Two-phase Flow In Minichannels Research Articles

Flow transitions during laminar stratified two-phase flow in mini channels

Flow transitions during laminar stratified two-phase flow in mini channels

Flow Pattern Identification for Gas-Liquid Two-Phase Flow in Minichannel Based on a New Optical Array Sensor

This work develops a new optical photodiode array sensor for flow pattern identification of gas-liquid two-phase flow in minichannel. The array sensor is developed by the following steps to acquire comprehensive information of the flow and maintain a simple structure: 1) optical signals of the flow are acquired by a matrix array sensor with 60 sensing elements; 2) the signals are preprocessed and divided into 5 clusters by hierarchical clustering; 3) one typical sensing element from each cluster is selected; 4) the selected elements of four typical flow patterns are combined and the final sensor structure with 7 elements is determined. Experiments of flow pattern identification based on support vector machine (SVM) is carried out to verify the feasibility of the developed sensor in a 4.04 mm diameter channel. In addition, three types of feature vectors are built, including mean value, standard deviation and frequency, and their performance on the identification is investigated. The flowrate of liquid and gas phase range from 55~332 mm/s and 8~41468 mm/s, respectively. The investigated flow patterns include bubble flow, slug flow, stratified flow and annular flow. Results verifies the feasibility of the optical sensor. Among the three types of feature vectors, the standard deviation has the best performance, while the frequency has the worst. Meanwhile, the results also demonstrate that the combination of some specific feature vectors is an effective way to improve the identification performance.

Analysis of Frictional Pressure Drop Correlations of Refrigerant Two-Phase Flow in Mini-Channel

Analysis of Frictional Pressure Drop Correlations of Refrigerant Two-Phase Flow in Mini-Channel

미니채널 내 물-에탄올 혼합물로 구성된 단일 액체 슬러그 계면 깨짐 현상에 대한 실험적 연구

A two-phase flow in mini-channels is consist with various flow regimes (such as bubble slug, annular, churn flow) according to gas and liquid phase flow rates. A previous researches revealed that in a case of slug flow in hydrophobic mini-channels, gas and liquid phase are perfectly separated by interfaces and triple contact line. In this study, the single dry slug flow experiments in circular mini-channel (D = 1.018 mm) are conducted to observe interfacial break-up phenomena in high capillary number range (Ca < 0.02). The slug is consist with D.I. water or D.I. water-ethanol binary mixtures (5% and 10%, mole fraction). On the base of previous researches, we calculate the pressure drop at moving triple contact line. In an addition, a single dry slug flow is visualized by using high-speed camera. Through the experiment, three regimes of pressure drop are observed; steady, loss, separation. As a result, criteria between steady and loss regimes is closely related to capillary number, and criteria between loss and separation regimes is related to surface tension.

Experimental study on the flow pattern and pressure gradient of air-water two-phase flow in a horizontal circular mini-channel

Experimental studies on the flow pattern and the pressure gradient of gas-liquid co-current two-phase flow in a mini-channel were conducted. The test section was a transparent circular channel of 1.6 mm inner diameter. The working fluids were air and water. The superficial velocities of gas and liquid were in the range of 0.025-66.300 m/s and 0.033-4.935 m/s, respectively. In the present works, the flow pattern and the pressure gradient data were obtained by analyzing the flow images captured bya high-speed camera, and by using the pressure transducer, respectively. As a result, it was found that (1) the obtained flow patterns were bubbly, plug, slug-annular, annular, and churn flows, (2) new experimental correlations on the bubble and plug lengths were proposed, whereas the lengths are the function of the homogeneous void fraction, (3) both gas and liquid superficial velocities affect proportionally to the pressure gradient, whereas it increases with the increase both of JG and JL. In addition, the obtained flow patterns are in a good agreement with that of the available flow pattern maps in the open literatures, such as, Triplett et al. (1999) and Chung and Kawaji (2004).

A Review on Thermal Characteristics of Single and Two-phase Flow inMini channel for Refrigeration

This paper presents an exercise in applying the bacterial foraging algorithm (BFA) optimisation method on a proportional—integral-derivative controller (PID) of a DC motor circuit. The paper presents the system description of the DC motor transfer function and the simulation of the close loop system using MATLAB. The BFA algorithm is described and discussed with the simulation results presented to illustrate the enhancement of the system response that in result enhances the operation of the DC motor system.

