The Experts below are selected from a list of 300 Experts worldwide ranked by ideXlab platform
Bofeng Bai - One of the best experts on this subject based on the ideXlab platform.
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Axial development of air–water Annular Flow with swirl in a vertical pipe
International Journal of Multiphase Flow, 2020Co-Authors: Wen Liu, Bofeng BaiAbstract:Abstract Annular Flow with swirl induced by a swirler has been widely used in industry. Swirl decay which closely related to working performance and length of the Flow is significantly important for its application in industry. Axial development of Annular Flow with and without swirl has been investigated in this work by means of experimentation and modelling. A vertical pipe system with 11 m long and 62 mm inner diameter was carried out to investigate axial development of Flow pattern, void fraction and pressure drop in the Annular Flow with and without swirl. The experimental results show that a swirling Annular Flow with swirling streak and less disturbed waves is observed downstream of the swirler. Void fraction decreases, total pressure drop increases and the PDF (probability density function) of pressure drop becomes more concentrated in the Annular Flow with swirl, compared with these in the Annular Flow without swirl. However, swirling Annular Flow is gradually transformed to Annular Flow without swirl along the streamwise direction. To qualitatively predict the decay in an Annular Flow with swirl, a simplified theoretical model was developed here. The results calculated with the theoretical model were in agreements with experimental results. The obtained results can be used in predicting working performance and length of devices, such as separators and heat exchangers.
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The effect of swirl on transition from churn Flow to Annular Flow in an intermediate diameter pipe
Experimental Thermal and Fluid Science, 2019Co-Authors: Wen Liu, Bofeng BaiAbstract:Abstract Swirling Annular Flow has been widely used in industries. The transition boundary of swirling Annular Flow which is important for its application in practice is rarely studied in published works. In this work, the effect of swirl on transition from churn Flow to Annular Flow in an intermediate diameter pipe has been investigated by experimentation and modelling. The experiments were conducted with air–water two-phase Flow in an 11-m vertical pipe (D = 62 mm) at the range of the test conditions: the liquid superficial velocity ranges from 0.0039 to 0.95 m/s and the gas superficial velocity ranges from 1.22 to 32.49 m/s. The experimental results showed that the churn Flow can be transformed to swirling Annular Flow under the effect of swirl, and the gas velocity required for the transition from churn Flow to swirling Annular Flow in a swirling Flow is lower compared with that for the transition from churn Flow to Annular Flow in a non-swirling Flow. Then a theoretical model based on separated Flow model was established to predict the transition boundary between churn Flow and swirling Annular Flow in a vertical pipe. Calculated results were in good agreements with experimental results.
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A mechanistic model for the prediction of swirling Annular Flow pattern transition
Chemical Engineering Science, 2019Co-Authors: Li Liu, Bofeng BaiAbstract:Abstract The accurate prediction of Flow patterns and their transition is extremely important for proper design, operation and optimization of two-phase Flow systems, since the parameters such as pressure loss and heat and mass transfer are strongly dependent on the Flow pattern. So far, the non-swirling gas-liquid Flow in straight pipes have been widely studied and various mechanisms that lead to Flow pattern transition have been clarified and modeled. However, the dynamics of gas-liquid Flow under swirling condition are not well understood, and no detailed models are available for the prediction of swirling Flow pattern transition. To address this, in our previous work (Liu and Bai, 2018), a visualization experiment aimed at classifying Flow regimes in swirling gas-liquid Flow was presented and three typical swirling Flow regimes, i.e., swirling gas column Flow, swirling intermittent Flow and swirling Annular Flow were classified and defined, respectively. As the swirling Annular Flow can be regarded as a special case of conventional Annular Flow (i.e., when tangential velocity does not equal zero), in present paper, a mechanistic model for the prediction of the swirling Annular Flow pattern transition was developed considering its physical interest and great practical significance. Two physical mechanisms that lead to the transition from swirling Annular Flow to other Flow patterns were revealed and modeled, respectively. The model was evaluated against a wide range of swirling and non-swirling experimental data and based on this model, the effects of different parameters (e.g., hydraulic diameter, working pressure and swirl angle) on the boundary of Flow pattern transition were presented. Results revealed that the range of swirling Annular Flow enlarges with the increase of the working pressure and swirl angle but narrows with the hydraulic diameter. Taking these influencing factors into account, a generalized formula for the prediction of the swirling Annular Flow pattern transition was proposed. Compared with existing empirical correlations for Annular Flow, the newly developed correlation provided more accurate and reasonable prediction of Flow pattern transition for both swirling Annular Flow and Annular Flow.
