Gas Reynolds Number Research Articles

Analysis of interfacial dynamics in stratified and wavy-stratified flow using Laser Doppler Velocimetry

Interfacial behaviour of stratified and wavy-stratified flow is analysed in terms of measured velocity signals in liquid phase using Laser Doppler Velocimetry. Measurement of liquid height (interface level) is achieved using Laser Doppler Velocimetry synchronized with a computerised 3-dimensional traverse system. The precision obtained in measurement of air sheared interface level (liquid height) in this approach is 0.032±0.01 mm. First part of this paper deals with influence of gas and liquid superficial Reynolds numbers on the liquid height for stratified and wavy-stratified flow. With increase in liquid depth, waves are initiated at the gas-liquid interface which is precursor to slug formation. A critical liquid height for onset of slug formation is obtained in this part. The second part deals with the measurement of fluctuations occurring near to the air-sheared interface. These fluctuations are recorded in terms of local velocity of liquid phase and have been used to characterize the behaviour of air-water interface for stratified and wavy-stratified flow. Furthermore, influence of gas and liquid flow rates on local liquid velocity for different stratified and wavy-stratified flow conditions is analysed by plotting the axial velocity profiles in radial direction.

Measurement of thickness and analysis on flow characteristics of upper swirling liquid film in gas-liquid cylindrical cyclone

The gas-liquid cylindrical cyclone (GLCC) is a device used to separate gas from liquid in offshore or subsea oil and gas production systems. The liquid film swirling along the upper cylinder wall in the GLCC is referred to as “upper swirling liquid film” (USLF). The flow patterns of USLF have a great influence on GLCC’s separation performance. However, the dynamics of the gas-liquid flow in a GLCC, especially the USLF characteristics, have not been well understood. In this study, experiments were conducted to investigate flow characteristics of USLF in a GLCC. The range of gas and liquid Reynolds numbers, Reg and Rel, was 27,869 ≤ Reg ≤ 68,120 and 2,881 ≤ Rel ≤ 14,335 respectively. The USLF’s thickness was measured using button electrodes. The results showed that the liquid film became thinner after leaving the inlet and the circumferential fluctuation of the thickness was not significant. The gas-liquid velocities had significant influences on film thickness, which increased almost linearly as liquid velocity increased, while presented a roughly S-shaped distribution as gas velocity increased. The friction factors of GLCC were determined based on the measured liquid film thickness and pressure drop. Additionally, the USLF’s flow patterns include swirling annular flow and swirling churn flow. Finally, a judgment criterion for flow pattern transition was established under the minimum gas-liquid interfacial stress theory. The model could accurately predict the transition condition. This work may provide a basis for comprehensive understanding of USLF characteristics.

Force balance droplet entrainment model for the horizontal stratified flow condition

Under the horizontal stratified flow condition, a droplet with a large interfacial area influences the mass, momentum, and heat transfer between the gas and liquid phases. In this study, we developed a force balance droplet entrainment rate model applicable to the horizontal stratified flow condition. This model is based on the balance of forces that act on the interfacial wave, which consists of an interfacial shear force, a surface tension force, and the force of gravity. In addition, the force balance droplet entrainment rate model includes constitutive relations for the parameters that are related to the geometry and the characteristics of the interfacial wave. This includes the wave frequency, wave height, wave slope, the wave velocity along the flow direction, and the lateral length of the interfacial wave along the circumferential direction of the flow pipe. The prediction of the onset of entrainment by the proposed force balance droplet entrainment rate model was compared to that with the existing models. Subsequently, the model was evaluated with the latest droplet deposition rate correlation from the literature against the experimental data obtained under the horizontal stratified flow condition. It showed a good prediction capability with a MAPE of 15.34%. Finally, the applicability of the force balance droplet entrainment rate model to a large-sized pipe was investigated. The force balance model showed a reasonable prediction performance. The applicable ranges of the gas and liquid Reynolds numbers (Reg and Rel, respectively) proposed by droplet entrainment rate model are 65,500–571,400 and 170–11,000, respectively.

