Study On The Heat Transfer Of Nanofluid And Bioconvective Fluid Flows

As an emerging science,nanoscience is playing increasingly important role in our daily life and technology development such as industrial production,natural science,life science and medicine field.As a new heat transfer enhancement medium,nanofluid has a good heat transfer performance and the unique fluid properties.It plays a significant rolein the field of metallurgy,energy,transportation,microelectronics,chemical engineering,spacecraft thermal control and manufacturing.Due to its applications in several fields,nanofluid flow has attracted broad interest among many researchers from various areas.On the other hand,biotechnology and microbial engineering are also an important aspect of the current world technological revolution.It has played an important role in agriculture,mining,chemical industry,food industry,medical health and environmental protection.In some practical applications,microorganisms are added to a base fluid.For instance,microbial sewage treatment,microbial oil recovery.Because the microorganisms have biological tropism,its own movement will drive the surrounding fluid motion leading to bioconvection.Therefore,the study of microbial movement mechanism is necessary.The mathematical models describing nanofluid or bioconvection fluid flow problems are typically nonlinear,and to effectively solving such type of nonlinear system is one of the challenges faced by scientists.In this study,a solution technique of hybrid analytical-numerical method is applied to obtain and evaluate the velocity distribution of the nanofluid and microorganisms’ fluid,as well as the temperature and concentration distribution for a problem under consideration.Then the important physical quantities of practical interests,such as local friction coefficient,local Nusselt number,local mass flux,are analyzed and discussed.The main work of this thesis is as follows:Firstly,combining the homotopy analysis method(HAM)with the combination of finite difference method(FDM),the free convection problem of nanofluid in three-dimensional stagnation point region is investigated.Based on the Buongiorno’s nanofluid model,the governing equations are established,namely,the conservation of the mass,the momentum,the thermal energy,the nanoparticles and the microorganisms.And then the governing equations after the similar transformation are solved by HAM-FDM technique.It is noted that HAM-FDM technique not only inherits the advantages of homotopy analysis method in its ability of solving strong nonlinear problems,but also greatly improves the computational efficiency.Based on the quantitative results,the influence of the different parameters on the velocity profile,temperature profile,nanoparticles concentration distribution and microorganism concentration distribution are examined in detail.Secondly,the nanofluid flow behaviours in the stagnation-point region of a twodimensional body in the presence of the homogeneous-heterogeneous reactions is modelled by means of the Buongiorno’s model.The governing equations are solved by using the shooting method associate with fourth-order Runge-Kutta scheme.Based on the model verification,the step size is adjusted for different values of the parameters to maintain higher accuracy during the computation.In addition,the step value between 0.001 and 0.01 are used,in order to obtain the mesh independent numerical values.It is found that the chemical reaction equations return multiple solutions.For this reason,there is a certain advantage to choose shooting method to solve the problem.Through the analysis of data,it is revealed that both the homogeneous and the heterogeneous reaction rate parameters and the diffusivity ratio can lead to multiple solutions.Furthermore,the characteristics of nanofluid flow in a horizontal microchannel with the effects of the electrical double layer is investigated.Compared with the traditional model,the mathematical model of nanoparticles concentration distribution is established based on the Buongiorno’s model,and the viscous dissipation term is considered in the energy equation.The electrical body force resulting from the electric double layer and electrokinetic effect are considered in the momentum equation.Through a set of non-dimensional transformation,the governing equation is solved by homotopy analysis method.Based on the corresponding boundary conditions,the exact solutions of electric potential and velocity are obtained.In the case of electrokinetic separation distance is large,Homotopy-Pad′e technique is used to accelerate the convergence of homotopy series.Moreover,the influence of various parameters on the electrostatic potential,streaming potential,velocity profile,temperature profile,as well as the local friction coefficient,local Nusselt number and local Sherwood number are discussed in detail.Finally,the unsteady squeezing flow of an incompressible viscous fluid with suspension of small motile microorganisms between two infinite parallel plates in the presence of both chemical reaction and magnetic effect is investigated.The governing equations embody the total mass,momentum,thermal energy,chemical reaction and microorganisms are reduced to a set of nonlinear ordinary differential equations via a set of similarity transformations.The reduced governing equations solved by means of the shooting method associate with fourth-order Runge-Kutta scheme.The effects of the various parameters on the distributions of velocity,temperature,chemical reaction concentration,density of motile microorganisms,as well as the important physical quantities are examined in detail.