Comparison of void fraction correlations for different flow patterns in horizontal and upward inclined pipes

Woldesemayat, Melkamu A.; Ghajar, Afshin J.

doi:10.1016/j.ijmultiphaseflow.2006.09.004

Cited by 404 publications

(234 citation statements)

References 60 publications

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“…It is easy to implement because the void fraction is expressed as an explicit function of the total mass flux. It has been shown that the Steiner version of the Rouhani-Axelsson drift flux model can also be used to estimate the void fraction for inclined and vertical flows with reasonable accuracy (capturing > 80% date points with < 15% error) [60]. The Steiner version of the Rouhani-Axelsson drift flux model was consequently an accurate model to flexibly investigate either horizontal, inclined or vertical configurations.…”

Section: Two-phase Flow Model Inside Tubesmentioning

confidence: 99%

Modeling and design guidelines for direct steam generation solar receivers

et al. 2018

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• A computational model for solar receiver for direct steam generation is developed.• Experiments are conducted and used to validate the model.• Practical designs, operational conditions and material choices are investigated.• Model provides design tool for direct steam generation solar cavity receivers. A R T I C L E I N F OKeyword: Solar energy Multi-mode heat transfer modeling Two-phase flow modeling Solar receiver Steam generator Concentrated solar A B S T R A C T Concentrated solar energy is an ideal energy source for high-temperature energy conversion processes such as concentrated solar power generation, solar thermochemical fuel production, and solar driven high-temperature electrolysis. Indirectly irradiated solar receiver designs utilizing tubular absorbers enclosed by a cavity are possible candidates for direct steam generation, allowing for design flexibility and high efficiency. We developed a coupled heat and mass transfer model of cavity receivers with tubular absorbers to guide the design of solardriven direct steam generation. The numerical model consisted of a detailed 1D two-phase flow model of the absorber tubes coupled to a 3D heat transfer model of the cavity receiver. The absorber tube model simulated the flow boiling phenomena inside the tubes by solving 1D continuity, momentum, and energy conservation equations based on a control volume formulation. The Thome-El Hajal flow pattern maps were used to predict liquid-gas distributions in the tubular cross-sections, and heat transfer coefficients and pressure drop along the tubes. The heat transfer coefficient and fluid temperature of the absorber tubes' inner surfaces were then extrapolated to the circumferential of the tube and used in the 3D cavity receiver model. The 3D steady state model of the cavity receiver coupled radiative, convective, and conductive heat transfer. The complete model was validated with experimental data and used to analyze different receiver types and designs made of different materials and exposed to various operational conditions. The proposed numerical model and the obtained results provide an engineering design tool for cavity receivers with tubular absorbers (in terms of tube shapes, tube diameter, and water-cooled front), support the choice of best-performant operation (in terms of radiative flux, mass flow rate, and pressure), and aid in the choice of the component materials. The model allows for an indepth understanding of the coupled heat and mass transfer in the solar receiver for direct steam generation and can be exploited to quantify the optimization potential of such solar receivers.

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Section: Two-phase Flow Model Inside Tubesmentioning

confidence: 99%

Modeling and design guidelines for direct steam generation solar receivers

et al. 2018

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“…Available void fraction measurements in helical coils [7,9,10,14,16,18] suggest that curvature effects on the void fraction are small and negligible, so that straight tube void fraction prediction methods can be extrapolated to helically coiled tubes, at least in first approximation. Therefore, the void fraction prediction method of Woldesemayat and Ghajar [51] was used here, as this is one of the most accurate general purpose void fraction correlations currently available for straight tubes [50]. Notably, with the databank in Table 1 the acceleration and gravitational components of the pressure gradient never account for more than 10-20% of the total pressure gradient, so that the void fraction prediction method used in the analysis has little impact on the final results.…”

Section: Comparison With Existing Correlationsmentioning

confidence: 99%

Two-phase pressure drop prediction in helically coiled steam generators for nuclear power applications

Cioncolini

Santini

2016

International Journal of Heat and Mass Transfer

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This study considers the prediction of the pressure gradient with water-steam two-phase flows through helically coiled steam generator tubes, focusing in particular on the operating conditions of low-medium pressure, low mass flux and low heat flux typical of once-through steam generators with in-tube boiling adopted in small modular nuclear reactor systems. Twenty-five widely used empirical correlations have been tested against an experimental pressure drop databank drawn together in this study containing 980 data points. Since no existing correlation is capable of collapsing and satisfactorily fitting the collected databank, a new pressure drop prediction method for helically coiled tubes is proposed. This new prediction method is very simple to implement, as it is based on the homogeneous flow model, is asymptotically consistent with straight tube twophase flows and is largely superior in accuracy to existing prediction methods (mean absolute error of 7.3%, and 9 points out of 10 captured to within ±15%). The new prediction method is applicable for operating pressures in the range of 0.75-9.0 MPa, mass fluxes from 400 kg/m 2 s to 1191 kg/m 2 s, heat fluxes up to 750 kW/m 2 , tube diameters within 5-20 mm and coil to tube diameter ratio above 32.4. Curvature effects on the pressure gradient in helical coil two-phase flows can be significant, particularly with high velocity flows in tight curvature coils where the centrifugal force is intense.2

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“…Extensive lists of void fraction models and correlations for internal flow are given by Rice (1987), Woldesemayat and Ghajar (2007), and Dalkilic et al (2008). Among them, one of the most common are the slip ratio correlations, where the void fraction depends on the vapour quality and some fluid properties (Wallis, 1969).…”

Section: Introductionmentioning

confidence: 99%