Simulation Of Nanofluid Rayleigh-Benard Flow And Heat Transfer Enhancement With LBM

With the rapid development of science and technology, industrial products tend to miniaturization, both the product integration and performance indicators of the heat transfer equipment are needed to be improved. However, with the continuous improvement of heat transfer equipment and the special requirements of the environment, the traditional method of heat transfer enhancement is subjected to some restrictions in the application. Therefore, some scholars have proposed a new type of heat transfer medium-nanofluid. As a potential heat transfer enhancement fluid, because of the high conductivity of nanoparticles. nanofluid is not only able to improve the heat transfer performance of heat transfer equipment effectively, but also can improve the performance indicators including high efficiency and compactedness of the equipment. Nanofluid could be widely used in the aerospace, electronics and other fields. It is necessary to study and understand the mechanism of nanofluid heat transfer in order to make full use of nanofluid. In this paper, the lattice Boltzmann method is used to simulate the fluid flow and heat transfer characteristics of nanofluid.The lattice Boltzmann method (LBM) is a kind of mesoscopic simulation method and developes from the kinetic theory. Compared with the traditional methods, the lattice Boltzmann method has many unique advantages. For example, the clear physical images, easier boundary conditions, simple calculation procedure, good parallelism and so on. Considering the random diffusion and discontinuous distribution of nanoparticles. the lattice Boltzmann method is used to study the nanofulid, which has overcome the deficiencies of the traditional simulation method. This method is based on discrete microscopic model, and easy to deal with the problems such as the interaction force between the nanoparticles, the force between the nanoparticles and fluid. And this method can show fluid dynamics at the macro level through the derivation. The basic theory of LBM, the basic calculation models, the common boundary treatment methods and the simulation process of this method are introduced in this paper.Firstly, the single-phase LBM is used to simulate Rayleigh-Benard natural convection of pure fluid in the closed cavity. And the temperature and streamline distribution of the pure fluid at different Ra number is obtained. Secondly, multiphase and multicomponent model of LBM is used to simulate the flow and heat transfer of nanofluid Rayleigh-Benard convection in the rectangular cavity. The heat transfer performance of nanofluid is compared with that of traditional medium. The isotherms and streamlines of nanofluid are obtained. The influences of volume fraction of nanoparticles and nanoparticle size on the average Nusselt number of nanofluid at different Ra number are analyzed. The effects of these factors on flow and heat transfer of nanofluid are concluded. Finally, the Zheng’s model and Inamuro’s thermal model of the LBM are used to simulate the changes of the droplet shape in the process of single droplet evaporation in square cavity whose bottom is heated, and the temperature field and flow field of the droplet and its surrounding are analyzed.