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ABSTRACT
The turbulent mixed convection heat transfer of supercritical water flowing in a vertical tube roughened by V-shaped grooves has been numerically investigated in this paper. The turbulent supercritical water flow characteristics within different grooves are obtained using a validated low-Reynolds number κ-ε turbulence model. The effects of groove angle, groove depth, groove pitch-to-depth ratio, and thermophysical properties on turbulent flow and heat transfer of supercritical water are discussed. The results show that a groove angle γ = 120° presents the best heat transfer performance among the three groove angles. The lower groove depth and higher groove pitch-to-depth ratio suppress the enhancement of heat transfer. Heat transfer performance is significantly decreased due to the strong buoyancy force at Tb = 650.6 K, and heat transfer deterioration occurs in the roughened tube with γ = 120°, e = 0.5 mm, and p/e = 8 in the present simulation. The results also show that the rapid variation in the supercritical water property in the region near the pseudo-critical temperature results in a significant enhancement of heat transfer performance.
Nomenclature
| A | = | cross section area |
| = | buoyancy parameter | |
| c | = | specific heat |
| D | = | tube diameter |
| e | = | groove depth |
| g | = | acceleration of gravity |
| Gκ | = | buoyancy production |
| Gr | = | Grashof number |
| h | = | heat transfer coefficient |
| m | = | mass flux |
| p | = | groove pitch |
| Pκ | = | shear stress production |
| Pr | = | Prandtl number |
| q | = | heat flux |
| r | = | radial distance |
| Re | = | Reynolds number |
| T | = | temperature |
| u | = | velocity components in x-direction |
| v | = | velocity components in r-direction |
| y | = | distance from inner wall surface |
| y+ | = | non-dimensional distance from wall |
| x | = | axial distance |
| β | = | volumetric coefficient of expansion |
| ε | = | turbulent energy dissipation |
| γ | = | groove angle |
| κ | = | turbulent kinetic energy |
| λ | = | thermal conductivity |
| μ | = | dynamic viscosity |
| ν | = | kinematic viscosity |
| σκ | = | diffusion Prandtl number for κ |
| σϵ | = | diffusion Prandtl number for ε |
| ρ | = | density of fluid |
| Subscripts | = | |
| b | = | evaluated at bulk |
| e | = | effective |
| p | = | pressure |
| pc | = | pseudo-critical |
| s | = | evaluated in smooth tube |
| t | = | turbulent |
| wi | = | evaluated at interior wall |
| w | = | evaluated at wall |
Nomenclature
| A | = | cross section area |
| = | buoyancy parameter | |
| c | = | specific heat |
| D | = | tube diameter |
| e | = | groove depth |
| g | = | acceleration of gravity |
| Gκ | = | buoyancy production |
| Gr | = | Grashof number |
| h | = | heat transfer coefficient |
| m | = | mass flux |
| p | = | groove pitch |
| Pκ | = | shear stress production |
| Pr | = | Prandtl number |
| q | = | heat flux |
| r | = | radial distance |
| Re | = | Reynolds number |
| T | = | temperature |
| u | = | velocity components in x-direction |
| v | = | velocity components in r-direction |
| y | = | distance from inner wall surface |
| y+ | = | non-dimensional distance from wall |
| x | = | axial distance |
| β | = | volumetric coefficient of expansion |
| ε | = | turbulent energy dissipation |
| γ | = | groove angle |
| κ | = | turbulent kinetic energy |
| λ | = | thermal conductivity |
| μ | = | dynamic viscosity |
| ν | = | kinematic viscosity |
| σκ | = | diffusion Prandtl number for κ |
| σϵ | = | diffusion Prandtl number for ε |
| ρ | = | density of fluid |
| Subscripts | = | |
| b | = | evaluated at bulk |
| e | = | effective |
| p | = | pressure |
| pc | = | pseudo-critical |
| s | = | evaluated in smooth tube |
| t | = | turbulent |
| wi | = | evaluated at interior wall |
| w | = | evaluated at wall |