A universal entrance nusselt number for internal slip flow

A universal finite Nusselt number is found for laminar slip flow heat transfer at the entrance of a conduit. The Nusselt number expression is valid for both isothermal and isoflux thermal boundary conditions and for any conduit geometry. The value of the entrance Nusselt number is found to be dependent on two nondimensional parameters that include effects of rarefaction, fluid properties, and the fluid/wall interaction.