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The multieffect bioconvective heat transfer in porous media is essential for many technological applications. However, the literature governing practical applications is very scarce. The bioconvective transport of magnetohydrodynamic cross nanofluid carrying oxytactic microorganisms across a flexible cylinder with velocity slip, viscous dissipation, thermal radiation, and chemical reaction with a heat source in Darcy–Forchheimer porous medium is predicted in this piece of work. The random movement and thermophoresis processes are revealed by the Buongiorno model. Using a suitable similarity transformation and boundary layer approximation, the simplified model equations are converted into coupled highly nonlinear ordinary differential equations (ODEs). The resulting ODEs are dealt with numerically utilizing the BVP4C and the shooting method with predetermined thermal radiation, heat source, chemical reaction, and so forth parameters. The velocity field is inversely influenced by the Forchheimer number and porosity parameter. The Sherwood number is significantly influenced by chemical reactions. For heat source parameter (S) and increasing radiation parameter (Rd), the Nusselt number increases and convection is shown for the value of Rd near about 3. Overall, this study will help researchers in science and engineering to understand the intricate and multieffective dynamic system and industrial applications like microbiology, and biodynamical systems, biological tissues, biofilms, soil, or filter media. [ABSTRACT FROM AUTHOR]

The electrically conducting rotational microbial nanofluid with Coriolis and Lorentz force over a moving plate in the vertical direction with the velocity ratio at the boundary condition is considered in this article. The modeled equations are converted into nonlinear ordinary with boundary conditions by using some similarity transformation. The governing equations are numerically solved by a bivariate spectral quasi-linearization technique. The influence of the numerous parameters is analyzed graphically for the velocity, thermal, solutal, and microorganism profiles. The collection points and error graph are also included in the manuscript for justifying the technique. The increasing values of the magnetic field parameters reduce the flow profile, and similar behavior is observed for the velocity ratio and buoyancy ratio parameters. The microbial profile is enhanced with the increment of Hall current, Brownian motion for microbial, and buoyancy ratio constraints. The comparison graph was also included, and the results are in favor of our model. [ABSTRACT FROM AUTHOR]

AbstractThis article investigates the bioconvection flow within a porous circular cylinder filled with oxytactic microorganisms and incorporating nano-encapsulated phase change materials (NEPCMs). The circular cylinder, equipped with T-fins, is situated within the cylinder’s domain. The governing equations are solved using the ISPH method based on a time-fractional derivative. An ISPH simulation, coupled with an artificial neural networks (ANN) model, is employed to predict the values of the average Nusselt number (Nu¯). Utilizing bioconvection flow within a porous circular cylinder containing oxytactic microorganisms and integrating NEPCMs presents opportunities for progress in thermal management, environmental engineering, energy storage, and materials science. During the conducted simulations, we have investigated the impacts of Darcy, Lewis, Peclet, Rayleigh, and bioconvection Rayleigh numbers on a range of parameters, encompassing isotherms, heat capacity ratio, concentration profiles of oxygen and microorganisms, velocity field, and Nu¯. The results obtained highlight the significant influence of changes in the inner cylinder’s radius and fin length on regulating the intensity of bioconvection flow and improving heat transfer within a cavity. Additionally, the fusion temperature causes a shift in the heat capacity ratio toward the heat sources located within the cavity. The velocity field decreases by 97.39% as the Darcy number decreases from 10−2 to 10−5 due to the challenges posed by porous media. Increasing the length of the T-fin enhances the cooling area, causing the isotherms to contract and altering the heat capacity ratio. In comparison to the target values, the ANN model demonstrates accurate prediction of Nu¯, bolstering confidence in its predictions. [ABSTRACT FROM AUTHOR]

A novel treatment of fractional-time derivative using the incompressible smoothed particle hydrodynamics (ISPH) method is introduced to simulate the bioconvection flow of nano-enhanced phase change materials (NEPCM) in a porous hexagonal cavity. The fractional-time derivative is based on the Caputo style, which reflects the fractional order behavior in complex systems. In this work, the circular rotation of the embedded four-pointed star and the motion of oxytactic microorganisms in a hexagonal cavity are conducted. Due to the significance of fractional derivatives in handling real physical problems with more flexibility than conventional derivatives, the present scheme of the ISPH method is developed to solve the fractional-time derivative of the bioconvection flow in a porous hexagonal cavity. This study implicates the variations of a fractional-time derivative, a parametric of an inner four-pointed star, and the pertinent physical parameters on the behavior of a bioconvection flow of a nanofluid in a hexagonal-cavity containing oxytactic microorganisms. The presence of microorganisms has a significant role in many biological, engineering, and medical phenomena. From the present numerical investigation, it is well mentioned that the computational time of the transient processes can be reduced by applying a fractional-time derivative. The variable sizes of an inner four-pointed star enhance the bioconvection flow in a hexagonal cavity.

