In order to ensure that the initial conditions of the experiment are
consistent and reach a steady-state as soon as possible, pre-wetting of
the particles was carried out as follows according to the Levec
pre-wetting method34. The particles were completely
immersed in water for 20 min, then placed in a stainless drum with a
screen at the bottom and naturally filtered for 30 min. The pre-wetted
particles were fed into the silo to ensure a continuous and stable flow
of particles during the experiment. Since the first bed layer packed by
free-falling of particles had lower bed porosity, it would take at least
one bed volume time to ensure the densely packed bed had been entirely
discharged14. And during the experiment, each time the
experimental conditions were changed, it was necessary to wait for at
least 10 min to ensure that the system had reached a steady state.
The pressure drop and exit liquid distribution were acquired
simultaneously in the same bed. The pressure drop was measured by the
differential pressure transducer (CYG1219 type, Baoji Research Center of
Transducer, China). The measuring range is 0-30 kPa, with a relative
accuracy of ±0.25% on the full scale. The sampling frequency was set as
400 Hz and the sampling time was set as 180 s in all cases. At the top
and bottom of the column, two pressure pipes were inserted via drills
(distance 750 mm). The front end of the pressure pipe was covered with a
screen to prevent particles from entering the pressure measuring system.
The gas-liquid separators were installed between the pressure pipes and
the differential pressure transducer to maintain the pressure
measurement completely in a single-phase gas condition according to
Sai35. The dynamic liquid holdup was measured by
switching off the inlet gas and liquid flows and collecting the drained
liquid within 30 min.
In order to quantify liquid distribution at the outlet, a
maldistribution factor Mf was defined according
to the following equation36:
In Eq. (1), N accounts for the number of collectors (4 in this
case), Li is the liquid mass flow rate through a
given collector referenced by i and Lmeanis the mean mass flow rate through all sections of the bed.