Pressure Drop In Slug Flow Research Articles

Experimental study on length, liquid film thickness and pressure drop of slug flow in horizontal narrow rectangular channel

In this paper, a visualization investigation for the characteristic parameter (velocity, length, liquid film thickness, etc.) and pressure drop of slug flow in a narrow rectangular channel with a cross-sectional area of 68 mm × 1.9 mm was carried out under horizontal condition. The slug bubble velocity is linearly related to the two-phase mixture velocity. The slug bubble velocity of laminar flow zone (Relo<2500) and turbulent flow zone (Relo≥2500) was fitted, respectively. The slug bubble liquid film thickness was measured based on PCB (Printed Circuit Board) liquid film sensor. The experiment results show that the liquid film thickness increased with increasing Ca under Reb<3100, while liquid film thickness approximately a constant under Reb≥3100. A new correlation for predicting liquid film thickness was proposed and validated with 210 available data. Moreover, based on the present and published data, a new slug bubble length correlation was also developed. The slug frequency increases significantly with the increasing liquid flow rate and decreases slightly with the increasing gas flow rate. But the flow condition has little influence on the slug length. Existing correlations for pressure drop based on separated flow model were summarized and evaluated with the current data. Lee’s correlation perform well for the region dominated by surface tension(Reb<3100) while Chisholm’s correlation perform well for the region dominated by inertia force (Reb≥3100).

Effect of fluid viscosities on the liquid-liquid slug flow and pressure drop in a rectangular microreactor

The hydrodynamics of liquid–liquid slug flow with various fluid systems were investigated, aiming at revealing the viscous effects of both phases. The operation range, droplet formation, film thickness and pressure drop of slug flow were studied and discussed. The results reveal the importance of inertia and viscous forces of both phases in the transition of flow patterns. Accordingly, a universal flow map based on composite terms of CacRec0.5 and CadRed0.5 was adopted, which worked well for a wide viscosity range. For droplet formation in the present system, both the squeezing and shearing regimes deviated from the classical ideal models. Under higher capillary number, the film was accumulated at the corners and lateral planes, leading to distinct droplet shapes from literature. For the two-phase pressure drop, new empirical correlations were proposed to describe the recirculation inside both the droplets and slugs. The findings can provide better guidance for optimized reactor design.

Experimental analysis of horizontal liquid-gas slug flow pressure drop in d-type corrugated pipes

Slug flows are commonly found in oil and gas offshore production operations, where pressure drop estimation is essential for facilities design. Several studies have been made to evaluate pressure drop for slug flows in smooth pipes. However, many offshore oil production lines consist of corrugated pipes, and the drag induced by the discrete cavities is rarely investigated for slug flows. For this purpose, an experimental flowloop was designed to measure pressure drop of air-water slug flows in 26mm-ID corrugated pipes with four different groove geometries, consistent with the groove configurations used in offshore petroleum exploitation. The experimental data is regressed using the concept of pressure drop multipliers. Whilst this procedure is well established in literature for smooth pipes, an additional multiplier associated to the effect of the corrugated pipe on the pressure drop is proposed in this work. With such approach, a correlation for the pressure drop in horizontal liquid-gas slug flows in corrugated pipes is obtained by means of the groove geometry and the flow input data. Comparison of the proposed model predictions with experimental data shows ±7% accuracy.