A novel treatment of fractional-time derivative using the incompressible smoothed particle hydrodynamics (ISPH) method is introduced to simulate the bioconvection flow of nano-enhanced phase change materials (NEPCM) in a porous hexagonal cavity. The fractional-time derivative is based on the Caputo style, which reflects the fractional order behavior in complex systems. In this work, the circular rotation of the embedded four-pointed star and the motion of oxytactic microorganisms in a hexagonal cavity are conducted. Due to the significance of fractional derivatives in handling real physical problems with more flexibility than conventional derivatives, the present scheme of the ISPH method is developed to solve the fractional-time derivative of the bioconvection flow in a porous hexagonal cavity. This study implicates the variations of a fractional-time derivative, a parametric of an inner four-pointed star, and the pertinent physical parameters on the behavior of a bioconvection flow of a nanofluid in a hexagonal-cavity containing oxytactic microorganisms. The presence of microorganisms has a significant role in many biological, engineering, and medical phenomena. From the present numerical investigation, it is well mentioned that the computational time of the transient processes can be reduced by applying a fractional-time derivative. The variable sizes of an inner fourpointed star enhance the bioconvection flow in a hexagonal cavity. [ABSTRACT FROM AUTHOR]

The current study focuses on how a magnetic field and oxytactic microorganisms influence the flow of a micropolar nanofluid around a wedge in a bioconvective field. It has practical implications in numerous industries and fields, including oil and gas, aircraft, biological waste processing, bio-microsystems etc. We begin the analysis by transforming the dimensionality of the governing equations via non-similar transformations. The obtained equations are linearized using the Quasilinearization method before being discretized using the implicit finite difference approach. The literature study reveals that the earlier studies on wedge are restricted to only similarity solutions rather than non-similarity without the impact of oxytactic microorganisms. This study concentrates on the effect of oxytactic microorganisms in the nonlinear mixed convective micropolar nanofluid flow around a wedge. The Micropolar fluid reduces the velocity while increasing friction between the surrounding fluid and the wedge's wall. The greater Peclet and microbial density difference ratio values blunted the effects of the rise in microorganisms on the density profile changes. The growth in the oxytactic microbial parameter Δ1 improves the microorganism's mass transfer rate(Rex−1/2NSh). Specifically, a rise of approximately 21% is seen in Rex−1/2NSh in the presence of oxytactic microbes as compared to their absence at ξ=2 and Le=10. The microrotation parameter boosts the entropy for enhancing values of the Brinkman number. And the entropy is almost the same for the Newtonian and micropolar fluid cases for Br=0.1.

The current research integrates artificial intelligence (AI) with computational fluid dynamics (CFD) to explore the magneto-bioconvective phenomenon of hybrid nanofluid within an inclined porous annulus containing oxytactic microorganisms. Initially, we analyze bioconvection dynamics and energy distribution by simulating the nonlinear governing equations. Owing to the involvement of multiple variable parameters, simulation technique demands significant resources and time to determine the optimal parametric values. To surmount this challenge, CFD-ANN-GA method is proposed to identify the optimum parameter values. Leveraging 212 CFD dataset, we developed an artificial neural network (ANN) model, tested with new dataset, and achieved an accuracy of 99.03 % and 94.82 % respectively, for average Nusselt and Sherwood numbers. This highly accurate ANN model's predictions unveiled significant insights that remained elusive from the CFD data. The CFD data suggested that the parameter set: Ra = 10 6 , R b = 10 , Ha = 0 , Da = 10 − 1 , Φ = 45 ° , Pe = 1 , Le = 1 , experience maximum heat dissipation. However, the genetic algorithm (GA) recommended a different parameter set: Ra = 10 6 , R b = 10 , H a = 0 , Da = 10 − 1.5644 , Φ = 40.67 ° , Pe = 0.100388 , Le = 1 , providing maximum thermal transport. Subsequently, the GA recommended parameter set has been tested through simulation technique and found to exhibit comparatively greater thermal transport. Furthermore, we identified the hierarchy of parameters influence on heat and oxygen mass transport within the enclosure by conducting sensitivity analysis. [ABSTRACT FROM AUTHOR]

