Characteristics Of Direct Contact Condensation Of Steam Jets Discharging Into Subcooled Water

Direct contact condensation (DCC) of steam and water is a phenomenon of steam, with high temperature, introduced into sub-cooled water. In ADS automatic depressurization system of AP1000 nuclear power plant, steam with high temperature and high pressure in the reactor core sprays into the in-containment refueling water storage tank (IRWST) for condensation by this way, so that the primary loop is depressurized rapidly. The changing processes in direct contact condensation have great influence on the speed of pressure relief. Hence, it is of great significance to understand mechanism of direct contact condensation so as to guarantee the safety of nuclear reactor. Based on commercial software CFX14.0, the κ-ε turbulent model and the phase change model have been used to simulate the phenomenon of direct contact condensation (DCC) as the steam with low mass flux injected into the sub-cooled water by the nozzle or multiple holes. According to the results of simulation perfectly coinciding with the experimental one, these models chosen for simulating the phenomenon is feasible. The results of numerical simulation show that: (1) As to the heat model adopted by numerical simulation, full thermal model is applicable to steam and water DCC through the nozzle, while thermal enthalpy model is suitable to that through holes. (2) The number of nozzles has a great influence on the flow field of sub-cooled water near the nozzle. Almost no sub-cooled water flow towards the steam through single nozzle above the spraying steam, while large amounts of sub-cooled water does so through double nozzle. (3) Steam plume, discharged through holes to sub-cooled water, expand and shrink periodically and its intensity is weakest at 50℃ of sub-cooled water. What’s more, when the temperature of sub-cooled water is relatively high, the lengths of steam plume are variant through different holes with the longest one through holes in the middle two rows as well as the closest one through holes in the up and down rows. However, the above phenomenon is not obvious for sub-cooled water of lower temperature. (4) By the comparison of stream discharge through nozzle and holes, it turns out that there is a huge difference in the flow fields of steam plume. The shape of the former is firstly convergence then divergence, while the latter merely divergence. (5) In the initial stage of steam discharge through nozzle, the closer it is from the nozzle, the shorter pressure fluctuations period in the sub-cooled water is. While in the spraying and condensing process of steam through double nozzles, the corresponding pressure fluctuations period doesn’t alter with distance. However, in the process of steam discharge through multiple orifices, when the temperature of sub-cooled water is relatively low, the closer it is from the nozzle, the longer pressure fluctuations period in the sub-cooled water is. But when the temperature of water is relatively high, the pressure fluctuations period is invariant with distance.