A Lattice Boltzmann Investigation Of The Two-Phase Natural Convection And Heat Transfer Of Ferrofluid

Nanofluid is a class of suspension that contains nanometer-sized solid particles,called nanoparticles,with typical particle size between 1 and 100 nm in base fluids.The high thermal conductivity of the suspended nanoparticles in nanofluids has given rise to its superior advantages over the conventional heat transfer fluids such as oil,water,and ethylene glycol mixture in terms of transport properties and heat transfer performance.Nanofluid can serve as a prospective functional liquid material for applications such as nuclear reactors,solar collectors,heat pipes,automobile radiators,electronic cooling systems,etc.Ferrofluid is a new type of nano-functional material,which has a wide range of applications due to its unique magnetic response characteristics and liquid mobility,playing an important role in the fields of sealing,vibration damping,sensing,driving,optics,medicine,etc.Consequently,a comprehensive and accurate understanding of the unique properties of the general nanofluid and ferrofluid in the field of heat transfer has important practical significance.With the study focusing on this topic,the following work is carried out:(1)The research progress of nanofluid and ferrofluid under the action of external magnetic field in the field of heat transfer is discussed.A brief summary of the history of research and development of nanofluid is introduced.The research status of traditional numerical methods and the lattice Boltzmann method,which has appeared in recent years,has been compared and analyzed.(2)Based on the main slip mechanism of nanoparticles relative to the carrier liquid,the dimensionless parameters and dimensionless numbers in fluid mechanics are introduced to establish a generalized non-dimensional nanofluid two-phase flow model.The external magnetic field is further introduced to establish the magnetic responsive non-dimensional ferrofluid two-phase flow model.(3)A novel volume fraction-thermal lattice Boltzmann method is established.The partial differential control equations,which are based on the conservation of mass,momentum and energy,describing the nanofluid two-phase flow,are directly considered into the simulation calculation and evolution process.Furthermore,the external magnetic field is taken into account in the simulation algorithm,and the magnetic responsive volume fraction-thermal lattice Boltzmann equation is established.(4)Programs are written independently in the C++code language,to realize the algorithm of LBM simulation.By executing the programs to simulate classic examples in computational fluid dynamics(CFD)and computational heat transfer and comparing with standard results,the accuracy and reliability of the programs are verified.(5)Cu-water nanofluid is taken as a typical example to calculate and analyze the two-phase natural convection of nanofluid in a square cavity.The flow and heat transfer characteristics are analyzed.Necessary conditions for adopting the two-phase flow model which takes into account the nanoparticle slip mechanisms,instead of the traditional one-phase model are discussed.(6)Water-based Fe3O4 ferrofluid is taken as a typical example to study the hydrodynamics and heat transfer characteristics of ferrofluid under constant gradient external magnetic field,to explore the effects of the external magnetic field on flow and heat transfer characteristics,and to find out the relationship between the significance of these effects and the physical properties of the fluid.There are 28 figures,5 tables,88 references in this thesis.