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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 |