Effects of Increasing Particle Loading in an Axisymmetric, Vertical, Liquid-Solid Sudden Expansion Flow

1999 ◽  
Vol 121 (1) ◽  
pp. 171-178 ◽  
Author(s):  
Maria Founti ◽  
Thomas Achimastos ◽  
Athinodoros Klipfel
Keyword(s):  
Single Phase ◽  
Particle Dispersion ◽  
Solid Particles ◽  
Sudden Expansion ◽  
Wall Region ◽  
Phase Flow ◽  
Particle Loading ◽  
Single Phase Flow ◽  
Two Phase ◽  
Flow Mechanisms

Measurements of particle and fluid velocities are reported for a turbulent, liquid-solid, sudden expansion flow flowing in the direction of gravity and laden with solid particles, at loadings equal to 1, 2, 3, 4, and 5 percent per volume. The measured two-phase flow velocities are compared to the characteristics of the corresponding single phase flow. Forces and flow mechanisms affecting particle dispersion in the various flow regimes are identified and it is indicated that there exist regions where the transverse Saffman lift force attains high values and controls particle dispersion. A consistent correlation between the mean reattachment point and the volumetric particle loading is indicated. All the two phase flows examined reattached upstream the corresponding mean reattachment location measured for the single phase flow. Increasing particle concentration affected locally the flow behaviour, with most obvious consequences within the recirculation zone and the near wall region.

An Experimental Investigation of Gas-Liquid Heat Transfer in Rectangular Micro-Channels

2013 ◽  
Author(s):  
Sira Saisorn ◽  
Somchai Wongwises ◽  
Piyawat Kuaseng ◽  
Chompunut Nuibutr ◽  
Wattana Chanphan
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Two Phase ◽  
Camera System ◽  
Micro Channels ◽  
Flow Mechanisms

The investigations of heat transfer and fluid flow characteristics of non-boiling air-water flow in micro-channels are experimentally studied. The gas-liquid mixture from y-shape mixer is forced to flow in the 21 parallel rectangular microchannels with 40 mm long in the flow direction. Each channel has a width and a depth of 0.45 and 0.41 mm, respectively. Flow visualization is feasible by incorporating the stereozoom microscope into the camera system and different flow patterns are recorded. The experiments are performed under low superficial velocities. Two-phase heat transfer gives better results when compared with the single-phase flow. It is found from the experiment that heat transfer enhancement up to 53% is obtained over the single-phase flow. Also, the change in the configuration of the inlet plenum can result in the different two-phase flow mechanisms.

Experimental Study on Heat Transfer of Single-Phase Flow and Boiling Two-Phase Flow in Vertical Narrow Annuli

2002 ◽  
Author(s):  
Suizheng Qiu ◽  
Minoru Takahashi ◽  
Guanghui Su ◽  
Dounan Jia
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Two Phase Flow ◽  
Annular Channel ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Narrow Annuli ◽  
Narrow Gaps

Water single-phase and nucleate boiling heat transfer were experimentally investigated in vertical annuli with narrow gaps. The experimental data about water single-phase flow and boiling two-phase flow heat transfer in narrow annular channel were accumulated by two test sections with the narrow gaps of 1.0mm and 1.5mm. Empirical correlations to predict the heat transfer of the single-phase flow and boiling two-phase flow in the narrow annular channel were obtained, which were arranged in the forms of the Dittus-Boelter for heat transfer coefficients in a single-phase flow and the Jens-Lottes formula for a boiling two-phase flow in normal tubes, respectively. The mechanism of the difference between the normal channel and narrow annular channel were also explored. From experimental results, it was found that the turbulent heat transfer coefficients in narrow gaps are nearly the same to the normal channel in the experimental range, and the transition Reynolds number from a laminar flow to a turbulent flow in narrow annuli was much lower than that in normal channel, whereas the boiling heat transfer in narrow annular gap was greatly enhanced compared with the normal channel.

