Dissolution of a Steam Air Stratification by Natural Convection

摘要

Tests combining thermally driven natural convection which dissolves steam air stratifications have been performed at the technical scale THAI test facility. This continues a series of gas distribution tests with increasing complexity intensively used for validation and development of computational fluid dynamics (CFD) and lumped parameter (LP) codes. As in an earlier test performed with a helium air stratification a naturally driven convection flow in the THAI vessel has been established by cooling the upper vessel walls while heating the lower vessel walls. At comparable wall temperature difference it has been found that the erosion of the steam air cloud is much faster than the erosion of a comparable helium air cloud. The condensation of steam at the upper plenum walls has been balanced by injecting steam at small flow rate during the erosion test phase. So the faster erosion is attributed to the lower density difference between air and steam compared to air and helium. Reducing the wall temperature difference in two additional tests reduced the erosion speed and allowed to determine erosion velocities of 1.1 mm/s and 1.7 mm/s which are still faster than 0.7 mm/s determined in the former helium stratification test.