The flow field inside a large-capacity air tray dryer chamber was examined by computational fluid dynamics. The numerical results for the original chamber showed that the velocity distribution is significantly inhomogeneous, and the products are not expected to be dried uniformly. Guide vanes were installed in the drying chamber to reduce the low-velocity region and increase the spatial homogeneity of the velocity above the product. The numerical simulations showed that the flow uniformity is increased significantly by modification of the flow field owing to these guide vanes. In addition, the attachment of a solid plate to the bottom of the upper trays can enhance the uniformity of the flow further. Finally, the effects of the permeability of trays on the flow field were also examined.