Two-Phase Flow Behavior in Channels With Sudden Area Change Using Experimental and Computational Approach

2017 ◽  
Author(s):  
Ashish Kotwal ◽  
Che-Hao Yang ◽  
Clement Tang
Keyword(s):  
Experimental Data ◽  
Pressure Drop ◽  
Experimental Analysis ◽  
Single Phase ◽  
Computational Analysis ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Two Phase ◽  
Flow Rates ◽  
Area Change

The current study shows computational and experimental analysis of multiphase flows (gas-liquid two-phase flow) in channels with sudden area change. Four test sections used for sudden contraction and expansion of area in experiments and computational analysis. These are 0.5–0.375, 0.5–0.315, 0.5–0.19, 0.5–0.14, inversely true for expansion channels. Liquid Flow rates ranging from 0.005 kg/s to 0.03 kg/s employed, while gas flow rates ranging from 0.00049 kg/s to 0.029 kg/s implemented. First, single-phase flow consists of only water, and second two-phase Nitrogen-Water mixture flow analyzed experimentally and computationally. For Single-phase flow, two mathematical models used for comparison: the two transport equations k-epsilon turbulence model (K-Epsilon), and the five transport equations Reynolds stress turbulence interaction model (RSM). A Eulerian-Eulerian multiphase approach and the RSM mathematical model developed for two-phase gas-liquid flows based on current experimental data. As area changes, the pressure drop observed, which is directly proportional to the Reynolds number. The computational analysis can show precise prediction and a good agreement with experimental data when area ratio and pressure differences are smaller for laminar and turbulent flows in circular geometries. During two-phase flows, the pressure drop generated shows reasonable dependence on void fraction parameter, regardless of numerical analysis and experimental analysis.

Turbulence Structure of a Liquid-Solid Two-Phase Jet by Means of Laser Techniques

2003 ◽  
Author(s):  
Toshimichi Arai ◽  
Naoki Kudo ◽  
Tsuneaki Ishima ◽  
Ismail M. Youssef ◽  
Tomio Obokata ◽  
...  
Keyword(s):  
Particle Size ◽  
Single Phase ◽  
Two Phase Flow ◽  
Volume Ratio ◽  
Water Phase ◽  
Phase Flow ◽  
Size Discrimination ◽  
Single Phase Flow ◽  
Particle Volume ◽  
Two Phase

Characteristics on particle motion in a liquid-solid two-phase jet flow were studied in the paper. The water jet including glass particle of 389 μm in mean diameter was injected into water bath. The experimental conditions were 0.21% of initial particle volume ratio, 5mm in pipe diameter and 1.84 m/s of mean velocity on outlet of the jet. A laser Doppler anemometer (LDA) with size discrimination was applied for measuring the time serious velocities of the single-phase flow, particle and water phase flow. A particle image velocimetry (PIV) was also applied in the two-phase flow. The normal PIV method can hardly measure the particle size and perform the particle size discrimination. In the experiment, using the gray scales related with the scattering light intensity, measuring method with size discrimination in two-phase flow was carried out. The experimental results show less difference between velocities of single-phase flow and water-phase flow under this low particle volume ratio condition. Particles have the relative motion with the water-phase and large rms velocity. The PIV used in this experiment, which is called multi-intensity-layer-PIV: MILP, can measure water-phase velocity with good accuracy.

Bubble-Driven Convection Around Cylinders Confined in a Channel

2003 ◽  
Author(s):  
Yuichi Murai ◽  
Toshio Sasaki ◽  
Masa-aki Ishikawa ◽  
Fujio Yamamoto
Keyword(s):  
Particle Tracking Velocimetry ◽  
Single Phase ◽  
Bubble Velocity ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Two Phase ◽  
Detailed Mechanism ◽  
Bubble Distribution ◽  
Measurement Results ◽  
Rectangular Chamber

This paper concerns with flow visualization and image measurement of bubbly flows around various shapes of cylinders. A coaxial confined double rectangular chamber is constructed in order to provide a wide two-dimensional uniform bubble distribution upstream of the obstacle. The experiment shows that a wide two-phase convection is induced around the obstacle, though such an effect is not observed in research on the single-phase flow around objects. The spatial scale of the two-phase convection depends sensitively on the shape of the obstacle. Dense arrangement of cylinders is also investigated to find the interaction among the convection. The measurement results of void fraction, bubble velocity and liquid phase flow, which are obtained by image processing including particle tracking velocimetry (PTV), explore the detailed mechanism of generating the convection.

