A detailed computational study is carried out to investigate the effects of Grashof (Gr) and Reynolds (Re) numbers on the three-dimensional (3-D) flow structures and heat transfer characteristics in a horizontal chemical vapor deposition (CVD) reactor with a circular heated disk which simulates a 12-inch wafer. The Grashof number is varied from 8.13 x 10(4) to 813 and the Reynolds number is from 100 to 25. For the range of parameters studied, both the transverse (return flow) and longitudinal rolls are observed to appear in 3-D. Computed flow structures and heat flux distributions suggest that for constant Grashof number condition the size and location of longitudinal rolls have direct impact on the homogeneity of deposition, while the size and location of transverse rolls have a minor effect on the heat flux and hence on the deposition rate. In addition, the effect of Reynolds number on the averaged heat flux is negligible under a fixed Grashof number condition. The buoyancy-to-inertia ratio is found to play an effective role in retarding the formation of transverse and longitudinal rolls. (c) 2006 Elsevier B.V. All rights reserved.