Study On The Characteristics Of Single-Phase And Two-Phase Boiling Flow Heat Transfer And Flow Resistance In Tube-Bundle Channels

Liquid-vapor two-phase flow and heat transfer were widely used in heat exchangers of industry of dynamics, nuclear energy, chemistry, petroleum and so on. There were typical problems of two-phase flow in reactor, steam generators, steam turbines and steam condensers. The research of flow and heat transfer characters in tube-bundle channels had an important meaning in improving the safety and economy of steam generators and nuclear reactors. And it was helpful to promote the nationalization level of nuclear power technology, and could ensure the safety and effective utilization of nuclear energy. The thesis attempted to investigate the flow and heat transfer characteristics in this special channel, thus provided a reference basis for the engineering design and application.The research was carried out on the basis of plenty of documents and accumulated research results of our studying team. The experimental bench of tube-bundle channel was set up with the support of National Natural Science Foundation of China. Experimental research and theoretical analysis on single-phase and two-phase boiling flow characteristics and heat transfer were conducted. The main content of research is presented as follows,(1) Experiments were carried out on Onset of Nucleate Boiling (ONB) of R113 flow in vertical and inclined tube-bundle channels. Three means were adopted to ascertain ONB in the experiments. The influences of factors (for example, geometric dimension, heat flux, mass flow rate and the dip angle, etc.) on ONB were investigated. On the foundation of Gad formula, a correlation for calculating the altitude of ONB in tube-bundle channels was put forward, which had a good accordance with the experimental results. In addition, producing conditions of ONB were presented, and an equation to calculate the heat flux of ONB was presented on the basis of experiments. Comparisons between this equation and Bergles & Rohsenow formula and Davis & Anderson formula were made, and their similarities and differences were analyzed.(2) Visualization experiments were conducted on the flow patterns in tube-bundle channels. There were three main flow patterns in the experiments, which were bubble flow, churn flow and annular flow. The influences of geometric dimension on flow patterns and flow pattern transitions were analyzed. On the basis of experimental research, comparative analyses were made on the differences between boiling flow patterns in circular tubes and tube-bundle channels.(2) Experiments were conducted on the characteristics of single-phase and two-phase boiling heat transfer in tube-bundle channels. The influences of factors (for example, geometric dimension, heat flux, mass flow rate, dip angle, Bo number,Nconf number, and heating orientation etc.) on the characteristics of single-phase and two-phase boiling heat transfer in tube-bundle channels were investigate. It was found that the characteristics of single-phase heat transfer in tube-bundle channels were different from that in circular tubes with normal size. It was found that the heat transfer coefficients gained by different data processing methods were different, through analyzing the characteristics of single-phase and two-phase heat transfer. In the experiments, the transition from laminar heat transfer to turbulent heat transfer in tube-bundle channels was earlier than that in normal tubes. The correlations were brought forward to calculate the heat transfer of single-phase and two-phase flow in tube-bundle channels. Comparisons and analyses between these correlations and conclusions of other researchers were carried out.(3) On the basis of experimental research and theoretical analysis, the differences between flow resistance in tube-bundle channel and that in circular or annular channels were discussed. The influences of multi-factors on single-phase flow resistance and boiling pressure drop were analyzed. By amending the formulas of Chisholm B and Tran, equations for calculating single-phase flow resistance and boiling pressure drop in tube-bundle channels were put forward(4) According to the geometric dimension of tube-bundle channels, physical model of sub-channel was set up to describe boiling flow and heat transfer in tube-bundle channels. Simulation was carried out to calculate the velocity field, temperature field and pressure field in tube-bundle channels. Through the comparisons between the calculating results and experimental values, it was shown that the calculation of the physical model set up had a good accordance with the experimental results, and this model could be adopted to simulate boiling flow and heat transfer in tub-bundle channels.