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 |