Investigations of natural convection heat transfer in nanofluids filled horizontal semicircular-annulus using nonhomogeneous dynamic model

In this paper, the problem of unsteady convective flow of nanofluid in a horizontal semicircular-annulus using nonhomogeneous dynamic mathematical model has been investigated. The outer wall of the annulus is considered a colder wall and the inner is maintained at three different temperatures (constant, quadratic and sinusoidal) while two other walls are thermally insulated. The Galerkin weighted residual finite element method has been employed to solve the governing partial differential equations after converting them into non-dimensional form using suitable transformation of variables. In the numerical simulations, the cobalt-kerosene nanofluid has been taken to gain insight into the flow, thermal fields as well as concentration levels of nanofluids. Local Nusselt number and temperature gradient magnitude on the hotter and colder wall are displayed as line graphs. The average Nusselt number for cobalt-kerosene nanofluid is displayed as line graphs for different flow parameters including amount, shape and size of nanoparticles. Also, the average Nusselt number is presented as a bar diagram for 12 types of nanofluids. The result shows that 1-20 nm size nanoparticles are uniform and stable in the solution. The average Nusselt number increases significantly, as nanoparticle volume fraction, Rayleigh number increases and nanoparticle diameter decreases. Sinusoidal heating inner wall of annulus exhibits higher heat transfer rate. Average Nusselt number of cobalt-kerosene nanofluid is higher than that of other 11 types of nanofluids which are studied in the present analysis.