<p>The main purpose of this research is to investigate liquid entrainment mechanisms of annular flow by computational fluid dynamics (CFD) techniques. A numerical model is developed. The model is based on the physics of an upward annular flow. In the modeling, a transient renormalization group (RNG) k-å model in conjunction with enhanced wall treatment method was employed. In order to reconstruct the two-phase interface, the geometric reconstruction scheme of volume of fluid (VOF) model was adopted. Fluent® 6.18 was used as the solution tool. Simulation results indicated that disturbance waves were generated first on the two-phase interface and their evolution eventually resulted in the liquid entrainment phenomena. The most significant accomplishment of this work is that details of the entrainment mechanisms are well described by the numerical simulation work. In addition, two new entrainment mechanisms are presented. One entrainment mechanism demonstrates that the evolution of individual waves causes the onset of liquid entrainment; the other mechanism shows that the coalescence of two adjacent waves (during the course of their evolution) plays an important role in the progression of liquid entrainment. The newly developed entrainment mechanisms are based on conservation laws.
In order to explore the flow physics of the targeted annular flow, the law of the wall, in conjunction with an analytical model based on a force balance, was applied to previously collected experimental data. Results indicated that the film flow had strong features of near-wall flow. In addition, based on prior experimental work and a newly developed physical wave model by researchers in the Microgravity Research Group, University of Saskatchewan, a steady RNG k-å model, in conjunction with the enhanced wall treatment method, was applied to the gas core. The simulation results showed turbulent flow features in the gas core and strong effects of the interfacial waves on the simulation results. The above information forms the physical foundation for the simulation work on the entrainment mechanism.</p><p>One significant contribution to the authors research group is the liquid entrainment fraction data. A new method was introduced to make the measurements. The method combined a chemically-based titration method with a newly-designed instrument, a separator, to effectively measure the entrainment fraction. Experiments were conducted at low system pressure (~ 1 atm) and relatively low gas and liquid superficial velocities (Vsg = 25.8 m/s to 45.5 m/s, and Vsl = 0.15 m/s to 0.30 m/s, respectively). The entrainment fraction was found to be under 7 %, with a maximum uncertainty of 0.26 % for all the experimental set points. Repeatability test results and comparisons with previous entrainment data indicated that the new technique can perform as well as other measurement techniques.</p>
| Identifer | oai:union.ndltd.org:USASK/oai:usask.ca:etd-05302005-182511 |
| Date | 01 June 2005 |
| Creators | Han, Huawei |
| Contributors | Shedd, Tim, Pugsley, Todd, Gabriel, Kamiel S., Dolovich, Allan T., Bugg, James D., Sumner, David |
| Publisher | University of Saskatchewan |
| Source Sets | University of Saskatchewan Library |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-05302005-182511/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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