Using incompressible smoothed particle hydrodynamics (ISPH), this study examines the bioconvection flow of oxytactic microorganisms in a porous annulus populated by nano-encapsulated phase change material (NEPCM). Artificial neural network (ANN) is joined with the ISPH method to accurately predict the values of average N u ‾. Between the outside hexagonal-shaped domain and the embedded wavy cylinder, a new annulus is produced. The ranges of the pertinent parameters are wave amplitude of an embedded cylinder A = 0.1 − 0.5 , Hartmann number H a = 0 − 80 , a radius of the cylinder R c y l d = 0.05 − 0.5 , Darcy number D a = 10 − 2 − 10 − 5 , undulation number K u n d = 2 − 32 , bioconvection Rayleigh number R a b = 1 − 1000 , Rayleigh number R a = 10 3 − 10 6 , and Lewis number L e = 1 − 20. The regulated geometric characteristics of an embedded wavy cylinder, such as wavy amplitude, cylinder radius, and undulation numbers, have been found to contribute significantly to widening the cooling region and minimizing the oxytactic microorganisms. Hence, the embedded wavy cylinder can be applied for various thermal uses including cooling devices and heat exchangers. The average N u ‾ is enhanced under an increment in the geometric parameters of the embedded cylinder. Increasing Rayleigh/bioconvection Rayleigh numbers enhances the buoyancy forces that accelerate the velocity field. [ABSTRACT FROM AUTHOR]

The peristaltic flow of Carreau–Yasuda fluid through a micro-vessel involving oxytactic microorganisms and nanoparticles in a vertical asymmetric channel is examined. In early times, scientific research shows that the cancer cells exposed to low oxygen conditions had the advantage of staying in the bloodstream more and can invade healthy cells as well, whereas the oxytactic microorganisms exhibit negative chemotaxis to gradients of oxygen (oxygen repellents). So, it had to be studied the behavior of oxytactic microorganisms and nanoparticle and their roles in the drug-carriers system. All non-dimensional physical parameters are supposed to be variable as the viscosity of blood variable with fluid temperature and nanoparticle concentration. This system of partial differential equations was formulated and transformed mathematically using new theories of differential transform method combined by Pade' approximation (DTM-Pade′). The solution of the mentioned system is displayed digitally in tables and graphically in sketches. The existing study assured that the microorganism density in the direction near to the hypoxic tumor tissues regions grows with a rising in oxygen concentrations and the blood viscosity diminutions. Results show that the number of pores increases the flow and the particles of fluid moving more freely with increment in distribution of temperature. [ABSTRACT FROM AUTHOR]

This investigation aims to introduce a new solution with aid of numerical methods to the blood flow of Carreau–Yasuda fluid through a microvessel. Swimming of gyrotactic microorganisms with nanoparticles is considered. A resulting system of partial differential equations is simplified by the meaning of low Reynolds number and long wavelength. This system of partial differential equations was formulated and transformed mathematically using new theories of differential transform method. Variable nonndimensional physical parameters effects, such as numbers of bioconvection Peclet and bioconvection Rayleigh, and so forth on velocity, temperature, and concentration distribution as well as oxytactic microorganism and oxygen concentration profiles are studied. All results are constructed in two cases of viscosity on the same figure, one of them in the case of variable parameters and the other in constant parameters. The existing study assured that the microorganism density in the direction near to the hypoxic tumor tissues regions grows with a rise in oxygen concentrations and the blood viscosity diminutions. [ABSTRACT FROM AUTHOR]

In this paper, the bioconvective flow in a porous square cavity containing oxytactic microorganism in the presence of chemical reaction is investigated. The bioconvection flow and heat transfer in porous media are formulated based on the Darcy model of Boussinesq approximation. The governing partial differential equations are solved using the Galerkin finite element method. The computational numerical results are exhibited by the streamlines, isotherms, isoconcentrations of oxygen, isoconcentrations of microorganisms, average Nusselt number, average Sherwood numbers of oxygen concentration and microorganisms. The effects of key parameters such as bioconvection Rayleigh number (Rb), chemical reaction parameter (Kr) and thermal Rayleigh number (Ra) are presented and analyzed. It can be deduced that the chemical reaction reduces the strength of isoconcentrations of both oxygen and microorganisms. It has been revealed that the chemical reaction has a greater effect on the swimming of the microorganisms, average Nusselt number, and average density number.

