Disk and donut trays are slightly sloped trays located inside a column in such a manner that the liquid and vapour are brought in to direct contact by forcing vapour through falling liquid. Liquid descends from one tray to the next either as a curtain of liquid raining down or as liquid rivulets passing through holes in the tray deck. It offer a higher capacity and lower pressure drop compared with conventional sieve and valve trays, The trade-off is a considerably lower contacting efficiency. having an extremely high open area, they are most suitable for dirty service and heavy fouling applications. Examples are heavy oil refining and petrochemical heat transfer services having a petroleum coke / high solids content.