Numerical study on water draining process pushed by nitrogen in EAST upper divertor

Highlights: • The study on drainage process for the EAST divertor was firstly carried out. • The pressure difference between the outlet and inlet of the divertor should be at least of 4 KPa to effectively blow the residual water out of the cooling channels of the upper divertor. • The hydraulic characteristics of drainage process were analyzed in detail, such as the water volume fraction, flow velocity, the draining water flow rate, and the pressure distribution. In the Experimental Advanced Superconducting Tokamak (EAST), the water in the cooling channels of the upper divertor is difficult to be pushed out by the current drainage system resulting in the possible divertor damage. Therefore, studies on the draining process using the gas pushing for this divertor is essential to improve the current drainage system. In this paper, the hydraulic characteristics of the developing gas-liquid two-phase flow were investigated in detail by using the FLUENT code. The results showed that the pressure difference between the inlet and outlet of the cooling channel should be larger than 4 kPa to effectively blow out the residual water from the cooling channels by the nitrogen gas pressure. Also, it was found that the draining process can be divided into five stages in regards to the different hydraulic characteristics, such as the flow velocity, the draining water flow rate, and the pressure distribution. These results will provide a theoretical basis for future improvements in the EAST drainage systems.