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ABSTRACT
The paper reports the natural thermo-bio-convection of gyrotactic microorganisms in a square cavity with two smaller square heat sources inside the cavity. The flow is assumed to be two-dimensional, steady, buoyancy-driven, and Newtonian. The work investigates the influences of thermal Rayleigh number, bio-convection Rayleigh number, Lewis number, and Peclet number on the natural convection heat transfer, entropy generation, and micro-organism concentration. The governing equations are discreted by finite element method. The diffusion equation is used for the motion of microorganisms, and the energy equation is considered for the effects of temperature. The main finding of this study is that both thermal and bio-convection Rayleigh number improve thermo-bio-convection performance of gyrotactic microorganisms in a square cavity with two square heaters inside the cavity. For high thermal Rayleigh numbers (Rat = 105), increasing Rab from 10 to 100 causes 4.5% enhancement in average Nusselt number and average Sherwood number decreases by 4.5%. These findings are applicable in various fields of expertise such as ocean ecosystems, oil recovery and fuel cells.
Nomenclature
Symbols
| u | = | Velocity in x direction (m/s) |
| v | = | Velocity in y direction (m/s) |
| ρ | = | Density (kg/m3) |
| p | = | Pressure (Pa) |
| γ | = | Average volume of microorganisms (m3) |
| n | = | Density of motile microorganisms (kg/m3) |
| β | = | Volume expansion coefficient |
| α | = | Effective thermal diffusivity (Wm2/J) |
| C | = | Concentration |
| T | = | Temperature (K) |
| D | = | Diffusivity (Wm2/J) |
| δn | = | Consumption of microorganisms |
| L | = | Length of cavity (m) |
| σ | = | Rate of oxygen consumption to diffusion |
| ψ | = | Stream function |
| W | = | Swimming speed (m/s) |
Subscripts
| f | = | Fluid |
| c | = | Cold |
| h | = | Hot |
| min | = | minimum |
| m | = | Microorganisms |
| t | = | Thermal |
| b | = | Bio convection |
| o | = | Oxygen |
| ce | = | Cell |
Abbreviation
| MHD | = | Magneto-Hydro-Dynamic |
Disclosure statement
No potential conflict of interest was reported by the authors.