Wen Liu - One of the best experts on this subject based on the ideXlab platform.
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Axial development of air–water Annular Flow with swirl in a vertical pipe
International Journal of Multiphase Flow, 2020Co-Authors: Wen Liu, Bofeng BaiAbstract:Abstract Annular Flow with swirl induced by a swirler has been widely used in industry. Swirl decay which closely related to working performance and length of the Flow is significantly important for its application in industry. Axial development of Annular Flow with and without swirl has been investigated in this work by means of experimentation and modelling. A vertical pipe system with 11 m long and 62 mm inner diameter was carried out to investigate axial development of Flow pattern, void fraction and pressure drop in the Annular Flow with and without swirl. The experimental results show that a swirling Annular Flow with swirling streak and less disturbed waves is observed downstream of the swirler. Void fraction decreases, total pressure drop increases and the PDF (probability density function) of pressure drop becomes more concentrated in the Annular Flow with swirl, compared with these in the Annular Flow without swirl. However, swirling Annular Flow is gradually transformed to Annular Flow without swirl along the streamwise direction. To qualitatively predict the decay in an Annular Flow with swirl, a simplified theoretical model was developed here. The results calculated with the theoretical model were in agreements with experimental results. The obtained results can be used in predicting working performance and length of devices, such as separators and heat exchangers.
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The effect of swirl on transition from churn Flow to Annular Flow in an intermediate diameter pipe
Experimental Thermal and Fluid Science, 2019Co-Authors: Wen Liu, Bofeng BaiAbstract:Abstract Swirling Annular Flow has been widely used in industries. The transition boundary of swirling Annular Flow which is important for its application in practice is rarely studied in published works. In this work, the effect of swirl on transition from churn Flow to Annular Flow in an intermediate diameter pipe has been investigated by experimentation and modelling. The experiments were conducted with air–water two-phase Flow in an 11-m vertical pipe (D = 62 mm) at the range of the test conditions: the liquid superficial velocity ranges from 0.0039 to 0.95 m/s and the gas superficial velocity ranges from 1.22 to 32.49 m/s. The experimental results showed that the churn Flow can be transformed to swirling Annular Flow under the effect of swirl, and the gas velocity required for the transition from churn Flow to swirling Annular Flow in a swirling Flow is lower compared with that for the transition from churn Flow to Annular Flow in a non-swirling Flow. Then a theoretical model based on separated Flow model was established to predict the transition boundary between churn Flow and swirling Annular Flow in a vertical pipe. Calculated results were in good agreements with experimental results.
G F Hewitt - One of the best experts on this subject based on the ideXlab platform.
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churn and wispy Annular Flow regimes in vertical gas liquid Flows
Energy & Fuels, 2012Co-Authors: G F HewittAbstract:Two-phase Flows are extremely complex and, traditionally, attempts have been made to classify the myriad of possible Flow configurations into “Flow regimes” or “Flow patterns”. Classically, vertical two-phase Flows have been classified into the regimes of bubbly Flow, slug Flow, and Annular Flow. This paper makes an appeal for two other regimes, namely, “churn Flow” and “wispy Annular Flow”, to be given more attention. As shown, these regimes are of considerable technological importance and possess unusual features that justify their separate designation and make them ripe for further study.
