scholarly journals Influence of Capillary Number on the droplet Shape, Film Thickness, and Pressure Drop in a Liquid-Liquid Taylor Flow inside a Microcapillary

2019 ◽  
Vol 4 (6) ◽  
pp. 1407-1419
Author(s):  
S. V. B. Vivekanand ◽  
S. Chandrasekhar ◽  
V. R. K. Raju
Keyword(s):  
Fluid Flow ◽  
Pressure Drop ◽  
Film Thickness ◽  
Flow Regime ◽  
Capillary Number ◽  
Slug Flow ◽  
Internal Diameter ◽  
Droplet Shape ◽  
Taylor Flow ◽  
Circular Microchannel

Numerical analysis of a two-dimensional, axisymmetric, incompressible, laminar liquid-liquid Taylor flow inside a vertical circular microchannel is carried out in the present study. The focus is laid on fluid flow characteristics in the slug flow regime. Although many researchers have performed numerical and experimental studies of two-phase flows in narrow channels, their efforts seem to have been fairly successful in explaining the underlying mechanisms of fluid flow phenomena, especially for slug flow regime. Here, an attempt has been made to explore the hydrodynamics of such flows. In the present study, dodecane and Pd5 have been used as the carrier phases and water is used as the discontinuous phase. The internal diameter of the circular microchannel is 1.5 mm with its wall being insulated. The flow and volume fraction equations are solved by the finite volume approach (FVM). The volume of fluid (VOF) method has been adopted for capturing the interface. The effect of Capillary number on film thickness and interfacial pressure drop is explained. The film thickness is found to increase with Capillary number and is also found to be in a close match with the models available in the literature. The pressure drop per unit length obtained from the CFD study is compared with a standard model available in the literature. The pressure drop across the unit cell is found to be following the phenomenological model. It is observed that the pressure drop at the interface has the highest contribution to the total pressure drop in contrast to the other pressure drops in the channel, with ~50-55% in dodecane-water and ~55-62% in Pd5-water systems. Besides, the distribution of the velocity, axial, and wall pressure fields inside the microcapillary are also discussed.

Investigation of Liquid Loading in Gas Well: Simultaneous Measurements of Drop-Size, Film Thickness and Pressure Drop

2010 ◽  
Author(s):  
Mhunir B. Alamu ◽  
Barry J. Azzopardi ◽  
Gerrit P. van der Meulen ◽  
Valente Hernandez-Perez
Keyword(s):  
Pressure Drop ◽  
Film Thickness ◽  
Drop Size ◽  
Two Phase Flow ◽  
Measurement Instrument ◽  
Dominant Frequency ◽  
Internal Diameter ◽  
Phase Flow ◽  
Two Phase ◽  
Frequency Space

The mechanism of atomization of part of the liquid film to form drops in annular two-phase flow is not entirely understood. It has been observed that drop creation only occurs when there are large disturbance waves present on the film interface. Woodmansee and Hanratty [1] observed that ripples on these waves were a precursor to drops. Though it has been reported that drops occur in bursts by Azzopardi [2], all previous drop size or concentration measurements have always been time integrated to simplify data analysis. Dynamic time averaged drop-size measurements are reported for the first time for annular two-phase flow. Experiments were carried out on a 19mm internal diameter vertical pipe with air and water as fluids. Spraytec, a laser diffraction-based, drop size measurement instrument, was used in the data acquisition. Simultaneous time-resolved measurements were made of: film thickness using conductance probes employing a pair of flush mounted rings as electrodes; and pressure gradient. The gas superficial velocity was 13–43 m/s at liquid superficial velocities of 0.05 and 0.15 m/s. Additional tests were carried out with the gas velocity at 14 m/s for liquid superficial velocities of 0.03–0.18 m/s. Though structures are not clearly visible in the signals acquired, they have been analyzed in amplitude and frequency space to yield Probability Density Function (PDF) and to identify the dominant frequency. Cross-correlation between two film thickness probes provides the wave velocities. Based on the signal analysis, links between film thickness, drop concentration and pressure drop have been identified.

