Investigation of Bubble Frequency for Slug Flow Regime in a Uniformly Heated Horizontal Microchannel

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Amen Younes ◽  
Ibrahim Hassan ◽  
Lyes Kadem
Keyword(s):  
Flow Pattern ◽  
Flow Regime ◽  
Slug Flow ◽  
Flow Boiling ◽  
Operating Conditions ◽  
Bubble Frequency ◽  
Drift Flux Model ◽  
Wide Range ◽  
Bubble Length ◽  
Bubble Zone

Slug flow is an essential flow pattern observed in microchannels where its transition boundaries in microchannels are characterized by two complex hydrodynamic phenomena, the bubble confinement and the bubble coalescence. Slug flow may be classified in terms of bubble size into two major zones: isolated bubble zone and coalescence bubble zone. In this paper, a semi-analytical model is developed for predicting the main characteristics of isolated bubble zone for flow boiling in a horizontal microchannel. The influences of surface tension, shear, and inertial forces have been taken into account. The model is developed on the basis of drift flux model, and a fully developed slug unit is chosen as a control volume for deriving the equations of motion. The effects of main operating conditions, mass and heat fluxes, on bubble length and bubble frequency have been investigated. The boundaries of slug flow regime have been identified based on the most proper diabatic flow pattern maps available in the literature for the chosen database. The model has been validated using the database available in the literature for flow boiling of R134a and R245fa in 0.509 mm and 3.0 mm inner diameter horizontal mini-tubes, respectively, and over wide range of mass fluxes (300≤G≤1000 kg/m2 s). This study has shown that the mass flux has a significant effect on the slug length and the bubble frequency. The model gave a good agreement with the experimental data of bubble length and bubble frequency with a mean absolute error (MAE) of 18.0% and 27.34%, respectively.

Multiphase Fluid Structure Interaction in Bends and T-Joints

2010 ◽  
Author(s):  
Marcos F. Cargnelutti ◽  
Stefan P. C. Belfroid ◽  
Wouter Schiferli ◽  
Marlies van Osch
Keyword(s):  
Flow Regime ◽  
Slug Flow ◽  
Gas Flow ◽  
Single Phase ◽  
Scaling Factor ◽  
Operating Conditions ◽  
Phase Flow ◽  
Large Radius ◽  
Single Phase Flow ◽  
Wide Range

Air-water experiments were carried out in a horizontal 1″ pipe system to measure the magnitude of the forces induced by the multiphase flow. Forces and accelerations were measured on a number of bends and T-joint configurations for a wide range of operating conditions. Five different configurations were measured: a baseline case consisting of straight pipe only, a sharp edged bend, a large radius bend, a symmetric T-joint and a T-joint with one of the arms closed off. The gas flow was varied from a superficial velocity of 0.1 to 30 m/s and the liquid flow was varied from 0.05 to 2 m/s. This operating range ensures that the experiment encompasses all possible flow regimes. In general, the slug velocity and frequency presented a reasonable agreement with classical models. However, for high mixture velocity the measured frequency deviated from literature models. The magnitude of the measured forces was found to vary over a wide range depending on the flow regime. For slug flow conditions very high force levels were measured, up to 4 orders of magnitude higher than in single phase flow for comparable velocities. The annular flow regime resulted in the (relative) lowest forces, although the absolute amplitude is of the same order as in the case of slug flow. These results from a one inch pipe were compared to data obtained previously from similar experiments on a 6mm setup, to evaluate the scaling effects. The results for the one inch rig experiments agreed with the model proposed by Riverin, with the same scaling factor. A modification of this scaling factor is needed for the model to predict the forces measured on the 6mm rig. The validity of the theories developed based on the 6mm experiments were tested for validity at larger scales. In case of slug flow, the measured results can be described assuming a simple slug unit model. In annular and stratified flow a different model is required, since no slug unit is present. Instead, excitation force can be estimated using mixture properties. This mixture approach also describes the forces for the slug regime relatively well. Only the single phase flow is not described properly with this mixture model, as would be expected.

