longitudinal dispersion in nonuniform isotropic porous media

the sand pack. Constant head is maintained in the inlet chamber
through an overflow weir. When the valve at the outflow end of the
column is open, water percolates through the sand into the end chamber
93
of the column and drains into a constant head receiving reservoir which
overflows to drain. The flow rate is controlled by a ball valve at the
outflow end of the column. Flow rate is measured by directing the
outflow from the column into a volumetric flask and measuring its time
to fill.
Changes in salinity within the column are measured by a
conductivity probe-recording system. A block diagram of the system is
given in Figure 4.4. Conductivity probes are placed at three locations
along the column, with the probe plates lying close to the column axis.
The probes are held in Swage lock fittings attached to the column and
the probe rod penetrates the entire diameter of the column. The probes
(Figure 4.5), constructed in the Keck lab machine shop, are made of
6.4mm (outside diameter) lucite tubing. The tubing is cut and grooved
such that two stainless steel rings slide onto each grooved end with
their outer surface flush with the tubing outside diameter. To join
the pieces, the tubing ends are bored and grooved such that one end
will slide into the other. A lucite spacer ring separates the
stainless steel rings and provides additional strength to the joint. A
fine conducting W1re is soldered to each stainless steel ring and drawn
through the lucite tube to connect the probe with the external
circuitry. The pieces are assembled and glued together to produce the
finished probe.