30
Exercise C - Determination of the Residence Time using
tracer techniques
Theory
Effect of a step input change, calculation of the average residence time.
If C = concentration in reactor at time
t
after input step change
C
0
= concentration of the input
Then
where tr = time constant
Hence t
c
may be found graphically.
Method
Make up 2.5 litres of a solution of 0.1M KCL and fill one of the feed bottles. Fill the
other feed bottle with demineralised water.
Using the Armfield data logger, initiate the program.
Set the reactor stirrer to a speed of '50%' and press ‘Power on’ button to start it up.
The experiment can be carried out at room temperature initially. If other reactor
temperatures are required this is achieved using the hot water circulator and setting
the PID temperature controller in the software as detailed in previous experiments.
Start the water feed pump by setting the pump speed control to maximum in order to
fill the reactor to the overflow as quickly as possible. When the reactor is full, stop the
feed pump.
Start the KCL solution feed pump by setting the pump speed to 100 ml/min.
The conductivity of the reactor contents will begin to increase and, after a period of
approximately 45 minutes to 1 hour, will approach the conductivity of the feed
solution and will reach the steady state.
On conclusion of the experiment using the Armfield data logger, a set of readings of
conductivity with time among other calculations will be stored in the computer.
At this point, only conductivity with time data can be transferred onto the
spreadsheet.
Start the spreadsheet program.