Pressure Drop of Liquid-Liquid Taylor Flow in Mini-Scale Coiled and Curved Tubing

2019 ◽  
Author(s):  
W. Adrugi ◽  
Y. S. Muzychka ◽  
K. Pope
Keyword(s):  
Experimental Study ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Slug Flow ◽  
Silicone Oil ◽  
Radius Of Curvature ◽  
Asymptotic Model ◽  
Dean Number ◽  
Taylor Flow ◽  
Low Viscosity

Abstract This paper presents an experimental study on pressure drop using non-boiling liquid-liquid Taylor flow in mini scale coiled and curved tubing. Experiments were carried out to measure the pressure drop characteristics by varying the numbers of turns in coiled tubes and the lengths of curved tubes of less than one turn, such that Dean number, Reynolds number, radius of curvature, and coil pitch were considered. A set of narrow coiled tubes (ID = 1.59 mm, 1.27 mm, 1.016 mm) was used as test sections with different radii of curvature and overall lengths, and thus a different quantity of turns. Water and 1 cSt low viscosity silicone oil were used to create a segmented slug flow. An asymptotic model is developed based on the experimental results and previous models to predict the pressure drop, based on Dean number and dimensionless slug length. The effects of varying tube curvature and tube diameter are also studied. The results provide new insights into the effect of coiling and secondary flow on pressure drop for a liquid-liquid Taylor flow in mini scale systems.

An Improved Correlation for Two-Phase Frictional Pressure Drop in Boiling and Adiabatic Downflow in the Annular Flow Regime

1991 ◽  
Vol 205 (5) ◽  
pp. 317-328 ◽  
Author(s):  
J F Klausner ◽  
B T Chao ◽  
S L Soo
Keyword(s):  
Pressure Drop ◽  
Film Thickness ◽  
Flow Regime ◽  
Annular Flow ◽  
Volume Fraction ◽  
Interfacial Shear Stress ◽  
Published Data ◽  
Two Phase ◽  
Frictional Pressure Drop ◽  
Wide Range

An improved correlation is presented for annular two-phase frictional pressure drop data for vertical downflow. An ideal dimensionless film thickness based on the vapour volume fraction, a characteristic friction factor based on the two-phase frictional pressure gradient and a Weber number relevant for the interfacial capillary wave structure are the correlating parameters. The proposed new correlating scheme is tested against a wide range of data obtained in this investigation for refrigerant R11 in forced convection boiling and in adiabatic test sections of 19 mm cylindrical cross-section as well as published data for air-water and air-glycerine solution mixtures in the annular flow regime. Over 80 per cent of the measured values fall within ±30 per cent of those predicted from the correlation. Due to the wide range of liquid film thickness covered, 0.05–2.9 mm, its validity extends past the range where previously reported downflow pressure drop correlations fail. A paradox connected with previously reported annular downflow pressure drop correlations based on the liquid-vapour interfacial shear stress is pointed out. Upflow frictional pressure drop data in the annular flow regime can also be correlated by the proposed scheme.

Pressure drop and fluid flow regime of air inspired into the human lung

1970 ◽  
Vol 28 (4) ◽  
pp. 482-494 ◽  
Author(s):  
D. E. Olson ◽  
G. A. Dart ◽  
G. F. Filley
Keyword(s):  
Fluid Flow ◽  
Pressure Drop ◽  
Flow Regime ◽  
Human Lung

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.

Liquid Film Thickness in Micro Channel Slug Flow

2009 ◽  
Author(s):  
Naoki Shikazono ◽  
Youngbae Han
Keyword(s):  
Boundary Layer ◽  
Film Thickness ◽  
Liquid Film ◽  
Capillary Number ◽  
Slug Flow ◽  
Thin Liquid Film ◽  
Inertial Force ◽  
Liquid Film Thickness ◽  
Micro Channel ◽  
Viscous Boundary Layer

Slug flow is the representative flow regime of two-phase flow in micro channels. It is well known that the thin liquid film formed around the confined vapor bubble plays an important role in micro channel heat transfer. In the present study, experiments are carried out to clarify the effects of parameters that affect the formation of the thin liquid film in micro channel slug flow. Laser focus displacement meter is used to measure the thickness of the thin liquid film. Air, ethanol, water and FC-40 are used as working fluids. Circular tubes with five different diameters, D = 0.3, 0.5, 0.7, 1.0, 1.3 mm, and square channels with two different sizes, 0.3 × 0.3 and 0.5 × 0.5 mm, are used. It is confirmed that the liquid film thickness is determined only by capillary number at small capillary numbers. However, the effect of inertial force and flow acceleration cannot be neglected as capillary number increases. The effect of cross sectional shape is also investigated. Experimental correlation for the adiabatic liquid film thickness in circular tubes based on capillary number, Reynolds number and Weber number is proposed. When viscous boundary layer is thin, liquid film thickness is limited by the viscous boundary layer thickness. Thus, in order to develop precise flow boiling models in micro tubes, it is important to consider the effects of inertial force and boundary layer thickness on the liquid film thickness.

