Buoyancy-assisted flow reversal and combined mixed convection–radiation heat transfer in symmetrically heated vertical parallel plates: Influence of two radiative parameters

AbstractThe present article encompasses the laminar ascending flow and combined mixed (free and forced) convective-radiative heat transfer within symmetrically heated vertical parallel plates. Radiative heat transfer between two opposite walls is considered and the gas is assumed as gray, absorbing, emitting and scattering. Elliptic governing equations for the case of buoyancy assisted flow are solved numerically employing a home-made CFD code based on the finite volume method. The radiative transfer equation is solved using the discrete ordinates method, adopting its S6 quadrature scheme. The influence of two important radiative parameters, namely, wall emissivity and scattering albedo, while the extinction coefficient is either constant or not, on the occurrence of flow reversal, fanning friction coefficient, flow and thermal fields, is investigated. Present results show that the occurrence of reversed flow enhances both heat transfer and the fanning friction coefficient, and the radiation mode amplifies heat transfer, while reducing the fanning friction coefficient. As wall emissivity increases from 0 to 1, effects of radiation on flow and thermal fields rise. However, there is no linear relationship for the whole range of ε. As scattering albedo varies between 0 and 0.75, radiation effects on flow and thermal fields for the constant and variable extinction coefficient are entirely opposite

Analysis of Particle Dispersion in Turbulent Mixed Convection of CuO-water Nanofluid

In the present paper, turbulent convection of CuO-Water Nanofluid in a vertical channel is investigated numerically. In order to simulate the flow, the fluid is considered as a continuous phase while the discrete nanoparticles are dispersed through it. The dispersion of CuO nanoparticles in different flow conditions are studied in order to find the effective mechanisms of particles dispersion in the channel. The results show that in the fully developed turbulent convection flow, thermophoresis is more dominant than Brownian motion of nanoparticles and therefore the nanoparticles aggregation are more in the central areas of the channel. While in entrance region, where the boundary layer is not fully formed, the particles dispersion are more uniform. Also, an increase in the nanoparticles concentration will increase the turbulent velocity fluctuations in regions near the wall and this two-sided effect will cause improvement in turbulent flow thermal transmitance than the laminar flow

Analysis of Various Inflow Turbulence Generation Methods in Large Eddy Simulation Approach for Prediction of Pollutant Dispersion around Model Buildings

The purpose of the present study is to investigate and analyze numerically, the effective mechanisms on the flow field and pollutant dispersion around a simple and long street canyon by means of Large Eddy Simulation (LES) approach using various inflow turbulence generation methods. For this purpose, four methods i.e. vortex, mapping, synthetic and no-inlet perturbation methods are used as inflow turbulence generators in LES. Results suggest that all methods are capable of capturing the two important structures of canyon vortex and corner eddy, which have great influences on air ventilation inside the street canyon. The magnitudes of concentration on the leeward wall of the first building are approximately four times as much as those of windward wall of the second building. Among the various inflow turbulence generation methods, the vortex method is the most precise method and no-inlet perturbation method is the least precise method