Experimental study on the bubble trajectory in an axial gas-liquid separator applied for tritium removal for molten salt reactors

In the tritium removal system applied in the thorium molten salt reactor, an axial gas-liquid separator was developed to separate the dilute dispersed bubbles from the reactor coolant. In order to quantify the separation efficiency for the separator and provide useful guidelines to design the separator, the separation trajectories of bubbles with different sizes in the swirl flow inside the separator are needed. To do this, an experimental study using the high speed visualizing and image processing was implemented to investigate the separation trajectories of bubbles under various bubble sizes and Reynolds numbers. A special bubble generator which is capable of generating single bubbles with controllable diameters was devised and incorporated into the separator test. By adjusting the parameters of the single bubble generator, i.e. the diameter of the needle and the rotation speed of the peristaltic pump, the trajectories of bubbles with diameters ranging from 0.2 mm to 1.1 mm, Reynolds numbers from 40,000 to 100,000 are recorded by the high speed camera and processed by a specialized image processing and analyzed. The results indicate that the bubble presents a convergent spiral path in the separating duration and eventually is entrapped by the air core. The separation length defined as the axial distance the bubble takes from the periphery of the separator to the air core will increase when decreasing the bubble diameter or increasing the Reynolds number. The experimental data obtained in this paper provides a detailed benchmark for the modeling of the bubble dynamics in the swirling flow.