Non-similar radiative bioconvection nanofluid flow under oblique magnetic field with entropy generation

Motivated by exploring the near-wall transport phenomena involved in bioconvection fuel cells combined with electrically conducting nanofluids, in the present article, a detailed analytical treatment using homotopy analysis method (HAM) is presented of non-similar bioconvection flow of a nanofluid under the influence of magnetic field (Lorentz force) and gyrotactic microorganisms. The flow is induced by a stretching sheet under the action of a oblique magnetic field. In addition, nonlinear radiation effects are considered which are representative of solar flux in green fuel cells. A second thermodynamic law analysis has also been carried out for the present study to examine entropy generation (irreversibility) minimization. The influence of magnetic parameter, radiation parameter and bioconvection Rayleigh number on skin friction coefficient, Nusselt number, micro-organism flux and entropy generation number (EGN) is visualized graphically with detailed interpretation. Validation of the HAM solutions with published results is also included for the non-magnetic case in the absence of bioconvection and nanofluid effects. The computations show that the flow is decelerated with increasing magnetic body force parameter and bioconvection Rayleigh number whereas it is accelerated with stronger radiation parameter. EGN is boosted with increasing Reynolds number, radiation parameter and Prandtl number whereas it is reduced with increasing inclination of magnetic field

Numerical investigation of Von Karman swirling bioconvective nanofluid transport from a rotating disk in a porous medium with Stefan blowing and anisotropic slip effects

In recent years, significant progress has been made in modern micro- and nanotechnologies related to applications in micro/nano-electronic devices. These technologies are increasingly utilizing sophisticated fluent media to enhance performance. Among the new trends is the simultaneous adoption of nanofluids and biological micro-organisms. Motivated by bio-nanofluid rotating disk oxygenators in medical engineering, in the current work, a mathematical model is developed for steady convective Von Karman swirling flow from an impermeable power-law radially stretched disk rotating in a Darcy porous medium saturated with nanofluid doped with gyrotactic micro-organisms. Anisotropic slip at the wall and blowing effects due to concentration are incorporated. The nano-bio transport model is formulated using non-linear partial differential equations (NPDEs), which are transformed to a set of similarity ordinary differential equations (SODEs) by appropriate transformations. The transformed boundary value problem is solved by a Chebyshev collocation method. The impact of key parameters on dimensionless velocity components, concentration, temperature and motile microorganism density distributions are computed and visualized graphically. Validation with previous studies is included. It is found that that the effects of suction provide a better enhancement of the heat, mass and microorganisms transfer in comparison to blowing. Moreover, physical quantities decrease with higher slip parameters irrespective of the existence of blowing. Temperature is suppressed with increasing thermal slip whereas nanoparticle concentration is suppressed with increasing wall mass slip. Micro-organism density number increases with the greater microorganism slip. Radial skin friction is boosted with positive values of the power law stretching parameter whereas it is decreased with negative values. The converse response is computed for circumferential skin friction, nanoparticle mass transfer rate and motile micro-organism density number gradient. Results from this study are relevant to novel bioreactors, membrane oxygenators, food processing and bio-chromatography

Influence of Stefan blowing on nanofluid flow submerged in microorganisms with leading edge accretion or ablation

The unsteady forced convective boundary layer flow of viscous incompressible fluid containing both nanoparticles and gyrotactic microorganisms, from a flat surface with leading edge accretion (or ablation), is investigated theoretically. Utilizing appropriate similarity transformations for the velocity, temperature, nanoparticle volume fraction and motile microorganism density, the governing conservation equations are rendered into a system of coupled, nonlinear, similarity ordinary differential equations. These equations, subjected to imposed boundary conditions, are solved numerically using the Runge-Kutta-Fehlberg fourth-fifth order numerical method in the MAPLE symbolic software. Good agreement between our computations and previous solutions is achieved. The effect of selected parameters on flow velocity, temperature, nano-particle volume fraction (concentration) and motile microorganism density function is investigated. Furthermore, tabular solutions are included for skin friction, wall heat transfer rate, nano-particle mass transfer rate and microorganism transfer rate. Applications of the study arise in advanced micro-flow devices to assess nanoparticle toxicity

Steady Boundary Layer Flow Of Nanofluid With Microorganism

In this thesis, an analysis of two and three dimensional laminar convective boundary layer flow of a nanofluid with microorganism is investigated. It involves two and three dimensional laminar convective external boundary layer flow with heat and mass transfer under various physical configurations as well as geometries

