3.4. Distribution of rotational and perforated flow for the
gas-liquid phase of the blade
unit
The proportion of the gas-liquid rotational and perforated flow on the
blade unit affects the hydrodynamics in the unit. In this section, the
rotational flow ratio is introduced to study the distribution mechanisms
of the rotational and perforated flow for the gas-liquid phase. The
rotational flow ratio is divided according to the liquid phase
arrangement method in the experiment.
The bottom area of the rotational flow separation chamber is the same as
that of the perforated separation chamber. Thus, the liquid rotational
flow ratio η lr (liquid rotational flow ratio) can
be calculated with the liquid level heights:
(3)
Where the level height of the rotational flow separation chamber ish lr(liquid rotational flow), andh lp (liquid perforated flow) represents the level
height for the perforated flow separation chamber.
As shown in Fig. 2, the outlets for the gas phase have the same
diameter. The gas-phase rotational flow ratio can be calculated with the
average velocity of the outlets.
(4)
Here, u grand u gp are the mean gas velocity for the
rotational flow and perforated flow, respectively;η gr-s(spray)
and η lr-s (spray) represent the rotational ratio
for the gas and liquid phase under the spray distribution of liquid,
respectively, andη gr-o(overflow) and η lr-o (overflow) are the
rotational ratio for the gas and liquid phase under overflow
distribution, respectively.
3.4.1. Rotational flow ratio in overflow
distribution
Fig. 13 shows the variations of the rotational ratio for the gas and
liquid phases with the operating conditions. As shown in Fig. 13a, the
rotational flow of the gas-phase increases first, then decreases with
the increasing gas-phase kinetic factor, and the decreasing trend is
larger. For the liquid spray density L W = 26
m3/(m2*h) and the gas-phase kinetic
factor F s ≤ 1.6
(m/s*(kg/m3)0.5), the flow pattern
corresponds to the BFF, and the sieve holes of the unit are covered by
the liquid layer. The resistance for the gas-phase perforated flow is
large because of the smaller driving force of the gas phase. Therefore,
most of the gas phase flows in rotational flow. Thus, the rotational
flow ratio is larger than 0.6. In addition, in this flow pattern,
although the gas-phase kinetic factor increases continuously, the
driving force of the gas phase cannot break the liquid layer above the
sieve holes. Therefore, more gas phase flows in the form of rotational
flow, and the rotational flow ratio for the gas phase increases slowly.
For the gas-phase kinetic factor F s> 1.6 (m/s*(kg/m3)0.5),
the flow pattern changes to CPF and then changes to DMF with the
increasing gas-phase kinetic factor. Under these two flow patterns, the
driving force for the gas phase increases gradually, making the liquid
layer above the sieve holes flow out in the form of liquid jet streams
and dispersed droplets and renew rapidly. During this process, the
perforated gas phase increases with the increasing gas phase kinetic
energy factor. Thus, the gas-phase rotational flow ratio decreases
rapidly. Compared to the perforated flow, the gas-phase rotational flow
ratio remains above 0.5 (see Fig. 13a), indicating that the rotational
flow for the gas phase occupies a large proportion. For a comparison,
the gas-phase rotational flow ratios at L W = 0
are shown in Fig. 13a. The gas phase rotational flow ratio remains at
approximately 0.5 with increasing gas-phase kinetic factor. Thus, under
the structure parameters of this blade unit, the gas phase of the
swirling and perforated flows account for half of each other. The
addition of the liquid phase increases the resistance of the perforated
flow for the gas phase and reduces the proportion of the perforated
flow. For the range of liquid phase spray densityL W = 52-104
m3/(m2*h), the turning point of the
rotational flow ratio for the gas phase changes toF s = 2.0
(m/s*(kg/m3)0.5), corresponding to
the transition conditions of the flow pattern.