Increase In Average Velocity Research Articles

Investigation of Cross‐Sectional Characteristics of Internal Meshing Screw Mixing Flow Field for Dough Paste

ABSTRACTThe internal meshing screw mixer, driven by extensional rheology, demonstrates excellent mixing efficiency for high‐viscosity materials while minimizing fiber damage. This study developed a computational model for the mixing process of high‐viscosity fluids based on the motion equations of the internal meshing screw. The model was validated through experiments involving the mixing of corn syrup, flour and water. The results reveal the flow field's cross‐sectional streamlines and confirm the presence of chaotic mixing states at the system interface through horseshoe mapping and the existence of hyperbolic points. By comparing the extensional and shear rates, as well as analyzing the distribution of mixing indices, this paper establishes that the primary mixing mechanism within the cross‐section is extensional force, highlighting the role of the internal meshing screw as a mixer dominated by extensional flow fields. We investigate the variations in fluid velocity, velocity uniformity index, extensional rate, shear rate, and mixing index over time under different conditions of eccentricity, rotor radius, and rotational speed. The findings indicate that while eccentricity has a limited impact on average velocity, it significantly enhances velocity disturbances and increases the ratio of extensional effects within the fluid domain. In contrast, rotor radius and speed lead to a linear increase in average velocity but have little effect on velocity disturbances and the extensional effects in the fluid domain. This study provides valuable insights into how various cross‐sectional parameters influence the flow field of the internal meshing screw mixing process, offering crucial support for its application in mixing high‐viscosity non‐Newtonian fluids within the food industry.

The comprehensive analysis of magnetohydrodynamic Casson fluid flow with rectangular porous medium through expanding/contracting channel

PurposeThis study examines fluid flow within a rectangular porous medium bounded by walls capable of expansion or contraction. It focuses on a non-Newtonian fluid with Casson characteristics, incompressibility, and electrical conductivity, demonstrating temperature-dependent impacts on viscosity.Design/methodology/approachThe flow is two-dimensional, unsteady, and laminar, influenced by a small electromagnetic force and electrical conductivity. The Hybrid Analytical and Numerical Method (HAN method) resolves the constitutive differential equations.FindingsThe fluid’s velocity is influenced by the Casson parameter, viscosity variation parameter, and resistive force, while the fluid’s temperature is affected by the radiation parameter, Prandtl number, and power-law index. Increasing the Casson parameter from 0.1 to 50 results in a 4.699% increase in maximum fluid velocity and a 0.123% increase in average velocity. Viscosity variation from 0 to 15 decreases average velocity by 1.42%. Wall expansion (a from −4 to 4) increases maximum velocity by 19.07% and average velocity by 1.09%. The average fluid temperature increases by 100.92% with wall expansion and decreases by 51.47% with a Prandtl number change from 0 to 7.Originality/valueUnderstanding fluid dynamics in various environments is crucial for engineering and natural systems. This research emphasizes the critical role of wall movements in fluid dynamics and offers valuable insights for designing systems requiring fluid flow and heat transfer. The study presents new findings on heat transfer and fluid flow in a rectangular channel with two parallel, porous walls capable of expansion and contraction, which have not been previously reported.

Effect of Process Parameters on Yttria‐Stabilized Zirconia Particles In‐Flight Behavior and Melting State in Atmospheric Plasma Spraying

The preparation of coatings by atmospheric plasma spraying gives rise to complex physical processes, which present challenges to the study of plasma jet characteristics and particle in‐flight behavior. Herein, a 3D numerical model that integrates multiple physical phenomena, including electromagnetism and thermal and gas dynamics, to simulate the heating, acceleration, and melting of particles under the thermal–mechanical effect, is developed. Meanwhile, yttria‐stabilized zirconia (YSZ) coatings are prepared under varying process parameters. The DPV‐2000 system is employed for the diagnosis of particle velocity, surface temperature, and diameter. Following comparison, the simulation exhibits errors of 4.5% and 14.8% for the maximum temperature and velocity, respectively. An increase in current intensity from 500 to 600 A results in a rise in the proportion of particles exhibiting temperatures above the melting point (2963 K), from 75.1 to 93.4%, accompanied by an increase in average velocity of ≈16.6%. As the spraying distance increases from 60 to 100 mm, the proportion of particles melting decreases from 93.5 to 66.3%, and the average velocity decreases by ≈9.2%. This work will provide a theoretical foundation for the optimization of process parameters to adjust particle behavior and melting state, thus achieving an optimal spraying effect.

