TWO PHASE FLOW COLUMN LAB MANUAL
EXPERIMENTAL PROCEDURE
Description of Apparatus
The primary piece of equipment used in this experiment is a packed bed column standing perpendicular to the floor and made of clear Plexiglas. The packed portion of the column has an inner diameter of 7.642 cm (Dimenstein, 1984) and a length of 152 cm (Dimmenstein, 1984). The column packing consists of glass spheres 0.3 cm. Water is fed to the column by a closed-loop cycle. The water enters the top of the column, passes through the packed bed, and then is collected in a water storage tank. The water collected in the storage tank is pumped through rotometers and then back to the top of the column. The small rotometer is capable of measuring 0.00 to 0.25 gallons per minute (GPM), while the large rotometer is used for larger desired water flow rates ranging from 0.0 to 3.0 GPM. The flow through each rotometer is controlled by a manual valve. A fresh water supply is available when there is no water in the storage tank. The air is supplied to the system from a compressor. The compressed air is fed to a water separator and air filter before flowing through either flow air rotometers. The small air rotometer measures air flows from 0.0 to 3.2 standard cubic feet per minute (SCFPM). The large air rotometer measure flow rates in the range of 0 to 250 SCFPM. The compressed air enters at the top of the column and flows co-currently with the water.
Three pressure transducers are mounted on the column. The top pressure transducer is mounted above the packed portion of the column to transmit a signal indicating the entering pressure of fluid(s). A 5.0-inch axial distance separates the middle and bottom transducers. These pressure transducers are used to obtain a pressure drop gradient in the packed bed column. The transducers feed a signal to a nearby desktop computer. The computer receives and analyzes the signals using a Basic program. The Basic program outputs the three pressure readings in psig to a PRN file. The pressure signals are typically received at a rate of 50 per second over a 2 second period once the column reached a steady flow pattern.
Experimental Procedure
Gauge pressure data from three pressure transducers mounted along the axis of the column was obtained by use of a computerized data acquisition program.
I.Diagnostic Run
The column is stored under the atmospheric pressure of air, and is void of water. First the data acquisition computer is turned on and a diagnostic run is made. No gas or liquid is flowing to the column. The diagnostic run tests the pressure transducers to see if the transducers are reading there correct zero values. The diagnostic run is also used to set the data acquisition parameters.
The user to selects the number of data points taken per second and the length of time the data is going to be collected over. Values of 50 points per second, and 5 sec are typically adequate in trickling flow while 500 points per second is adequate for pulsing flow. The acquisition program displays the pressure data in a graphical form as the data is acquired.
II.Pump and Compressor Activation
The column is coupled to a centrifugal water pump that feeds the top of the column with water. An air compressor is also coupled to the column and feeds the top of the column with pressurized air. Circuit breakers control the power to the compressor and water pump, and are located on the wall by the computer station. The flow of air and water to the column are controlled by two sets of control valves.
The control valves are opened, to avoid any pressure build up in the pipes, and then the water pump and the compressor are turned on, allowing air and water to flow into the column.
III.Experimental Measurements
By varying the gas and liquid flow rates to the column a full range of operating conditions can be explored. Both trickling and pulsing flow patterns are explored during our experiment. The gas flow rate and the liquid flow rate were simultaneously adjusted to observe trickle and pulse flow.
The liquid and gas rate are set as desired, then the flow pattern in the column is allowed to stabilize. The stability of the column is determined through the data acquisition program. The program plots the transducer pressure readings as a function of time. Stability for trickling flow is achieved when the pressure is a constant value with time. Stability for pulsing flow occurs when the pulses occur with some periodic behavior. When stability is achieved the past 5 seconds of data acquired are saved as a (*.prn) file on a floppy disk.
IV.Column Shut Down
At the end of each experimental session, the flow of water to the column is cut and the gas valve is opened. This forces all of the waer in the bed packing to exit the column, so that it is dry for the next laboratory session. The computer program is deactivated and the computer is turned off. When the column is dry the air compressor is turned off. The control valves are then closed completely to avoid back flow.
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