UBC Theses and Dissertations
Flow characteristics of single and double liquid jet impingement Mohajer, Behzad
In the past few decades, the increasing demands for superior cooling systems in various industries have shifted the focus onto impinging liquid jets as an efficient, powerful cooling technique. Although much has been done on the thermal aspects of jet impingement, the available knowledge still lacks an in-depth understanding of the fluid dynamics involved in the phenomena that dictate the associated transport mechanisms. The present thesis has been planned to study the fluid dynamics of the interaction between a liquid, free-surface impinging jet with a solid surface, and also with a neighboring jet. The circular hydraulic jump as a key feature of a free-surface jet impingement was analyzed. The focus was given to the influence of the target plate on the behavior of the hydraulic jump. Two conditions for the target plate were examined: large plates with capillary limit at the edge, and also small target plates. It was experimentally and theoretically discussed that the circular jumps with these two conditions exhibit different behaviors from those presented in the literature. Furthermore, a systematic Froude number analysis on circular hydraulic jumps was carried out and the significant differences between circular jumps and the open-channel jumps were Highlighted. It was shown that due to the significant influence of the surface tension in circular jumps, the critical Froude number differs from that observed in the classical jumps and could be larger than unity. Moreover, the interaction between the flow fields formed by two jets impinging on a solid surface was investigated in detail. Understanding of this interaction is of significant importance due to the promising potentials of multiple jets for high heat flux applications. Two different configurations were studied: two vertical jets, and two inclined jets. The fluid dynamics involved in the collision between two thin liquid films formed on the surface was theoretically analyzed. A systematic experimental study was also carried out to examine the effects of different parameters on the flow field interaction. The experimental results were then compared to the theoretical predictions to verify the presented models. Good agreements were observed between the presented theory and the experimental data.
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