3-D investigation of coupled free convection and thermal radiation in interconnected cavities.

Abstract

Coupled free convection and thermal radiation heat transfer and fluid flow characteristics on vertical cylinder in interconnected cavities have been investigated numerically in laminar regimes. The study is carried out for varying Rayleigh numbers ranging from (7x103 to 2.5x106) and also for emissivity values between 0 to 1. The effects of various cavity geometries, hole geometries, hole dimensions, and cavity hole arrangements on heat transfer attributes have been evaluated. In this study, the algebraic multi-grid solver of Ansys fluent is used to perform the simulations of the Navier-Stokes equation combined with the energy equation in the computational domain. A thorough grid sensitivity analysis and validation of the numerical methodology used in the simulation are carried out. The results are validated against the published data in the literature. It is found that the circular hole of 15mm radius at 45⁰ orientations on an alternate interconnected cavity exhibits the highest rate of heat transfer. It is seen that as the hole radius is increased, the value of the Nusselt number also increases significantly. However Nusselt number gets saturated beyond 15mm, thereafter no significant increase in the Nusselt number is observed. For a maximum Ra (2.5x105) and hole radius of 15mm at 45⁰ orientations exhibits, the total increment in the rate of heat transfer is ∼110%. Correlations are established to forecast the Nusselt number for vertical annular interconnected cavities as a function of cavity width to cylinder diameter ratio (w/d) and Rayleigh number (Ra), using least square linear regression method.