The condensation of particles into bulk powders in low velocity regions is quantitatively analogous to the condensation of molecules into bulk liquids in low temperature regions. In a vertical vessel the former leads to streamers or clusters or an annular layer flowing down at the walls; the latter leads to downflowing droplets, rivulets or annular films at the walls. The limiting countercurrent flow restricting area, or thickness of such annular layers or films, is shown to be predictable from the dimensionless gravity flow equation.