Flow structure of gas-liquid two-phase flow in a vertical downcomer

The flow structure of the gas-liquid two-phase flow in the vertical descending tube It can be seen from Figure 3.90 that the fine-bubble flow structure of the gas-liquid two-phase vertically descending flow is different from the fine-bubble flow structure of the vertically ascending flow , the former fine bubbles are concentrated in the core of the tube, while the latter are scattered throughout the tube section. When the liquid phase flow remains unchanged and the gas phase flow increases, the fine bubbles will gather into gas bombs, forming a gas-liquid two-phase flow with a descending elastic flow structure. The vertically descending gas-liquid two-phase flow can also form a descending annular flow structure. When the flow rate of the gas phase and liquid phase is small, there is a layer of liquid film flowing downward on the tube wall, and the central part of the tube is a gas nucleus flowing downward. This flow structure is called an annular flow structure with a descending liquid film. If the flow rate of the liquid phase increases, the bubbles will enter the liquid film, forming a ring flow structure with a descending liquid film containing bubbles. When the gas-liquid two-phase flow rate increases, a block-like flow structure with downward flow will appear. When the flow rate of the gas phase continues to increase, the gas-liquid two-phase flow can have a circular flow structure in which there is a descending liquid film on the tube wall, and the center part of the tube is a descending gas core with liquid droplets. This annular flow structure is similar to the annular structure of the vertically ascending gas-liquid two-phase flow, but the flow direction is opposite.