Chaoxing Yan

Two-Phase Slug Flow in a Narrow Rectangular Channel Under Inclined Conditions

The characteristics of two-phase slug flow in a narrow rectangular channel with cross section of 3.25 mm × 43 mm under vertical and inclined conditions are investigated using a high speed video camera system. It is found that the velocity of Taylor bubble in vertical continuous slug flow could be well predicted by the Nicklin et al. (1962) correlation, in which C0 is given by the correlation of Ishii (1977), and the drift velocity given by the correlation of Sadatomi et al. (1982) or Clanet et al. (2004). For low two-phase superficial velocity (FrTP ≤ 3.5), the Taylor bubble velocities gradually increase with the increasing in inclination angles and almost approximate the maximum value for θ = 30°. For high two-phase superficial velocity (FrTP > 3.5), the influence of the inclination angles on the Taylor bubble velocity is insignificant, and the bubble velocity under vertical condition is slight lower than those under inclined conditions. For the inclined cases, the nose of Taylor bubble is deviated from the centerline and its position is the function of the two-phase superficial velocity as well as the inclination angle.Copyright

Experimental Study on Resistance Characteristics in a 3 × 3 Rod Bundle

Experimental study on resistance of air-water two-phase flow in a vertical 3 × 3 rod bundle was carried out under normal temperature and pressure. The rod diameter and pitch were 8 mm and 11 mm, respectively. The ranges of gas and liquid superficial velocity were 0.013∼3.763 m/s and 0.076∼1.792 m/s, respectively. The result indicated that the existing correlations for calculating frictional coefficient in the rod bundle and local resistance coefficient could not give favorable predictions on the single-phase experimental data. For the case of two-phase flow, eight correlations for calculating two-phase equivalent viscosity poorly predicted the frictional pressure drop, with the mean absolute errors around 60%. Meanwhile, the eight classical two-phase viscosity formulae were evaluated against the local pressure drop at spacer grid. It is shown that Dukler model predicted the experimental data well in the range of Rel<9000 while McAdams correlation was the best for Rel⩾9000. For all the experimental data, Dukler model provided the best prediction with MRE of 29.03%. Furthermore, approaches to calculate two-phase frictional pressure drop and local resistance were proposed by considering mass quality, two-phase Reynolds number and densities in homogenous flow model, resulting in a good agreement with the experimental data.Copyright

Characteristics of slug flow in narrow rectangular channels under vertical condition

Gas-liquid slug flow is widely encountered in many practical industrial applications. A detailed understanding of the hydrodynamics of gas slug has important significance for modeling of the slug flow. Non-intrusive flow visualization using a high speed video camera system is applied to study characteristics of slug flow in a vertical narrow rectangular channel (3.25×40 mm2). Ideal Taylor bubbles are hardly observed, and most of the gas slugs are deformed, much more seriously at high liquid superficial velocity. The liquid film thicknesses of left and right narrow sides surrounding gas slug are divergent and wavy, but it has weak effect on liquid film velocity. The gas and liquid velocity as well as the length of gas slug have significant effect on the separating liquid film thickness. The separating liquid film velocity is decreased with the increase of gas superficial velocity at low liquid velocity, and increased with the increase of liquid superficial velocity. The film stops descending and the gas su...

Flow regimes of adiabatic gas-liquid two-phase under rolling conditions

Characteristics of adiabatic air/water two-phase flow regimes under vertical and rolling motion conditions were investigated experimentally. Test sections are two rectangular ducts with the gaps of 1.41 and 10 mm, respectively, and a circular tube with 25 mm diameter. Flow regimes were recorded by a high speed CCD-camera and were identified by examining the video images. The experimental results indicate that the characteristics of flow patterns in 10 mm wide rectangular duct under vertical condition are very similar to those in circular tube, but different from the 1.41 mm wide rectangular duct. Channel size has a significant influence on flow pattern transition, boundary of which in rectangular channels tends asymptotically towards that in the circular tube with increasing the width of narrow side. Flow patterns in rolling channels are similar to each other, nevertheless, the effect of rolling motion on flow pattern transition are significantly various. Due to the remarkable influences of the friction s...

Study on the Characteristics in the Liquid Slug of Rising Slug Flow in Narrow Rectangular Channel

Gas-liquid slug flow is widely encountered in many practical industrial applications. A detailed understanding of the hydrodynamics of the liquid slug is of great importance in modeling the slug flow. A visualized study using a high speed video camera system was conducted to study liquid slug characteristics of slug flow in a vertical narrow rectangular channel (3.25×40mm2). It is found that three regions could be distinguished in the stable liquid slug tagging along the leading gas slug in most cases. The characteristics of a gas slug are greatly influenced by its position in the liquid slug, and the leading slug has a significant effect on the trailing slug in laminar or transition flow. The wake region of leading slug is also actually a sudden enlargement region where the water jet out of the liquid flim. The minimum stable liquid slug length Lmin is obtained in the experiments ranging from 9 to 17Dh in fully developed turbulence flow.Copyright

Experimental Investigation on Bubbly Flow in Rectangular Channel Under Rolling Condition

Experimental study of rolling effects on characteristics of bubbly flow in a rectangular duct (43 mm×3.25 mm×2000 mm) was performed under ambient temperature and pressure. The characteristics of bubbly flow in vertical, inclined and rolling channels have been obtained through visualization and photographic recording. In the experiment, the gas and liquid superficial velocities ranged from 0.07 m/s to 0.15 m/s and from 1.6 m/s to 2.39 m/s respectively. The bubble clusters contained no less than two bubbles exist in vertical, inclined and rolling channels. With the inclined and rolling angle increase, the bubble clusters tend to contain more bubbles. In vertical case, most bubbles aggregate in the intervals near the narrow wall, thus forms high number fraction peaks at the position around 2x/w = ±0.5. As the inclination and rolling angle increase, the bubble number fraction near the lower wall decreases and that near the upper wall increases. In addition, the number fraction peak close to the lower wall disappears and that near the upper wall becomes higher and sharper at the inclined and rolling angle no less than 10°. There exist no significant differences in bubble lateral distribution under inclined and rolling conditions at the same angle. To identify the influence of rolling on bubble lateral distribution, comparison between lateral buoyancy and additional buoyancy is made theoretically. The results show that the influence of additional buoyancy on lateral bubble distribution can be neglected result from the magnitude of lateral buoyancy is much larger than that of additional buoyancy.Copyright