Lattice Boltzmann Simulation Of Double Diffusion Natural Convection Of Nanofluids In A Square Cavity Of Porous Media

Double diffusion natural convection phenomenon is widespread in nature and industrial production,such as ocean circulation,asthenosphere movement in the crust,crystal material growth and so on.To explore the mechanism under the practical application background of different factors.Based on lattice Boltzmann method(LBM),the natural convection of thermal and solute in the cavity under the action of horizontal temperature gradient and concentration gradient is numerically simulated.Firstly,we analyzed the influence of the basic characteristic criterion number on the heat and mass transfer and entropy generation of the cavity,and explored the influence of nanofluids on the wall heat and mass transfer efficiency and entropy generation under sinusoidal boundary conditions.Secondly,the variation of heat and mass transfer efficiency and entropy generation in square cavity was studied under the consideration of Soret and Dufour effects.Finally,the influence of Lorentz force of external magnetic field on heat and mass transport and entropy generation is investigated.The specific studies as follows:Firsrly,the effects of ?、Ra、Br、Le and γ on double diffusion natural convection uniform boundary condition has been investigated.The results show that the wall Nuave number increases along with the augment of ?,but it decrease at high ?.The heat and mass transfer efficiency and total entropy production of the fluid increased exponentially with the rais of Ra.With the increase of Br number,the rate of heat transfer and entropy generation in the square cavity decreased first and then increased;with the increase of Le number.The heat transfer rate decreases slowly and the mass transfer rate increases greatly.When the inclination Angle of 40° is applied to the square cavity,the Nuave,Shave and the total entropy production on the wall increase significantly.When the inclination Angle of 80° is applied,the heat and mass transfer are weakened and the irreversible degree in the system increases.At the same time,we studied the effects of ?,Ra,? and N on heat and mass transfer efficiency and entropy production of nanofluids under sinusoidal boundary conditions.The results show that,similar to the conclusions obtained with uniform boundary conditions,the wall surface Nuave increases first and then decreases with the increase of ? under the sinusoidal boundary condition,peaks at ? = 0.7,while the wall surface Shave number gradually decreases as the ? increases.The total entropy production in the square cavity increases obviously.The heat and mass transfer efficiency and irreversible entropy production in the cavity under the model increase exponentially with the increase of Ra number.For a given Ra,when N>1,the wall Nuave increases gradually with a raise of N,and the Shave reaches the minimum value at N=2.When N<1,the wall surface Shave gradually decreases as a increase of N,and the Nuave reaches the minimum value at N=1/2.When N=1,the comprehensive efficiency of heat and mass transfer capacity is the highest,and the total entropy production in the square cavity is the smallest at the low Ra,and the peak value is reached at the high Ra.Secondly,when the Soret and Dufour effects are considered,the double-diffusion natural convection of the nanofluid in the partially filled porous medium cavity is numerically simulated.The results show that the Shave,Nuave and Stot gradually decrease with the increase of ?,and the decrease of Stot is more obvious at the low porosity.The Shave,Nuave and Stot increase with the increase of Da number.At high Da,the permeability of the porous medium has little effect on the heat and mass transfer efficiency of the fluid,and the viscosity dissipation irreversibility SF due to flow friction in the cavity increases significantly.As the Sr increasing,the Shave increases significantly,while Nuave showed a weak growth trend,and the Stot in the square cavity was mainly affected by SF and it showed a weak growth trend.As the Df increasing,the Nuave of the wall surface increases significantly,and the heat transfer capacity in the square cavity increases,while the Shave shows a weak growth trend.The Stot in the square cavity is mainly affected by SF and shows a weak growth trend.Finally,we explored the external magnetic field for numerical simulation of double diffusion natural convection of nanofluids in a square cavity of local porous media.The results show that when ξ = 90°,the Shave and Nuave reach the maximum,and the total entropy production has a minimum,but when ξ = 0° or 180°,the heat and mass transfer efficiency is decreases,and the irreversible degree in the cavity is higher.For ξ = 90°,the Shave and Nuave of the wall decrease with the increase of the Ha,and it increase significantly with the increase of the Ra.when ξ = 90°,the irreversible degree of the fluid generated by the magnetic field inhibition is small,and the total entropy production of the square cavity reaches the minimum value at Ha=100.With the increase of Ra,the intensity of circulation in the square cavity increasing,the effect of the magnetic field on the Lorentz force generated by the conductive fluid is more obvious,and the total entropy production will be mainly affected by SM.