Enhancing solar chimney power plant performance through innovative collector curved-guide vanes configurations

A solar chimney is a one source used newly in power generation by converting solar energy to kinetic energy. One of the limitations of using a solar chimney is the availability of large areas for building the chimney system to obtain sufficient kinetic energy at the chimney entrance. Addressing spatial constraints in chimney systems, this study pioneers an innovative approach to augment energy generation within existing footprints. By integrating swirl guide blades into the collector, the air movement path is extended, resulting in an increase in energy at the chimney entrance. Rigorous examination of four swirl guide blade configurations is conducted through advanced numerical simulations, employing the CFDRC code with a structured grid. In addition, the study meticulously investigates the impact of collector diameter variations on overall system efficiency. Finally, the selected best configuration was studied at different numbers inside the collector. The results showed an increase in average velocity at the chimney entrance and system power of 115.1 % and 30.2 % using eight guide vanes, respectively.

Electroosmosis of viscoelastic fluids in pH-sensitive hydrophobic microchannels: Effect of surface charge-dependent slip length

We analytically investigated the electroosmotic flow characteristics of complex viscoelastic liquids within a charged hydrophobic microchannel, considering the pH and salt concentration-dependent surface charge effects in our analysis. We examined the variation of the electric-double layer (EDL) potential field, the surface charge-dependent slip (SCDS) length, the flow field, the viscosity ratio, and both normal and shear stresses in relation to the bulk pH, bulk salt concentration, and Deborah number of the solution. Our current findings indicate that, under strong flow resistance due to increased electrical attraction on counter ions, a highly basic solution with a high EDL potential magnitude results in a significant decrease in the slip length. Neglecting the effect of SCDS leads to an overestimation of flow velocity, with this overprediction being more pronounced for highly basic solutions. This overestimation diminishes as bulk salt concentration increases, particularly when compared to strongly acidic solutions. Furthermore, a noticeable increase in average velocity is observed as the Deborah number rises for highly basic solutions compared to highly acidic ones. This is attributed to the substantial reduction in apparent viscosity caused by the shear-thinning nature of the liquid at higher shear rates, supported by a larger zeta potential modulated strong electrical force for basic solutions. Additionally, we found that the intensity of shear and normal stresses tends to increase with bulk pH, primarily due to the rise in electric body force at higher zeta potential. These results can potentially inform the design and development of a compact, nonmoving electroosmotic pump for transporting biological species with varying physiological properties, such as solution pH. This technology could be applied in subsequent processes involving mixing, separation, flow-focusing for cell sorting, and other related applications.

A novel method for multiscale digital core reconstruction based on regional superposition algorithm

To characterize matrix pores and microfractures which are widely developed in unconventional reservoirs and also to analyze flow law in multiscale flow region, some related research has been carried out in this study. Based on the statistical characteristics of microscale and nanoscale scanning images of cores, digital cores of microfractures are reconstructed by an improved Voronoi method and the digital cores of matrix pores are reconstructed by the quartet structure generation set (QSGS). By means of regional superposition algorithm, the digital cores of microfractures are firstly magnified in each divided region and then integrated with the corresponding digital cores of matrix pores. After the superposition is completed in whole regions, numerical model after superposition is reduced to the original size of the digital core of microfractures. Finally, the multiscale digital core is reconstructed. Based on reconstructed multiscale digital core, flow simulation considering the permeability of matrix is carried out by the gray lattice Boltzmann method (GLBM). The results show that by constraining the generation areas of random points, the improved Voronoi method can better reflect the geometric characteristics of specific microfractures and the average relative errors of the two-point function and variation function are 13.36% and 2.52% respectively compared with the original microfractures. The multiscale digital core reconstructed by the regional superposition algorithm integrates the anisotropy of matrix pores while retaining the original characteristics of microfractures. With the increase of permeability of matrix, pressure drop range in the flow simulation region expands, and the average velocity at the outlet of microfractures increases. Compared with the case not considering the permeability of the matrix, the maximum increase of average velocity at the outlet of microfractures can reach 48.37% when the permeability of the matrix is set as 0.75 mD. When the flow direction in the microfractures is transverse, compared with the multiscale digital core with transverse connectivity in the matrix, the multiscale digital core with longitudinal connectivity in the matrix has higher flow velocity at the outlet of microfractures, and the average increase of velocity is up to 1.73%.

Влияние широкополосных флуктуаций скорости вращения на течения в сферических слоях

The results of a numerical study of isothermal axisymmetric flows of a viscous incompressible fluid in rotating spherical layers in the presence of random small-amplitude oscillations in the rotation velocity of the inner sphere relative to a constant in time average value are presented. Two cases are considered: rotation of the inner sphere only and rotation of spheres with equal angular velocities. It was shown that in these two cases flows response to the introduction of perturbations is different. A comparison with the experiment was made, which confirms the possibility, obtained during calculations, of average velocity increase in certain areas of the flow with an increase in the fluctuations amplitude.

