Convectional heat transfer characteristics of single-phase natural circulation flow in a narrow rectangular channel

To investigate the heat transfer characteristic of single-phase natural circulation flow in a one-side heating narrow rectangular channel, experiments were performed at pressures of 0.2 and 0.3 MPa, at an inlet sub-cooling temperature from 35 K to 60 K, and heat flux from 30 kW/m2 to 90 kW/m2. Experimental results indicate that the heat transfer coefficient agrees with the predictions of the Gnielinski correlation, and 92% of the experimental results are within a ±20% error range of the correlation predictions. The heat transfer performance was investigated by introducing the Stanton number. The heat transfer coefficient increased with an increase in heat flux and a decrease in inlet sub-cooling. For upward natural circulation flow in a narrow rectangular channel, the increase in buoyancy induced by increasing the inlet sub-cooling resulted in the relaminarization effect, leading to a passive effect on heat transfer. However, the increase in thermal driven force induced by increasing heat flux makes the boundary layer unstable, thereby enhancing heat transfer. © 2017, Editorial Department of Journal of HEU. All right reserved.