Addressing Two-Phase Flow Maldistribution in Microchannel Heat and Mass Exchangers

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Dhruv C. Hoysall ◽  
Khoudor Keniar ◽  
Srinivas Garimella
Keyword(s):  
Void Fraction ◽  
Two Phase Flow ◽  
Flow Distribution ◽  
Interfacial Area ◽  
Fluid Distribution ◽  
High Speed Photography ◽  
Phase Flow ◽  
Water Mixture ◽  
Two Phase ◽  
Microchannel Array

Multiphase flow phenomena in single micro and minichannels have been widely studied. Characteristics of two-phase flow through a large array of microchannels are investigated here. An air–water mixture is used to represent the two phases flowing through a microchannel array representative of those employed in practical applications. Flow distribution of the air and water flow across 52 parallel microchannels of 0.4 mm hydraulic diameter is visually investigated using high-speed photography. Two microchannel configurations are studied and compared, with mixing features incorporated into the second configuration. Slug and annular flow regimes are observed in the channels. Void fractions and interfacial areas are calculated for each channel from these observations. The flow distribution is tracked at various lengths along the microchannel array sheets. Statistical distributions of void fraction and interfacial area along the microchannel array are measured. The design with mixing features yields improved flow distribution. Void fraction and interfacial area change along the length of the second configuration, indicating a change in fluid distribution among the channels. The void fraction and interfacial area results are used to predict the performance of different microchannel array configurations for heat and mass transfer applications. Results from this study can help inform the design of compact thermal-fluid energy systems.

Visualization of Two-Phase Flow Through Microchannel Heat Exchangers

2015 ◽  
Author(s):  
Dhruv C. Hoysall ◽  
Khoudor Keniar ◽  
Srinivas Garimella
Keyword(s):  
Void Fraction ◽  
Two Phase Flow ◽  
Flow Distribution ◽  
Interfacial Area ◽  
High Speed Photography ◽  
Phase Flow ◽  
Water Mixture ◽  
Two Phase ◽  
Microchannel Array ◽  
Flow Through

Multiphase flow phenomena in single micro- and minichannels have been widely studied. Characteristics of two-phase flow through a large array of microchannels are investigated here. An air-water mixture is used to represent the two phases flowing through a microchannel array representative of those employed in practical applications. Flow distribution of the air and water flow across 52 parallel microchannels of 0.3 mm hydraulic diameter is visually investigated using high speed photography. Two microchannel configurations are studied and compared, with mixing features incorporated into the second configuration. Slug and annular flow regimes are observed in the channels. Void fractions and interfacial areas are calculated for each channel from these observations. The flow distribution is tracked at various lengths along the microchannel array sheets. Statistical distributions of void fraction and interfacial area along the microchannel array are measured. The design with mixing features yields improved flow distribution. Void fraction and interfacial area change along the length of the second configuration, indicating a change in fluid distribution among the channels. The void fraction and interfacial area results are used to predict the performance of different microchannel array configurations for heat and mass transfer applications. Results from this study can help inform the design of compact thermal-fluid energy systems.

Axial Development of Vertical Upward Bubbly Flow in a Minipipe

2005 ◽  
Author(s):  
Tatsuya Hazuku ◽  
Naohisa Tamura ◽  
Norihiro Fukamachi ◽  
Tomoji Takamasa ◽  
Takashi Hibiki ◽  
...  
Keyword(s):  
Void Fraction ◽  
Two Phase Flow ◽  
Constitutive Relations ◽  
Interfacial Area ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Measurements ◽  
Local Flow ◽  
Interfacial Area Concentration ◽  
Drift Flux Model

