This study examines rarefied thermally-driven flow in a square cavity (Case 1) and rectangular bend (Case 2) with various uniform wall temperatures in two dimensions.. We employed the direct simulation Monte Carlo (DSMC) to solve problems at a wide range of Knudsen numbers Kn=0.01 to 10, and the discrete unified gas kinetic scheme (DUGKS) solver was used at Kn=0.01. The scenario is that the bottom side and its opposite were set hot, and the other sides were set cold in case 1. Diffuse reflector boundary conditions were set for all walls. The imposed temperature differences create four primary vortices. The results of the continuum set of equations of slow non-isothermal flow (SNIT) solver prove the primary vortices in the square cavity are caused by nonlinear thermal stress effects, and other smaller vortices appear at Kn=0.01, 0.1 are brought on by thermal creep processes. As Kn increases, vortices generated by thermal creep disappear, and ed-dies created by nonlinear thermal stress occupy the cavity. In case 2, i.e., rectangular bend, two sides were set cold, and the others were hot. Two primary vortices are formed, which are caused by nonlinear thermal stress effects. The direction of streamlines in the two main vortices is opposite from the warm-to-cold zone, as some eddies on the left are counterclockwise, and others are clockwise.

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