Experimental and theoretical investigations on reverse flow characteristics in vertically inverted U-tube steam generator under transient condition

In order to study the reverse flow characteristics in U-tubes of steam generator in the natural circulation case, the code RELAP5/MOD3.3 is used to model and calculate single-phase water flow for PWR under some typical operating conditions in the natural circulation case. The U-tubes of steam generator are classified according to their length and then are divided into different nodes and flow lines. The calculated results show that reverse flow exists in some inverted U-tubes of the steam generator, the natural circulation capacity of the primary coolant circuit system declines and the calculated net mass flux of the natural circulation accords with the experimental data. The traditional lumped parameter method can not simulate the reverse flow characteristics in inverted U-tubes and its result is much greater than the experimental data. When the steam generator outlet pressure is higher than inlet pressure, and gravitational pressure drop is lower than the total of frictional pressure drop and area change pressure drop, the reverse flow will occur. As to the nuclear power plant described in this paper, the mass flux of the shorter U-tubes drops more quickly and at last reverse flow will occur. The temperature distribution is uniform in inverted U-tubes, and it is almost identical with that of SG in secondary side. The occurrence of reverse flow can be judged by that whether the steam generator inlet temperature is lower than reactor outlet temperature obviously. It is indicated that reverse flow occurred in the U-tubes of the steam generator reduces the mass flux in the natural circulation system.

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Homotopy pertubation method analysis to MHD flow of a radiative nanofluid with viscous dissipation and ohmic heating over a stretching porous plate

Thermal Science ◽

10.2298/tsci150731209k ◽

2018 ◽

Vol 22 (1 Part B) ◽

pp. 413-422 ◽

Cited By ~ 2

Author(s):

Hitesh Kumar

Keyword(s):

Boundary Layer ◽

Viscous Dissipation ◽

Reverse Flow ◽

Ohmic Heating ◽

Complete Solution ◽

Porous Plate ◽

Flow Characteristics ◽

Mhd Flow ◽

Future Research ◽

Layer Flow

An analytical study is performed to explore the flow and heat transfer characteristics of nanofluid (Al2O3-water and TiO3-water) over a linearly stretching porous sheet in the presence of radiation, ohmic heating, and viscous dissipation. Homotopy perturbed method is used and complete solution is presented, the results for the nanofluids velocity and temperature are obtained. The effects of various thermophysical parameters on the boundary-layer flow characteristics are displayed graphically and discussed quantitatively. The effect of viscous dissipation on the thermal boundary-layer is seen to be reverse after a fixed distance from the wall, which is very strange in nature and is the result of a reverse flow. The finding of this paper is unique and may be useful for future research on nanofluid.

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Numerical Study on Supersonic Combustor with an Allotype Cavity

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.694.187 ◽

2014 ◽

Vol 694 ◽

pp. 187-192

Author(s):

Jin Xiang Wu ◽

Jian Sun ◽

Xiang Gou ◽

Lian Sheng Liu

Keyword(s):

Alternative Model ◽

Numerical Study ◽

Reverse Flow ◽

Three Dimensional ◽

Flow Characteristics ◽

Experimental Result ◽

Navier Stokes ◽

Cold Flow ◽

Hypersonic Inlet ◽

Good Agreement

The three-dimensional coupled explicit Reynolds Averaged Navier–Stokes (RANS) equations and the two equation shear-stress transport k-w (SST k-w) model has been employed to numerically simulate the cold flow field in a special-shaped cavity-based supersonic combustor. In a cross-section shaped rectangular, hypersonic inlet with airflow at Mach 2.0 chamber, shock structures and flow characteristics of a herringbone-shaped boss and a herringbone-shaped cavity models were discussed, respectively. The results indicate: Firstly, according to the similarities of bevel-cutting shock characteristics between the boss case and the cavity case, the boss structure can serve as an ideal alternative model for shear-layer. Secondly, the eddies within cavity are composed of herringbone-spanwise vortexes, columnar vortices in the front and main-spanwise vortexes in the rear, featuring tilting, twisting and stretching. Thirdly, the simulated bottom-flow of cavity is in good agreement with experimental result, while the reverse flow-entrainment resulting from herringbone geometry and pressure gradient. However, the herringbone-shaped cavity has a better performance in fuel-mixing.

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CFD investigation on reverse flow characteristics in U-tubes under two-phase natural circulation

Progress in Nuclear Energy ◽

10.1016/j.pnucene.2019.03.005 ◽

2019 ◽

Vol 114 ◽

pp. 145-154

Author(s):

Xi Chu ◽

Wenzhen Chen ◽

Yanlong Shang ◽

Jianli Hao ◽

De Zhang

Keyword(s):

Reverse Flow ◽

Natural Circulation ◽

Flow Characteristics ◽

Two Phase

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Numerical simulation of the stalled flow within a vaned centrifugal pump

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1177/095440620421800407 ◽

2004 ◽

Vol 218 (4) ◽

pp. 425-435 ◽

Cited By ~ 23

Author(s):

K M Guleren ◽

A Pinarbasi

Keyword(s):

