Direct numerical simulation of FTM (Front Tracking Method) was used to study free rising motion of single bubble in a tube with fins in gravity. Ratio of fin height and pitch to tube length of a side are chosen as geometric characteristics. Morton number is used as characteristic parameter of fluid. With analysis on free rising motion of bubbles at different fin height, pitch and Morton number effects of geometric characteristics of tube and parameters of fluid on motion trajectory of bubbles are studied. It shows that under effect of fins bubble shape is asymmetry and bubbles have lateral displacement like a "snake".This phenomenon is associated with geometric structure of fin and fluid around bubble. The higher fin height is, the more obvious phenomenon becomes. The smaller the viscosity of fluid around bubble is, the greater the horizontal displacement is.

Natural convection heat transfer in a porous medium with partially thermally active walls is studied with lattice Boltzmann method. Convective flow heat transfer with different heating and cooling zones, porosity, Darcy number and Rayleigh number is investigated. It reveals that at Da=10^-4 a circulating flow pattern at the middle of the cavity is found, and porosity have great influence on heat transfer at large Rayleigh numbers; As Darcy number is increased to 10^-2, streamlines exhibit a flow pattern with two vortices, and porosity have great influence on heat transfer at low Rayleigh numbers. Location of partially thermally active walls has significant influence on flow pattern and heat transfer in cavity. Bottom-top with bottom heating and top cooling provides a greater heat transfer rate compared with other partial heating. It is better than fully heated wall of cavity.