Thermo-bioconvection performance of nanofluid containing oxytactic microorganisms inside a square porous cavity under constant and periodic temperature boundary conditions

Thermal performance of natural convection heat transfer of nanofluid containing oxytactic microorganisms saturated a square porous cavity under constant and sinusoidal temperature boundary conditions is numerically investigated. Scrutinizing the literature review reveals that microorganisms' impact on the rate of heat transfer may be contributory or destructive, depending on the problem under consideration. Accordingly, the objective of the current study is set to remove the detrimental effect of microorganisms on the average Nusselt number seen in some previous studies by applying a periodic temperature distribution on the sidewalls to introduce microorganisms as being an always heat transfer intensifier method. For this aim, the Buongiorno model is adopted to simulate the nanofluid flow and the Darcy model is employed to analyze the fluid flow inside porous media. By the definition of a series of appropriate dimensionless numbers, the governing equations are initially converted to a non-dimensional form of governing equations, and then, they are solved numerically using the FEM approach. The accuracy of the numerical method has successfully been validated by comparing it with the available study in the literature. Simulations are undertaken for different parameters including Rayleigh number, bioconvection Rayleigh number, bioconvection Peclet number, and bioconvection Lewis number. Obtained results are provided in the form of tabular and graphical contours related to streamlines, isothermal lines, isoconcentration of nanoparticles, oxygen, and microorganisms. Based on the outcomes, it is concluded that opposed to the constant wall temperature in which microorganisms’ presence leads to the Nusselt number attenuation for the majority of the considered cases, in sinusoidal temperature distribution, microorganisms lead to improvement of the heat transfer in all considered cases. These new findings will likely lead to revolutionary changes in the use of microorganisms in the heat transfer industry. Several applications exist for the concepts developed in this study, including cooling towers, microbial fuel cells, and nanotechnology-based bioconvection.

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