Research on Pendulum Characteristic of Natural Convection Gas within Three-dimensional Closed Cavity

In this paper, the pendulum characteristic of natural convection gas within the 3D spherical closed cavity are discussed. By using the finite element method, the flow and temperature field caused by heat source within the 3D spherical closed cavity under different tilted conditions are calculated. The results are as follow: (1) Under buoyancy effect, the direction of natural convection gas in the cavity always stays in the direction of the buoyancy. (2) The isotherm is approximately oval. The temperature field in the direction of buoyancy is stretched and in the vertical direction of buoyancy is compressed. The temperature gradient which is parallel to the baseline near the heat source O is equal with the cavity horizontal. The temperature gradients are not equal with the tilted angle of 10°. The temperature gradient difference Δδ=4.7 K/mm, when the temperature of heat source is 473K and the radius of the closed cavity is 10mm. The temperature gradient difference Δδ=9.5 K/mm with the tilted angle of 20°. (3) The difference of the temperature gradients on both sides increases with the increase of tilted angle. There is a linear relationship between the temperature gradient difference Δδ and the tilted angle θ.