微細流路内における気液二相流動特性に関する研究

微細流路内における気液二相流動特性に関する研究

Characterisation of gas-liquid two-phase flow in minichannels with co-flowing fluid injection inside the channel, part II: gas bubble and liquid slug lengths, film thickness, and void fraction within Taylor flow

Current research proofs the potential of apparatuses containing minichannel flow structures to intensify gas-liquid-solid contacting processes. The excellent heat and mass transfer in these devices as well as a sharp RTD mainly result from the Taylor flow regime. A proper design of corresponding contactors requires precise information on the provided interfacial areas. However, the characterisation of gas-liquid Taylor flow with industrially relevant fluids at elevated pressure and created by capillary injection devices gained little attention so far.This work analyses adiabatic gas-liquid Taylor flow in a square minichannel of 1.0mm hydraulic diameter using water, water-glycerol, or water-ethanol mixtures as liquid phase and hydrogen or nitrogen as gas phase to cover a broad range of material parameters. In the mixing zone located within the flow channel, gas was injected into the co-flowing liquid by so-called capillary injectors with variable inner diameter (0.184, 0.317, 0.490mm).Two different bubble forming mechanisms were identified leading to a complex interaction between physical properties of the fluids, geometrical parameters and the observed gas bubble and liquid slug lengths. According to the Pi-theorem, these lengths were affected by 6 dimensionless groups, namely (uG,s/ uL,s), ReL, WeL, (dIn,CI/ dh), (dOu,CI / dh), and Θ*. Based on more than 370 experimental data, novel correlations to predict gas bubble and liquid slug lengths were developed.

Characterisation of gas-liquid two-phase flow in minichannels with co-flowing fluid injection inside the channel, part I: unified mapping of flow regimes

Present research highlights the potential of apparatuses with integrated minichannel packings to intensify gas-liquid-solid contacting. Especially an operation of these devices within the Taylor flow regime gained extraordinary attention due to its excellent heat and mass transfer and the segmented flow characteristics. However, criteria for flow regime transitions are mainly developed from water-similar fluids and are contradictory which hinders uniform flow regime prediction.This work presents a systematic analysis of adiabatic gas-liquid downflow in a square minichannel of 1.0mm hydraulic diameter. In the mixing zone located within the flow channel, gas was injected into the co-flowing liquid by so-called capillary injectors with variable inner diameter (0.184, 0.317, 0.490mm). Experiments were conducted using water, water-glycerol, and water-ethanol mixtures to cover a broad range of material properties. The gas and liquid superficial velocities were varied between 9.81·10-4…2.72m/s and 1.7·10−4…0.80m/s, respectively. Taylor flow, Taylor-annular flow, annular flow, churn flow, and bubbly flow were observed. Using the Pi-theorem, 8 significant dimensionless groups dictating the flow transition were identified, namely uG, s/uL, s, ReG, ReL, WeG, WeL, Θ*, dIn, CI/dh, and dOu, CI/dh. Based on more than 1500 experimental data, criteria for the regime transitions of Taylor flow are provided. The derived flow regime map shows good agreement for all applied liquids and for the two larger injector geometries.

Pressure drop of HFE7000 and HFE7100 during flow condensation in minichannels

Attention is focused on the issues of flow resistance and pressure drop of perspective refrigeration fluids during condensation in the two-phase flow in minichannels. The case of the flow through a cylindrical single channel of 2.3 mm inner diameter was carefully analyzed. Pressure drop tests have been performed in diabatic flow conditions. The effect of heat flux, mass flux, vapour quality and saturation temperature on the two-phase pressure drop have been scrutinised. In the course of investigations, the new fluids, namely HFE 7100 and HFE 7000, have been tested. Calibration of the measurement system for the case of single phase flow and comparison of the results with the Blasius friction correlation show the accuracy of ±15%. Additionally, the data were compared with some well established correlations for two-phase flow exhibiting that the correlation due to Fronk and Garimella (2010) and the in-house model are found in best agreement with the experimental data.

Investigation of Ring Waves in Gas–Liquid Two-Phase Flow in a Microchannel

Gas–liquid two-phase flow in minichannels and microchannels displays a unique flow pattern called ring film, in which stable waves of relatively large amplitudes appear at seemingly regular intervals and propagate in the flow direction. In this paper, the behaviors of ring waves, which correspond to ring films that appeared in ring film flow and disturbed ring film flow regions, have been investigated experimentally in gas–liquid two-phase flows of nitrogen-distilled water and nitrogen/30 wt% ethanol–water solution in a 150-μm-diameter silica tube to elucidate their generation mechanism and propagation behavior. In order to clarify the existence region and characteristics of ring waves, the flow patterns observed in a microchannel were investigated and flow pattern maps were made. Furthermore, the velocity of the ring wave was also investigated and compared with the gas slug velocity. In these velocity measurements, high-speed video images were taken at 6,000 frames per second and the formation of ring films and the relationship between the wave amplitude and velocity were determined. The results indicate an interfacial instability leading to the formation and growth of ring waves with both low and high wave amplitudes. The wave velocity is correlated to the wave amplitude, with the large amplitude waves moving much faster than the low amplitude waves. As a result, coalescence of large and low amplitude waves has been observed.