An experimental study of refrigerant distribution in an automotive condenser

The literature shows almost no prior investigations on two-phase flow distribution in a parallel flow condenser. In the present study, R-134a flow distribution tests were conducted in the test section, which simulated an actual parallel flow condenser having 58 mini-channel tubes and 4 passes. R-134a gas was supplied at 25 °C superheat, which exited the test section at 5 °C subcooled condition. At inlet of the header, the flow distribution was relatively uniform, except at topmost channels. At the second and third pass, the flow distribution was also relatively uniform except at topmost and bottommost channels. At the exit of each pass, two-phase jets were issued from the tubes of the previous pass, which hit opposite wall of the header, and flowed downward forming a liquid film. At the bottom of the header, the remnant liquid, which was not supplied into the next pass, formed a liquid pool. The thermal degradation due to flow mal-distribution was not significant (0.1–2.82%), which increased as mass flux decreased. Flow distribution correlations were developed to predict the fraction of liquid or gas taken off by downstream channel as a function of gas Reynolds number and channel inlet vapor quality.

Effect of Gas Area Fraction and Reynolds Number on Mixing Flow in Microchannel having Superhydrophobic Transverse Grooves

Effect of Gas Area Fraction and Reynolds Number on Mixing Flow in Microchannel having Superhydrophobic Transverse Grooves

Characterization of the Velocity Field External to a Tube Bundle Using Spatial Filter Velocimetry Based on Variable Meshing Scheme

This paper presents results for the experimental vector velocity field obtained through spatial filter velocimetry in a triangular tube bundle with tubes of 20 mm O.D. and a transverse pitch of 25.2 mm. The experiments were conducted for single-phase water flows with Reynolds numbers ranging from 447 to 1842, and for air–water two-phase bubbly flow with liquid Reynolds number of 909 and gas Reynolds number of 42. The vector velocity field for each experimental condition was obtained using a variable meshing scheme to improve the spatial resolution in regions of low velocities. The results indicate that the variable meshing strategy is promising to increase the spatial resolution of the spatial filter velocimetry technique and to release from the constraint imposed by the uniform window sizes, especially for experimental data obtained with relatively low frame rates. Details of the flow structure of external flow across tube bundles, such as the near-wall velocity profiles, wake region and the effects of the gas buoyancy on vertical mean velocities are presented in this paper with high temporal and spatial resolution, which can be useful for validation of numerical models.

Study on inertial capture of micron and submicron aerosol particles flowing through the corrugated falling-film channel

A novel Corrugated Falling-Film Channel was developed in this work for application to industrial dust removal. Its pressure drop, inertial capture pattern, and grade capture efficiency were evaluated by simulation and experiments. The different inertial capture patterns were investigated on the windward side and leeward side by calculating aerosol particle trajectories, which show the particles captured on the leeward side get into the vortex first and then captured by the leeward wall with a certain probability. With the increase of particle diameter, the capture efficiency on the windward side increases gradually. However, the capture efficiency on the leeward side increases at first, then decreases to 0 due to the large size particle being too hard to be caught by the vortex. The increase of inlet gas Reynolds number will result in higher capture efficiency. The increase ratio of capture efficiency on the leeward side is higher when particles smaller than 9 μm, while on the windward side it is higher when particles size over 9 μm. Based on the simulation results, a new capture efficiency model was established and verified with experimental data.

Linear and nonlinear instabilities of a co-current gas-liquid flow between two inclined plates analyzed using the Navier–Stokes equations

The paper is devoted to a theoretical analysis of a co-current gas-liquid flow between two inclined plates. As a first step, we linearized the Navier-Stokes equations in both phases and carried out a linear stability analysis of the basic steady-state solution over a wide variation of the liquid Reynolds number and the gas superficial velocity. We obtained two modes of the unstable disturbances and computed the wavelength and phase velocity of their neutral and the fastest growing disturbances varying the liquid and gas Reynolds number. The first mode corresponds to the Kapitza's waves at small values of the gas superficial velocity. The second mode of the unstable disturbances corresponds to the transition to a turbulent flow in the gas phase. We found that the co-current gas velocity destabilize the film flow at all values of the inclination angle and distance between the plates considered in the paper. The range of the wavelength of the unstable disturbances essentially increases with the gas velocity increasing. As a second step, we have performed the systematic study of nonlinear wave regimes. We found that the gas flow affects significantly the wave characteristics decreasing the amplitude and increasing the phase velocity. The complex multi-fold and multi-sheet surface, found on the plane of parameters (wavelength and the liquid Reynolds number) for the gravitational film flow, exists at all velocities of the co-current gas flow. We carried out investigation of the “optimal” waves for several folders and presented comparison with the regimes observed in experiments. Using of the strict equations without any additional assumptions is an important feature of this paper.

