The beauty of natural convection is on its passiveness, i.e., there is no need for an external driving force, i. e., no mechanical devices involved in the system, consequently the system is free of noise . Natural convection in enclosures has been received extensive research efforts due to its importance in many applications. In some of these applications, it is intended to reduce the rate of heat transfer, such as double glazing windows, solar collectors, gap between walls of buildings and appliances, etc. In other applications, enhancement of the rate of heat transfer is desirable, such as electronic device cooling in a compartment.
The present work is intended to address the process of heat transfer by diffusion and advection mechanisms and passive method to control these mechanisms. It is possible to suppress or enhance the rate of heat transfer by properly placing an obstacle inside the enclosure. The effect of location and size of an obstacle on the rate of heat transfer is discussed for enclosures of aspect ratios of 1, 2 and 4. The results presented for a fixed Prandtl number of 0.71 (air) and for Rayleigh numbers of 10⁶, 10⁷ and 10⁸.