Numerical study of the influence of geometrical characteristics of a vertical helical coil on a bubbly flow

Experiments were carried out at IFREMER Brest to obtain data on the displacement of Steel Catenary Risers (SCR) in the Touch-Down Zone (TDZ) induced by top motion. Measurements were conducted both in the section on the ground (2D motion) and in the section above the touch-down point (3D motion) with an optical tracking system. In the model test, the bottom 1/10 of the riser was represented at a scale of about 1/10. The present paper is focusing on Heave-Induced Lateral Motion (HILM) in the bottom part of the riser. The model riser is based on a full scale case which is first described. Based on Froude’s similitude, the geometrical characteristics of the model are derived. The tracking system and the various instrumentation are then detailed. In the last section, experimental results on one specific case are presented. Numerical calculations with a coupled fluid/structure solver are performed. A comparison for the amplitude and frequencies of HILM is presented. Comments are made on the analogy between the present experiments and some simpler experiments on a one-degree-of-freedom cylinder/spring system sinusoidally excited. Such an analogy should prove itself very fruitful in understanding and quantifying HILM.

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Three Dimensional Numerical Modelling of Staggered Tube Bundle Turbulent Crossflow in Duct

Heat Transfer: Volume 3 ◽

10.1115/ht2005-72532 ◽

2005 ◽

Author(s):

Ahad Ramezanpour ◽

Hassan Shirvani ◽

Ramin Rahmani ◽

Iraj Mirzaee

Keyword(s):

Nusselt Number ◽

Numerical Study ◽

Tube Bundle ◽

Three Dimensional ◽

Cross Flow ◽

Reynolds Numbers ◽

Wall Function ◽

Flat Plates ◽

Geometrical Characteristics ◽

Commercial Code

A numerical study has been conducted to investigate the three dimensional (3D) staggered tube bundle turbulent cross flow confined between two parallel flat plates using RNG k-ε model and standard wall function utilizing commercial code FLUENT. The maximum Reynolds numbers of 1000, 5000, and 50000 and the distance between plates of H = 3, 5, 10, 15, and 20 mm have been considered. The arrangement of the staggered tube bundle is fix with geometrical characteristics of Sn/D = 1.5 and Sp/D = 1.2 which has been found optimum in previous two-dimensional studies. The constant temperature of 360K on tubes, constant inlet flow and plates’ temperature of 300K have been set as the boundary conditions. The global Nusselt number, friction factor for the dissimilar Reynolds numbers, distance between plates, local Nusselt number and different angles on first and third tubes have been evaluated.

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Numerical Study of Natural Convection Heat Loss from Cylindrical Solar Cavity Receivers

ISRN Renewable Energy ◽

10.1155/2014/104686 ◽

2014 ◽

Vol 2014 ◽

pp. 1-7 ◽

Cited By ~ 11

Author(s):

M. Prakash

Keyword(s):

Natural Convection ◽

Cylindrical Cavity ◽

Numerical Study ◽

Three Dimensional ◽

Working Fluid ◽

Helical Coil ◽

Fluid Temperature ◽

Medium Temperature ◽

Inclination Angles ◽

Temperature Levels

The numerical study of the natural convection loss occurring from cylindrical solar cavity receivers is reported in this communication. These cavity receivers can be used with solar dish concentrators for process heat applications at medium temperature levels. Three cylindrical cavity receivers of diameter 0.2, 0.3, and 0.4 m with aspect ratio equal to one and opening ratios of 1 and 0.5 are used for the analysis. Fluent CFD software is used for the analysis of the three-dimensional (3D) receiver models. In this study the receiver tubes within the cylindrical cavity are modeled as a helical coil similar to those existing in actual systems. The flow of the working fluid within the helical coil is also modeled. The simulations are performed for fluid inlet temperatures of 150°C and 250°C and for receiver inclination angles of 0 (sideways-facing cavity), 30, 45, 60, and 90 degree (vertically downward-facing receiver). It is found that the convective loss increases with increasing mean fluid temperature and decreases with, increase in receiver inclination. The convective loss is found to increase with, opening ratio. These observations are true for all cavity receivers analysed here. A Nusselt number correlation involving Rayleigh numbers, receiver inclinations, and opening ratios is proposed for the convective loss.

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Experimental and Numerical Study of the Flow and Heat Transfer in a Bubbly Turbulent Flow in a Pipe with Sudden Expansion

Energies ◽

10.3390/en12142735 ◽

2019 ◽

Vol 12 (14) ◽

pp. 2735 ◽

Cited By ~ 7

Author(s):

Pavel Lobanov ◽

Maksim Pakhomov ◽

Viktor Terekhov

Keyword(s):

Heat Transfer ◽

Liquid Velocity ◽

Numerical Study ◽

Bubbly Flow ◽

Fluid Phase ◽

Reynolds Stress Model ◽

Sudden Expansion ◽

Two Phase ◽

Carrier Fluid ◽

Carrier Liquid

The flow patterns and heat transfer of a downstream bubbly flow in a sudden pipe expansion are experimentally and numerically studied. Measurements of the bubble size were performed using shadow photography. Fluid phase velocities were measured using a PIV system. The numerical model was employed the Eulerian approach. The set of RANS equations was used for modelling two-phase bubbly flows. The turbulence of the carrier liquid phase was predicted using the Reynolds stress model. The peak of axial and radial fluctuations of the carrier fluid (liquid) velocity in the bubbly flow is observed in the shear layer. The addition of air bubbles resulted in a significant increase in the heat transfer rate (up to 300%). The main enhancement in heat transfer is observed after the point of flow reattachment.

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On the Numerical Study of Bubbly Flow Created by Ventilated Cavity

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.29-32.143 ◽

2010 ◽

Vol 29-32 ◽

pp. 143-148

Author(s):

Min Xiang ◽

S.C.P. Cheung ◽

Ji Yuan Tu ◽

Wei Hua Zhang ◽

Yang Fei

Keyword(s):

Flow Field ◽

Void Fraction ◽

Numerical Study ◽

Fluid Model ◽

Bubbly Flow ◽

Bubble Diameter ◽

Flow Region ◽

Valuable Insight ◽

Two Phase ◽

Ventilated Cavity

The aim of the study was to develop a numerical model to reproduce the bubbly flow field created by ventilated cavity which includes three different regions. The model was established based on the Eulerian-Eulerian two-fluid model coupled with a population balance approach which is solved by the Homogeneous Multiple-Size-Group (MUSIG) model to predict bubble size distribution. Base on the model, the simulation was carried out at the experimental condition of Su et al. (1995). Firstly three regions were successfully captured proved by the spatial voidage distribution and streamline shape. Then distributions of void fraction and Sauter mean bubble diameter at various sections below the cavity corresponding to three regions respectively were plotted against experimental data. A close agreement was observed in the void fraction distribution which indicates that qualitative details of the structure of the two-phase flow field below the cavity was successfully produced. The Sauter mean bubble diameter in the pipe flow region was under-predicted for about 10%. In conclusion, the proposed model was validated in predicting the multi-region flow field below the ventilated cavity which will provide a valuable insight in designing and controlling of the two phase systems with the detailed flow field information obtained.

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