[ Plan ] [ Schematics ] [ Procedure ] [ Raw Data ]

The air-water simulator of a sieve plate and bubble plate column is shown in Figure 2 & Photo 1. It consists of a 60.0 cm diameter column 3.04 meters high constructed from transparent plastic into which have been inserted two sieve plates and a bubble cap plate. Each plate has a segmented downcomer and a 6.5 cm weir. The top plate is a sieve plate of conventional design installed to ensure gas and liquid distribution in/and on the bubble cap tray chamber immediately below. The compartments above and below the bubble cap plate contain ports through which pass the lines to the pressure tappings. One pressure point enables the pressure in the vapor space above the bubble caps to be measured; five pressure points give the pressures on "top of the risers" of five bubble caps, and finally the sixth pressure tapping gives the pressure below the bubble cap plate in the lower sieve plate compartment. In addition, provision is made for the atmospheric pressure to be obtained and the pressure below the lower sieve plate to be measured.

The liquid reservoir is situated in the base of the column and is provided with a drain and a connection to a centrifugal pump (Photo 2) that recirculates water to the top sieve tray after which it passes down the downcomers and over the bubble cap tray and then the lower sieve plate. The water flow rate is measured by the rotameter shown and the air flow admitted through the 31.4 cm port just above the water reservoir is measured by the electronic anemometer or by an alternate method.

Details of the cap plate and bubble caps are presented in Figures and Photos 3 and 4. There it will be seen that the plate contains 27 bubble caps each 59 cm diameter arranged on a 14.0 cm triangular pitch. The caps possess slots 0.3 cm wide 1.5 cm long as shown.

Experimental Method

Fill the water reservoir at the base of the column with water, making sure that the base of the downcomer from the lower sieve plate is immersed below the water level thereby preventing air being short circuited up the downcomer. Start the pump and control the water flowrate at 12 cm on the rotameter scale (22.4 l/min). When the water flow has been established switch on the air fan and slowly open the diaphragm valve to admit air into the column. Adjust this valve to give an air flow rate approximately equal to the value assigned to your group (see below).

Allow steady state operation for 15 minutes and then record the pressures on the column manometer. Allow the column to operate for a further 10 minutes and then repeat the pressure readings. If constant steady state operation has been maintained over this second period, measure the head over the exit weir of the bubble cap and sieve plate. Next increase the water flowrate to 15.0 cm on the rotameter scale (27 l/min), and when steady state has been attained, again record the pressures and the head over the weir of each of the bubble cap and sieve plates.

Repeat the experiment a third time with a water rotameter reading of 27.0 (49.3 l/min).

Analyze the results to test stability of the plate for all the experimental conditions and compare the measured pressure drop and hydraulic gradient at all conditions to those predicted using the correlations. Discuss how each varies with air and water flow rate.

last update: 01/25/00