The plate-type fuel element is widely used in ship-based nuclear reactors. The typical coolant channel in such reactor is a narrow rectangular one with a relatively large aspect ratio. The thermal-hydraulic characteristics in narrow rectangular channels may be different from that in conventional pipe. It could be expected that the geometry of narrow channels has some impact on the bubble behaviors in subcooled flow boiling.

In this paper, the bubble behaviors were simulated by using CFD software FLUENT in narrow rectangular channel with different widths under both stagnation conditions and flow conditions. The main concern was placed on the parameters of bubble departure time, departure diameter and departure velocity.

In the model setup process, the VOF model and PISO algorithm were selected. The results were compared against the experimental data and showed the models good capability of capturing the interface between gas and liquid. Furthermore, for stagnation cases, the width of the channel played an important role for bubble departure diameter. In flow cases, the width also had a great impact on departure diameter and departure velocity as well. The departure time and departure velocity showed strong relevance with each other under different contact angle conditions.

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