Forces on Bends and T-Joints due to Multiphase Flow

2010 ◽  
Author(s):  
S. P. C. Belfroid ◽  
M. F. Cargnelutti ◽  
W. Schiferli ◽  
Marlies van Osch
Keyword(s):  
Multiphase Flow ◽  
Flow Regime ◽  
Slug Flow ◽  
Annular Flow ◽  
Gas Flow ◽  
Stratified Flow ◽  
Operating Conditions ◽  
Large Radius ◽  
Flow Conditions ◽  
Wide Range

To be able to assess the mechanical integrity of piping structures for loading to multiphase flow conditions, air-water experiments were carried out in a horizontal 1″ pipe system. Forces and accelerations were measured on a number of bends and T-joint configurations for a wide range of operating conditions. Five different configurations were measured: a baseline case consisting of a straight pipe only, a sharp edged bend, a large radius bend, a symmetric T-joint and a T-joint with one of the arms closed off. The gas flow was varied from a superficial velocity of 0.1 to 30 m/s and the liquid flow was varied from 0.05 to 2 m/s. This operating range ensures that the experiment encompasses all possible flow regimes. The magnitude of the measured forces was found to vary over a wide range depending on the flow regime. For slug flow conditions very high force levels were measured, up to 4 orders of magnitude higher than in single phase flow for comparable velocities. The annular flow regime resulted in the (relative) lowest forces, although the absolute amplitude is of the same order as in the case of slug flow. In case of slug flow, the measured results can be described assuming a simple slug unit model. For both the frequency and amplitude the available models can be used in assessments. In annular and stratified flow a different model is required, since no slug unit is present. Instead, the amplitude of the excitation force can be estimated using mixture properties. To predict the main frequency for the annular flow and stratified flow additional experiments are required.

scholarly journals Flow Pattern Map of Flow Boiling in a Rectangular Channel Filled with Porous Media

Energies ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2440
Author(s):  
Youngwoo Kim ◽  
Dae Yeon Kim ◽  
Kyung Chun Kim
Keyword(s):  
Porous Media ◽  
Flow Pattern ◽  
Flow Regime ◽  
Annular Flow ◽  
Flow Boiling ◽  
Rectangular Channel ◽  
Flow Patterns ◽  
Flow Pattern Map ◽  
Mist Flow ◽  
Churn Flow

A flow visualization study was carried out for flow boiling in a rectangular channel filled with and without metallic random porous media. Four main flow patterns are observed as intermittent slug-churn flow, churn-annular flow, annular-mist flow, and mist flow regimes. These flow patterns are clearly classified based on the high-speed images of the channel flow. The results of the flow pattern map according to the mass flow rate were presented using saturation temperatures and the materials of porous media as variables. As the saturation temperatures increased, the annular-mist flow regime occupied a larger area than the lower saturation temperatures condition. Therefore, the churn flow regime is narrower, and the slug flow more quickly turns to annular flow with the increasing vapor quality. The pattern map is not significantly affected by the materials of porous media.

On the Nature of Critical Heat Flux in Microchannels

2005 ◽  
Vol 127 (1) ◽  
pp. 101-107 ◽  
Author(s):  
A. E. Bergles ◽  
S. G. Kandlikar
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Boiling ◽  
Flow Distribution ◽  
High Heat ◽  
Operating Conditions ◽  
High Heat Flux ◽  
Clear Understanding ◽  
Wide Range ◽  
Parallel Microchannels

The critical heat flux (CHF) limit is an important consideration in the design of most flow boiling systems. Before the use of microchannels under saturated flow boiling conditions becomes widely accepted in cooling of high-heat-flux devices, such as electronics and laser diodes, it is essential to have a clear understanding of the CHF mechanism. This must be coupled with an extensive database covering a wide range of fluids, channel configurations, and operating conditions. The experiments required to obtain this information pose unique challenges. Among other issues, flow distribution among parallel channels, conjugate effects, and instrumentation need to be considered. An examination of the limited CHF data indicates that CHF in parallel microchannels seems to be the result of either an upstream compressible volume instability or an excursive instability rather than the conventional dryout mechanism. It is expected that the CHF in parallel microchannels would be higher if the flow is stabilized by an orifice at the entrance of each channel. The nature of CHF in microchannels is thus different than anticipated, but recent advances in microelectronic fabrication may make it possible to realize the higher power levels.