In this paper, the bioconvective nanofluid flow in porous square enclosure containing oxytactic microorganism associated with viscous dissipation, is discussed. The bioconvection flow in porous medium is framed by Darcy-Boussinesq approximation. Galerkin finite elements method is employed to solve the governed equations. The computational numerical results are exhibited by the surface plots of stream function, temperature, concentration of oxygen and microorganisms, average Nusselt number, average Sherwood numbers of oxygen and microorganism concentrations. The effects of key parameters such as Peclet number (Pe), Rayleigh number of bioconvection (Rb), viscous dissipation (Ec), thermophoretic parameter (Nt), parameter of Brownian movement (Nb), Lewis number (Le) and Rayleigh number (Ra) are presented and analyzed. [ABSTRACT FROM AUTHOR]

This investigation addresses bioconvection of oxytactic microorganisms in a porous square enclosure by thermal radiation impact. The bioconvection flow and heat transfer in porous media are formulated based on Darcy model of Boussinesq approximation. Appropriate transformations lead to the non-dimensionalized governing partial differential equations. Galerkin finite element method for the resulting equations is computed. The role of relevant parameters on the streamlines, isotherms, isoconcentrations of oxygen and microorganisms and average Nusselt number is analysed in the outputs. It is revealed that the flow intensity of bioconvection is pronounced with larger Rayleigh number and reduced with radiation parameter. Furthermore, the temperature distribution is affected significantly with Rayleigh number. Radiation parameter serves to fasten the heat transfer in the enclosure. Oxygen density is enhanced with Rayleigh number and radiation parameter. The profile of motile isoconcentrations is boosted with Rayleigh number. The stability of microorganisms is improved with the radiation parameter. [ABSTRACT FROM AUTHOR]

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This work’s primary purpose is to implement a numerical study that simulates blood flow through a microvessel involving oxytactic microorganisms and nanoparticles. The oxytactic microorganisms exhibit negative chemotaxis to gradients of oxygen (oxygen repellents). These microorganisms are to batter infected hypoxic tumor cells as drug-carriers. The viscosity of blood is to vary with temperature, shear-thinning, and nanoparticle concentration. We have formulated a mathematical model then simplified it under assumptions of long wavelength and low Reynold’s number. The resulting non-linear coupled differential equation system is solved numerically with the MATHEMATICA software aid using the built-in command (ParametricNDSolve). This study treated all non-dimensional parameters defined in terms of viscosity to be variables (VP-Model), unlike some previous literature attempts that have considered these parameters mentioned above as constants (CP-Model). The achieved results assured the reliability of the (VP-Model) over the (CP-Model). Our results reveal that temperature and microorganism density increase with the thermophoresis parameter. The impact of increasing the Brownian motion parameter is to increase temperature and lessen microorganism density. Outcomes also indicate an enhancement in the microorganism density towards the hypoxic tumor regions located aside the microvessel walls by boosting oxygen concentrations in the streamflow. The current study is believed to provide further opportunities to improve drug-carrier applications in hypoxic tumor regions by better recognizing the flow features, heat, and mass transfer in such zones.

The present work focuses on the numerical investigations of the existence of oxytactic microorganisms on the bioconvection flow of nano-encapsulated phase change material (NEPCM) inside an annulus. The novel geometry of an annulus contains an inner wavy cylinder and an outer circular cylinder considering a rotational circular velocity of an inner wavy cylinder. The incompressible smoothed particle hydrodynamics (ISPH) method solved the dimensionless form of controlling equations. The novel annulus between the embedded circular cylinder and the outer circular cylinder can be applied in the tube bundles in heat exchangers. Further, rotation of an inner wavy cylinder in a circular cavity can be used in thermal fin's vibration and cooling of the electric devices. The effects of pertinent parameters such as a rotational frequency number ω , bioconvection Rayleigh number Ra b , thermal radiation Rd , Lewis number Le , and Hartmann number Ha on the contours of oxygen concentration ϕ , temperature θ , heat capacity ratio Cr , oxytactic microorganisms N , and velocity field V as well as the average Nusselt & Sherwood numbers Nu ¯ and Sh ¯ are conducted. Increasing ω enhances the maximum of V by 56.6% and lowers Nu ¯. The variations of Ra b are enhanced the contours of N and maximized the velocity field from 0.86 at Ra b = 1 to 8.22 at Ra b = 100 due to the power in bioconvection flow. Increasing Le diminishes the strength of oxygen concentration ϕ and microorganisms N. Increasing Ha from 0 to 50 slows down the velocity field's maximum by 47.2 % and enhances the value of Nu ¯. [ABSTRACT FROM AUTHOR]

