Heat transfer behavior of temperature-dependent viscoelastic non-Newtonian fluid with buoyancy effect in 2:1 rectangular duct

This numerical study investigates the flow characteristics and heat transfer mechanism of a viscoelastic non-Newtonian fluid in a 2:1 rectangular duct. The combined effect of temperature-dependent viscosity, buoyancy, and secondary flow caused by a second normal-stress difference is considered. The Reiner-Rivlin constitutive equation was adopted to model the viscoelastic fluid characteristics. An axially constant heat flux on the bottom wall and peripherally adiabatic boundary condition (H2) were both used. The numerical results for a polyacrylamide (Separan AP-273) solution showed a significant heat transfer enhancement compared to those of a constant property fluid, and exhibited a good consistency with experimental results for both thermal developing and thermally developed regions. In a bottom-wall-heated 2:1 rectangular duct, the main cause of the heat transfer enhancement of the viscoelastic fluid was viscoelastic-driven secondary flow, with temperature-dependent viscosity and buoyancy-induced secondary flow playing supporting roles. (C) 2000 Elsevier Science Ltd.