Two-Phase Flow Instability for Low-Flow Boiling in Vertical Uniformly Heated Thin Rectangular Channels

Flow experiment and analysis were performed to determine flow instability condition in a single thin vertical rectangular flow channel (1.98 mm in channel gap, 50.8mm in width, and 121.92 or 60.96 cm in heated height), which represents one of the Advanced Test Reactor’s inner coolant channels between fuel plates. The maximum surface heat flux and flow rate are 159.8kW/m² and 462.5 kg/s-m², respectively, which simulates decay heat removal from the single heated surface of the Advanced Test Reactor. The tests are conducted at atmospheric and subatmospheric pressure, simulating expected conditions during a hypothetical loss-of-coolant accident. The precursor of the flow instability [the point of net void generation and the onset of flow instability (OFI) defined by Saha and Zuber] was compared, and the OFI map (power density versus minimum mass flux at OFI) was developed in this study.