Experimental Study On Boiling Flow Heat Transfer In A Narrow Channel

The channel in the plate fuel assembly of nuclear reactor is commonly a rectangle one, with its width2-3mm. The flow boiling heat transfer in the channel appears as the thermal characteristics in the one dimensional confined space for the existence of space constraint. In the present study, the flow and thermal phenomena in the subcooled flow boiling are investigated experimentally and it has significant role in the engineering and scientific research.The study in this paper is based on the existing experimental system on circular channel flow boiling. In addition, a typical narrow channel test section is designed for the experimental research. The flow and thermal characteristics of boiling in the mini narrow channel at atmospheric pressure are visualized, with DI water as the working fluid. Further more, the experiments focus on the effect of heat flux, fluid subcooling degree, mass flow rate of inlet, etc on the thermal characteristics of the flow boiling in the narrow channel systematically. Meanwhile, study on the bubble dynamics charac-teristics in the channel is also conducted according to the analysis on the images rec-orded by the high speed camera.The experimental results indicated that, within the range of the studied experi-mental parameters, the heat transfer coefficient in flow boiling increases with the inlet mass flow rate while decreases with the subcooling degree. The Rohsenow correlation for flow boiling in large space is revised and the heat transfer correlation for2mm nar-row channel is obtained based on a great amount of experimental data. It is found that the revised correlation is in good agreement with the experimental data. The effect of channel wall subcooling degree, mass flow rate and fluid subcooling rate on the bubble departure diameter, bubble departure frequency and nucleation site density are given in the paper through the study of bubble dynamics characteristics. Additionally, the corre-lation of bubble departure diameter, bubble departure frequency and nucleation site density for the model is revised based on the nucleation boiling bubble dynamics model proposed by Nilanjana Basu. Hence, a more correct subcooled-nucleation boiling corre-lation for2mm narrow channel is obtained. The results in this paper can be generalized to the design and engineering analysis of the thermal-hydraulic characteristics of the plate fuel assembly. Meanwhile, the ob-tained revised bubble dynamics model for subcooled boiling can be coupled with the two-phase flow pattern model to simulate the flow boiling thermal characteristics in the narrow channel accurately. This method, which utilizes the visualization experimental results to achieve the dynamic model correction, not only can be extended to the model investigation for other equipment or structure, but also laid a solid foundation for the study of CHF in the plate element.