Analysis of particle deposition in a new‐type rectifying plate system during shale gas extraction

AbstractMuch less attention has been focused on the particle deposition in rectifying plate though it is a common problem in shale gas pipe systems. The effects of particle parameter and flow field on the deposition and distribution of particle in a new‐type rectifying plate system are investigated. Both the computational fluid dynamics (CFD) method and the experiment method are used in order to analyze the particle deposition under various conditions. The accuracy of simulation model is verified with measurements in the experiment and from analyzing, and it is found that the Boltzmann equation can well describe the relationship between gas Reynolds number and particle deposition in the rectifying plate system. It is also found from investigation that the particle deposition is greatly affected by the particle parameter. Deposition rate rises with the increase of the particle diameter; however, it reduces gradually with the decrease of particle shape factor. Moreover, the particle mass concentration is an essential dimension that can give a prediction of where the particle may deposit.

Artificial neural network modeling on the prediction of mass transfer coefficient for ozone absorption in RPB

It has been proved that Higee technology can intensify the processes involving the multiphase mass transfer, and be applied to the ozone-based advanced oxidation processes. Modeling and prediction of mass transfer coefficient are rare in this field. A modeling approach based on artificial neural network (ANN) was developed in this work to predict mass transfer coefficient of ozone absorption process in rotating packed bed (RPB). Serial experiments were conducted to obtain data for the establishment of ANN model, which was then employed to predict the overall mass transfer coefficient (KLa) using dimensionless quantities such as Reynolds number of gas and liquid, Froude number and Weber number, calculated in terms of the geometry of RPB and operating conditions. To optimize the model structure and performance, random grid search for hyperparameters was adopted in this work. The final model exhibits a prediction ability with R2 of 0.9896 and 0.9877, RMSE of 0.01801 and 0.03085, and MAE of 0.01265 and 0.02219 on the training set and the test set, respectively.

Gas-driven thin liquid films: Effect of interfacial shear on the film waviness and convective heat transfer

This study is aimed at experimental investigation of hydrodynamics and convective heat transfer in gravity and gas-driven thin liquid wall films. The liquid film has been annularly applied on a vertically aligned heated tube mounted in a flow channel. In the arranged two-phase flow domain, both the liquid film flow and co-current air flow were thermally and hydrodynamically developing. The Reynolds numbers of liquid and gas flows have been varied between 80−800 and 104−105, respectively. The wall heat flux was kept constant at 15W/cm2. In order to elucidate the effect of the film waviness on the convective heat transfer between the heated wall and the liquid film, the wave frequencies and standard deviations of film thickness have been evaluated by applying high-speed shadowgraphy technique. The wall temperature distribution in streamwise direction has been measured. The experimentally obtained average Nusselt numbers have been compared with the wave frequencies and standard deviations of film thickness. Up to a gas Reynolds number of 4⋅104 and for liquid Reynolds numbers between 80 and 800, the convective heat transfer preliminary depends on the liquid Reynolds number rather than the Reynolds number of the gas flow. For this range, the average Nusselt numbers from the gas-driven film experiments are close to those for falling film flows. At the gas Reynolds numbers starting from 7⋅104, significant heat transfer enhancement with the gas flow has been registered over the full range of liquid Reynolds number.

Experimental design for estimation of the distribution of the convective heat transfer coefficient for a bubbly impinging jet

In this study, a two-dimensional inverse algorithm is developed to determine the heat transfer coefficient distribution of a two-phase air–water bubbly jet impinging on a steel cylindrical thermal mass. All procedures of thermal mass heating and cooling are simulated by solving two-dimensional, transient heat conduction equations using finite difference method. Afterward, the nonlinear inverse heat conduction problem is implemented to directly predict the local convective heat transfer coefficient of the bubbly jet. The sum of squared differences between calculated and measured temperature data is the objective function. Conjugate gradient method is employed sequentially in every time step to optimize the objective function at four gas Reynolds numbers which represent four different two-phase jets. The inverse scheme is validated using exact temperature data without noise. Local heat transfer coefficients are then estimated by inverse technique at five data acquisition times and four initial temperatures of thermal mass in the presence of noise. Furthermore, the effects of uncertainties due to indefinite lateral boundary conditions, temperature dependency of thermal conductivity, and the non-uniformity of the initial temperature distribution are investigated. A satisfactory agreement between exact and estimated heat transfer coefficients is achieved. However, the results show a greater sensitivity to the highest value of initial temperature, the shortest data acquisition time, and the lowest gas Reynolds number allowing a better estimation of heat transfer distribution for the bubbly jet.

