Longitudinal Vortex (LV) is produced by Longitudinal Vortex Generators (LVGs) with high heat transfer efficiency and acceptable pressure loss. Due to the relative long influence distance and simple structure, LVGs may be used in narrow channels with flat surface under high temperature and high pressure water medium, in this paper, the critical heat flux (CHF) is one of most important focus. The test channel has the size of 600 mm (length) × 40 mm (width) × 3 mm (height), was used to research the CHF characteristic of CHF affected by LVGs. The test channel is visual in three sides and remains one side for power supply. The LVGs used in the experiments are 14 mm (length) × 2.2 mm (width) × 1.8 mm (height) in dimensions, and periodically mounted on the inner wall of the steel plate. The parameters that are varied during the experiments as follows, system pressure from 0.43 to 0.85 MPa, inlet mass flow flux from 40.2 to 745.7 kg·m−2·s−1, inlet subcooling from 46.8 to 104.2 °C, exit quality from 0.183 to 0.997, surface heat flux from 0.294 to 2.316 MW·m−2. The experiments show that the CHF is improved by 24.3% while the total pressure drop through the test section is improved by 62.9%. The bubble growth and its evolutionary process in narrow rectangular channel with LVGs have been obtained during a short term when the CHF occurs, and it is found that the bubbles have been affected intensely by LV. Based on these experiment data, the growth and aggregation of bubbles have been depressed by LV, the mass, momentum and energy exchange between cold and hot areas in the test section have been strengthened. As a result, the heat transfer enhancement by LV can be explained by the destruction of thermal boundary layer.

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