Fig. 12 Distribution diagram of the PSD under different liquid
arrangement methods with the liquid spray densities. (a)F s = 1.2
(m/s*(kg/m3)0.5) and (b)F s = 2.0
(m/s*(kg/m3)0.5) in overflow
distribution; (c) F s = 1.2
(m/s*(kg/m3)0.5) and (d)F s = 2.4
(m/s*(kg/m3)0.5) in spray
distribution.
Fig. 12a, b shows the PSD distributions with different liquid spray
densities under an overflow distribution of the liquid. The gas-phase
kinetic factors are F s = 1.2
(m/s*(kg/m3)0.5) and 2.0
(m/s*(kg/m3)0.5). For the liquid
spray density L W ≤ 78
m3/(m2*h), the two main frequencies
move within (2.36 Hz–5.28 Hz). The PSD value changes in the range
(0.0044 dB/Hz–0.0104 dB/Hz) and decreases with the increasing liquid
spray densities (see Fig. 12a). At this point, the flow pattern
corresponds to BFF. The two-phase flow is more stable, and the
rotational flow is dominant. The increase in the proportion of the
liquid phase will increase the resistance of the gas phase and consume
gas-phase energy, resulting in a decrease in the PSD value. For the
increasing spray density L W = 104
m3/(m2*h), the flow pattern is CPF.
The liquid layer on the unit is thicker, and the liquid phase perforates
out from the sieve holes affected by gravity and the driving force of
airflow. As shown in Fig. 12b, the gas-phase kinetic factor has
increased to 2.0 (m/s*(kg/m3)0.5).
The liquid spray density is L W ≤ 52
m3/(m2*h), and the two main
frequencies vary within the range of (2.48 Hz–5.64 Hz), compared with
BFF. The PSD value is increased and varies in the range of (0.0184
dB/Hz–0.0403 dB/Hz). At this time, the corresponding flow pattern is
DMF. The gas-phase ratio and intensity of the perforated flow is
increased. The PSD value for the first main frequency increases. When
the spray density continues to increase to L W> 52 m3/(m2*h), the two
main frequencies remain unchanged, and the PSD value is within (0.0155
dB/Hz–0.0226 dB/Hz), showing a decreasing trend. Then, the flow pattern
is transformed into CPF. The liquid layer above the sieve holes is
thickened. The gas-phase perforation channel and intensity strength
became smaller. The flow is blocked, resulting in a decrease in the PSD
values for the main frequencies.
Fig. 12c, d shows the variations of the PSD values under different
liquid spray densities, with the kinetic factorsF s = 1.2
(m/s*(kg/m3)0.5) and 2.4
(m/s*(kg/m3)0.5), under a spray
distribution of the liquid phase. As shown in Fig. 12c, the two main
frequencies change in the range of (2.36 Hz–5.16 Hz), remaining
unchanged with the liquid spray densities, and the PSD values show an
increasing trend, ranging from (0.0115 dB/Hz–0.0623 dB/Hz). At this
operating condition, the corresponding flow pattern at each liquid spray
density is FJF, and the liquid phase plays a leading role. The strength
of the liquid jet streams hitting the surface of the unit increases with
increasing spray density, which intensifies the gas-liquid mixing. In
addition, the interaction of the two phases increases, increasing the
energy of the main frequencies. For the increasing gas-phase kinetic
factor F s = 2.4
(m/s*(kg/m3)0.5), the range of the
main frequencies is similar to that of FJF. The PSD value increases,
ranging from (0.0189 dB/Hz–0.1925 dB/Hz), (see Fig. 12d). The flow
pattern changes to JMF, and the perforation intensity is increased. The
velocities of the liquid jet streams increase with the spray densities.
The liquid phase flow is more disordered. The liquid jet streams hit the
surface of the unit, and then, the interaction between the two phases is
more intense. The strength of the two phases is increased. The PSD
values of the main frequencies are significantly improved. For the
liquid phase spray density L W = 260
m3/(m2*h), the turbulence intensity
of the gas-liquid phase flow on the unit surface reaches the maximum.
The perforated resistance of the gas-phase flow is also the largest, and
the interaction intensity of the gas-liquid phase is the strongest
within the experimental operating conditions.
3.3 Operating conditions
Combined with the flow pattern image recognition, time domain, and PSD
analysis of the differential pressure pulsation signal, in the range of
the experimental operating conditions (0 <F s ≤ 4.0
(m/s*(kg/m3)0.5), 0 <L W ≤ 260
m3/(m2*h)), the distribution of each
flow pattern is shown listed in Table 2.
Table. 2 Distribution of the flow patterns within the operation domain