Pressure drop of three-phase liquid–liquid–gas slug flow in round microchannels

In this paper we present a model for the calculation of pressure drop of three-phase liquid–liquid–gas slug flow in microcapillaries of a circular cross section. Introduced models consist of terms attributing for frictional and interfacial pressure drop, incorporating the presence of a stagnant thin film at the wall of the channel. Different formulations of the interfacial pressure drop equation were employed, using expressions developed by Bretherton (J Fluid Mech 10:166–188, 1961), Warnier et al. (Microfluid Nanofluid 8:33–45, 2010) or Ratulowski and Chang (Phys Fluids A 1:1642–1655, 1989). Models were validated experimentally using oleic acid–water–nitrogen and heptane–water–nitrogen three-phase flows in round Teflon or Radel R microchannels of 254- and 508-µm nominal inner diameter, for capillary numbers Cab between 10−4 and 4.9 × 10−1 and Reynolds numbers Re between 0.095 and 300. Best agreement between measured and calculated values of pressure drop, with relative error between −22 and 19 % or −20 and 16 %, is reached for Warnier’s or Ratulowski and Chang’s interfacial pressure drop equation, respectively. The results prove that three-phase slug flow pressure drop can be successfully predicted by extending existing two-phase slug flow correlations. Good agreement of Bretherton’s equation was reached only at lower Ca numbers, indicating that an extension of the interfacial pressure drop equation as performed by Warnier et al. (Microfluid Nanofluid 8:33–45, 2010) or Ratulowski and Chang (Phys Fluids A 1:1642–1655, 1989) for higher capillary numbers is necessary. Additionally it was demonstrated that pressure drop increases substantially if dry slug flow occurs or if microchannels with significant surface roughness are employed. Those influences were not accounted for in the models presented.

An improved version of drift-flux model for predicting pressure-gradient and void-fraction in vertical and near vertical slug flow

Slug flow research has received continuous and strong attention by many investigators for many years and various predictive models have been developed for calculating slug hydrodynamics. Some researchers relied on experimental data correlation while some modelled the slug flow to simulate the behaviour sufficiently accurately to estimate pressure drops. Because slug flow is the most common flow in producing wells, this leads to the pressure drop being underestimated/overestimated significantly. The intent of this study is to present an alternative approach to modelling slug flow. The proposed model considered wall shear stress in the liquid slug zone and the wall shear stress in the film zone in estimating the pressure drop in slug flow which have been neglected in most literatures. The proposed models are compared with published data from diverse sources and agree well with the experimental data.

Gas–liquid–liquid three-phase flow pattern and pressure drop in a microfluidic chip: similarities with gas–liquid/liquid–liquid flows

We report a three-phase slug flow and a parallel-slug flow as two major flow patterns found under the nitrogen-decane-water flow through a glass microfluidic chip which features a long microchannel with a hydraulic diameter of 98 μm connected to a cross-flow mixer. The three-phase slug flow pattern is characterized by a flow of decane droplets containing single elongated nitrogen bubbles, which are separated by water slugs. This flow pattern was observed at a superficial velocity of decane (in the range of about 0.6 to 10 mm s(-1)) typically lower than that of water for a given superficial gas velocity in the range of 30 to 91 mm s(-1). The parallel-slug flow pattern is characterized by a continuous water flow in one part of the channel cross section and a parallel flow of decane with dispersed nitrogen bubbles in the adjacent part of the channel cross section, which was observed at a superficial velocity of decane (in the range of about 2.5 to 40 mm s(-1)) typically higher than that of water for each given superficial gas velocity. The three-phase slug flow can be seen as a superimposition of both decane-water and nitrogen-decane slug flows observed in the chip when the flow of the third phase (viz. nitrogen or water, respectively) was set at zero. The parallel-slug flow can be seen as a superimposition of the decane-water parallel flow and the nitrogen-decane slug flow observed in the chip under the corresponding two-phase flow conditions. In case of small capillary numbers (Ca ≪ 0.1) and Weber numbers (We ≪ 1), the developed two-phase pressure drop model under a slug flow has been extended to obtain a three-phase slug flow model in which the 'nitrogen-in-decane' droplet is assumed as a pseudo-homogeneous droplet with an effective viscosity. The parallel flow and slug flow pressure drop models have been combined to obtain a parallel-slug flow model. The obtained models describe the experimental pressure drop with standard deviations of 8% and 12% for the three-phase slug flow and parallel-slug flow, respectively. An example is given to illustrate the model uses in designing bifurcated microchannels that split the three-phase slug flow for high-throughput processing.

