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.