Effects of the void fraction and the entrance geometry of sudden contraction on the pressure drops in horizontal air-water flow

Abstract

Local or bulk boiling is allowed within a nuclear reactor core to promote a longer core life and higher operating power capability for advanced PWRs. For twophase flow operation it is of particular importance to maintain the hydraulic stability. The realization of stable operation is dependent on the accurate determination of pressure drop. In forced convective flow, losses through sudden contractions and enlargements can usually be neglected or, at least, considered of minor importance. However, in natural convection, these losses may consistute a significant portion of the total pressure drop. In the present work, a series of experiments were carreid out to investigate the effects of the void fraction and the entrance geometry of sudden contraction on the pressure drop in horizontal air-water flow. Four test sections were made to simulate typical entrance geometries of sudden contraction, and pressure drops were measured with each test section in horizontal air-water flow for various flow rates and void fractions under atmospheric condition. In the case of two-phase flow, a set of experimentally determined pressure drop due to a sudden contraction of each different entrance geometry in airwater flow were compared with predicted values obtained from the Homogeneous and Hoopes`` models. The result shows that the agreement between the experimental data and the Hoopes`` model is better than that of Homogeneous model.