Direct numerical simulation of heated CO2 flows at supercritical pressure in a vertical annulus at Re=8900

2008 ◽  
Vol 20 (5) ◽  
pp. 055108 ◽  
Author(s):  
Joong Hun Bae ◽  
Jung Yul Yoo ◽  
Donald M. McEligot
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Supercritical Pressure ◽  
Vertical Annulus

Direct Numerical Simulation of Heated Turbulent Pipe Flow at Supercritical Pressure

2016 ◽  
Vol 2 (3) ◽  
Author(s):  
Xu Chu ◽  
Eckart Laurien
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Forced Convection ◽  
Reynolds Shear Stress ◽  
Streamwise Velocity ◽  
Supercritical Pressure ◽  
Turbulent Pipe Flow ◽  
Working Fluid ◽  
Convection Flow ◽  
Flow Turbulence

For fluids at supercritical pressure, the phase change from liquid to gas does not exist. Meanwhile, the fluid properties change drastically in a narrow temperature range. With supercritical fluid as working fluid in a heated pipe, heat-transfer deterioration and recovery have been observed, which corresponds to the turbulent flow relaminarization and recovery. Direct numerical simulation (DNS) of supercritical carbon dioxide flow in a heated vertical circular pipe is developed with the open-source code OpenFOAM in this study. Forced-convection and mixed-convection cases including upward and downward flow have been considered in the simulation. In the forced convection, flow turbulence is attenuated due to acceleration from thermal expansion, which leads to a peak of the wall temperature. However, buoyancy shows a stronger impact on the flow. In the upward flow, the average streamwise velocity distribution turns into an M-shaped profile because of the external effect of buoyancy. Besides that, negative buoyancy production caused by the density variation reduces the Reynolds shear stress to almost zero, which means that the flow is relaminarized. Further downstream, turbulence is recovered. This behavior of flow turbulence is confirmed by visualization of turbulent streaks and vortex structures.

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

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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