Weir flow and liquid height on sieve and valve trays

Mechanisms for the flow of liquid over outlet weirs of distillation and abs orption trays are described in this paper. Weir flow contributes to the liq uid height on a tray, and this height is important for the design and opera tion of trayed columns. Comparisons of available experimental data with Fra ncis' weir equation and with new stochastic liquid flow models showed that the traditionally used Francis' equation needs modification. The stochastic flow models Link the weir flow to the flow mechanisms upstream of the tray outlet. These upstream mechanisms provide the input needed for a new weir crest equation. The existence of a so-called 'edge-vortex' (a horizontal ro ll cell at the boundary of the gassed and the ungassed region) is shown to play an important role, when a calming zone is present upstream of the outl et weir. (C) 1999 Elsevier Science S.A. All rights reserved.