2006 Volume 14 Issue 3 Pages 35-46
This paper attempts to study numerically a differentially heated square cavity, which is formed by horizontal adiabatic walls and vertical isothermal walls. Two perfectly insulated baffles were attached to its horizontal walls at symmetric position. Heat transfer by natural convection of dry air was studied by solving mass, momentum and energy equations numerically. Streamlines and isotherms are produced and heat transfer is calculated. A parametric study is carried out using following parameters: Rayleigh number from 104 to 108, non-dimensional thin baffles length are 0.6, 0.7, and 0.8, non-dimensional baffle positions Sb from 0.2 to 0.8. It was observed that the two baffles trap some fluid in the cavity and affect the flow fields. The flow for cavities with Sb<0.5 at low Ra tends to circulate as a primary vortex strangled by the baffles while at high Ra it tends to separate into two different vortexes. For the cavities with Sb>0.5 it tends to separate into two different vortexes at low Ra while at high Ra tends to circulate as a primary vortex strangled by the baffles. It is found that Nusselt number is an increasing function of Ra, a decreasing one of baffle length, and strongly depends on Sb. Another interesting phenomenon of the typical cavity is that a particular case is the opposite of the other case as long as the sum of Sb is equal to 1. Thus, the typical cavity can allow the heat flow in one direction but significantly blocks it in the opposite direction. The typical cavity can be proposed as a heat version of a diode. The heat may be transferred up to 42% from one direction but blocked up to 98% in the opposite direction by using a particular cavity with Lb=0.7 and Sb=0.4 at Ra=108.