Accurate prediction of the interfacial area concentration is essential to successful development of the interfacial transfer terms in the two-fluid model. Mechanistic modeling of the interfacial area concentration entirely relies on accurate local flow measurements over extensive flow conditions and channel geometries. From this point of view, accurate measurements of flow parameters such as void fraction, interfacial area concentration, gas velocity, bubble Sauter mean diameter, and bubble number density were performed by the image processing method at five axial locations in vertical upward bubbly flows using a 1.02 mm-diameter pipe. The frictional pressure loss was also measured by a differential pressure cell. In the experiment, the superficial liquid velocity and the void fraction ranged from 1.02 m/s to 4.89 m/s and from 0.980% to 24.6%, respectively. The obtained data give near complete information on the time-averaged local hydrodynamic parameters of two-phase flow. These data can be used for the development of reliable constitutive relations which reflect the true transfer mechanisms in two-phase flow. As the first step to understand the flow characteristics in mini-channels, the applicability of the existing drift-flux model, interfacial area correlation, and frictional pressure correlation was examined by the data obtained in the mini-channel.

scholarly journals Experimental Study on Interfacial Area Transport of Two-Phase Flow under Vibration Conditions

2017 ◽  
Vol 2017 ◽  
pp. 1-13 ◽  
Author(s):  
Xiu Xiao ◽  
Qingzi Zhu ◽  
Shao-Wen Chen ◽  
Mamoru Ishii ◽  
Yajun Zhang ◽  
...  
Keyword(s):  
Experimental Study ◽  
Void Fraction ◽  
Vibration Frequency ◽  
Two Phase Flow ◽  
Bubble Diameter ◽  
Interfacial Area ◽  
Phase Flow ◽  
Two Phase ◽  
Vibration Direction ◽  
Local Parameters

An experimental study on air-water two-phase flow under vibration condition has been conducted using double-sensor conductivity probe. The test section is an annular geometry with hydraulic diameter of 19.1 mm. The vibration frequency ranges from 0.47 Hz to 2.47 Hz. Local measurements of void fraction, interfacial area concentration (IAC), and Sauter mean diameter have been performed along one radius in the vibration direction. The result shows that local parameters fluctuate continuously around the base values in the vibration cycle. Additional bubble force due to inertia is used to explain lateral bubble motions. The fluctuation amplitudes of local void fraction and IAC increase significantly with vibration frequency. The radial distribution of local parameters at the maximum vibration displacement is specifically analyzed. In the void fraction and IAC profiles, the peak near the inner wall is weakened or even disappearing and a strong peak skewed to outer wall is gradually observed with the increase of vibration frequency. The nondimensional peak void fraction can reach a maximum of 49% and the mean relative variation of local void fraction can increase to more than 29% as the vibration frequency increases to 2.47 Hz. But the increase of vibration frequency does not bring significant change to bubble diameter.

Interfacial Area Concentration and Void Fraction of Two-Phase Flow in Narrow Rectangular Vertical Channels

1997 ◽  
Vol 119 (4) ◽  
pp. 916-922 ◽  
Author(s):  
T. Wilmarth ◽  
M. Ishii
Keyword(s):  
Void Fraction ◽  
Two Phase Flow ◽  
Ccd Camera ◽  
Interfacial Area ◽  
Separate Flow ◽  
Image Processing Technique ◽  
Phase Flow ◽  
Two Phase ◽  
Interfacial Area Concentration ◽  
Local Average

Adiabatic concurrent vertical two-phase flow of air and water through narrow rectangular channels, gap widths 1 mm and 2 mm, was investigated. This study involved the observation of flow using a charge coupled device (CCD) camera. These images were then digitized and examined by applying an image processing technique to determine local average void fraction and local average interfacial area concentration. The void fraction data were then plotted using a drift flux plot to determine the distribution parameter and vapor drift velocity for each separate flow regime.

Numerical Investigation of Air-Oil Two-Phase Flow Pattern Transition in the Scavenge Line of an Aeroengine

2021 ◽  
Author(s):  
Ghofrane Sekrani ◽  
Jean-Sebastien Dick ◽  
Sébastien Poncet ◽  
Sravankumar Nallamothu
Keyword(s):  
Void Fraction ◽  
Two Phase Flow ◽  
Numerical Models ◽  
Interfacial Area ◽  
Sudden Expansion ◽  
Phase Flow ◽  
Two Phase ◽  
Ansys Fluent ◽  
Before And After ◽  
Interfacial Area Density