Unique Characteristics of Adiabatic Gas-Liquid Flows in Microchannels: Diameter and Shape Effects on Flow Patterns, Void Fraction and Pressure Drop

2003 ◽  
Author(s):  
M. Kawaji ◽  
P. M.-Y. Chung
Keyword(s):  
Pressure Drop ◽  
Void Fraction ◽  
Slug Flow ◽  
Annular Flow ◽  
Two Phase Flow ◽  
Interfacial Structure ◽  
Phase Flow ◽  
Two Phase ◽  
Circular Microchannel ◽  
Square Microchannel

Microfluidics is a rapidly developing area of research with great potential for a wide range of applications in many fields. One area of microfluidics is gas-liquid two-phase flow in microchannels, which is important for the development of microreactors, lab-on-a-chip systems, micro heat exchangers and micro-heat pipes, among others, that are highly relevant to industry. Recently, much interest has also been shown toward studying the two-phase flow in micro fuel cells. This keynote paper presents a state-of-the-art review of past and present research on adiabatic two-phase flow in minichannels and microchannels, which are considered to have channel diameters between 250 μm–6 mm, and less than 250 μm, respectively. From this review, certain differences between minichannels and microchannels are identified. These notable differences are also explained, based on some of our recent experiments on two-phase flow in microchannels. Our experiments have been performed using several microchannels to determine the effects of the microchannel diameter and shape on the adiabatic two-phase flow of nitrogen gas and de-ionized water. The effect of channel geometry was examined by characterizing the two-phase flow in a circular and square microchannel of similar hydraulic diameter. A video camera was used to capture images of the gas-liquid interfacial structure. From the video recordings, it became clear that the channel size strongly influences the two-phase flow patterns occurring in the circular microchannel. The flow pattern was predominantly intermittent, exhibiting alternating sequences of liquid and gas slugs. Only slug flow was observed in the microchannel for all flow conditions tested. There were no instances of bubbly flow, churn flow, slug-annular or annular flow, as reported for minichannels. Instead, four new sub-classes of slug flow were defined to better describe the interfacial structure in the time average sense: slug-ring flow, ring-slug flow, semi-annular flow and multiple flow. The time-averaged void fraction was estimated from the recorded images of the two-phase flow structure. It was found that as the channel diameter decreased, the void fraction data deviated more from those obtained for minichannels. A new void fraction correlation was developed for both the circular and square microchannels, which differs significantly from those developed for minichannels. In both microchannels, the two-phase pressure drop was best predicted by treating the two phases as being non-homogeneous and having a large velocity difference. This result was consistent with the occurrence of slug flow and significant departure of the average void fraction from those in minichannels. A possible explanation for the strong deviation of void fraction data in microchannels from the correlations applicable to minichannels is offered based on a phenomenological examination of the flow structure. Regarding the effect of microchannel geometry, the experimental results showed little difference in the void fraction and pressure drop data. However, the two-phase flow regime maps were not the same between the circular and square microchannels. The transition boundaries of the sub-categories of slug flow were noticeably shifted. The region of ring-slug flow in the circular microchannel disappeared in the square microchannel, which can be attributed to the suppression of the liquid-ring film due to the accumulation of liquid in the corners of the square microchannel.

scholarly journals Experimental Investigation of Annular Flow Behaviour in Horizontal Pipe

2021 ◽  
Vol 13 (6) ◽  
Author(s):  
Osokogwu Osokogwu ◽  
◽  
Uche Uche ◽  
Keyword(s):  
Film Thickness ◽  
Liquid Film ◽  
Slug Flow ◽  
High Speed ◽  
Annular Flow ◽  
Flow Behavior ◽  
Liquid Film Thickness ◽  
Experimental Investigations ◽  
Internal Diameter ◽  
Horizontal Pipe

The experimental investigations of annular flow were conducted in horizontal pipe using water/air in a 0.0504m internal diameter pipe loop with a total length of 28.68m. To understand annular flow behaviors, conductivity ring sensors, conductance probe sensors and Olympia high speed digital camera were used. In all the experiments, emphasis were on annular flow behavior, phase distribution and liquid film thickness. Liquid film thickness was observed to be thicker mostly when the superficial gas velocities were within 8.2699 m/s to 12.0675 m/s. Above the aforementioned superficial gas velocities, the flow became uniformly distributed on the walls of the internal pipe diameter hence reducing the thicker liquid film at the bottom with gas core at the center of the pipe. More so, annular-slug flow was discovered in the investigation. At superficial liquid velocity of 0.0505 m/s-0.1355 m/s on superficial gas velocities of 8.2699 m/s – 12.0675 m/s, annular-slug flow was prominent. Also discovered was at superficial liquid velocities of 0.0903 m/s - 0.1355 m/s with respect to superficial gas velocities of 13.1692 m/s – 23.4575 m/s, the pipe walls are fully covered with liquid film at very high speed at the entire walls (upper walls and bottom). Also discovered in this experiment is the wavy flow of the upper walls. The liquid film thickness that flows at the upper pipe walls, creeps in a wavy flow. Therefore, the entire flow behavior in an annular flow could be grouped into; wavy-flow at the upper walls, annular-slug flow and thicker liquid film at the bottom with gas core at the center.