Flow Boiling in Horizontal Tubes: Part 1—Development of a Diabatic Two-Phase Flow Pattern Map

1998 ◽  
Vol 120 (1) ◽  
pp. 140-147 ◽  
Author(s):  
N. Kattan ◽  
J. R. Thome ◽  
D. Favrat
Keyword(s):  
Flow Pattern ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Parameters ◽  
Horizontal Tubes ◽  
Flow Pattern Map ◽  
Wide Range ◽  
Data Points

An improved two-phase flow pattern map is proposed for evaporation in horizontal tubes. The new map was developed based on flow pattern data for five different refrigerants covering a wide range of mass velocities and vapor qualities. The new map is valid for both adiabatic and diabatic (evaporating) flows and accurately identifies about 96 percent of the 702 data points. In addition, the new flow pattern map includes the prediction of the onset of dryout at the top of the tube during evaporation inside horizontal tubes as a function of heat flux and flow parameters.

Modeling of Dry-Out Incipience for Flow Boiling in a Circular Microchannel at a Uniform Heat Flux

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Amen Younes ◽  
Ibrahim Hassan
Keyword(s):  
Heat Flux ◽  
Liquid Film ◽  
Flow Regime ◽  
Annular Flow ◽  
Flow Boiling ◽  
Operating Conditions ◽  
Inertia Force ◽  
Saturated Flow ◽  
Working Fluids ◽  
Dry Out

Dry-out is an essential phenomenon that has been observed experimentally in both slug and annular flow regimes for flow boiling in mini and microchannels. The dry-out leads to a drastic drop in heat transfer coefficient, reversible flow and may cause a serious damage to the microchannel. Consequently, the study and prediction of this phenomenon is an essential objective for flow boiling in microchannels. The aim of this work is to develop an analytical model to predict the critical heat flux (CHF) based on the prediction of liquid film variation in annular flow regime for flow boiling in a horizontal uniformly heated circular microtube. The model is developed by applying one-dimensional (1D) separated flow model for a control volume in annular flow regime for steady, and sable saturated flow boiling. The influence of interfacial shear and inertia force on the liquid film thickness is taken into account. The effects of operating conditions, channel sizes, and working fluids on the CHF have been investigated. The model was compared with 110 CHF data points for flow boiling of various working fluids, (water, LN2, FC-72, and R134a) in single and multiple micro/minichannels with diameter ranges of (0.38≤Dh≤3.04 mm) and heated-length to diameter ratios in the range of (117.7 (117.7≤Lh/D≤470)470). Additionally, three CHF correlations developed for saturated flow boiling in a single microtube have been employed for the model validation. The model showed a good agreement with the experimental CHF data with mean absolute error (MAE) = 19.81%.

The Drift Flux Model After Fifty Years: A Personal, Problem Solving Survey

2013 ◽  
Author(s):  
Peter Toma
Keyword(s):  
Flow Pattern ◽  
Liquid Flow ◽  
Operating Conditions ◽  
Gas Oil ◽  
Local Flow ◽  
Drift Flux Model ◽  
Drift Flux ◽  
Discrete Phase ◽  
Flux Model ◽  
Gas Liquid Flow