In many industries as well as medical science, process intensification dealing with proper mixing is dictated by the thermo-fluidic transport process, and mass transfer rate. Modeling as well as controlling such a device/system comprising multiphysical consequences and multifaceted geometries is a rather challenging task. In this exercise, an effort has been taken to explore the bioconvective heat and mass transfer phenomena of Cu-water nanofluid with the suspension of motile oxytactic microorganisms in a complex wavy porous enclosure heated at the left and cooled at the right imposing the magnetic field. The resulting mathematical model is converted into nonlinear partial differential equations (PDEs), which are then solved with a developed, validated computing code based on the finite volume-based technique. The investigation is conducted for various emerging parameters such as bioconvective Rayleigh number (Rb), Darcy number (Da), Darcy-Rayleigh number (Ra), Hartmann number (Ha), Peclet number (Pe), Lewis number (Le), oxygen diffusion ratio (χ), undulation numbers (n). This work focuses on the in-depth concept of flow-physics in the bioconvection environment by the wavy heated wall in a porous environment with the applied magnetic field. The various emerging parameters severely affect undergoing the thermo-magneto-bioconvective process, and reveal critical roles in the heat and mass transport dynamics. An undulation in the wavy wall raises bioconvection, heat, and mass transfer effects. The bioconvection effect is more at a low convection regime. It also showed that higher the bioconvection and mass transfer rate corresponds to lower heat transfer. It is worth remarking here that bioconvection always favors heat and mass transfer. The present investigation showed the extent of controllability of nano-bioconvective heat and mass transport phenomena. This concept and findings could be useful in the design of nano-bio-fuel cells and similar devices in sustainable and cleaner energy production. • This work focuses bioconvection in porous environment under applied magnetic field. • Heat transfer drops despite localized heating at the top heating wall. • An undulation in the wavy wall raises bioconvection and heat transfer effect both. • Bioconvection effect is more at low convection regime. • The present concept could be adopted in the design of nano-bio-fuel cell. [ABSTRACT FROM AUTHOR]

This paper presents novel treatments for the Ellis non-Newtonian nanofluids flow over a rotating cone in the presence of motile oxytactic microorganisms. These treatments are depending on solutions of the stress tensor equations at specific values of the power-law index α (α = 0,0.5,1, 2) and introducing the stress as expressions in terms of the velocity gradients. Here, four systems of the governing equations for each value of α are presented and the non-similar forms for these systems are obtained. An efficient finite difference method based on the Blottner technique is applied to solve the converted systems. Various important impacts are examined in these simulations such as, magnetic field, non-linear radiation, viscous dissipation, heat generation and Joule heating. Wide ranges of the non-similar parameters are considered, namely, 0 ≤ ξ ≤ 10, 0 ≤ η ≤ 35. The major results revealed that, the skin friction gets higher values at the Ellis case α = 2 while the Newtonian nanofluids α = 1 gives the highest heat transfer rate. Both the velocity and temperature gradients are diminishing as the bioconvection Rayleigh number is enhanced. [ABSTRACT FROM AUTHOR]

