Computation of metallic nanofluid natural convection in a two-dimensional solar enclosure with radiative heat transfer, aspect ratio and volume fraction effects

As a model of nanofluid direct absorber solar collectors (nano-DASCs), the present article describes recent numerical simulations of steady-state nanofluid natural convection in a two-dimensional enclosure. Incompressible laminar Newtonian viscous flow is considered with radiative heat transfer. The ANSYS FLUENT finite volume code (version 19.1) is employed. The enclosure has two adiabatic walls, one hot (solar receiving) and one colder wall. The Tiwari-Das volume fraction nanofluid model is used and three different nanoparticles are studied (Copper (Cu), Silver (Ag) and Titanium Oxide (TiO2)) with water as the base fluid. The solar radiative heat transfer is simulated with the P1 flux and Rosseland diffusion models. The influence of geometrical aspect ratio and solid volume fraction for nanofluids is also studied and a wider range is considered than in other studies. Mesh-independence tests are conducted. Validation with published studies from the literature is included for the copperwater nanofluid case. The P1 model is shown to more accurately predict the actual influence of solar radiative flux on thermal fluid behaviour compared with Rosseland radiative model. With increasing Rayleigh number (natural convection i.e. buoyancy effect), significant modification in the thermal flow characteristics is induced with emergence of a dual structure to the circulation. With increasing aspect ratio (wider base relative to height of the solar collector geometry) there is a greater thermal convection pattern around the whole geometry, higher temperatures and the elimination of the cold upper zone associated with lower aspect ratio. Titanium Oxide nano-particles achieve slightly higher Nusselt number at the hot wall compared with Silver nano-particles. Thermal performance can be optimized with careful selection of aspect ratio and nano-particles and this is very beneficial to solar collector designers

Effect of radiation on transient MHD flow of micropolar fluid between porous vertical channel with boundary conditions of the third kind

The present work is devoted to investigate the effect of thermal radiation on fully developed flow of micropolar fluid flowing between the two infinite parallel porous vertical plates in the presence of transverse magnetic field. The fluid is considered to be a gray, absorbing–emitting but non-scattering medium, and the Cogley–Vincent–Gilles formulation is adopted to simulate the radiation component of heat transfer. The rigid plates are assumed to exchange the heat with an external fluid by convection. The governing equations are solved numerically by Crank–Nicolson implicit finite difference method. The effect of various physical parameters such as transient, Hartmann number, micropolar parameter, radiation parameter, Prandtl number, Biot number and Reynolds number on the velocity and temperature field are discussed graphically. The important finding of the present work is that the temperature of the fluid is reduced by applying thermal radiation. Further, the results obtained under the limiting conditions were found to be in good agreement with the existing one

Impact of aspect ratio on a nanofluid-saturated porous enclosure

The aim of the present numerical simulation is to investigate the mixed convection flow and heat transfer characteristics in a two dimensional porous cavity filled with nanofluid for different aspect ratios. The top and bottom walls are assumed to have the uniform temperatures θh and θc, respectively, with θh > θc while the vertical walls are kept to be adiabatic. The governing equations are solved by using finite volume method with the SIMPLE algorithm. The variations of isotherms, streamlines, mid-plane velocity profiles, and Nusselt numbers were discussed in detail over a wide range of pertinent parameters, viz., aspect ratio, Richardson number, Darcy number, and solid volume fraction. Although the addition of nanoparticles in the porous medium is to increase the overall heat transfer rate in most flow regimes, the overall heat transfer rate is appeared to decrease slightly or stay nearly the same with the increase of solid volume fraction for Ar = 0.25 and 0.5 porous cavities in the forced convection regime

Coupled buoyancy and Marangoni convection in a hybrid nanofluid-filled cylindrical porous annulus with a circular thin baffle

The purpose of the current article is to evaluate the impact of coupled buoyancy and thermocapillary driven convection in a cylindrical porous annulus saturated with Ag/MgO–water hybrid nanofluid along with viscous dissipation effects. The left side wall of the annulus is kept heated, while the right side wall of the annulus is kept cold. The top and bottom limits are supposed to be adiabatic. A thin circular baffle is anchored to the inner cylinder. The primary goal of this research is to look into the effect of baffle size and location on Marangoni convection, thermal behaviour, and flow fields. Here, the effects of viscous dissipation are taken into account. The governing equations are subjected to the finite difference approach, which employs the ADI, SOR, and central differencing schemes. In this work, contour plots and average Nusselt number profiles are used to demonstrate the flow type, temperature behaviour, and thermal variations along the enclosure. The research demonstrates that the size and location of the fin plays a prominent role in influencing fluid flow within the annulus. An improvement in thermal transfer rate is reported for $$\phi$$ and for the higher value of Ma considering the viscous dissipation, length and location of the baffle

Marangoni convection in a hybrid nanofluid-filled cylindrical annular enclosure with sinusoidal temperature distribution

The current research numerically investigates the Marangoni convection in a cylindrical annulus filled with hybrid nanofluid saturated porous media. The interior and exterior walls are subjected to spatially varying sinusoidal thermal distributions with various amplitude ratios and phase deviations. The limits at the top and bottom are adiabatic. To solve the system of non-dimensional governing equations, the finite difference approach is applied. The main objective of the ongoing study is to investigate the impact of the Marangoni number, nanoparticle volume fraction and the radii ratio on the amplitude ratio and phase deviation. Also, the fluid flow, thermal characteristics, local and average Nusselt numbers are analysed in the hybrid nanofluid-filled vertical cylindrical annulus with magnetic effects. The findings indicate that the sinusoidal temperature promotes multicellular flow in the porous annular region. In the annulus with sinusoidal boundaries, the Marangoni number underperforms while the nanoparticle volume fraction outperforms

Radiation effect of ND–Ni nanocomposite, water-filled multiport cavity with heated baffle

The control of the thermal radiation influence on free convection of a multiple-port open cavity packed with water supported nanocomposite nanofluid is investigated numerically . One inlet port and two outlet ports are situated on the perpendicular walls. The remaining cavity walls are adiabatic. The heated thin baffle is located inside the cavity. The cavity is crammed with the water-supported nanodiamond–nickel nanocomposite. The governing Navier–stokes equations are written in the term of vorticity stream function transport. An ADI scheme-based finite difference process is used for discretization of the governing equations. The results are discussed graphically with the various parameters of radiation parameter, Reynolds number, Rayleigh number, solid volume fraction, widths of the opening, and locations of baffle position. It reveals that the average heat transfer rate reduces with the baffle placed far from the inlet