Numerical study of slip effects on unsteady aysmmetric bioconvective nanofluid flow in a porous microchannel with an expanding/ contracting upper wall using Buongiorno’s model

In this paper, the unsteady fully developed forced convective flow of viscous incompressible biofluid that contains both nanoparticles and gyrotactic microorganisms in a horizontal micro-channel is studied. Buongiorno’s model is employed. The upper channel wall is either expanding or contracting and permeable and the lower wall is static and impermeable. The plate separation is therefore a function of time. Velocity, temperature, nano-particle species (mass) and motile micro-organism slip effects are taken into account at the upper wall. By using the appropriate similarity transformation for the velocity, temperature, nanoparticle volume fraction and motile microorganism density, the governing partial differential conservation equations are reduced to a set of similarity ordinary differential equations. These equations under prescribed boundary conditions are solved numerically using the Runge-Kutta-Fehlberg fourth-fifth order numerical quadrature in the MAPLE symbolic software. Excellent agreement between the present computations and solutions available in the literature (for special cases) is achieved. The key thermofluid parameters emerging are identified as Reynolds number, wall expansion ratio, Prandtl number, Brownian motion parameter, thermophoresis parameter, Lewis number, bioconvection Lewis number and bioconvection Péclet number. The influence of all these parameters on flow velocity, temperature, nano-particle volume fraction (concentration) and motile micro-organism density function is elaborated. Furthermore graphical solutions are included for skin friction, wall heat transfer rate, nano-particle mass transfer rate and micro-organism transfer rate. Increasing expansion ratio is observed to enhance temperatures and motile micro-organism density. Both nanoparticle volume fraction and microorganism increases with an increase in momentum slip. The dimensionless temperature and microorganism increases as wall expansion increases. Applications of the study arise in advanced nanomechanical bioconvection energy conversion devices, bio-nano-coolant deployment systems etc

Bioconvection nanofluid slip flow past a wavy surface with applications in nano-biofuel cells

A theoretical study is presented to examine free convective boundary layer flow of water-based bio-nanofluid containing gyrotactic microorganisms past a wavy surface. Buongiorno’s nanofluid model with passively controlled boundary condition is applied to investigate the effects of the emerging parameters on the physical quantities namely, skin friction, Nusselt numbers and density number of motile microorganisms. The effects of the both hydrodynamic and thermal slips are also incorporated. Local similarity and non-similarity solutions are obtained using the seventh-order Runge-Kutta-Fehlberg method (RKF7) coupled with shooting quadrature. In order to compare our numerical results with the existing data, the active mass flux boundary condition is also used to benchmark MAPLE numerical solutions with earlier similar and non-similar solutions for a smooth stationary surface. It is found that the passive boundary condition reduces the skin friction and enhances local Nusselt numbers. Also the wavy surface is found to result in higher skin friction and higher local Nusselt numbers compared with a stationary surface. It is found that motile micro-organism density number is elevated with increasing bioconvection Péclet number whereas the motile micro-organism species boundary layer thickness is reduced with increasing bioconvection Lewis number. The work finds applications in heat transfer enhancement in bio-inspired nanoparticle-doped fuel cells

Computation of electroconductive gyrotactic bioconvection from a nonlinear inclined stretching sheet under non-uniform magnetic field : simulation of smart bio-nano-polymer coatings for solar energy

Incompressible, steady-state, boundary layer magneto-bioconvection of a nanofluid (containing motile gyrotactic micro-organisms) over a nonlinear inclined stretching sheet subjected to non-uniform magnetic field is studied theoretically and numerically. This regime is encountered in novel bio-nano-material electroconductive polymeric processing systems currently being considered for third generation organic solar coatings, anti-fouling marine coatings etc. Buongiorno’s two-component nanofluid model is deployed with the OberbeckBoussinesq approximation. Ohmic dissipation (Joule heating) is included. The governing nonlinear partial differential equations are reduced to a system of ordinary differential equations and appropriate similarity transformations. The normalized system of equations with associated boundary conditions features a number of important dimensionless parameters including magnetohydrodynamic body force parameter (M), sheet inclination (δ), Brownian motion nanoscale parameter (Nb), thermophoresis nanoscale parameter (Nt), Richardson number (Ri=GrRe2 , where Gr is thermal Grashof number and Re is Reynolds number), buoyancy ratio parameter (Nr), Eckert (viscous dissipation) number (Ec), bioconvection Rayleigh number (Rb), Lewis number (Le), bioconvection Lewis number (Lb), Péclet number (Pe), nonlinear stretching parameter (n) are solved with a variational Finite Element Method (FEM). Validation is conducted with earlier published studies of Khan and Pop (2010) for the case of non-magnetic stretching sheet nanofluid flow without bioconvection. Further validation of the general magnetic bioconvection nanofluid model is achieved with a generalized differential quadrature (GDQ) numerical technique developed by Bég and Kuharat (2017). The response of non-dimensional velocity, temperature, nanoparticle concentration, motile microorganism density function, local skin friction coefficient, Nusselt number, Sherwood number, wall motile density gradient function to variation in physically pertinent values of selected control parameters (representative of real solar bio-nano-magnetic materials manufacturing systems) are studied in detail. Interesting features of the flow dynamics are elaborated and new future pathways for extension of the study identified in bio-magneto-nano polymers (BMNPs) for solar coatings

