Two-Phase flow characteristics of pressure drop and flow pattern change for flow from a small round tube across the sudden expansion into rectangular channel
| Autor: | Chih-yung Tseng, 曾智勇 |
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| Rok vydání: | 2009 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 97 Recently, the advances of the high performance electronic devices have been resulted a great demand in developing efficient heat removal techniques for dissipating increasingly large heat flux from compact heat exchangers in small rectangular channels. In the limited space of compact heat exchangers, the adjacent channels can be connected by abrupt flow area changes. Due to the nature of the geometries involved, the flow would induce a region of flow separation and cause significant pressure loss at the abrupt flow area change. The knowledge of frictional pressure drop and flow characteristics at the abrupt flow area change is very needed for the design of such compact heat exchangers. However, very few data are available for the two-phase flow pressure drop at the sudden expansion and contraction in smaller rectangular channels. Therefore, this research is proposed to visualize the flow structure and measure the two-phase pressure drop at the sudden expansion in small rectangular channels. The effects of the aspect ratio of the rectangular test section, area ratio, flow rate and gas quality for flow across the abrupt flow area change will be considered in this study. The test sections will also be arranged in horizontal longitudinal and transverse orientations to see the influence of gravity force on the flow pattern and pressure drop. Seven test sections are made of transparent acrylic resin, so that the flow pattern and flow structure could be visualized. The test sections have the same overall structures with 6x2, 6x4, 4x2, 4x4. The four rectangular channels are connected with a 2 mm diameter tube, 9x3, 6x3, 3x6 are connected with a 3 mm diameter tube. The area of the tube is smaller than the area of the rectangular channels. As fluid flows into the tube and then enters the rectangular channel, it will observe a sudden expansion at the interconnection between the round tube and the rectangular channel. The total mass flux of the air-water mixture is ranged from 500 to 2000 kg/m2.s and quality is changed from 0.01 to 0.7. Based on the obtained data of void fraction, generated flow regime and frictional loss, the adequacy of the existing predictive methods will be examined and their differences will be discussed. In addition, the two-phase frictional pressure drop data at the sudden expansion will be correlated to propose correlations for the prediction of two-phase pressure drops at the sudden expansion. The flow separation and flow pattern change at the sudden expansion and contraction will be visualized for the interpretation of the large pressure change in the sudden expansion areas. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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