In this paper, a six-inch cylindrical column was used to study a certain hydraulic characteristic of the perforated trays in air-water system. To obtain better understanding about the effect of the liquid head on the performance, two types of experiment were used : in one type（A） the liquid was supplied into the test column from the constant head tank ; in the other type(B) it was flowed in through the downcomer and out over the outlet weir as in usual industrial usage. The various kind of the trays used are shown in Table 1 and the equivalent liquid height varied up to 20 cm in the Type A. Time averaged air flow rate covered the range upto 10 l/sec and water rate upto 260 ml/sec.
In these experiments we observed the froth layer and correlated the total pressure drop, relative froth density, etc.