Flow Structure and Pressure Loss for Two Phase Flow in Return Bends

1984 ◽  
Vol 106 (1) ◽  
pp. 30-37 ◽  
Author(s):  
K. Hoang ◽  
M. R. Davis
Keyword(s):  
Flow Structure ◽  
Pressure Loss ◽  
Single Phase ◽  
Velocity Slip ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Two Phase ◽  
Phase Loss ◽  
Loss Coefficients ◽  
Flow Effects

Experimental observations of flow structure and pressure loss have been made for froth flow within 180 deg circular pipe bends. Within the bend the distributions of pressure observed reflected the onset of rotation and phase separation effects, whilst secondary flow effects were apparent in the voidage distributions at outlet. Significant components of the overall pressure drop were found both within the bend itself and in the pipe immediately downstream of the bend. Velocity slip between gas and liquid was found to increase observed loss coefficients by approximately 10 percent. The overall loss coefficients were substantially larger than in single phase flow, particularly for bends with larger radius of centerline curvature where they increased by as much as five times the single phase value. The overall pressure loss coefficients were highest for the sharper radius bends, and it was deduced that flow separation and remixing contributed mainly to the increase over single phase loss coefficients.

Measurement of Pressure Loss Throughout a Clogged Steam Generator Tube Support Plate in Single Phase Flow

2010 ◽  
Author(s):  
Olivier Brunin ◽  
Geoffrey Deotto ◽  
Franck David ◽  
Joe¨l Pillet ◽  
Gilles Dague ◽  
...  
Keyword(s):  
Pressure Loss ◽  
Single Phase ◽  
Experimental Approach ◽  
Two Phase Flow ◽  
Loss Coefficient ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Steam Generators ◽  
Two Phase ◽  
Pressure Loss Coefficient

After a period of several years of operation, steam generators can be affected by fouling and clogging. Fouling means that deposits of sludge accumulate on tubes or tube support plates (TSP). That results in a reduction of heat exchange capabilities and can be modelled by means of a fouling factor. Clogging is a reduction of flow free area due to an accumulation of sludge in the space between TSP and tubes. The increase of the clogging ratio results in an increase of the overall TSP pressure loss coefficient. The link between the clogging ratio and the overall TSP pressure loss coefficient is the most important aspect of our capability to accurately calculate the thermal-hydraulics of clogged steam generators. The aim of the paper is to detail the experimental approach chosen by EDF and AREVA NP to address the calculation uncertainties. The calculation method is classically based on the computation of a single-phase (liquid-only) pressure loss coefficient, which is multiplied by a two-phase flow factor. Both parameters are well documented and can be derived on the basis of state of the art methods such as IDEL’CIK diagrams and CHISHOLM formula. The experimental approach consists of a validation of the correlations by performing tests on a mock-up section with an upward flow throughout a vertical array of tubes. A mixture of water and vapour refrigerant R116 is used to represent two-phase flows. The tube bundle is composed of a 25 tubes array in a square arrangement. The overall height of the mock-up is 2 m. Eight test TSPs were manufactured, considering eight different clogging configurations: six plates with a typical clogging profile at six clogging ratios (0, 44%, 58%, 72%, 86%, 95%), and two plates with a clogging ratio of 72% associated with two different clogging profiles (large bending radius profile and rectangular profile). A series of tests were performed in 2009 in single-phase flow conditions. Two-phase flow tests with a mixture of liquid water and vapour refrigerant R116 will be performed in 2010. The paper illustrates the main results obtained during the single-phase tests performed in 2009.

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.

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