Visual investigation on the interface morphology of Taylor bubble and the characteristics of two-phase flow in mini-channel

A visual experimental investigation on Taylor bubble behavior of two-phase flow was carried out in vertical circular channels, with the length of 1000mm and inner diameter of 1mm, 2mm, 3mm and 6mm. Deionized water was used as the liquid-phase working fluid, and air, nitrogen, argon and carbon dioxide were adopted as the gas-phase working fluids. The interface morphology of Taylor bubble was recorded by a high speed camera, and the variations of pressure drop and liquid-phase mass flux were measured simultaneously. The effects of different working conditions on the interface morphology of Taylor bubble were discussed in detail, and the effect of surface tension on the Taylor bubble behavior was investigated based on the Eo (Eötvös) number and the Mo (Morton) number. Also, the fluctuations of pressure drop and liquid-phase mass flux were analyzed in detail based on the Taylor bubble behavior. Finally, a model for prediction of the two-phase flow pressure drop in mini-channel was proposed, and this model was validated based on the experimental result with good agreement.

Visual experimental investigation on oscillations of pressure drop and flow rate of two-phase flow in mini-channel

Visual experimental investigation on oscillations of pressure drop and flow rate of two-phase flow in mini-channel

510 Characteristics of gas-liquid two-phase flow in mini-channel with branch

510 Characteristics of gas-liquid two-phase flow in mini-channel with branch

Analytical and numerical investigation of heat transfer and entropy generation of stratified two-phase flow in mini-channel

In this study, developing and fully developed heat transfer and entropy generation are numerically and analytically studied in the stratified two-phase flow in a mini-channel. In the numerical study, the governing equations are solved by implementing a second order finite difference method based on the projection algorithm and the interface is reconstructed through the application of the volume of fluid method. The numerical study is carried out for two cases: one, a stratified air–water flow and the other, a stratified oil–water flow. Effects of several important parameters on the velocity and temperature fields and total entropy generation are studied. The study indicates that the total entropy generation for both cases becomes maximum at a specific Reynolds number. In the analytical investigation, the fully developed velocity and temperature profiles are derived and relations for the fully developed Nusselt numbers as well as the local entropy generation are obtained. In addition, the effects of existing parameters are studied in such a way that simplifies using the results of the analytical study by presenting generalized diagrams for the pressure gradient, interface height and Nusselt numbers in the fully developed region.

Some problems of hydrodynamics of two-phase flow mixtures in minichannels

Abstract Gas-liquid two-phase flow in minichannels has been the subject of increased research interest in the past few years. Evaluation, however, of today’s state of the art regarding hydrodynamics of flow in minichannels shows significant differences between existing test results. In the literature there is no clear information regarding: defining the boundary between minichannels and conventional channels, labelling of flow patterns. The review of literature on the hydrodynamics of gas-liquid flow in minichannels shows that, despite the fact that many research works have been published, the problem of determining the effect of diameter of the minichannel on the hydrodynamics of the flow is still at an early stage. Therefore, the paperpresents the results of research concerning determination of flow regime map for the vertical upward flow in minichannels. The research is based on a comprehensive analysis of the literature data and on the research that has been carried out. Such approach to the mentioned above problems concerning key issues of the two-phase flow in minichannels allowed to determine ranges of occurrence of flow structures with a relatively high accuracy.