Characterization of wettability effects on pressure drop of two-phase flow in microchannel

The Characterization of the effects of surface wettability and geometry on pressure drop of slug flow in isothermal horizontal microchannels is investigated for circular and square channels with hydraulic diameter (Dh) of 700 μm. Flow visualization is employed to characterize the bubble in slug flow established in microchannels of various surface wettabilities. Pressure drop increases with decrease in surface wettability, while the channel geometry influences slug frequency. It is observed that the gas–liquid contact line in advancing and receding interfaces of bubble change with surface wettability in slug flows. Flow resistance, where capillary force is important, is estimated using Laplace–Young equation considering the change of dynamic contact angles of bubble. The experimental study also demonstrates that the liquid film presence elucidates the pressure drop variation of slug flows at various surface wettabilities due to diminishing capillary effect.

Pressure drop of slug flow in microchannels with increasing void fraction: experiment and modeling

Pressure drop in a gas-liquid slug flow through a long microchannel of rectangular cross-section was investigated. Pressure measurements in a lengthy (∼0.8 m) microchannel determined the pressure gradient to be constant in a flow where gas bubbles progressively expanded and the flow velocity increased due to a significant pressure drop. Most of the earlier studies of slug flow in microchannels considered systems where the expansion of the gas bubbles was negligible in the channel. In contrast, we investigated systems where the volume of the gas phase increased significantly due to a large pressure drop (up to 1811 kPa) along the channel. This expansion of the gas phase led to a significant increase in the void fraction, causing considerable flow acceleration. The pressure drop in the microchannel was studied for three gas-liquid systems; water-nitrogen, dodecane-nitrogen, and pentadecane-nitrogen. Inside the microchannel, local pressure was measured using a series of embedded membranes acting as pressure sensors. Our investigation of the pressure drop showed a linear trend over a wide range of void fractions and flow conditions in the two-phase flow. The lengths and the velocities of the liquid slugs and the gas bubbles were also studied along the microchannel by employing a video imaging technique. Furthermore, a model describing the gas-liquid slug flow in a long microchannel was developed to calculate the pressure drop under conditions similar to the experiments. An excellent agreement between the developed model and the experimental data was obtained.

Liquid–liquid slug flow: Hydrodynamics and pressure drop

In this paper, the hydrodynamics and the pressure drop of liquid–liquid slug flow in round microcapillaries are presented. Two liquid–liquid flow systems are considered, viz. water-toluene and ethylene glycol/water-toluene. The slug lengths of the alternating continuous and dispersed phases were measured as a function of the slug velocity (0.03–0.5 m/s), the organic-to-aqueous flow ratio (0.1–4.0), and the microcapillary internal diameter (248 and 498 μm). The pressure drop is modeled as the sum of two contributions: the frictional and the interface pressure drop. Two models are presented, viz. the stagnant film model and the moving film model. Both models account for the presence of a thin liquid film between the dispersed phase slug and the capillary wall. It is found that the film velocity is of negligible influence on the pressure drop. Therefore, the stagnant film model is adequate to accurately predict the liquid–liquid slug flow pressure drop. The influence of inertia and the consequent change of the slug cap curvature are accounted for by modifying Bretherton’s curvature parameter in the interface pressure drop equation. The stagnant film model is in good agreement with experimental data with a mean relative error of less than 7%.

Two-Phase Slug Flow Pressure Drop in a Tee-Junction

Two-Phase Slug Flow Pressure Drop in a Tee-Junction

Experimental Apparatus for Measurements of Two-Phase Slug Flow Pressure Drop in a T-Junction

An experimental test loop system was designed, developed, and constructed to study the two-phase flow field in the undergraduate fluid mechanics laboratory. The purpose of this experimental apparatus is to measure the pressure drop of a two-phase mixture in a tee-junction. This paper describes a fluid mechanics experiment designed for undergraduate students to examine the pressure differences through a T-junction of an air–water mixture in slug two-phase flow regime with equal-sided diameters. This can be carried out at different inlet qualities and extraction rates. Sample results are presented.

