Second-law analysis of heat transfer in swirling flow through a cylindrical duct

Abstract

A second-law analysis is made on a swirling flow in a cylindrical duct with constant wall temperature. A purely tangential entry of the fluid is considered and a simplified model, consisting of a central air core enclosed by a potential, free vortex region and a boundary layer, is assumed. The approximate hydrodynamic boundary layer equations, and the continuity equation, are set up and solved numerically for the velocity gradients in the boundary layer. Similarly, the temperature gradients within the thermal boundary layer are obtained from the energy equation. The local Nusselt number and rate of entropy generation are calculated and used to evaluate the rate of heat transfer and loss of available energy, respectively. A merit function, defined as the ratio of exergy transferred to the sum of exergy transferred and exergy destroyed, is evaluated for various values of Reynolds number, based on the inlet tangential velocity, and conclusions are drawn about the influence of inlet swirl on irreversibility.