A mathematical model has been developed for steady-state boundary layer flow of a nanofluid past an impermeable vertical flat wall in a porous medium saturated with a water-based dilute nanofluid containing oxytactic microorganisms. The nanoparticles were distributed sufficiently to permit bioconvection. The product of chemotaxis constant and maximum cell swimming speed was assumed invariant. Using appropriate transformations, the partial differential conservation equations were non-dimensionalised to yield a quartet of coupled, non-linear ordinary differential equations for momentum, energy, nanoparticle concentration and dimensionless motile microorganism density, with appropriate boundary conditions. The dominant parameters emerging in the normalised model included the bioconvection Lewis number, bioconvection Peclet number, Lewis number, buoyancy ratio parameter, Brownian motion parameter, thermophoresis parameter, local Darcy-Rayleigh number and the local Peclet number. An implicit numerical solution to the well-posed two-point non-linear boundary value problem is developed using the well-tested and highly efficient Keller box method. Computations are validated with the Nakamura tridiagonal implicit finite difference method, demonstrating excellent agreement. Nanoparticle concentration and temperature were found to be generally enhanced through the boundary layer with increasing bioconvection Lewis number, whereas dimensionless motile microorganism density was only increased closer to the wall. Temperature, nanoparticle concentration and dimensionless motile microorganism density were all greatly increased with a rise in Peclet number. Temperature and dimensionless motile microorganism density were reduced with increasing buoyancy parameter, whereas nanoparticle concentration was increased. The present study found applications in the fluid mechanical design of microbial fuel cell and bioconvection nanotechnological devices. [ABSTRACT FROM AUTHOR]

The aim of this paper is to develop a theory describing the onset of convection instability (called here nanofluid bioconvecion) that is induced by simultaneous effects produced by oxytactic microorganisms, nanoparticles, and vertical temperature variation. The theory is developed for the situation when the nanofluid occupies a shallow horizontal layer of finite depth. The layer is defined as shallow as long as oxygen concentration at the bottom of the layer is above the minimum concentration required for the bacteria to be active (to actively swim up the oxygen gradient). The lower boundary of the layer is assumed rigid, while at the upper boundary both situations when the boundary is rigid or stress free are considered. Physical mechanisms responsible for the slip velocity between the nanoparticles and the base fluid, such as Brownian motion and thermophoresis, are accounted for in the model. A linear instability analysis is performed, and the resulting eigenvalue problem is solved analytically using the Galerkin method. [ABSTRACT FROM AUTHOR]

• Impact of vertical vibration on the thermo-bioconvection in a suspension of oxytactic microorganisms is investigated. • Galerkin method, linear stability analysis and time-averaged method are utilized to solve the mathematical model. • Vertical vibration always stabilizes the suspension. • Depth parameter has stabilizing effect in the presence of vertical vibration whereas it has destabilizing effect otherwise. • For every considered cases, rigid-rigid boundaries are found more stable in comparison to a stress-free-rigid boundaries. This current article study the significance of vertical vibration on a dilute suspension containing oxytactic microorganisms heated from below in a shallow horizontal layer. A time-averaged method and linear stability analysis are employed to attain the governing equations describing the mean flow of suspension. Under time-averaged method, it is permissible to break the set of solutions of governing equations into two distinct parts, the first one runs gradually with time while second one runs rapidly with time. A simple Galerkin method is employed to find the eigenvalue equation and the thermal stability curves for onset of thermo-bioconvection. The values of RT cr , Rb cr and a c are compared and found in close agreement with earlier reported articles. It is concluded that vertical vibration of high frequency and low amplitude always stabilizes the suspension of oxytactic microorganisms heated from below in shallow horizontal layer. In addition, the depth parameter ω stabilizes the suspension while, in case of no vertical vibration depth parameter destabilizes the suspension. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of vertical vibration on the stability of a dilute suspension of oxytactic microorganisms in a shallow horizontal fluid layer. For the case of high-frequency vibration, an averaging method is utilized to derive the equations describing the mean flow by decomposing the solutions of governing equations into two components: one that varies slowly with time, and a second that varies rapidly with time. Linear stability analysis is used to investigate the stability of the obtained averaged equations. It is predicted that high-frequency, low-amplitude vertical vibration has a stabilizing effect on a suspension of oxytactic microorganisms confined in a shallow horizontal layer. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this paper is to present a continuum model for thermo-bioconvection of oxytactic bacteria in a porous medium and investigate the combined effects of microorganisms'' upswimming and heating from below on the stability of bioconvection in a horizontal layer filled with a fluid saturated porous medium. Different from traditional bioconvection, thermo-bioconvection has two destabilizing mechanisms that contribute to creating the unstable density stratification. This problem may be relevant to a number of geophysical applications, such as the investigation of the dynamics of oxytactic species of thermophiles (heat loving microorganisms) living in hot springs, microbial-enhanced oil recovery, and modeling oil- and gas-bearing sedimentary basins. The utilization of the Galerkin method to solve a linear stability problem leads to a correlation between the critical value of the bioconvection Rayleigh number and the traditional “thermal” Rayleigh number. [Copyright &y& Elsevier]

