Results of 4-equation turbulence models in the prediction of heat transfer to supercritical pressure fluids

• A comparison of different available models for modelling the heat transfer is performed.
• Capabilities of four-equation models when dealing with supercritical fluids are assessed.
• The application of the Algebraic Heat Flux Model (AHFM) for modelling the turbulence heat flux is considered.

The paper summarises the results obtained in the assessment of different turbulence models including low-Reynolds k–ɛ and kθ–ɛθ equations, in the attempt to improve the prediction by RANS techniques of heat transfer to fluids at supercritical pressure. The work has been mainly developed in two phases. Firstly, 4-equation models available in literature were applied to a broad range of experimental data making use of the relationships suggested in their formulations for evaluating turbulent thermal diffusivity. These models were herein used with an Algebraic Heat Flux Model (AHFM), aiming at evaluating the turbulent heat flux; in the present work it was used only in the formulation of turbulence production due to buoyancy while the SGDH was used in the energy equation. In a second phase, the same models were applied repeatedly to a subset of the addressed experimental information with different calculation options, including constant values of the turbulent Prandtl number, mixing models for k–ɛ and kθ–ɛθ equations in order to identify possible improvements. The results show that recourse to these models, which are more complex than common 2-equation ones, provides limited improvements in the comparison with experimental data.