Fin shape effects in turbulent heat transfer in tubes with helical fins

Abstract

From both local and global analysis of the flow field and heat transfer, it was indicated that significant variations (as much as 20%) in both friction factors and Nusselt numbers can occur depending on small changes in fin profile in microfin tubes. A complete set of local flow visualization results and analysis for four different fin shapes are presented to help explain governing flow mechanisms which cause this phenomenon.

Numerical results show that under fully developed flow conditions without flow separation in the streamwise direction, only two layers of elements in the streamwise direction are needed to resolve the entire flow field, thus leading to significant computational savings. Efficient heat transfer simulations are also realized by reusing and periodically copying the converged flow field information without simulating the entire geometry. Issues encountered in the simulation of complex geometries such as turbulent time scales, laminarization, non-trivial initial conditions for ??-ε models, and performance comparison of four popular RANS turbulence models (Spalart-Allmaras model, ??-ε model ofLam-Bremhorst, SST model of Menter, and ??-ε model of Goldberg) are discussed.

A stabilized finite element solver is used to solve turbulent flows and heat transfer in complex, three-dimensional spirally finned tubes. One- and two-equation turbulence models are implemented and evaluated for their performance. Details of the stabilized finite element formulations for incompressible flow are presented, and cost effective model simplifications and solution procedures are introduced.