A model for the droplet deposition rate in horizontal annular two-phase flow PDF Download
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Author: N. S. Wilkes
Publisher:
ISBN:
Category : Fluid mechanics
Languages : en
Pages :
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Author: N. S. Wilkes
Publisher:
ISBN:
Category : Fluid mechanics
Languages : en
Pages :
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Author: Mohammad Emamzadeh
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
The thesis presents a general one-dimensional mathematical model to simulate two-phase, gas-liquid, annular flow in horizontal as well as vertical pipes, and to mechanistically predict the transition from stratified to annular flow in horizontal pipes. The method is based on the transient one-dimensional two-fluid model whereby the two phases are considered as (i) liquid layer and (ii) a mixture of the gas and liquid droplets in which the droplet concentration in the mixture is considered as a flow variable. The model entails the introduction of a scalar transport equation for the conservation of mass of liquid droplets accounting for liquid transfer to and from the film liquid layer. The interface curvature is modelled by a double circle geometric configuration incorporating a new empirical relation for the specification of wetted angle. The droplet exchange rate between the liquid film and gas core is modelled by employing droplet entrainment and deposition rates derived from modifications of models existing in the literature. Using the new model the droplet entrained fraction (E), which is defined as the ratio of the droplet mass flow rate to the total liquid mass flow rate, is computed and validated against different experimental data for both horizontal and vertical pipes. The predictions show good agreement with most of the measurements, being within 30% of the data. This is a significant development since, unlike all other exist- ing models, both horizontal and vertical annular flows can be predicted well with the same model. Moreover, the transition point from the stratified to the annular regimes in horizontal flow can also be predicted and the transition points compare very well with the usual regime boundaries found in existing flow regime maps.
Author: Chee Hwa Danny Yeo
Publisher:
ISBN:
Category : Heat
Languages : en
Pages : 186
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Book Description
![Entrainment and Deposition Rates of Droplets in Annular Two-phase Flow. [PWR ; BWR]. PDF](https://books.google.com/books/content/images/frontcover/jw9yAQAACAAJ?fife=w80-h100)
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
The droplet entrainment from a liquid film is important to the mass, momentum, and energy transfer processes in annular two-phase flow. For example, the amount of entrainment as well as the rate of entrainment significantly affect the occurrences of the dryout, whereas the post CHF heat transfer depends strongly on the entrainment and droplet sizes. Despite the importance of the entrainment rate, there have been no satisfactory correlations available in the literature. In view of these, correlations for entrainment rate covering both entrance region and equilibrium region have been developed from a simple model in collaboration with data. Results show that the entrainment rate varies considerably in the entrainment development region, however, at a certain distance from an inlet it attains an equilibrium value. A simple approximate correlation has been obtained for the equilibrium state where entrainment rate and deposition rate becomes equal. The result indicates that the equilibrium entrainment rate is proportional to Weber number based on the hydraulic diameter of a tube.
Author: Lawrence Robert Williams
Publisher:
ISBN:
Category :
Languages : en
Pages : 322
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Book Description
The effect of pipe diameter on horizontal annular flow is examined. Measurements of the local film height, the local droplet flux, the local velocity, and the entrained fraction for annular flow in a 9.53 cm horizontal pipe have been obtained. The measurements are compared with the results from previous investigators for horizontal annular flow in pipes with diameters of 2.54 cm and 5.08 cm. A new large scale two-phase flow facility has been designed and constructed. The facility has the ability to incline a 26.5 m pipe at angles between positive and minus 2.5 degrees from the horizontal. Local film height measurements show that the film distribution becomes increasingly asymmetric with increasing pipe diameter. The effect of pipe diameter on the asymmetries of the liquid film distribution is predicted approximately by a Froude number. At Froude numbers below 50, the liquid is stratified as a pool at the pipe bottom. A turbulent diffusion model developed by a co-researcher for the droplet concentration distribution is in good agreement with measurements at low gas velocities and low droplet concentrations. At higher droplet concentrations, velocity measurements suggest the existence of a secondary flow in the gas which inhibits droplet settling. Entrainment correlations developed from experiments in small diameter pipes, over predict the entrained fraction in large diameter pipes. A generalized entrainment correlation based on an equilibrium rate balance between the rate of atomization of droplets from the liquid film and the rate of deposition of droplets back to the liquid film is developed. The correlation is easily interpreted for two extremes of the liquid film distribution. When the film is distributed uniformly around the pipe wall, the entrainment relation reduces to a form developed by previous researchers. For conditions where the liquid film is stratified as a pool at the pipe bottom, a new entrainment relation is developed which is in good agreement with the results.
Author: Charles R. Kopplin
Publisher:
ISBN:
Category :
Languages : en
Pages : 136
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Book Description
Author: Yiak Mong Yeoh
Publisher:
ISBN:
Category : Fluid dynamics
Languages : en
Pages : 134
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Book Description
Author: Thomas J. Hanratty
Publisher: Cambridge University Press
ISBN: 1107512972
Category : Technology & Engineering
Languages : en
Pages : 359
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Book Description
Presenting tools for understanding the behaviour of gas-liquid flows based on the ways large scale behaviour relates to small scale interactions, this text is ideal for engineers seeking to enhance the safety and efficiency of natural gas pipelines, water-cooled nuclear reactors, absorbers, distillation columns and gas lift pumps. The review of advanced concepts in fluid mechanics enables both graduate students and practising engineers to tackle the scientific literature and engage in advanced research. It focuses on gas-liquid flow in pipes as a simple system with meaningful experimental data. This unified theory develops design equations for predicting drop size, frictional pressure losses and slug frequency, which can be used to determine flow regimes, the effects of pipe diameter, liquid viscosity and gas density. It describes the effect of wavy boundaries and temporal oscillations on turbulent flows, and explains transition between phases, which is key to understanding the behaviour of gas-liquid flows.
Author: David Ruey-Chyi Chang
Publisher:
ISBN:
Category : Two-phase flow
Languages : en
Pages : 484
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Book Description
Author: Geoffrey Hewitt
Publisher: Elsevier
ISBN: 1483285235
Category : Technology & Engineering
Languages : en
Pages : 327
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Book Description
Annular Two-Phase Flow presents the wide range of industrial applications of annular two-phase flow regimes. This book discusses the fluid dynamics and heat transfer aspects of the flow pattern. Organized into 12 chapters, this book begins with an overview of the classification of the various types of interface distribution observed in practice. This text then examines the various regimes of two-phase flow with emphasis on the regions of occurrence of the annular flow regime. Other chapters consider the single momentum and energy balances, which illustrate the differences and analogies between single- and two-phase flows. This book discusses as well the simple modes for annular flow with consideration to the calculation of the profile of shear stress in the liquid film. The final chapter deals with the techniques that are developed for the measurement of flow pattern, entrainment, and film thickness. This book is a valuable resource for chemical engineers.