Correcting interface turbulence viscosity using CFD modeling for predicting stratified gas–liquid flow shear stress in horizontal pipes

Abstract The prediction of different shear stresses is one of the great challenges of turbulent–turbulentstratified two-phase flow in horizontal pipes. In this work, VOF method, near-wall differential viscosity and local turbulence viscosity distribution coefficient function are introduced and offer an efficient tool to correct the interface turbulence viscosity. The results show that the new method can better predict the shear stresses, liquid holdup and pressure drop of stratified two-phase flow. The fitting relationship between interfacial and wall friction factor ( f i ∕ f W ) is in good agreement with the experimental data. It is found that f i ∕ f W is predicted with a relative error of 12.62% by the new method, which is much less than that by any other method when the gas and liquid superficial Reynolds numbers are 8000 ≤ Re S G ≤ 90000 and 5000 ≤ Re S L ≤ 170000. It provides a reliable method for achieving the closure of stratified flow to predict the shear stresses.

Experimental study on a swirl-vane separator for gas–liquid separation

Experimental research on a swirl-vane gas–liquid separator has been conducted with the aim to explore its application in downhole gas–water separation systems. With the help of a high-speed camera, the effect of gas content, Reynolds number and flow conditioning elements on the separation performance were investigated. The change of flow pattern will lead to the oscillation of air core inside the separator, which has significant influence on the separation performance. Experimental results show that both the increase of Reynolds number and the arranging of flow conditioning elements can only restrain the oscillation of air core to a certain degree. In addition, according to the evolution of air core, the flow pattern can be divided into: rod air core flow, tadpole-shaped air core flow, oscillating air core flow and swirling annular flow. Compared with the gas–liquid flow pattern map in vertical tube with the same inner diameter, it can be found that the flow pattern of gas–liquid mixture before entering the separator has significant influence on the state of the air core. In the end, the operational envelope limits of the separator were determined experimentally. Due to the effect of flow pattern, the separator is more suitable to be operated at low gas content. This research leads to a better understanding of hydraulic characteristics in this kind of separator.

Elucidation of hydrodynamics and heat transfer characteristic of converging and equivalent uniform riser for dilute phase gas–solid flow

An investigation on the influence of a riser geometry on gas–solid hydrodynamics and heat transfer in dilute phase vertical pneumatic conveying system was studied using a simplified one-dimensional simulation program. Risers of equivalent uniform and converging diameters were considered for the comparative studies. The effects of riser shape on gas velocity, relative velocity, Reynolds number, pressure drop, and heat transfer coefficient is also investigated. The effect of convergence angle on total pressure drop and gas–particle heat transfer has been also studied. The significant findings of the present study shows that the converging shape of the riser enhances the gas–particle heat transfer due to higher gas–particle Reynolds number. The heat transfer coefficient and pressure drop is 0.6146W/m2 K and 415N/m2 for converging riser and 0.3938W/m2 K and 364N/m2 for uniform diameter riser. A cost estimation on the net energy benefit has been also done and found 20.67% improvement of heat recovery by solids at the expense of additional 14.02% of pumping energy by using converging riser in place of uniform diameter riser. Thus it can be revealed that the converging riser can enhance the gas–solid heat transfer and hydrodynamics parameter.

Experimental investigation of droplet entrainment and deposition in horizontal stratified wavy flow

An experimental study of the local droplet parameters for an atmospheric horizontal stratified wavy flow was conducted in a horizontal circular pipe with an inner diameter of 40 mm and a length of 5.5 m. The local distributions of the droplet fraction, droplet velocity, droplet diameter, and droplet mass flux in the cross section of the pipe were measured using single optical fiber probes at four locations with length-to-diameter ratios of 17.5, 55.0, 80.0, and 105.0 from the inlet of the test section. The average droplet mass flow rate along the axial direction of the flow channel was also obtained from the droplet parameters. The combination of the droplet entrainment and deposition rate models of Schimpf et al. was evaluated for droplet mass flow rates obtained from five different experiments including the present experiment in the horizontal stratified flow. However, its prediction accuracy was not good for the present and REGARD data. Finally, new droplet entrainment and deposition rate models for the horizontal stratified flow were proposed based on those five experiments. The applicable ranges of the proposed models are 65,500–571,400 and 170–11,000 for the gas (Reg) and liquid (Rel) Reynolds numbers, respectively.

