Direct numerical simulation analysis of heat transfer deterioration of supercritical fluids in a vertical tube at a high ratio of heat flux to mass flowrate

The flow characteristic of fluid at low Prandtl number is of continued interest in the nuclear industry because liquid metals are to be used in the next-generation nuclear power reactors. In this work we performed direct numerical simulation (DNS) for turbulent channel flow with fluid of low Prandtl number. The Prandtl number was set to 0.025, which is representative of the behavior of liquid metals. Constant heat flux was imposed on the walls to study heat transfer behavior, with different boundary conditions for temperature fluctuation. The bulk Reynolds number was set as high as 50,000, with a corresponding friction Reynolds number of 1,200, which is closer to the situation in a reactor or a heat exchanger than used in normally available databases. Budgets for turbulent variables were computed and compared with predictions from several RANS turbulence models. In particular, the Algebraic Heat Flux Model (AHFM) has been the focus of this comparison with DNS data. The comparisons highlight some shortcomings of AHFM along with potential improvements.

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Direct numerical simulation of turbulent heat transfer in annuli: Effect of heat flux ratio

International Journal of Heat and Fluid Flow ◽

10.1016/j.ijheatfluidflow.2009.02.018 ◽

2009 ◽

Vol 30 (4) ◽

pp. 579-589 ◽

Cited By ~ 20

Author(s):

M. Ould-Rouiss ◽

L. Redjem-Saad ◽

G. Lauriat

Keyword(s):

Heat Transfer ◽

Numerical Simulation ◽

Heat Flux ◽

Direct Numerical Simulation ◽

Flux Ratio ◽

Turbulent Heat Transfer ◽

Turbulent Heat

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Direct numerical simulation of convective heat transfer of supercritical pressure in a vertical tube with buoyancy and thermal acceleration effects

Journal of Fluid Mechanics ◽

10.1017/jfm.2021.705 ◽

2021 ◽

Vol 927 ◽

Author(s):

Y.L. Cao ◽

R.N. Xu ◽

J.J. Yan ◽

S. He ◽

P.X. Jiang

Keyword(s):

Heat Transfer ◽

Numerical Simulation ◽

Direct Numerical Simulation ◽

Turbulent Flow ◽

Vertical Tube ◽

Supercritical Pressure ◽

Dominant Factor ◽

Turbulent Structures ◽

Flow Acceleration ◽

Flow And Heat Transfer

Supercritical pressure fluids are widely used in heat transfer and energy systems. The benefit of high heat transfer performance and the successful avoidance of phase change from the use of supercritical pressure fluids are well-known, but the complex behaviours of such fluids owing to dramatic thermal property variations pose strong challenges to the design of heat transfer applications. In this paper, the turbulent flow and heat transfer of supercritical pressure $\textrm {CO}_2$ in a small vertical tube influenced by coupled effects of buoyancy and thermal acceleration are numerically investigated using direct numerical simulation. Both upward and downward flows with an inlet Reynolds number of 3540 and pressure of 7.75 MPa have been simulated and the results are compared with corresponding experimental data. The flow and heat transfer results reveal that under buoyancy and thermal acceleration, the turbulent flow and heat transfer exhibit four developing periods in which buoyancy and thermal acceleration alternately dominate. The results suggest a way to distinguish the dominant factor of heat transfer in different periods and a criterion for heat transfer degradation under the complex coupling of buoyancy and thermal acceleration. An analysis of the orthogonal decomposition and the generative mechanism of turbulent structures indicates that the flow acceleration induces a stretch-to-disrupt mechanism of coherent turbulent structures. The significant flow acceleration can destroy the three-dimensional flow structure and stretch the vortices resulting in dissipation.

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