Computational and experimental investigation of the drag reduction and the components of pressure drop in horizontal slug flow using liquids of different viscosities

Computational and experimental investigation in 10-cm ID horizontal pipes have been carried out utilizing carbon dioxide as the gas phase and two types of oil with different viscosities; namely 0.0025 Pa s and 0.05 Pa s, as the liquid phase. The influence of oil viscosity on the magnitude of total pressure drop and each of its components as well as the effectiveness of a drag reducing additive (DRA, CDR WS 500 M flow improver) in decreasing the pressure loss was investigated in two-phase oil–gas slug flow. The effects of changing oil viscosity on the contribution of frictional and accelerational components to total pressure drop in slug flow were also examined and analyzed. Computations of accelerational and frictional components of pressure drop were performed. The accelerational component of pressure drop was dominant in the 0.0025 Pa s oil while the frictional component had significant contributions in the 0.05 Pa s oil. Despite the fact that the magnitude of drag reduction was higher in the 0.05 Pa s oil, the DRA was more effective in reducing the total pressure drop and its components in the 0.0025 Pa s oil.

Influence of Liquid Viscosity on the Pressure Loss and the Effectiveness of Drag-Reducing Agents in Horizontal Slug Flow

Measurements of drag reduction in two-phase oil-gas slug flow are presented in this study. Two types of oil with markedly different viscosities were examined in 10-cm inner diameter horizontal pipes to evaluate the influence of oil viscosity on the total pressure loss and the effectiveness of drag-reducing agents (DRAs) in reducing the pressure drop in slug flow. The total pressure drop in the 50-cP oil was always more significant than in the 2.5-cP oil, especially when increasing the gas flow rate. However, the DRA was more effective in reducing the total pressure drop in the 2.5-cP oil. Furthermore, increasing liquid velocity, thus increasing liquid volume fraction, resulted in an increase in the DRA effectiveness for both oils.

Quantitative Analysis of Drag Reduction in Horizontal Slug Flow

Summary Calculations have been made to predict the components of pressure drop in slug flow. This analysis is aimed at understanding, in a quantitative manner, the contributions of both frictional and accelerational components to total pressure drop in horizontal slug flow and the effect of drag reducing agents (DRAs) on each component. Experimental results were in good agreement with predicted values. The DRA used in this study was effective in reducing both components of the pressure drop. The accelerational component was found to be dominant and formed more than 80% of the total pressure drop. It increased dramatically with increasing superficial gas velocity. With the addition of 20 ppm DRA, the accelerational and frictional components were noticed to decrease by a factor of 70%. At DRA concentration of 50 ppm, they decreased by a factor of 80%. Total drag reduction was found to generally decrease at higher superficial gas velocities. In sharp contrast with expectations, the drag reduction was recovered mainly from the accelerational component, indicating that the DRA worked not only in the buffer zone but also in the mixing zone in the slug body. The accelerational drag reduction reached values as high as 89% of total drag reduction.

A slugh-churn flow model for small-diameter airlift pumps

In an airlift pumping process, air is injected into the pipe containing the fluid to be transferred. Small-diameter airlift pumps are in particular used for corrosive or radioactive liquids. Detailed experiments including differential pressure and void fraction measurements, are carried out on a 10 mm-diameter setup. Based on the results obtained, it is shown that existing models are not appropriate for small diameter airlifts, particularly because they overpredict the frictional pressure drop in slug flow. A new steady state airlift model is proposed. The pressure gradient in the riser is predicted by a combination of specific models describing slug and churn flow. These models are based on the available literature on two-phase flow. The particular structure of slug flow is accounted for by a cellular model. The model proposed represents an accurate analysis tool for the design of small diameter (up to 40 mm), tall (length-to-diameter ratio greater than 250) airlifts.