Residence time on the tray
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Could you please explain the significance of the residence time on a tray, as well as the downcomer residence time? Thank you!
Does it also indicate the degree of backmixing? Chen Minheng, Principles of Chemical Engineering (3rd Edition), Volume 2, P115: Mixing of Liquids on Tray Sheets. The main flow direction of the liquid on a tray sheet is from the liquid inlet side toward the liquid outlet side. Due to the agitation of the gas, a flow opposite to that of the mainstream method inevitably occurs, namely the so-called backmixing. Only when backmixing is extremely severe can the liquid on the plate be evenly mixed. In actual trays, especially large ones, the fluid travels a long distance; the mixing that occurs is not sufficient to achieve uniform distribution. As a result, a certain concentration gradient forms in the fluid along its main flow direction, with the liquid composition at the inlet end being higher than that at the outlet end.
Standard answer: 1. The residence time on a tray refers to the time from when the fluid flows out of the downcomer of the previous tray and enters the current tray, to when it leaves this tray and enters the inlet of the downcomer of the next tray ； 2. Different fluid droplets have different flow paths and residence times on the tray, so the residence time on the tray is an average value ； 3. The residence time on the tray is one of the aspects considered in the hydrodynamic calculations of trays, and it is of great importance for accurate calculations in reactive distillation ； 4. WTR (available on this forum) is one of the ideal software tools for calculating tray fluid dynamics.
This post was last edited and replied to by wiseboy on 2011-7-24 09:12. Reply 4# vs_loveblack: The specific calculation for the residence time on the tray can be performed only using VVETA’s fluid dynamics software, WTR. The formula below is taken from WTR’s “WTR Software Development Technical Documentation”: Tr = (At – Af)·hl/L. Where: Tr – Residence time on the tray, s; At – Cross-sectional area of the tray, m2; Af – Area of the downcomer, m2; hl – Height of the clear liquid on the tray, m; L – Liquid flow rate, m3/s. With VVETA’s fluid dynamics software WTR provided by Xi’an VV Software Company, all these parameters are available. WTR is available on this forum.