Study on characteristics of vapor–liquid two-phase flow in mini-channels

To explore the mechanism of boiling bubble dynamics in narrow channels, two types of channels are investigated which have I- and Z-shaped with width of 2 mm. Using VOF model and self-programming, the whole flow field is simulated with two different kinds of media, namely, water and ethanol. The influence of wall contact angle on the process of bubble generating and growth is studied, and the relationship between different channel shapes and the pressure drop is also investigated taking into account the effects of gravity, viscosity, surface tension and wall adhesion. The bubble generation, growth and departure processes are analyzed through numerical simulation and self-programming, and the influence of interface movements and changes on internal pressure difference and average surface heat transfer coefficient is investigated by using geometry reconstruction and interface tracking. It is found that wall contact angle has a great influence on the morphology of bubble. The smaller the wall contact angles are, the more round the bubbles are, and the less time the bubbles take to depart from the wall. The variation of contact angle also has effect upon the heat transfer coefficient. The greater the wall contact angle is, the larger the bubble-covered area is, thus the wall thermal resistance gets higher, and bubble nucleation is suppressed, and the heat transfer coefficient becomes lower. The role of surface tension in the process of boiling heat transfer is much more important than the gravity in narrow channels. The generation of bubbles dramatically disturbs the boundary layer, and the bubble bottom micro-layer can enhance the heat transfer. The heat transfer coefficient of Z-shaped channels is larger than that of I-shaped ones, while the pressure drop of the former is obviously higher. In addition, surface tension and viscosity significantly impact the pressure drop of boiling system, and different specific heat and boiling point values result in different heat transfer coefficients. The simulation results in this paper match well with the experimental data revealed in other sources, both show that the heat transfer coefficient of water is higher than that of ethanol and Z-shaped channels have better heat transfer capability.

Two-Dimensional Simulations of Gas-Liquid Two-Phase Flow in Mini channels of PEM Fuel Cell Flow Field

Effective water management is one of the key strategies for improving the performance and durability of PEM fuel cells. Phenomena such as membrane dehydration, catalyst layer flooding and two-phase flow in flow-channels are all determined by the distribution and movement of water during cell operation. In this study, gas-liquid flow in mini-channels relevant to fuel cells was numerically studied using a CFD two-phase flow model in combination with a volume of fluid (VOF) method. The results show that the surface wettability of the channel wall can greatly affect the flow pattern, especially when the channel walls and the gas diffusion layer (GDL) surface possess different contact angles. When the channel walls are more hydrophobic, more water is accumulated on the GDL. An increase in the surface tension results in a slight increase of slug frequency and a slight decrease in slug length. The onset of slugging along the channel is determined by the gas-liquid mixture velocity, gas-to-liquid flow ratio and the way water is introduced into the gas flow channel. Furthermore, the calculated pressure drop fluctuations show a strong dependence on the channel liquid content and the slug length.

Gas−Liquid Two-Phase Flow in Minichannels with Liquid Side Introduction

In the present work, computational fluid dynamics (CFD) modeling with a volume of fluid (VOF) method was used to understand gas-liquid two-phase flow in PEM fuel cell flow channels under typical fuel cell flow conditions. Simulations with different liquid water introduction manners to flow channels were discussed to resemble liquid water transport in flow channels in active fuel cells. Those introduction methods included side liquid introduction through a number of ports, continuous liquid introduction along the channel with uniform and nonuniform flow rates, and liquid water introduction from the inlet together with the gas phase. The simulated results showed that the side introduction of water increases the water accumulation near the end of the channel and the gas slugs are significantly elongated, compared to the cases with water introduction from the inlet. When water was introduced nonuniformly along the channel with more near the outlet of the channel, there appears to be less probability of slug formation in the channel. With low liquid to gas volumetric flow ratios as encountered in fuel cells, the flow pattern changed between slug flow and stratified flow, depending on different liquid introduction manners. When water was introduced into the channel from ports on the bottom wall, it emerged and accumulated near the port region before slugs formed, detached, and purged out of the channel, causing high pressure drop and pressure drop fluctuations. When the wettability, or contact angle, of the channel walls varied, liquid water tended to attach to the wall surface with low contact angles, namely, more hydrophilic surface. In addition, the change in surface contact angle can also lead to the change in flow patterns. The slug frequency decreased with an increase in the port size. With increasing of the port number, more liquid tended to accumulate in the channel.

Two-Phase Flow in Minichannels: Hydrodynamics, Pressure Drop, and Residence Time Distribution

Two-phase flow in mini-channels (1 mm × 1.5 mm × 430 mm and 1.5 mm × 0.5 mm × 430 mm serpentine channel geometry) made in different materials (SS 316, PMMA and Teflon) was studied at different flow rate ratio (0.66, 1.0 and 1.56) of the two immiscible fluids. A dual syringe pump was used to pump the fluids (air−water and water-kerosene) through the channels. For characterization of the two phase flow, experiments were carried out to measure the slug size distribution and relevant hydrodynamic properties, pressure drop across a single serpentine unit (i.e., one sinusoidal unit that includes two 180° return bends connected by a straight portion of 20 mm) and also the residence time distribution of water. In all the cases, the effect of material of fabrication on the hydrodynamics was significant. Apart from flow rates and flow rate ratio of the two fluids, the slug size distribution was seen to have a strong effect of the channel orientation (vertical, horizontal) and also the flow direction (up-flow and do...