Numerical Simulation Of Conjugate Heat Transfer Of Non-Newtonian Nanofluids Based On Lattice Boltzmann Method

With the increasingly prominent energy problem,China's energy development is facing many major challenges,and it is urgent to achieve energy revolution and transformation through scientific and technological innovation."Nanofluid",as the heat transfer material in enhanced heat transfer technology,has a huge potential application prospect.It is of great significance to study the mechanism of nanofluid flow and heat transfer for scientific and technological innovation to promote energy revolution and transformation.At present,many scholars have carried out many experiments and numerical researches on the performance improvement of nanofluids.Generally speaking,there are still the following deficiencies.In the experimental research,nanofluids are faced with the difficulties of small scale,complex preparation process,high precision requirements,etc.the existing numerical simulation does not consider non-Newtonian nanofluids,unsteady boundary conditions and heat capacity between different phases.The influence of transient flow and heat transfer of meter fluid.These shortcomings limit people's understanding of non-Newtonian Nanofluids and become the bottleneck of new efficient heat transfer technology.In this paper,based on the existing research of nanofluids,an improved lattice Boltzmann model combined with the influence of heat capacity is used to study the influence of central solid on the unsteady natural convection of non-Newtonian fluids in a square cavity.The effects of power-law index,Rayleigh number,solid-liquid heat capacity ratio,solid-liquid thermal conductivity ratio,solid size,temperature change period and temperature change amplitude on fluid flow are analyzed in detail.The results show that the increase of the ratio of Rayleigh number to the thermal conductivity of solid-liquid phase and the decrease of power-law index can enhance the transient and overall heat transfer,while the increase of the ratio of solid-liquid heat capacity can only enhance the transient heat transfer,which has little effect on the overall heat transfer.The increase of the central solid size will simultaneously reduce the transient heat transfer rate and the total heat transfer rate,and the decrease of the temperature fluctuation period can enhance the transient heat transfer.The transient and total heat transfer rates increase with the increase of temperature fluctuation.The natural convection of power-law alumina water nanofluid in a square cavity with a cylinder is simulated.The effects of Rayleigh number,power-law index,volume fraction of nanoparticle,diameter of nanoparticle and radius of cylinder on the flow and heat transfer characteristics of nanofluid are discussed in detail.The results show that the heat transfer rate increases with the increase of Rayleigh number and cylinder radius,and decreases with the increase of power-law index and nanoparticle diameter.Finally,the conjugate natural convection of curved boundary nonNewtonian nanofluid based on lattice Boltzmann method is numerically simulated,focusing on the analysis of the thermal physical properties and wall thickness of the wall,as well as the influence of power-law index and nanoparticle volume fraction on non-Newtonian nanoparticle.It is found that the heat transfer rate increases with the decrease of wall thickness,and increases first and then decreases with the increase of power-law index.The research results can provide theoretical basis and data support for enhanced heat transfer technology.