ABSTRACT
The fluid dynamics and heat transfer characteristics of magnetohydrodynamic duct flow often degrade the laminarization caused by the magnetic field. The present work evaluates the performance of a system featuring alternating current injection from a point electrode as a vortex promoter for enhancement of the thermal-hydraulic characteristics. It is found that the vortices generated by the current injection alone generally induce a greater thermal-hydraulic performance with a significantly smaller additional pressure loss than configurations featuring a physical obstacle. A maximum overall efficiency index of 1.83 was recorded within the parameter space investigated.
Nomenclature
a | = | duct height (out-of-plane) |
B | = | uniform out-of-plane magnetic field strength |
Cp | = | constant pressure specific heat capacity |
CD | = | cylinder drag coefficient |
Ec | = | Eckert number |
f | = | vortex shedding frequency |
ff | = | current injection frequency |
f0 | = | natural vortex shedding frequency |
h | = | vortex street lateral spacing |
H | = | friction parameter |
Ha | = | Hartmann number |
HR* | = | overall heat transfer enhancement ratio |
I | = | current injection amplitude |
l | = | vortex street longitudinal spacing |
ly | = | transverse electrode position |
L | = | half duct width |
Ld | = | length of downstream flow region |
Lw | = | length of heated wall |
ℒ2 | = | integral of velocity magnitude throughout the domain |
n | = | number of Hartmann layers |
N | = | interaction parameter |
Nu | = | time averaged Nusselt number |
= | Nu for the same duct in the absence of a current injection and a cylinder | |
= | local instantaneous Nusselt number | |
p | = | pressure |
Δp | = | time-averaged pressure drop |
= | time-averaged pressure drop for a base case with no cylinder | |
= | overall net power enhancement | |
Pheat | = | heat power |
Pflow | = | pumping power |
PR* | = | overall pressure penalty ratio |
Pe | = | Peclet number |
Pr | = | Prandtl number |
ReL | = | Reynolds number based on half duct width |
St | = | Srouhal number |
t | = | time |
u | = | x-direction velocity component |
u⊥ | = | velocity projected onto (x,y) plane |
u0 | = | force vector field |
U0 | = | peak fluid velocity at duct inlet |
Uξ | = | wake advection velocity |
x | = | streamwise coordinate |
y | = | transverse coordinate |
z | = | spanwise coordinate |
α | = | duct aspect ratio |
β | = | blockage ratio |
δS | = | Shercliff boundary layer thickness |
η* | = | overall efficiency index |
κT | = | thermal diffusivity |
ν | = | fluid kinematic viscosity |
ρ | = | density |
σ | = | electrical conductivity |
θ | = | temperature |
τ | = | current injection pulse width |
ξp | = | peak vorticity |
ωf | = | current forcing frequency |
Nomenclature
a | = | duct height (out-of-plane) |
B | = | uniform out-of-plane magnetic field strength |
Cp | = | constant pressure specific heat capacity |
CD | = | cylinder drag coefficient |
Ec | = | Eckert number |
f | = | vortex shedding frequency |
ff | = | current injection frequency |
f0 | = | natural vortex shedding frequency |
h | = | vortex street lateral spacing |
H | = | friction parameter |
Ha | = | Hartmann number |
HR* | = | overall heat transfer enhancement ratio |
I | = | current injection amplitude |
l | = | vortex street longitudinal spacing |
ly | = | transverse electrode position |
L | = | half duct width |
Ld | = | length of downstream flow region |
Lw | = | length of heated wall |
ℒ2 | = | integral of velocity magnitude throughout the domain |
n | = | number of Hartmann layers |
N | = | interaction parameter |
Nu | = | time averaged Nusselt number |
= | Nu for the same duct in the absence of a current injection and a cylinder | |
= | local instantaneous Nusselt number | |
p | = | pressure |
Δp | = | time-averaged pressure drop |
= | time-averaged pressure drop for a base case with no cylinder | |
= | overall net power enhancement | |
Pheat | = | heat power |
Pflow | = | pumping power |
PR* | = | overall pressure penalty ratio |
Pe | = | Peclet number |
Pr | = | Prandtl number |
ReL | = | Reynolds number based on half duct width |
St | = | Srouhal number |
t | = | time |
u | = | x-direction velocity component |
u⊥ | = | velocity projected onto (x,y) plane |
u0 | = | force vector field |
U0 | = | peak fluid velocity at duct inlet |
Uξ | = | wake advection velocity |
x | = | streamwise coordinate |
y | = | transverse coordinate |
z | = | spanwise coordinate |
α | = | duct aspect ratio |
β | = | blockage ratio |
δS | = | Shercliff boundary layer thickness |
η* | = | overall efficiency index |
κT | = | thermal diffusivity |
ν | = | fluid kinematic viscosity |
ρ | = | density |
σ | = | electrical conductivity |
θ | = | temperature |
τ | = | current injection pulse width |
ξp | = | peak vorticity |
ωf | = | current forcing frequency |