Effect of active mixing on capture efficiency in heterogeneous microfluidic immunosensor

The enhanced capture of the antigen (Ag) by the surface-immobilized antibodies (Ab) in heterogeneous microfluidic immunosensors lowers (improves) the detection limit thus facilitating the early disease detection. The efficient capture of the antigen is subjected to the interaction of the transport parameters, reaction parameters and the microfluidic system geometry. In the present work, the role of active mixing in facilitating the transport in flow-based heterogeneous immunosensor was studied, both numerically and experimentally. The experiments were performed with the capture of prostate-specific antigen (PSA) by anti-PSA and the results were validated using numerical simulations. The average Sherwood number (Sh) for the experiments and simulations was comparable. First, the effect of the nature of the flow on the capture efficiency was tested, which showed the enhancement in the antigen capture using active mixing. Further, studies of individual active mixing parameter (average velocity, frequency and amplitude) on analyte capture were conducted. The increase in average velocity (uavg) increases the antigen capture but the corresponding pressure drop also increases, and the figure of merit (FOM) attains a maximum at Re ~ 0.6. Similar behavior was observed with the increase of the frequency. The continuous increase in the frequency reduces the reaction time scale and decreases the analyte capture. The amplitude has the least effect on the antigen capture. The flow profiles were also seen and the temporal variation was compared at different flow conditions with micro-PIV. We also proposed two correlations utilizing the parameters—the average surface concentration (Cs,avg), the Reynolds number (Re) and the Strouhal number (St). The correlations indicate that the dependency coefficient for St is higher than Re, and signify the impact of vortex propagation (i.e., active mixing) on antigen capture.

Heat transfer enhancement and drag reduction in transverse groove-bounded microchannels with offset

The shrinking physical scale of microfluidic chips brings significant benefits like less expense of chemicals, shorter diagnosing time and highly parallel testing, but at the same time presents big challenges in drag reduction and thermal management. The ridge/groove structure on the superhydrophobic surface inside microchannels, which entraps air so as to reduce the skin friction, is believed to affect the internal heat transfer. In the current study, the flow and heat transfer between two walls with eccentric transverse microgrooves was studied based on numerical simulations, to investigate its effect on overall drag reduction, heat transfer enhancement and possible mechanisms. The changes in drag reduction capability and convective heat transfer were respectively evaluated in terms of the effective slip length and Nusselt number. The overall thermal performance and efficiency were evaluated using the goodness factor. It was found that the eccentricity of transverse microgooves inside superhydrophobic channel increases the effective slip length but reduces heat transfer slightly, which is especially obvious at low Reynolds number, large pattern length and moderate shear free fraction. Besides drag reduction and heat transfer, the flow fields for different cases were investigated in details, which show that the increase in the effective slip length of superhydrophobic microchannel with offset can be attributed to the increase of average velocity on air-water interface.

Study the effect of vibration frequency and amplitude on the quality of fluidization of a vibrated granular flow using discrete element method

A granular media can be fluidized by using an injected fluid flow or vibration of its container. Different factors affect the quality of fluidization in both cases such as fluid density and viscosity, particle size and coefficients of restitution and friction. In the bubbling fluidization, the air flow velocity is a determining factor while in the vibrational fluidization, the frequency and amplitude of vibration should be effective. In the present study, it was of interest to quantitatively evaluate the degree of fluidization of a granular flow within a reservoir vibrated vertically with different frequencies and amplitudes. Discrete element method was used to model the fluidized granular media. The bouncing flow mode was observed in the beds with low vibration frequencies, while the flows developed in the beds shaken with high frequencies revealed undulations (waviness) near their bottom walls and abrupt jumps at their free surface. Average velocity of particles was calculated within three boxes at top, middle and bottom of the bed to study fluidization of particles adjacent to the bottom vibrating wall and at the bed free surface. It was found that the average velocity of particles inside the granular flow decreased as the vibration frequency increased. However, increasing the vibration amplitude resulted in the particles average velocity increase due to the larger kinetic energy of the fluidized bed. Therefore, it was concluded that increasing vibration amplitude in processes such as mixing, segregation and vibratory finishing would be more efficient than increasing vibration frequency for fluidization. It was found that this conclusion is in agreement with some previous experimental findings. Furthermore, the average packing fraction was studied throughout the media vibrated by different frequencies and amplitudes to explain how the media was fluidized.