This paper investigates the combined effect of density stratification due to oxytactic upswimming and heating from below on the stability of a suspension of motile oxytactic microorganisms in a shallow fluid layer. Different from traditional bioconvection, thermo-bioconvection has two destabilizing mechanisms that contribute to creating the unstable density stratification. This problem may be relevant to a number of geophysical applications, such as the investigation of the dynamics of some species of thermophiles (heat loving microorganisms) living in hot springs. By performing a linear stability analysis, we obtained a correlation between the critical value of the bioconvection Rayleigh number and the traditional, “thermal” Rayleigh number. It is established that heating from below makes the system more unstable and helps the development of bioconvection. [ABSTRACT FROM AUTHOR]

• The work presents impact of surface undulation on mixed MHD nano-bioconvective heat and mass transfer due to swimming of oxytactic bacteria in a porous enclosure. • Bioconvection from oxytactic organisms produces a secondary circulation on the left heated wavywall. The shape and strength of this circulation are markedly influenced by the involved flow controlling parameters n, Rb, Ha, Da, Le, Pe and Gr. • The curved surface enhances the heat transfer up to certain optimum undulations (n), whereas mass transfer increases with the increasing undulations (n). • The average value of Sh magnitude increases with undulations, bioconvection raises further the Sh value. Transport phenomena involving thermo-bioconvection have become an interesting field of research due to their novel application in various fields of engineering, bio-energy systems, fuel cells, medical science, etc. Design as well as proper control of such a system involving multiphysical transport in a complex geometry is a very difficult task. On such a system, the present study is conducted aiming to examine the magnetohydrodynamic (MHD) mixed bioconvection with oxytactic microorganisms suspended in copper-water nanofluid. The flow takes place through porous media in a top-wall-translating enclosure with a complex wavy sidewall heated uniformly. The right vertical wall is isothermally cooled; other walls are adiabatic. A magnetic field is imposed along the horizontal direction. Evolved flow physics are analyzed by modeling this complex problem involving an undulating heated wall and many coupled transport equations (due to the presence of motile bacteria or organisms) are numerically solved through a finite volume-based code. The thermo-fluid behaviors are studied extensively to explore the controllability of different involved parameters that could help the system's design and operation. The important parameters influencing the complex physics in the enclosure are the number of undulations (n), bioconvection Rayleigh number (R b), Darcy number (Da), Hartmann number (Ha), Peclet number (Pe), Lewis number (Le), oxygen diffusion ratio (χ), Grashof number (Gr). The study reveals that the undulating curved surface enhances the heat transfer up to certain optimal magnitudes of undulations at the different operating conditions. The mass transfer rate increases with all undulations and bioconvection supports this trend. Bioconvection always favors heat transfer. In general, it is found that by adjusting the involved flow parameters and number of undulations, the local as well as global transport mechanisms, can be controlled effectively. The concept of this investigation could be found in the designing of microbial fuel cells and different nanotechnology-based bioconvection. [Display omitted]. [ABSTRACT FROM AUTHOR]

This work's primary purpose is to implement a numerical study that simulates blood flow through a microvessel involving oxytactic microorganisms and nanoparticles. The oxytactic microorganisms exhibit negative chemotaxis to gradients of oxygen (oxygen repellents). These microorganisms are to batter infected hypoxic tumor cells as drug-carriers. The viscosity of blood is to vary with temperature, shear-thinning, and nanoparticle concentration. We have formulated a mathematical model then simplified it under assumptions of long wavelength and low Reynold's number. The resulting non-linear coupled differential equation system is solved numerically with the MATHEMATICA software aid using the built-in command (ParametricNDSolve). This study treated all non-dimensional parameters defined in terms of viscosity to be variables (VP-Model), unlike some previous literature attempts that have considered these parameters mentioned above as constants (CP-Model). The achieved results assured the reliability of the (VP-Model) over the (CP-Model). Our results reveal that temperature and microorganism density increase with the thermophoresis parameter. The impact of increasing the Brownian motion parameter is to increase temperature and lessen microorganism density. Outcomes also indicate an enhancement in the microorganism density towards the hypoxic tumor regions located aside the microvessel walls by boosting oxygen concentrations in the streamflow. The current study is believed to provide further opportunities to improve drug-carrier applications in hypoxic tumor regions by better recognizing the flow features, heat, and mass transfer in such zones. [ABSTRACT FROM AUTHOR]