Numerical Simulation ◽

Centrifugal Pump ◽

High Speed ◽

Stokes Equations ◽

Reverse Flow ◽

Flow Characteristics ◽

Navier Stokes ◽

Leakage Flow ◽

Navier Stokes Equations ◽

Low Pass

The main goal of the present work is to analyse the numerical simulation of a centrifugal pump by solving Navier-Stokes equations, coupled with the ‘standard k-∊’ turbulence model. The pump consists of an impeller having five curved blades with nine diffuser vanes. The shaft rotates at 890r/min. Flow characteristics are assumed to be stalled in the appropriate region of flowrate levels of 1.31-2.861/s. Numerical analysis techniques are performed on a commercial FLUENT package program assuming steady, incompressible flow conditions with decreasing flowrate. Under stall conditions the flow in the diffuser passage alternates between outward jetting when the low-pass-filtered pressure is high to a reverse flow when the filtered pressure is low. Being below design conditions, there is a consistent high-speed leakage flow in the gap between the impeller and the diffuser from the exit side of the diffuser to the beginning of the volute. Separation of this leakage flow from the diffuser vane causes the onset of stall. As the flowrate decreases both the magnitude of the leakage within the vaneless part of the pump and reverse flow within a stalled diffuser passage increase. As this occurs, the stall-cell size extends from one to two diffuser passages. Comparisons are made with experimental data and show good agreement.

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Numerical simulations for swirlmeter on flow fields and metrological performance

Transactions of the Institute of Measurement and Control ◽

10.1177/0142331216673424 ◽

2016 ◽

Vol 40 (4) ◽

pp. 1072-1081 ◽

Cited By ~ 12

Author(s):

Desheng Chen ◽

Baoling Cui ◽

Zuchao Zhu

Keyword(s):

Vortex Core ◽

Reverse Flow ◽

Pressure Fluctuations ◽

Flow Characteristics ◽

Turbulence Models ◽

Internal Flow ◽

Industrial Applications ◽

Throat Region ◽

Vortex Precession ◽

Metrological Performance

Measurements of flow rates of fluids are important in industrial applications. Swirlmeters (vortex precession meters) are widely used in the natural gas industry because of their advantage in having a large measurement range and strong output signal. In this study, using air as a working medium, computational fluid dynamics (CFD) simulations of a swirlmeter were conducted using the Reynolds-averaged Navier–Stokes (RANS) and renormalization group (RNG) k–ε turbulence models. The internal flow characteristics and the influence of the tube structure (geometric parameter of flow passage) on metrological performance were studied, with a particular focus on the meter factor. Calibration experiments were performed to validate the CFD predictions; the results show good agreement with those from simulations. From the streamline distributions, a clear vortex precession is found in the throat region. At the end of throat, the pressure fluctuation reached a maximum accompanied by the largest shift in the vortex core from the centreline. There exists a large reverse flow zone in the vortex core region in the convergent section. To mitigate the influence of reverse flow on vortex precession, a suitable length of throat is required. For a larger convergent angle, the fluid undergoes higher acceleration leading to an increase in velocity that produces more intensive pressure fluctuations. The minor diameter of the throat also produces a higher velocity and larger meter factor. Compared with both divergent angle and throat length, the convergent angle and throat diameter play a more important role in determining precession frequency.

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Reverse Flow Characteristics of Axial-Flow Pumps

Journal of the Society of Mechanical Engineers ◽

10.1299/jsmemag.64.507_602 ◽

1961 ◽

Vol 64 (507) ◽

pp. 602-610

Author(s):

Tomitaro TOYOKURA

Keyword(s):

Reverse Flow ◽

Flow Characteristics ◽

Axial Flow

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Flow Reversal in a Horizontal Type Natural Circulation Heat Recovery Steam Generator

Volume 4: Cycle Innovations; Electric Power; Industrial and Cogeneration; Manufacturing Materials and Metallurgy ◽

10.1115/gt2006-90689 ◽

2006 ◽

Cited By ~ 3

Author(s):

Heimo Walter ◽

Wladimir Linzer

Keyword(s):

Steam Generator ◽

Heat Recovery ◽

Reverse Flow ◽

Natural Circulation ◽

Heating Surface ◽

Heat Absorption ◽

System Pressure ◽

Horizontal Type ◽

The Stability ◽

The Individual

Natural circulation heat recovery steam generators (HRSG) are used in many applications for the thermal recycling of the waste flue gas. Many of these boilers are designed as a horizontal type HRSG (see fig. 1). The evaporator of such a steam generator is characterized by an array of parallel tubes with different heat input. The paper presents the results of a theoretical stability analysis for a HRSG with a vertical tube bank. For the horizontal type HRSG the static instability, namely the reverse flow was analysed. The study was done at low system pressures and under hot start-up conditions for the boiler. The investigations show the influence of the geometry, the system pressure and the heat absorption of the individual tubes in the evaporator on the stability of the boiler. The aim of the study was to find design criteria to avoid reverse flow in the tubes of the evaporator. Addition of flow resistance at certain locations of the evaporator can improve the stability. A higher stability will be also achieved by the homogenization of the heat absorption in the individual layers of the bundle heating surface.

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