In bubble cap trays, vapor flowing up through the tower contacts the liquid by passing through bubble caps (Figure 6-7a). Each bubble cap assembly consists of a riser and a cap. The vapor rising through the column passes up through the riser in the tray floor and then is turned downward to bubble into the liquid surrounding the cap. Because of their design, bubble cap trays cannot weep. However bubble cap trays are also more expensive and have a lower capacity/higher pressure drop than valve trays or sieve trays.