Mini- and Microchannel Research in Sweden

2003 ◽  
Author(s):  
Bjo¨rn Palm
Keyword(s):  
Heat Exchangers ◽  
Single Phase ◽  
Single Channels ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Two Phase ◽  
Compact Heat Exchangers ◽  
Micro Channels ◽  
Parallel Channels ◽  
Institute Of Technology

The purpose of the present paper is to present research and development within the area of mini- and micro channels in Sweden. A review is made of the historical development of highly compact heat exchangers within the country, starting with plate heat exchangers. The main focus is on the research performed at the Royal Institute of Technology, where mini-channel research has been going on since more than ten years. Single-phase flow as well as two-phase flow is treated, both in single channels and in full-size heat exchangers with multiple parallel channels.

Research on Two-Phase Flow Induced Vibration Characteristics of U-Tube Bundles

2017 ◽  
Author(s):  
Jiang Nai-bin ◽  
Gao Li-xia ◽  
Huang Xuan ◽  
Zang Feng-gang ◽  
Xiong Fu-rui
Keyword(s):  
Upper Bound ◽  
Single Phase ◽  
Two Phase Flow ◽  
Tube Bundle ◽  
Upper Bounds ◽  
Vibration Response ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Two Phase ◽  
Tube Bundles

In steam generators and other heat exchangers, there are a lot of tube bundles subjected to two-phase cross-flow. The fluctuating pressure on tube bundle caused by turbulence can induce structural vibration. The experimental data from a U-tube bundle of steam generator in air-water flow loop are analyzed in this work. The different upper bounds of buffeting force are used to calculate the turbulence buffeting response of U-tubes, and the calculation results are compared with the experimental results. The upper bounds of buffeting force include one upper bound based on single-phase flow, and two upper bounds based on two-phase flow. It is shown that the upper bound based on single-phase flow seriously underestimated the turbulence excitation, the calculated vibration response is much less than the experimental measurement. On the other hand, the vibration response results calculated with the upper bounds based on two-phase flow are closer to the measured results under most circumstances.

Phase Doppler anemometry measurements and analysis of turbulence modulation in dilute gas–solid two-phase shear flows

2010 ◽  
Vol 663 ◽  
pp. 434-455 ◽  
Author(s):  
FEI LI ◽  
HAIYING QI ◽  
CHANGFU YOU
Keyword(s):  
Linear Relationship ◽  
Single Phase ◽  
Particle Mass ◽  
Sudden Expansion ◽  
Phase Flow ◽  
Two Phase ◽  
Turbulence Modulation ◽  
Fluctuation Velocity ◽  
Phase Doppler Anemometry ◽  
Dilute Gas

Flow velocities of a dilute gas–solid two-phase flow in a vertical sudden expansion were measured using phase Doppler anemometry to study the behaviour of the turbulence modulation for the stronger shear for various particle mass loadings, inlet Reynolds numbers and particle diameters. The measurements show that the particles changed the gas turbulence by elongation of the entire gas flow field in the downstream direction, which displaced the axial profile of the section-averaged fluctuation velocity in comparison with that of the single-phase flow, and by either the particle inertia reducing the local turbulence or the wake eddy effects enhancing the turbulence. Both mechanisms resulted in an apparent turbulence modulation, which has not been referred to in the related literature, and have led to an ambiguous understanding of turbulence modulation. The elongation and inlet effects should be eliminated to estimate whether the gas turbulence was really modified. The linear relationship between the gas mean velocity gradient and the root-mean-square fluctuation velocity, which was found to be similar to that in single-phase flows, gradually disappeared as the flow developed and the shear intensity reduced. The linear relationship also varied with different conditions. Specifically, the turbulence modulation was enhanced by higher particle mass loadings and the linear relationship disappeared with increasing particle mass loading. This linearity can perhaps be regarded as a criterion for determining the effect of stronger turbulence modulation.

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