Numerical Computation on Natural Convection Heat Transfer From an Isothermal Sphere With Semicircular Ribs

Abstract

For the very first time, this study attempts to address the heat dissipation from an isothermal ribbed sphere under the action of pure natural convection. Semicircular ribs of different radii are superimposed azimuthally on the outer surface of a sphere. The addition of ribs on the sphere serves a dual purpose in its practical applications: beautification of electronic devices such as spherical light sources as well as an increase in heat dissipation from the hot surface, which prevents the electronic component from getting overheated. Finite volume method-based axisymmetric numerical simulations are performed in the laminar flow regime for the following ranges of nondimensional parameters: Rayleigh number (102 ≤ Ra ≤ 108), inter-rib-spacing to sphere diameter (0.191 ≤ P/D ≤ 0.785), and rib-radius to sphere diameter (0.03 ≤ R/D ≤ 0.083). The main target of this study is to identify the critical parameters for heat transfer enhancement from the ribbed sphere compared to a conventional plane sphere. The results obtained from this work show that the average Nusselt number increases with an increase in Ra and P/D, whereas it decreases as R/D increases. Effectiveness of the ribs (εrib) and critical Rayleigh numbers (Racr), corresponding to εrib = 1, are also calculated. Ribs are more effective in heat dissipation at low Ra and P/D and high R/D. A correlation for the average Nusselt number is also developed in this work, which would help design a better thermal management system.