Question: With a low-Prandtl-number fluid, the temperature profile in a tube develops more rapidly than the velocity profile. Thus, as the Prandtl number approaches zero, the temperature profile can approach a fully developed form before the velocity profile has even started to develop (although this is a situation of purely academic interest). Convection solutions based on a uniform velocity over the cross section, as described, are called slug-flow solutions. Develop an expression for the slug-flow, fully developed temperature-profile Nusselt number for constant heat rate per unit of tube length for a concentric circular-tube annulus with a radius ratio of 0.60 for the case where the inner tube is heated and the outer tube is insulated. Compare with the results in Table and discuss.
