| 1. |
- Mei, Y., et al.
(författare)
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A study on steam-water two phase flow distribution in a rectangular channel with different channel orientations
- 2018
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Ingår i: Experimental Thermal and Fluid Science. - : Elsevier Inc.. - 0894-1777 .- 1879-2286. ; 99, s. 219-232
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Tidskriftsartikel (refereegranskat)abstract
- Experimental study on steam-water two phase vertical and inclined upward flow (15–90°) was performed in a rectangular channel with cross section of 17 mm × 10 mm under atmospheric pressure to investigate the phase distribution and the average void fraction in the cross section which were obtained from the local void fraction measurement by a conductivity probe. The inlet superficial velocities of the steam and water varied from 0.72 to 3.85 m/s and from 0.11 to 0.3 m/s respectively. A high speed camera was used to identify the flow patterns. Experimental results show that the phase distribution curves are significantly affected by channel orientation and the average void fraction first decreases and then increases with the increase of orientation. Based on the drift-flux model, two parameters, namely, the distribution parameter (C0) and the drift velocity (Ugm) have been studied in detail. Both the distribution parameter and the drift velocity are found to be functions of orientation. The distribution parameter decreases with the increase of orientation while the drift velocity first increases and then decreases with the increase of orientation., Based on the experimental data, an improved drift-flux model is proposed especially for the slug and churn flow, which predicts the void fraction in an inclined channel with good accuracy.
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| 2. |
- Wang, Ke, et al.
(författare)
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Experimental Study on the Dynamics of a Thin Liquid Film under Shearing Force
- 2017
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Ingår i: Jixie Gongcheng Xuebao/Journal of Mechanical Engineering. - : Chinese Journal of Mechanical Engineering. - 0577-6686. ; 53:24, s. 70-76
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Tidskriftsartikel (refereegranskat)abstract
- The "scales-separation" phenomenon indicates that high heat-flux boiling and boiling crisis is dominated by micro-hydrodynamics of liquid microlayer on the heater surface. The techniques for liquid film measurement such as acoustic methods, nucleonic techniques, electrical methods, and optical methods are discussed in detail. Accordingly, a confocal optical sensor system is used to detect the dynamics of liquid film sheared by the co-flowing air from above in a horizontal aluminum channel. The impact of the gas shearing on film behaviors is analyzed and the integrity of liquid film is discussed in detail. The results indicate that the liquid film thickness decreases due to the entrainment and shows a linear or nonlinear variation under different flow conditions. Additionally, for a specific surface, the critical film thickness for an integral film is found to have no relation with the gas and liquid flow rates but the fluctuation of the liquid film increases with the increasing gas velocity.
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| 3. |
- Wang, Ke, et al.
(författare)
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On the Relation between Nucleation Site Density and Critical Heat Flux of Pool Boiling
- 2018
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Ingår i: Heat Transfer Engineering. - : TAYLOR & FRANCIS INC. - 0145-7632 .- 1521-0537. ; 39:17-18, s. 1498-1506
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Tidskriftsartikel (refereegranskat)abstract
- It is traditionally accepted that the critical heat flux (CHF) decreases with increasing nucleation site density (NSD). However, such a CHF-NSD relation was no longer observed in the BETA-B experiment performed on nano-film heaters; instead the increase of NSD resulted in a gain in CHF. To address this seeming contradiction in the relation between critical heat flux and nucleation site density, the present work employed probabilistic analysis to reveal the different tendencies. A concept of effective NSD was proposed, which concerns the active nucleation sites appear within a bubble lifetime, and the resulting bubbles have the chance of direct interaction. We assumed that the boiling crisis on a heater surface is mainly induced by two mechanisms: dry spot expanding in isolated bubble regime for low-NSD surface, coalescence of dry spots under multiple bubbles in fully developed nucleate boiling regime for high-NSD surface, or a combination of the two in the transition regime for medium-NSD surface. Accordingly, we estimated the critical heat flux of each boiling regime at which the boiling crisis occurs. The result indicated that there is a threshold of nucleation site density below which the increase of NSD is contributing to CHF enhancement, while the trend is inverted beyond the threshold.
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