RT Journal Article ID 123e99f957e69463 A1 Yadav, Dhananjay A1 Kim, MinChan T1 THE ONSET OF TRANSIENT SORET-DRIVEN BUOYANCY CONVECTION IN NANOPARTICLE SUSPENSIONS WITH PARTICLE-CONCENTRATION-DEPENDENT VISCOSITY IN A POROUS MEDIUM JF Journal of Porous Media JO JPM YR 2015 FD 2015-05-28 VO 18 IS 4 SP 369 OP 378 K1 Soret-driven convection K1 nanofluid K1 viscosity variation K1 linear stability analysis K1 porous media K1 spectral analysis AB The onset of transient Soret-driven convection in a horizontal layer of a porous medium saturated by a fluid with nanoparticles suspensions, which is heated from above, is studied where the viscosity depends on the local concentration of nanoparticles of practical importance. For the case of high solutal Darcy-Rayleigh number RsD with a large negative Soret coefficient DT, the applied even small temperature on the upper boundary creates Soret diffusion and then the convective motion occurs during the transient diffusion stage. In conjunction with the Soret diffusion, the nanoparticle concentration becomes stratified as given by Eq. (22), and hence the viscosity is stratified. The nanofluid is considered to be dilute, i.e., the volume concentrations of nanoparticles is very small 0.01%−2.0%, and this permits the porous medium to be taken as a weakly heterogeneous medium with variation in the vertical direction of viscosity. In turn this allows an approximate analytical solution to be obtained using a spectral method. The critical times of the onset of this Soret-driven convection are obtained as a function of the modified solute Rayleigh-Darcy number Rs*D for different values of viscosity variation parameter Q. Decreasing Q can enhanced these times Q. The results from theory are also compared with the experimental results. We show that the results from the theoretical predictions are too close to explain the experimental work. PB Begell House LK https://www.dl.begellhouse.com/journals/49dcde6d4c0809db,6147e63e31ad00a5,123e99f957e69463.html