Mixed bioconvection stagnation point flow towards a vertical plate in alumina-copper/water

Purpose: According to the previous research, bioconvection has been recognized as an important mechanism in current engineering and environmental systems. For example, researchers exploit this mechanism in modern green bioengineering to develop environmentally friendly fuels, fuel cells and photosynthetic microorganisms. This study aims to analyse how this type of convection affects the flow behaviour and heat transfer performance of mixed convection stagnation point flow in alumina-copper/water hybrid nanofluid. Also, the impact of a modified magnetic field on the boundary layer flow is considered. Design/methodology/approach: By applying appropriate transformations, the multivariable differential equations are transformed into a specific sort of ordinary differential equations. Using the bvp4c procedure, the adjusted mathematical model is revealed. Once sufficient assumptions are provided, multiple solutions are able to be produced. Findings: The skin friction coefficient is declined when the nanoparticle concentration is increased in the opposing flow. In contrast, the inclusion of aligned angles displays an upward trend in heat transfer performance. The presence of several solutions is established, which simply leads to a stability analysis, hence verifies the viability of the initial solution. Originality/value: The current findings are unique and novel for the investigation of mixed bioconvection flow towards a vertical flat plate in a base fluid with the presence of hybrid nanoparticles

Biomathematical model for gyrotactic free-forced bioconvection with oxygen diffusion in near-wall transport within a porous medium fuel cell

Bioconvection has shown significant promise for environmentally friendly, sustainable “green” fuel cell technologies. The improved design of such systems requires continuous refinements in biomathematical modelling in conjunction with laboratory and field testing. Motivated by exploring deeper the near-wall transport phenomena involved in bioinspired fuel cells, in the present article, we examine analytically and numerically the combined free-forced convective steady boundary layer flow from a solid vertical flat plate embedded in a Darcian porous medium containing gyrotactic microorganisms. Gyrotaxis is one of many taxes exhibited in biological microscale transport, and other examples include magneto-taxis, photo-taxis, chemotaxis and geo-taxis (reflecting the response of micro-organisms to magnetic field, light, chemical concentration or gravity, respectively). The bioconvection fuel cell also contains diffusing oxygen species which mimics the cathodic behavior in a proton membrane exchange (PEM) system. The vertical wall is maintained at iso-solutal (constant oxygen volume fraction and motile micro-organism density) and iso-thermal conditions. Wall values of these quantities are sustained at higher values than the ambient temperature and concentration of oxygen and biological micro-organism species. Similarity transformations are applied to render the governing partial differential equations for mass, momentum, energy, oxygen species and micro-organism species density into a system of ordinary differential equations. The emerging eight order nonlinear coupled, ordinary differential boundary value problem features several important dimensionless control parameters, namely Lewis number (Le), buoyancy ratio parameter i.e. ratio of oxygen species buoyancy force to thermal buoyancy force (Nr), bioconvection Rayleigh number (Rb), bioconvection Lewis number (Lb), bioconvection Péclet number (Pe) and the mixed convection parameter spanning the entire range of free and forced convection. The transformed non-linear system of equations with boundary conditions is solved numerically by a finite difference method with central differencing, tridiagonal matrix manipulation and an iterative procedure. Computations are validated with the symbolic Maple 14.0 software. The influence of buoyancy and bioconvection parameters on the dimensionless temperature, velocity, oxygen concentration and motile microorganism density distribution, Nusselt, Sherwood and gradient of motile microorganism density are studied. The work clearly shows the benefit of utilizing biological organisms in fuel cell design and presents a logical biomathematical modelling framework for simulating such systems. In particular, the deployment of gyrotactic micro-organisms is shown to stimulate improved transport characteristics in heat and momentum at the fuel cell wall