Numerical investigation on the flow and heat transfer characteristics of non-Newtonian viscoelastic fluids in stirred reactors

Abstract

Compared to Newtonian fluids, the flow and heat transfer behavior of non-Newtonian viscoelastic polymer solutions are more complex. In this study, a numerical investigation is carried out to analyze the flow dynamics and heat transfer characteristics of viscoelastic fluids in a stirred reactor. The Phan-Thien–Tanner viscoelastic constitutive model is employed to accurately capture the complex rheology of polymer solutions. This study focuses on exploring the potential influence of the inertial Reynolds number (Re, denoted by impeller rotational speed N) and fluid elasticity (denoted by relaxation time λ) on enhancing flow mixing and heat transfer. Results indicate that heat transfer performance improves with increasing rotational speed and relaxation time. Under sufficient inertia, increased elasticity leads to greater deformation of long-chain polymer molecules, triggering elastic instability phenomena. At the critical relaxation time of λ = 0.1, two distinct flow regimes are observed. Increased elasticity triggers elastic turbulence, which effectively enhances fluid mixing and convective heat transfer within the reactor. Under highly elastic conditions (λ > 0.1 s), the Nusselt number (Nu) exhibits non-monotonic temporal behavior. Dimensionless analysis further demonstrates that viscoelastic fluids achieve superior heat-transfer efficiency relative to Newtonian fluids, with Nu enhanced by 7.16% and 22.58% at Re = 405 and Re = 675, respectively, under highly elastic conditions. Furthermore, the optimized frame-type combined impeller exhibits excellent performance in the flow and heat transfer processes of viscoelastic fluids. The present work is conducive to the development and optimization of high-efficiency heat transfer reactors for polymerization processes.