Experimental And Numerical Investigation Of Subcooled Flow Boiling In Vertical Rectangular Narrow Channel

The phenomenon of subcooled flow boiling can be found in every field of life and industry extensively; Narrow channel is a kind of one-dimensional confined structure, which is widely used in heat exchanger. Because of the effect of channel dimension on bubble dynamics, the characteristics of subcooled flow boiling in narrow channels is different from that of conventional channels. Hence, the classical empirical corrections or models will be invalid. The ability of predicting the rule and development tendency of subcooled flow boiling in narrow channels can provide theoretical references for design and safe operation of heat exchangers, especially for nuclear reactor. The visualization experiments were conducted to study the characteristics of bubble dynamics on the heating surface in rectangular narrow channels and new corrections were proposed. Then numerical simulation was performed with two-fluid model and the new corrections. The results were used to develop a comprehensive description of phenomenon of subcooled flow boiling in rectangular narrow channels.The effects of system parameters on bubbles were studied in detail with visualization experiments. The new wall boiling model was established with four new corrections for ONB (onset of nucleate boiling), active nucleation site density, departure diameter and bubble departure frequency respectively. The comparison between the new corrections or experimental data and the classic correction which proposed based on conventional channels shows the uniqueness of narrow channel. The study for heat transfer associated with bubbles was also involved.The prediction of subcooled flow boiling phenomena in rectangular narrow channel was performed with two-fluid model and wall boiling model. An appropriate option of simulation was made by the sensitivity analysis of the parameters of two-fluid model. ONB model has also been incorporated into the corresponding code, which fills a gap of wall boiling model. Compared the default wall boiling model, the new wall boiling model can yield more accurate numerical results. Further analysis for partition of wall heat flux indicated that the different prediction for quenching heat transfer is the main reason that leads to above results.