Experimental investigations of thermo-exergitic behavior of a four-start helically corrugated heat exchanger with air/water two-phase flow

The present study provides experimental results of the thermal and exergitic behavior of horizontal four-start helically corrugated heat exchanger with none-boiling air water two-phase flow as the working fluid. Due to the ejection and throttling effect at corrugated tubes, the quality and quantity of flow inside corrugated tubes are significantly different from those in smooth tubes. The corrugated tube was put under constant heat flux. The heat flux was employed via heater wire. The inlet, outlet and wall temperature of the corrugated tube were measured to calculate the heat transfer coefficient of the corrugated tube. The superficial liquid Reynolds number (Resl) was between 4500 and 14500, and the gas superficial Reynolds (Resg) number was between 95 and 500. The results showed that the variation of both the superficial gas and liquid Reynolds number have significant effect on the thermal and exergitic behavior of the helically corrugated tube with air-water two-phase flow. Moreover, increment in the superficial gas Reynolds number makes increment at the overall heat transfer coefficient and exergy destruction. It was also found that the increment of the superficial liquid Reynolds number up to 11128 causes increment at both the overall heat transfer coefficient and exergy destruction. The maximum increment was related to superficial liquid Reynolds number equal to 11128 and was %19 and %32 for the heat transfer coefficient and exergy destruction respectively.

Two-dimensional two-fluid model for air-oil wavy flow in horizontal tube

This study concerns the development of a two-dimensional two-fluid model for wavy flows in horizontal tubes. To deal with the curved walls of the liquid and gas phases and the gas-liquid interface simultaneously, the bipolar coordinate system was used. Experiments on air-oil mixture flow in horizontal tubes with diameters of 20 and 40 mm were conducted to observe wavy flow patterns accompanying the two-dimensional (2D) and Kelvin-Helmholtz (KH) waves and to measure the pressure gradient under different flow conditions. Two different previous correlations for the interfacial friction factor were employed in the model for predicting the wavy flows with 2D and KH waves. Predictions of the model of the liquid film height, the average values of wall shear stresses of each phase, and the average interfacial shear stress were compared for different diameters and different superficial gas and liquid Reynolds numbers. Also presented are detailed predictions of the model for four different flow conditions, including the local values of interfacial shear stress, wall shear stress of the liquid phase, interfacial friction factor, liquid film height, and two-dimensional velocity distribution in the liquid phase at the cross-section of the tube.

Experimental study of horizontal two- and three-phase flow characteristics at low to medium liquid loading conditions

An experimental study is conducted using a 0.075-m ID pipe to investigate characteristics of two- and three-phase stratified flow in a horizontal pipeline. Experiments are conducted under low to medium liquid loading conditions which is common in wet-gas and long transportation pipelines. The flow characteristics investigated include flow pattern, liquid holdup and pressure drop. The experimental range covers superficial gas Reynolds numbers from 6314 to 200,734, superficial liquid Reynolds numbers from 160 to 4391 and water-cut values from 0 to 90%. Differential pressure transducers, quick closing valves and a high-speed camera are utilized to obtain the relevant data and the trends investigated. The observed flow patterns are stratified smooth, stratified wavy and stratified-annular flow. The transitions between flow patterns vary as a function of water-cut. The effect of water-cut on liquid holdup and pressure drop were relatively negligible especially at low water-cut conditions and the fine mixing of the oil-water mixture may be partially responsible for this. As a result, with the exception of flow pattern transitions, the performances of classical two-phase flow models (for the prediction of liquid holdup and pressure drop) appear unaffected when applied to air–oil–water 3-phase flows especially at high water-cuts.

The liquid wave characteristics during the transportation of air-water stratified co-current two-phase flow in a horizontal pipe

The understanding of the interfacial wave structure and its effect to the interfacial friction factor is important to reveal the transition from stratified to the slug flows. However, the available theoretical of models, as well as the correlations to predict the wave interfacial characteristics, is quite rare. The discrepancy among researchers is often found. In the present work, the wave characteristics of air-water stratified flow were investigated experimentally. The inner diameter was 26 mm. The liquid superficial velocity (JL) raised from between 0.02 m/s and 0.075 m/s while the gas superficial velocity (JG) ranged from 4 m/s to 16 m/s. A high speed camera was used to capture high-quality visual data which was later processed with the image processing technique.As a result, the quantitative parameters of the stratified flow were successfully determined and analyzed. Next, the dimensional analysis was carried out to develop correlation to predict the flow parameters of the wave such as the wave frequency, the wave velocity, the wave amplitude, and the wavelength. Furthermore, it is found that the ratio of gas and liquid Reynolds number and Martinelli Parameter plays important role in almost all of the proposed correlation.