scholarly journals Numerical Prediction of Heat Transfer and Fluid Flow Characteristics in a Circular Microchannel with Bifurcation Plate

2019 ◽  
Vol 4 (6) ◽  
pp. 1384-1396
Author(s):  
Valaparla Ranjith Kumar ◽  
Karthik Balasubramanian ◽  
K. Kiran Kumar
Keyword(s):  
Fluid Flow ◽  
Pressure Drop ◽  
Heat Dissipation ◽  
Numerical Study ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Channel Length ◽  
Plate Length ◽  
Circular Microchannel ◽  
Fluid Flow Characteristics

Hydrothermal characteristics in circular wavy microchannels (CWMCs) with bifurcation plate have been numerically studied and compared with hydrothermal performance of sinusoidal wavy microchannels (SWMCs). Numerical study were carried out considering the Reynolds number (Re) ranging from 100 to 300. It was observed that, as the fluid flows through CWMC, it continuously absorbs heat from the channel leading to decrease in the temperature difference between the channel and the fluid. Hence, heat dissipation along the channel length decreases. To augment the heat dissipation along the fluid flow direction in CWMC, bifurcation plate (BFP) is introduced in the middle of the channel. CWMC with bifurcation plate has shown higher Nusselt number (Nu) with pressure drop penalty. The parametric study on bifurcation plate length was also carried out to minimize the pressure drop penalty and to achieve higher Nu. It is identified that CWMC with bifurcation plate length of 12.5 mm gives higher Nu with pressure drop penalty. Nu is further enhanced by providing slots on bifurcation plate. It is concluded that CWMC with BFP(10 mm) having slots gives the highest Nu than any other designs with pressure drop penalty.

Simultaneous Investigation of Entrained Liquid Fraction, Liquid Film Thickness and Pressure Drop in Vertical Annular Flow

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
M. B. Alamu ◽  
B. J. Azzopardi
Keyword(s):  
Time Series ◽  
Data Analysis ◽  
Pressure Drop ◽  
Film Thickness ◽  
Liquid Film ◽  
Annular Flow ◽  
Drop Size ◽  
Liquid Fraction ◽  
Superficial Velocity ◽  
Internal Diameter

The mechanism of atomization of part of the liquid film to form drops in annular two-phase flow is not entirely understood. It has been observed that drop creation only occurs when there are large disturbance waves present on the film interface. (Woodmansee and Harrantty, 1969, “Mechanisms for the Removal of Droplets From a Liquid Surface by a Parallel Air Flow,” Chem. Eng. Sci., 24, pp. 299–307) observed that ripples on these waves were precursors to drops. Though it has been reported that drops occur in bursts by (Azzopardi, Gas-Liquid Flows Begell House Inc., New York, 2006), all previous drop size or concentration measurements have always been time integrated to simplify data analysis. Dynamic time averaged drop size measurements are reported for the first time in annular flow. Experiments were carried out on a 19 mm internal diameter vertical pipe with air and water as fluids. Spraytec, a laser diffraction-based, drop size measurement instrument, was used in the drop related data acquisition. Simultaneous time-resolved measurements were carried out for drop, film thickness, and pressure drop. Film thickness has been measured using the conductance probes employing a pair of flush mounted rings as electrodes. Pressure drop was logged using differential pressure cell connected to two pressure taps located within the test section. The gas superficial velocity was varied systematically from 13 to 43 m/s at fixed liquid superficial velocities of 0.05 and 0.15 m/s, respectively. Additional tests were carried out with the gas velocity fixed at 14 m/s while the liquid superficial velocity was varied from 0.03 to 0.18 m/s. Signal acquired are presented in form of time series to permit data analysis at different levels. Based on signal analysis, interrelationships between liquid film where the drops are sourced and the contribution of the entrained liquid droplets to the overall pressure drop in the system has been elucidated. Though structures are not clearly visible in the signals acquired, the time series have been analyzed in amplitude space to yield probability density function (Pdf). Beyond gas superficial velocity of 30 m/s, Pdf of drop size distribution becomes monomodal or single-peaked marking transition to mist annular flow.

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