Abstract Since most research investments in aeroengines have been targeted at the hot and cold sections, the oil system has remained an area poorly understood. Optimum sizing of the oil system can directly reduce the engine’s weight and specific fuel consumption while maximizing service life. The understanding of air/oil interaction in scavenge lines is required to influence the design of the oil systems and achieve those objectives. The challenge is in the existence of numerous possible flow regimes and phase interactions. In scavenge lines, a complex two-phase flow results from the interaction of sealing airflow and lubrication oil. Scavenge lines can have bends, junctions and sudden area changes which complicates their modeling by amplifying pressure gradients and turbulence generation, and causing the flow to change morphology (annular, slug, stratified, bubbly, mist, etc.). Several multiphase flow approaches have been developed to model two-phase flow in straight scavenge lines. However, up until now, no methodology is preferred by the community for simulating two-phase flow in such application. There are still many unknowns regarding the modeling of turbulence, phase interaction and the compressibility of immiscible mixtures such as air and oil. The present study compares the performance of two numerical models: Volume of Fluid (VOF) and Algebraic Interfacial Area Density (AIAD), for simulating the air/oil flow in a suddenly expanding scavenge line against the experimental data of Ahmed et al. [1–2]. The AIAD model is a two-fluid Eulerian approach newly implemented on Ansys Fluent. Discrepancies between the two models for predicting pressure loss and void fraction are evaluated and discussed into details. The flow regime before and after the sudden expansion is identified using iso-surfaces of the void-fraction and compared against visual data. Based on the results presented, recommendations are formulated for further work regarding the calibration of AIAD modeling parameters.

Numerical Simulation of the Air-Water Two-Phase Flow Across a 90-Degree Vertical-Upward Elbow

2020 ◽  
Author(s):  
Shouxu Qiao ◽  
Wenyi Zhong ◽  
Sijia Hao ◽  
Peiyao Qi ◽  
Sichao Tan
Keyword(s):  
Liquid Phase ◽  
Void Fraction ◽  
Cfd Simulation ◽  
Two Phase Flow ◽  
Fluid Model ◽  
Interfacial Area ◽  
Phase Flow ◽  
Two Phase ◽  
Interfacial Area Concentration ◽  
Flow Models

Abstract The present study investigates the air-water two-phase flow across a 90-degree vertical-upward elbow with the computational fluid dynamics (CFD) simulation. The Eulerian-Eulerian two-fluid model and the Multi Size Group (MUSIG) model are used to predict the development of the detailed interfacial structures between the two phases. The axial development of the void fraction and the interfacial area concentration are investigated and benchmarked with the experimental data measured using the four-sensor conductivity probe. It is concluded that CFD simulation can predict the characteristics distributions of void fraction and interfacial area concentration and their development downstream of the elbow. The double-peaked void fraction distribution is found to be caused by the secondary flow induced by the elbow. The liquid phase on the outer curvature moves to the inner curvature and forms a double counter rotating vortex, entraining the bubbles to form a double-peaked distribution. The elbow effects become dissipated between 33 and 63 hydraulic diameters. The simulation results of liquid-phase and gas-phase parameters can be used to develop the theoretical two-phase flow models for the elbow region.

Experimental Characterization of Two-Phase Flow Centrifugal Pumps

2010 ◽  
Author(s):  
Antonio Campo ◽  
Eugene A. Chisely
Keyword(s):  
High Speed ◽  
Two Phase Flow ◽  
Small Diameter ◽  
High Speed Photography ◽  
Phase Flow ◽  
Water Mixture ◽  
Centrifugal Pumps ◽  
Two Phase ◽  
Wide Range ◽  
Radial Pump

In this experimental work, the pressure distribution was measured in a rotating, partially shrouded, open, radial impeller, inlet diffuser and volute under a wide range of air-water two-phase flow conditions. To obtain these pressure measurements, small-diameter pressure-tap holes were drilled through the casing of the radial pump. High speed photography was the vehicle to determine the flow regime of the air-water mixture through the vane and in the volute. An analytical model was developed to predict the radial pump single- and two-phase flow pressure distributions. The distribution for the latter was compared with the test data for different suction void fractions. The physical mechanism responsible for pump performance degradation was also investigated.

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