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Previously, the homogenous models were predominant in hybrid nanofluid's studies. However, there is a serious deficiency in these models, that is, the heat transfer coefficients obtained by these models are inconsistent with the experimental results. To overcome this issue, we develop a novel hybrid nanofluid model based on the major slip mechanisms of nanofluids caused by Brownian diffusion and thermophoresis. The problem of flow and heat transfer of a hybrid nanofluid in a lid driven square cavity filled with porous medium is studied as an example to show the correctness and validity of this new model. Numerical results are given by means of the novel Coiflet wavelet homotopy analysis method in the terms of the Brownian motion and thermophoresis. The physical behaviors of hybrid nanofluids flow are discussed in terms of various quantities such as the stream-function, the isotherms, and the Nusselt and Sherwood numbers. The average Nusselt number evaluated with the help of the quadratic multiple regression analysis justifies that the thermophoretic effect is more dominant than the Brownian motion on Nusselt numbers at both walls. [ABSTRACT FROM AUTHOR]

Abstract: The laminar, fully developed mixed convection flow between two paralleled vertical flat plates filled by a nanofluid is investigated. By means of a new set of similarity variables, the governing equations are reduced to a set of three coupled equations with an unknown constant. The exact solutions are obtained by means of the homotopy analysis method for both the buoyancy-assisted and the buoyancy-opposing cases and their accuracies are checked in detail. The effects of the Grashof number Gr and the Prandtl number Pr on the nanofluid flows are then investigated successively. We further consider the effects of the buoyancy ratio Nr, the Brownian motion parameter Nb, the thermophoresis parameter Nt on the pressure parameter σ and the Nusselt number Nu. It is found that the heat transfer characteristic can be improved significantly as the proper nanofluids are applied. [Copyright &y& Elsevier]

Abstract: In this paper, the fully developed mixed convection flow in a vertical channel filled with nanofluids is investigated. Analytical solutions for both the buoyancy-assisted and -opposed flow are obtained. Further analysis shows that the analytical solution for the opposing flow is only valid for a certain region of the Rayleigh number Ra in physical sense. Besides, the effects of the nanoparticle volume fraction φ on the temperature and the velocity distributions are then exhibited. It is confirmed that the nanoparticle volume fraction φ plays a key role for improving the heat and mass transfer characteristics of the fluids. [Copyright &y& Elsevier]

The unsteady mixed convection of a hybrid nanofluid due to rotating disks is examined. The generialzied homogenous flow model that describes hybrid nanofluids containing multiple kinds of nanoparticles is developed for modelling the problem. Its simplified form is proposed based on the linear assumptions and verified by existing model. The argument that the corresponding nanofluid results by the homogenous model can be restored from those solutions of already solved regular problems via simple arithmetic operations is checked. The relation of similarity variables to nanoparticles volumetric fractions is discussed. [ABSTRACT FROM AUTHOR]

A mathematical model is constructed to analyze the mixed convection gravity-driven film flow of nanofluids in the presence of heterogeneous-homogeneous reactions. It is considered that heterogeneous reaction taking place on the surface of plate can be described by isothermal cubic autocatalator kinetics while homogeneous reaction happening at far field is given by first order kinetics. Hysteresis bifurcations incorporating the numerical method is used to obtain the multiple solutions for the system. The uniqueness of this problem lies in the fact that the multiple solutions are possible for the cases of favorable buoyancy ( σ < 0), non-buoyant ( σ  = 0) and unfavorable buoyancy ( σ > 0) for various diffusion coefficients of reactant and autocatalyst. The observed effect of nanofluids on the stability of chemical reactions in the film flow can make this problem practically useful in the related field. [ABSTRACT FROM AUTHOR]