Tutorial to CASE 1
1. Problem description
A tracer experiment was made in a straight pipe, more than 30
metres in length and 6 cm in diameter. The fluid was air at ambient
temperature and approximately atmospheric pressure. The tracer,
gamma-emitting 133Xe, was injected by a syringe at the inlet of the
pipe and monitored by two detectors separated by 18.15 metres:
18.15 m
6 cm
Injection 18.15 m
6 cm
Injection
Our objectives are to evaluate the flow rate and the dispersion
coefficient.
2. Running the software
First, click the “Run RTD” item. The graphical user interface
appears.
The data from detectors 1 and 2 are in the case1_1.txt and
case1_2.txt files in the code2 folder; time is in seconds and the
signals have been area-normalised. Select them as the inlet and
outlet signals in the Setup menu. It is a good idea to see what they
look like using Draw/Preview draw/Inlet and outlet. The strange
shape of the inlet signal is due to uneven movement of the syringe
piston during injection. The same shape is visible (though
attenuated) on the signal from detector 2.
Flow in a long pipe can be expected to be one-dimensional
convection plus some amount of dispersion. Axial dispersed plug
flow can therefore be selected in the Setup/Setup parameter menu.
An initial value for tau can be guessed from the pre-visualisation of
the tracer curves. The signals from detectors 1 and 2 are very
similar in height, width and shape, which indicate that the flow
should have little dispersion. Some not too small value for the
Péclet number Pe, say a few tens, should be adequate as an initial
guess. Click on the Yes box to ask for optimisation of these
parameters.
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