by 59.67% for d/D = 0.1. Also, the arrangement of the two cylinders differently affects the dynamic behavior of the fluid within the studied space.