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THE COMPUTATION OF FLOW AND HEAT TRANSFER THROUGH SQUARE-ENDED U-BENDS, USING LOW-REYNOLDS-NUMBER MODELS

Konstantinos-Stephen P. Nikas
Technological Education Institute of Piraeus, Mechanical Engineering Department, Fluid Mechanics Laboratory, Greece

Hector Iacovides
Turbulence Mechanics Group, School of Mechanical, Aerospace and Civil Engineering. The University of Manchester, Manchester M13 9PL, U.K.

Аннотация

This study considers the computation of turbulent flow and heat transfer in square-ended U-bends of strong curvature. Flows at two Reynolds numbers have been computed, one at 100,000 and one at 36,000 and in the thermal analysis the Prandtl number was either 5.9 (water) or 0.72 (air). The turbulence modelling approaches examined include a zonal and a low-Re k-ε model, a zonal and a low-Re basic DSM model and a realisable, wall-parameter-free second-moment closure. For the low-Re EVM and DSM models, an alternative length-scale correction term, independent of wall distance, has also been tested. All models produce similar flow predictions, suggesting that the flow development is mainly influenced by mean flow parameters rather than the turbulence field. The main flow features are reproduced, but predictive deficiencies after the 90° location have also been identified. The heat transfer comparisons, on the other hand, show that the low-Re DSM model with the alternative length scale correction produces the most reliable Nusselt number predictions for the Prandtl numbers examined.