Offspring of the nuclear reactor industry and gas-oil production, multiphase fluids handling technology appears to have matured into an entirely new field of inquiry, most notably following broad acceptance of the drift flux and flow pattern concepts and their widespread integration into engineering calculations. The drift flux model (DFM), first suggested by Nicklin in 1962 and, soon after, adapted and developed by Professor Zuber’s research group at General Electric, enables calculation of “locally averaged” phase velocity. Further progress made in selection of the flow patterns, calculated for each section of the pipe, provided the key to properly assessing the terminal velocity of the discrete phase and the local phase distributions. The flow pattern concept was first introduced by Canadian Charles Govier to describe oil-water laboratory experiments, then by Hewitt-Roberts and Baker in 1954. A decade later, the team of Dukler-Taitel-Barnea developed the qualitative flow pattern concept into a quantitative roadmap procedure leading to rational calculations of the local (cross-section averaged) gas-liquid flow geometry, or flow pattern. The homogeneous gas-liquid flow, presuming the equality of gas and liquid velocities, a simplification broadly accepted during the early days of two-phase flow engineering, came to be regarded, due to Hinze’s work (Shell, 1955), as an identifiable region in the local flow map, reflecting turbulent and high-shear breakup of the discrete phase. To illustrate the usefulness, validity, and importance of the DFM, and mechanistic modeling using the DFM, as well as the salient work of Prof. Zuber on boiling instability this paper discuses reduction of potential explosive droplet boiling risk during multiphase pumping of high–gas-oil ratio mixtures. To assess critical operating conditions of the multiphase pumps, the Ishi-Zuber criteria developed during 1970 for assessing potential boiling instabilities were adapted to multiphase pumping/compression equipment and the results compared to field instability data. The elucidation of this problem relies heavily on the DFM and on salient research performed during 70s by Prof. Zuber’s team.

The Flow Regime of Oil-Gas-Water Three-Phase Flow in Pipes

2001 ◽  
Author(s):  
Yueshe Wang ◽  
Fangde Zhou
Keyword(s):  
Flow Pattern ◽  
Flow Regime ◽  
Transition Zone ◽  
Water Flow ◽  
High Speed ◽  
Vertical Tube ◽  
Wide Range ◽  
Flow Pattern Transition ◽  
Three Phase Flow ◽  
Oil Gas

Abstract The experiment for oil-gas-water flow pattern transition is carried out in a vertical tube 40mm I.D. and 6m long with a wide range of mixture velocity. Applying the concept of Weisman’s flow pattern transition zone to the investigation on oil-gas-water flow regime, every transition is quantified. The flow regime map, which includes transition zone mentioned above, is compatible with a lot of other pattern transitions. Meanwhile, according to this map the divergence of numerous transitions can be explained. So, that provides a reliable for reasonable understanding of the pattern transitions. Consequently, a method for regime recognition has been put forward with using simultaneously optical fiber probes and conductance probes. The availability of the method can be proved by the images of High Speed Motion Analyzer, which is from Kodak Company.

Void Fraction, Pressure Drop, and Flow Pattern Behavior for Two-Phase Non-Newtonian Slug Flow

2021 ◽  
Author(s):  
Faraj Ben Rajeb ◽  
Syed Imtiaz ◽  
Yan Zhang ◽  
Amer Aborig ◽  
Mohamed M. Awad ◽  
...  
Keyword(s):  
Pressure Drop ◽  
Flow Pattern ◽  
Flow Regime ◽  
Void Fraction ◽  
Slug Flow ◽  
Two Phase Flow ◽  
Flow Patterns ◽  
Intermittent Flow ◽  
Phase Flow ◽  
Two Phase

Abstract Slug flow is one of the most common flow patterns in non-Newtonian two-phase flow in pipes. It is a very common occurrence in gas-liquid two-phase flow in the pipe. Usually, it is an unfavorable flow pattern due to its unsteady nature, intermittency as well as high pressure drop. The differences between slug flow and elongated bubble flow are not clear because usually these two types of flow combined under one flow category. In general, these two-phase flow regimes are commonly defined as intermittent flow. In the present study, pressure gradient, and wave behavior in slug flow have been investigated depending on experimental work. In addition, void fraction has been estimated regarding available superficial liquid and gas velocities. The experimental records of superficial velocities of gas and liquid for slug flow and other flow patterns is used to create flow regime map for the gas non-Newtonian flow system. The effect of investigated flow regime velocities for non-Newtonian/gas flow on pressure drop and void fraction is reported. Pressure drop has been discovered to be reduced in slug flow more than other flow patterns due to high shear thinning behavior.

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