THERMAL TAYLOR DISPERSION IN AN INSULATED CIRCULAR-CYLINDER .2. APPLICATIONS

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 UBAR* and thermal dispersivity alphaBAR* of the composite system for both laminar and turbulent flows. For each, the effect of the nonzero wall thickness is such that UBAR* is always less than the average fluid velocity VBAR. In a laminar flow system, alphaBAR* can either be larger or smaller than the fluid diffusivity alpha(f), depending upon the thermal properties of the fluid and wall, as well as upon the magnitude of the Peclet number. For turbulent flows, alphaBAR* can be either larger or smaller than both alpha(f) and the zero wall thickness effective thermal dispersivity, alpha0BAR*, although now it further depends upon the Prandtl number.