Fig. 8 Jet and mixed flow. (a) The front side; (b) The reverse side; (c)
Diagram of JMF.
The flow pattern of the JMF is shown in Fig. 8. The operating conditions
are L W = 156
m3/(m2*h), F s= 4.0 (m/s*(kg/m3)0.5). The gas
kinetic energy factor increases. The liquid film on the unit surface is
blown away by the air jet stream, and the distribution becomes more
unevenly distributed. As shown in Fig. 8b, the liquid phase blown out by
the gas airflow at the back of the unit is ejected. The dispersed
droplets and columns flow disorderly and mix. The flow mechanism of the
flow pattern is similar to that of the DMF.
3.2. Interaction intensity and operating conditions for
different flow
patterns
First, the acquired differential
pressure signal is processed to remove the singularity, and the moving
average method is used to denoise the signal to obtain the time-domain
characteristic diagram of the differential pressure signal29. Second, the Welch average period method, where the
Hanning window is adapted is used to estimate the frequency spectrum
density (PSD) of the de-noised differential pressure signal30. Finally, combined with the domain signal and power
spectrum density, the interaction intensity of the gas-liquid is
analyzed, and the operating field under different liquid distributions
of flow patterns can be divided 31.
3.2.1. Time-domain analysis for the pressure pulsation
signal
Fig. 9 and Fig. 10 show the time domain signals of the differential
pressure of all the flow patterns. The pressure signals of the gas phase
in the time domain under overflow distribution are shown in Fig. 9a, and
the liquid spray density is L W = 78
m3/(m2*h). With the increasing
kinetic energy factor of the gas phase, the average amplitude of the
pressure difference pulsation presents a stepped-upward trend. For the
range of the kinetic energy factor of the gas phaseF s ≤
1.2(m/s*(kg/m3)0.5), the pulsation
change in the pressure difference is stable. In this operating range,
the flow pattern is a bilateral flow. The surface and sieve holes of the
unit are covered by the liquid film. The gas phase mainly flows through
the unit in the form of rotational flow. In this case, the gas velocity
is low, and the interaction between the gas and liquid phases is weak;
therefore, the pressure difference fluctuation is weak.
When the gas-phase kinetic factor F s rises to 1.6
(m/s*(kg/m3)0.5), the pressure
difference amplitude increases as the gas velocity increases, and the
flow pattern of the unit starts to change into CPF, under the squeezing
influence of the gas phase. At this time, the gas phase perforation is
still hindered by the liquid layer at the sieve holes, and the
proportion of the rotational liquid phase is large. Although the
gas-liquid two-phase interaction is slightly strengthened, the overall
gas velocity is relatively small, and the pressure difference
fluctuation is stable. When the kinetic factor increases toF s = 2.4
(m/s*(kg/m3)0.5), the gas phase
propulsion becomes prominent, and the flow pattern changes from CPF to
DMF. The liquid layer above the sieve holes is continuously blown out by
the airflow and replenished immediately. The gas-liquid phase is mixed
on the back of the unit. The interaction force between the two phases is
increased, resulting in a sharp fluctuation in the pressure difference
signal.
The time-domain signal changes of differential pressure pulsation are
shown in Fig. 9b. The liquid spray density is L W= 156 m3/(m2*h). The pulsation
amplitude of the differential pressure signal gradually increases with
the increasing gas-phase kinetic energy factor, which is similar to that
under the overflow distribution. The flow pattern changes into the FJF
when the gas phase kinetic energy factor F s ≤ 1.6
(m/s*(kg/m3)0.5). At this point, the
gas-phase velocity is small, and the influence of the gas phase
decreases. The regular jet flow of the liquid is dominant on the reverse
side of the unit, and the mixing degree of gas-liquid is low. The
fluctuation of the differential pressure signal is stable.