Heat transfer enhancement in a ribbed channel: Development of turbulence closures

Abstract

The ability to accurately predict turbulent heat transfer in massively separated flows is of immense practical importance especially in the field of heat transfer enhancement in compact heat exchangers. This paper describes new developments in the modeling of the flow and the turbulent heat fluxes in a representative benchmark flow namely that in a heated channel with periodic surface ribs. This flow, which is well-documented by experiments, poses severe challenges to conventional closures due to the significant non-equilibrium effects that are present. Several closure strategies were therefore considered ranging from the eddy-viscosity closures that are routinely used in practice, to the more sophisticated full differential transport closures that can better capture rapidly-evolving flow and thermal fields. As the heat transfer rates are largely determined by the flow conditions in the near-wall region, low Reynolds number versions of these closures were also considered. As for the turbulent heat fluxes, two alternative models were considered: the conventional Fourier's law, and a more complete, algebraic model which is explicit in these fluxes and which correctly allows for their dependence on the turbulent stresses and on the gradients of mean velocity. The models were implemented in the open source software Open-FOAM and the computations were performed with cyclic boundary conditions that are appropriate for this periodic flow. Details of models implementation are reported. Comparisons with experimental measurement indicate significant improvements over existing approaches.

On the highly unsteady dynamics of multiple thermal buoyant jets in cross flows

“…Ma and Li 56 ; Xiao et al, 57 ; Harish and Venkatasubbaiah 58,59 ; Tsai et al, 60 ; Weihing et al, 61 ; Lou et al, 62 ), for the case of highly unsteady dynamics, LES (Large Eddy Simulation) seems to be a more relevant choice, especially when the phenomena of vortex coalescence and splitting become pervasive throughout the computational domain. The LES approach has been successfully applied to pure thermal convection (Eidson 54 ; Wong and Lilly 63 ; Kimmel and Domaradzki 64 ; Pham et al, 65 ; Yan 66 ; Devenish et al, 67 ; Pant and Bhattachary 68 ), circumstances involving various kinds of jets in cross flow (Morton et al, 69 ; Li and Wang 70 ; Li and Ma 71 ) and flows (without buoyancy) in ducts with "turbulators" (Ciofalo and Collins 72 ; Murataa and Mochizuki 73 ; Cui et al, 74 ; Lohász et al, 75 ;…”

- Introduction

“…Weihing et al (2014) have analysed different types of turbulence closures for RANS and made calculations of flow and temperature fields with eight of them for the same conditions and geometry of the channel with transverse ribs. These methods (referred to in the literature as Reynoldsaveraged Navier-Stokes, or RANS) remain the primary tool for engineering analysis despite the spectacular advances in computer technology that was expected to make them obsolete.…”

Heat Transfer in a Square Ribbed Channel: Evaluation of Turbulent Heat Transfer Models

“…The ERCOFTAC test case [1] was considered in the work carried out by Weihing et al [2]. The turbulent heat transfer was determined with a constant turbulent Prandtl number and the explicit algebraic approach according to Younis et al [3].…”