2.9 Critical Flow of Flashing Water through Long Tubes

For the solution of engineering problems require increasingly accurate estimates of the hydraulic characteristics of the water streams. To date, it is impossible to consider sufficiently complete theoretical and experimental justification of the main provisions of the theory of turbulence, hydraulic resistance, channel processes. The composition of tasks related to flows in wide channels, turbulence problems are of scientific and practical interest. Various interpretations of the determination of the critical Froude number in wide open water flows based on observations and theoretical transformations are considered. The conditions for the emergence of a critical regime of water flow in an open wide channel are analyzed in order to estimate the critical Froude number and critical depth. Estimates of the critical Froude number for laboratory and field conditions are given. The estimations allow us to consider the proposed approach acceptable for determining the conditions of occurrence of the critical flow regime. The General, physical interpretation of conditions of occurrence of the critical regime of water flow on the basis of phenomenological approach is specified. The results take into account the values of the components of the total specific energy of the section. This shows the estimated calculation. The results obtained theoretically make it possible to compare the above interpretations and determine their applicability, and the results of the analysis can be useful for the estimated calculations of flows in channels and river flows in rigid, undeformable boundaries and with minor channel deformations.

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Numerical Calculation of Speed of Sound for Vapor-Liquid Critical Flow from Pipe with Granular Layer

2020 International Multi-Conference on Industrial Engineering and Modern Technologies (FarEastCon) ◽

10.1109/fareastcon50210.2020.9271522 ◽

2020 ◽

Author(s):

D. Khramtsov ◽

D. Nekrasov ◽

B. Pokusaev

Keyword(s):

Numerical Calculation ◽

Speed Of Sound ◽

Granular Layer ◽

Critical Flow ◽

Vapor Liquid

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Hybrid Scour Depth Prediction Equations for Reliable Design of Bridge Piers

Water ◽

10.3390/w13152019 ◽

2021 ◽

Vol 13 (15) ◽

pp. 2019

Author(s):

Hossein Hamidifar ◽

Faezeh Zanganeh-Inaloo ◽

Iacopo Carnacina

Keyword(s):

Flow Velocity ◽

Critical Velocity ◽

Depth Estimation ◽

Hybrid Models ◽

Velocity Estimation ◽

Bridge Piers ◽

Critical Flow ◽

Scour Depth ◽

Critical Flow Velocity ◽

Estimation Equations

Numerous models have been proposed in the past to predict the maximum scour depth around bridge piers. These studies have all focused on the different parameters that could affect the maximum scour depth and the model accuracy. One of the main parameters individuated is the critical velocity of the approaching flow. The present study aimed at investigating the effect of different equations to determine the critical flow velocity on the accuracy of models for estimating the maximum scour depth around bridge piers. Here, 10 scour depth estimation equations, which include the critical flow velocity as one of the influencing parameters, and 8 critical velocity estimation equations were examined, for a total combination of 80 hybrid models. In addition, a sensitivity analysis of the selected scour depth equations to the critical velocity was investigated. The results of the selected models were compared with experimental data, and the best hybrid models were identified using statistical indicators. The accuracy of the best models, including YJAF-VRAD, YJAF-VARN, and YJAI-VRAD models, was also evaluated using field data available in the literature. Finally, correction factors were implied to the selected models to increase their accuracy in predicting the maximum scour depth.

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Role of Shearing Dispersion and Stripping in Wax Deposition in Crude Oil Pipelines

Energies ◽

10.3390/en12224325 ◽

2019 ◽

Vol 12 (22) ◽

pp. 4325

Author(s):

Zhihua Wang ◽

Yunfei Xu ◽

Yi Zhao ◽

Zhimin Li ◽

Yang Liu ◽

...

Keyword(s):

Crude Oil ◽

Flow Rate ◽

Critical Flow ◽

Wax Deposition ◽

Dominant Effect ◽

Critical Flow Rate ◽

Oil Pipelines ◽

Oil Flow ◽

Shearing Mechanism

Wax deposition during crude oil transmission can cause a series of negative effects and lead to problems associated with pipeline safety. A considerable number of previous works have investigated the wax deposition mechanism, inhibition technology, and remediation methods. However, studies on the shearing mechanism of wax deposition have focused largely on the characterization of this phenomena. The role of the shearing mechanism on wax deposition has not been completely clarified. This mechanism can be divided into the shearing dispersion effect caused by radial migration of wax particles and the shearing stripping effect caused by hydrodynamic scouring. From the perspective of energy analysis, a novel wax deposition model was proposed that considered the flow parameters of waxy crude oil in pipelines instead of its rheological parameters. Considering the two effects of shearing dispersion and shearing stripping coexist, with either one of them being the dominant mechanism, a shearing dispersion flux model and a shearing stripping model were established. Furthermore, a quantitative method to distinguish between the roles of shearing dispersion and shearing stripping in wax deposition was developed. The results indicated that the shearing mechanism can contribute an average of approximately 10% and a maximum of nearly 30% to the wax deposition process. With an increase in the oil flow rate, the effect of the shearing mechanism on wax deposition is enhanced, and its contribution was demonstrated to be negative; shear stripping was observed to be the dominant mechanism. A critical flow rate was observed when the dominant effect changes. When the oil flow rate is lower than the critical flow rate, the shearing dispersion effect is the dominant effect; its contribution rate increases with an increase in the oil flow temperature. When the oil flow rate is higher than the critical flow rate, the shearing stripping effect is the dominant effect; its contribution rate increases with an increase in the oil flow temperature. This understanding can be used to design operational parameters of the actual crude oil pipelines and address the potential flow assurance problems. The results of this study are of great significance for understanding the wax deposition theory of crude oil and accelerating the development of petroleum industry pipelines.

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