Viscosity correction in convective heat transfer correlation of non-Newtonian fluid pipe flow: Revisited.

• Viscosity correction factor derived from first principles for constant wall temperature. • Viscosity correction to Nusselt number for convective heat transfer in laminar flow. • Detailed thermal boundary layer analysis for Prandtl number >1. The role of variable viscosity on the heat transfer in non-Newtonian fluid flow has not been adequately explored in the past. Typically, non-Newtonian fluids are described by the power-law type behaviour as τ = K γ ̇ n (τ : shear stress; K : consistency index; γ ̇ : shear rate; n : power-law exponent). The viscosity correction factor in the form of K w K ∞ m (w : wall; ∞ : bulk) is a function of n. Traditionally, the Sieder-Tate correction for Newtonian fluid, μ w μ ∞ - 0.14 was the popular choice (μ w : fluid viscosity at the wall, μ ∞ : bulk) (Metzner et al. 1957). This is the first work on postulating the viscosity correction from the fundamental boundary layer analysis in non-Newtonian fluid. The mathematical predictions are validated with the literature experimental data. Inaccurate estimation of the viscosity correction leads to under- or over-predictions of the heat transfer coefficient, consequently, affects the effective heat transfer area. The correlations developed in this work would help in improved area calculations, thus, better performance and economic benefits. [ABSTRACT FROM AUTHOR]