Development of local two-phase flow parameters for vertical bubbly flow in a pipe with sudden expansion

Rinne, Achim; Loth, Ralf

doi:10.1016/0894-1777(96)00039-8

Cited by 32 publications

(11 citation statements)

References 9 publications

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“…Experimental works [3,4] were probably among the first studies of bubbly flows downstream of a sudden expansion. They studied bubbly flows behind a sudden expansion in a horizontal duct.…”

Section: Introductionmentioning

confidence: 99%

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

2019

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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.Energies 2019, 12, 2735 2 of 18 regime. Gas concentration increased immediately after the cross-section of the flow separation. Measurements by [7] were performed in an upward, vertical flow of a liquid (water) and CO 2 bubbles. The distribution of the mean carrier fluid velocity was strongly dependent on the bubbles' diameter. A review of the literature for two-phase flow in sudden expansions and contractions was performed in [8]. Wang et al. [8] have found that none of the existing eight correlations can accurately predict the experimental database. Most of these correlations greatly overpredicted the results for mini test sections. Some of the correlations also underpredicted the data for large test sections.There are only a few papers that consider the numerical modeling of isothermal bubbly flows in a pipe with sudden expansion [9,10]. Krepper et al. [9] presented a mathematical model for polydisperse flow in a vertical pipe with sudden expansion. The numerical predictions for bubbly pipe flow with an obstacle demonstrated very difficult nature of such flows [9]. The Eulerian model was developed to simulate bubbly flows in a pipe with sudden expansion in [10]. Predictions were carried out using the CFD commercial package STAR-CCM+. The developed model was validated against measurements of Bel Fdhila [11]. The eddy-viscosity k−ε model showed poor reproduction of the bubbly flow structure because it disregarded much of the information on fluid flow turbulence. The Second-Moment Closure and LES methods captured the main characteristic turbulent length-scales responsible for the diffusion of the bubble gas phase, and moreover, these methods predicted the flow patterns and bubble distributions across the pipe section [10].Recently published numerical works [12,13] investigated heat transfer in bubbly flows without an abrupt pipe or channel expansion. These studies showed the significant influence of bubble diameter and gas volumetric flow rate ratios on the flow patterns and heat transfer. Heat transfer in bubbly flow increased up to three times that of one-phase fluid flow. The liquid turbulence was modeled using an isotropic k−ε model [12]. The DNS of bubbly flow with heat transfer was performed [13]. The numerical [14...

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“…Experimental works [3,4] were probably among the first studies of bubbly flows downstream of a sudden expansion. They studied bubbly flows behind a sudden expansion in a horizontal duct.…”

Section: Introductionmentioning

confidence: 99%

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

2019

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“…This means that there exists a directional ambiguity. Therefore, this technique can only be used in unidirectional flows unless applying cross correlation with signals taken from multiple fibers ͑e.g., Cavalier et al, 9 Rinne and Loth, 5 Barrau et al, 6 Rensen and Roig, 8 and Kiambi et al͒ 7 is used to resolve the flow direction. Moreover, Eq.…”

Section: Principle and Experimental Apparatusmentioning

confidence: 99%

“…Less disturbance is caused by the optical fiber due to its small dimensions ͓125 m in diameter, compared with the conductivity probes of O͑1 mm͒ or larger͔. Reports in various applications using optical fiber probes in gas-liquid flows can be found in Rinne and Loth, 5 Barrau et al, 6 Kiambi et al, 7 and Rensen and Roig, 8 while reports on gas-solid flows can be found in Cavalier et al 9 and Herbert et al 10 Other techniques using acoustics for bubble sizing and velocity measurements ͑e.g., Vagle and Farmer͒ 11 in general, require relatively large dimensions for the instrument and create greater disturbance. They may be suitable for in situ or large-scale laboratory experiments but are outside the scope of this study and will not be discussed here.…”

Section: Introductionmentioning

confidence: 99%

Fiber optic reflectometer for velocity and fraction ratio measurements in multiphase flows

Chang

Lim

2003

Review of Scientific Instruments

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Reply to "Comment on 'Fiber optic reflectometer for velocity and fraction ratio measurements in multiphase flows' " [Rev. Sci. Instrum. 74, 3559 (2003)] Rev. Sci. Instrum. 75, 286 (2004); 10.1063/1.1634361Comments on "Fiber optic reflectometer for velocity and fraction ratio measurements in multiphase flows" [Rev.A technique based on the coherent mixing of scattered signal with Fresnel reflection signal from the tip of an optical fiber is used to demonstrate the feasibility of measuring the velocity and fraction ratio of solid particles and gas bubbles or liquid droplets in a liquid or gas flow. If the liquid or gas flow is seeded with small neutrally buoyant particles, the technique is then capable of measuring the velocity as well as the fraction ratio of all three phases of the flow at a given point. The method is briefly described as follows. An optical signal derived from a diode laser driven by a constant current is launched into a single-mode optical fiber and transmitted, through a fiber coupler, to the signal fiber inserted into the test fluid. The diode laser used is a multilongitudinal mode device that has a low coherence length of about 200 m. The coherently mixed signal propagates back to the signal fiber, through the fiber coupler, and detected by a detector. By analyzing the signal, the velocity and fraction ratio of each phase can be obtained. Using water seeded with small solid particles and air bubbles, it is demonstrated that the technique is capable of measuring the velocity in the direction parallel to the fiber. Since the only intrusion to the fluid is the tiny fiber probe ͑a dimension of 125 m in diameter͒, the disturbance to most fluid flows is negligible, therefore, the technique is nearly nonintrusive.

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“…This was achieved with a transputer-based measuring system. An earlier design of this system was used by Schmitt, Hoffmann, and Loth [l] and by Rinne and Loth [2] for investigations of steady two-phase flows. Fig.…”

Section: Experimental Set-upmentioning

confidence: 99%

Phase Distribution Measurements during Transient Bubbly Two-Phase Flow in a Vertical Pipe

Tillenkamp

Loth

2000

Chem. Eng. Technol.

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An experimental procedure for investigating transient bubble flow for an adiabatic air/water system with vertical upward flow in a pipe is presented. The results of the measured local transient two-phase flow parameters are shown along a pipe length of approx. four meters. From the measured radial phase distributions under steady and under transient conditions one can draw conclusions about the interfacial forces. Here, the effects indicate the action of forces such as a transverse lift force and a time dependent force like the virtual mass force during the transient. For modelling the transverse lift force which seems to play a dominant role for that flow regime the formulation of Zun was chosen and it was implemented into the commercial CFD-Code Fluent Release 4.4.4 via user-defined subroutines. Finally, results from the simulation of the steady states of start and end conditions of an experimental measured transient are shown.

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Development of local two-phase flow parameters for vertical bubbly flow in a pipe with sudden expansion

Cited by 32 publications

References 9 publications

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

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

Fiber optic reflectometer for velocity and fraction ratio measurements in multiphase flows

Phase Distribution Measurements during Transient Bubbly Two-Phase Flow in a Vertical Pipe

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