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liquid entrainment droplet concentration and pressure gradient at the onset of Annular Flow in a vertical pipe
International Journal of Multiphase Flow, 2002Co-Authors: Jader R Barbosa, G F Hewitt, G Konig, S M RichardsonAbstract:Abstract There is a dearth of data on Flow parameters in the transition region between churn and Annular Flow. To address this deficiency, adiabatic air–water experiments were carried out in a vertical test section (31.8 mm internal diameter, 10.8 m long) in which an isokinetic probe was employed to measure the local mass fluxes of gas and of entrained liquid droplets in the core region; pressure gradient was also measured. The tests covered pressures ranging from 1.7 to 5 bara and liquid superficial velocities ranging from 0.012 to 0.33 m s −1 . Average liquid entrained fraction and pressure gradient exhibited minima at gas Flow rates that, according to a widely applied Flow reversal criterion, correspond to the point of transition to upwards co-current Annular Flow. Also, the profiles of local droplet concentration characterise churn Flow as a region in which the radial gradients of droplet concentration tend to disappear with increasing gas Flow rate. As Annular Flow takes place, the local concentration is virtually constant with respect to radial position and gas Flow rate. An empirical correlation is finally proposed for the prediction of liquid entrained fraction at the onset of Annular Flow.
L.m. Portela - One of the best experts on this subject based on the ideXlab platform.
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Prediction of the interfacial shear-stress in vertical Annular Flow
International Journal of Multiphase Flow, 2009Co-Authors: R.j. Belt, J.m.c. Van’t Westende, L.m. PortelaAbstract:Many improvements of the Wallis correlation for the interfacial friction in Annular Flow have been proposed in the literature. These improvements give in general a better fit to data, however, their physical basis is not always justified. In this work, we present a physical approach to predict the interfacial shear-stress, based on the theory on roughness in single-phase turbulent pipe Flows. Using measured interfacial shear-stress data and measured data on roll waves, which provide most of the contribution to the liquid film roughness, we show that the interfacial shear-stress in vertical Annular Flow is in very close agreement with the theory. We show that the sand-grain roughness of the liquid film is not equal to four times the mean film thickness, as it is assumed in the Wallis correlation. Instead, the sand-grain roughness is proportional to the wave height, and the proportionality constant can be predicted accurately using the roughness density (or solidity). Furthermore, we show that our Annular Flow, which is in similar conditions to others in the literature, is fully rough. Hence, the bulk Reynolds number should not appear in the prediction of the interfacial friction coefficient, as is often done in the improvements of the Wallis correlation proposed in the literature.
Li Liu - One of the best experts on this subject based on the ideXlab platform.
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A mechanistic model for the prediction of swirling Annular Flow pattern transition
Chemical Engineering Science, 2019Co-Authors: Li Liu, Bofeng BaiAbstract:Abstract The accurate prediction of Flow patterns and their transition is extremely important for proper design, operation and optimization of two-phase Flow systems, since the parameters such as pressure loss and heat and mass transfer are strongly dependent on the Flow pattern. So far, the non-swirling gas-liquid Flow in straight pipes have been widely studied and various mechanisms that lead to Flow pattern transition have been clarified and modeled. However, the dynamics of gas-liquid Flow under swirling condition are not well understood, and no detailed models are available for the prediction of swirling Flow pattern transition. To address this, in our previous work (Liu and Bai, 2018), a visualization experiment aimed at classifying Flow regimes in swirling gas-liquid Flow was presented and three typical swirling Flow regimes, i.e., swirling gas column Flow, swirling intermittent Flow and swirling Annular Flow were classified and defined, respectively. As the swirling Annular Flow can be regarded as a special case of conventional Annular Flow (i.e., when tangential velocity does not equal zero), in present paper, a mechanistic model for the prediction of the swirling Annular Flow pattern transition was developed considering its physical interest and great practical significance. Two physical mechanisms that lead to the transition from swirling Annular Flow to other Flow patterns were revealed and modeled, respectively. The model was evaluated against a wide range of swirling and non-swirling experimental data and based on this model, the effects of different parameters (e.g., hydraulic diameter, working pressure and swirl angle) on the boundary of Flow pattern transition were presented. Results revealed that the range of swirling Annular Flow enlarges with the increase of the working pressure and swirl angle but narrows with the hydraulic diameter. Taking these influencing factors into account, a generalized formula for the prediction of the swirling Annular Flow pattern transition was proposed. Compared with existing empirical correlations for Annular Flow, the newly developed correlation provided more accurate and reasonable prediction of Flow pattern transition for both swirling Annular Flow and Annular Flow.