Thermal Taylor dispersion in an insulated circular cylinder—II. Applications

Abstract

The thermal dispersion theory derived in Part I is here applied to convective heat transfer in an externally insulated tube possessing a finite wall thickness. Expressions are derived for the mean axial thermal propagation velocity UU★ and thermal dispersivity \\ ̄ ga★ of the composite system for both laminar and turbulent flows. For each, the effect of the nonzero wall thickness is such that UU★ is always less than the average fluid velocity V . In a laminar flow system, \\ ̄ ga★ can either be larger or smaller than the fluid diffusivity α f , depending upon the thermal properties of the fluid and wall, as well as upon the magnitude of the Peclet number. For turbulent flows, \\ ̄ ga★ can be either larger or smaller than both α f and the zero wall thickness effective thermal dispersivity, \\ ̄ ga★ 0 , although now it further depends upon the Prandtl number.