A numerical investigation of heat transfer in a smooth bend part of a U-duct

Abstract

Purpose – The aim of this paper is to study two-dimensional numerical simulations of the flow and temperature fields inside the bend (turn) part of a U-duct. Design/methodology/approach – Several turbulence models based on two and five equations were used to solve the momentum and energy equations inside the bend (turn) part of the U-duct. For two-equation models, both the renormalization group and realizable k-ɛ turbulence models were implemented. The five-equation model used is a Reynolds stress model with different wall boundary conditions. Standard, non-equilibrium and enhanced wall functions were used in parallel with the two- and five-equation models to treat the turbulent flow near the duct walls. Findings – Several turbulence models were used to simulate the flow and temperature fields along the bend part of a U-duct with different inlet and thermal boundary conditions. The numerical results indicate that the renormalization and realizable k-ɛ turbulence models with standard wall function treatment gave the best results when compared with experimental data obtained for similar conditions. Research limitations/implications – For heat transfer analysis, two different thermal boundary conditions, i.e. constant wall temperature and constant heat flux at the wall are implemented. The results are calculated for Reynolds number equal 20,000. Practical implications – The results can be used in designing heat exchangers, piping and duct systems, and internal passage cooling of gas turbine blades. Originality/value – The numerical results obtained here concentrate on the detailed investigation of flow and temperature field at the outer wall of the bend part. Different boundary conditions at the inlet and the outer bend walls of the U-duct were applied to study how these boundary conditions affect the flow and temperature fields.