Effect of a rotating cylinder on the flow of a bingham plastic fluid in t-junction: momentum and heat transfer characteristics

Abstract

The present numerical work investigates the momentum and heat transfer characteristics of a Bingham plastic fluid in a rectangular T-channel. A rotating cylinder which is placed in a T-junction mimics the behaviour of a rotating valve to regulate the fluid flow and enthalpy in the two branches of the channel. Numerical simulations are carried out over a wide range of conditions (based on the cylinder diameter): Reynolds number ð10 2 6 Re 40Þ, Bingham number ð10 2 6 Bn 20Þ, Prandtl number ð10 6 Pr 100Þ and rotational velocity of the cylinder ð 5 6 a 5Þ where a is the circumferential velocity normalized by the inlet velocity. Extensive results are presented in the form of streamline patterns, isotherm contours and yielded/unyielded regions in the vicinity of the T-junction. In particular, the major thrust of this study is to predict the hydrodynamic forces and torque exerted on the cylinder, flow split ratio (i.e., flow rates in the two outlet branches), critical Bingham number (beyond which no flow separation occurs). Also, the outlet temperatures, enthalpy gain, distribution of Nusselt number over the cylinder surface and its average value as a function of the governing dimensionless parameters have been investigated. The present results show that the rotation of the cylinder can aid or suppress the formation of the recirculation zones effectively which appear on the left wall of the main branch and lower wall of the side branch depending upon the Reynolds number while it always suppresses the cylinder wake. As expected, the Bingham number stabilizes the flow by suppressing the recirculation zone while the Reynolds number tends to promote it. The flow split ratio is found to be significantly affected by the direction of the cylinder rotation. The cylinder rotation also shows a strong impact on the mean values of the hydrodynamic forces and torque. The temperature of the exiting relative streams is seen to be higher for the lower Reynolds and Prandtl numbers, and higher Bingham numbers while cylinder rotation shows a weak effect. The enthalpy gain by the main branch is found to be significantly affected by all the parameters. It has also been observed that the rate of heat transfer is higher for a clockwise rotating cylinder than in the case of an anticlockwise rotating cylinder.