A Computational Fluid Dynamics Model of Biological Heat and Gas Generation in a Dairy Holding Area

Abstract.The design and operation of ventilation systems for animal housing is a crucial component in maintaining a suitable environment for both animals and workers by removing heat, moisture, and gas species. However, important design and operational criteria, such as profiles of velocity and extent of mixing within animal housing, can be difficult to study experimentally. Thus, a computational fluid dynamics (CFD) model of a commercial dairy holding area, including the generation of transport of heat and gas species within the domain, was developed. The animal-occupied zone (AOZ) was modeled using porous media. The model was evaluated with experimental data of velocity and gas concentration. Results indicated that the airflow uniformity and air speed could be increased within the holding area by modifying the configuration of the side curtain openings and using concrete walls to guide airflow; a 20% increase in average velocity within the AOZ was achieved. Results of the CFD model have shown it to be an effective tool for gaining insight into the complex mixing patterns within holding areas to improve the design of animal housing. Keywords: Animal-occupied zone, Computational fluid dynamics, Greenhouse gas emissions, Holding area.

Sub-microsecond vapor plume dynamics under different keyhole penetration regimes in deep penetration laser welding

It is well-known that distinct vapor plume dynamics occur during deep penetration laser welding under different keyhole penetration states. However, there is little knowledge about the physical characteristics of vapor plumes (velocity, pressure, flow patterns, etc) located inside transient keyholes of varying penetration regimes in laser welding. This lack of knowledge is primarily because mesoscale vapor plumes are highly dynamic and generally invisible. Based on a well-tested three-dimensional multiphase laser welding model, we conducted a computational study on vapor plume dynamics inside transient keyholes during the fiber laser welding of 304 austenite stainless steel as a function of keyhole penetration regimes. We observed three keyhole regimes of penetration: full penetration, partial penetration and no penetration. We then physically analyzed the vapor plumes in these regimes. We determined that the vapor plume velocities and pressures in all three regimes were uneven and oscillated following the dynamic keyhole with a characteristic timescale in sub-microseconds. Only when the keyhole approached the full penetration regime did vapor plumes begin to violently eject from the bottom of the keyhole opening, whereas in the partial penetration regime, even when the bottom part of the keyhole was open, most of the vapor plume ejected from the upper keyhole opening. This latter observation was similar to that in the no penetration mode. We studied the physical mechanism of this behavior by analyzing the keyhole temperature and vapor plume velocity distributions. We determined that the upward ejection of the vapor plume from the upper keyhole opening was the result of an uneven micro-meter scale boiling phenomenon of the transient keyhole governed by Fresnel absorptions dependent on the local inclination angle of the keyhole wall. Similarly, we determined that the ejection of the vapor plume from the bottom of the keyhole opening resulted from pressure differences between the inside and outside of the keyhole (as long as there was a relatively stable open state at the bottom of the keyhole opening). Additionally, we conducted quantitative studies on the velocity and pressure of vapor plumes in transient keyholes for all three regimes. We observed a decrease in the average velocity of vapor plumes at the upper keyhole opening, and an increase in average velocity at the bottom opening when the penetration regime moved from no penetration to full penetration. Moreover, the pressure distributions of vapor plumes decreased and became more uniform as the penetration regime varied from no penetration to full penetration. For the investigated process parameters used for the fiber laser welding of 1 mm thick 304 stainless steel, the vapor plume pressure decreased approximately 500–1200 Pa inside the millimeter scale keyhole. The findings in this study give the first physical insights into vapor plume dynamics inside transient keyholes as a function of keyhole penetration states during deep penetration laser welding. Moreover, our findings can be used as theoretical references for welding process parameter optimization in industrial applications.

The role of visual information in maintaining postural stability after the maximum exercise for the upper and lower limb muscles

The postural stability on a seesaw generating anterior–posterior instability with the eyes open (EO) and then the eyes closed (EC) in young healthy subjects (n = 28) before and 6 min after the maximum bicycle exercise (Wingate test) performed using lower limbs (“leg exercise”) or upper limbs (“hand exercise”) was investigated. It was found that “hand exercise” caused the same increase in average velocity (V, mm/s) and in the average range of sway of the centre of pressure (Qy, mm) as “leg exercise.” However, the duration of V recovery (EC: 2 min 30 s and 50 s; EO: 60 s and 40 s after “leg exercise” and “hand exercise,” respectively) and Qy (EC: 1 min 10 s and 30 s after “leg exercise” and “hand exercise,” respectively; EO: no changes from baseline) was shorter after “hand exercise.” In the presence of visual information, the increment in V decreased more than 2 times after “leg exercise” (+100.5% and + 40.5%, p < 0.01 for EC and EO, respectively) and after “hand exercise” (+73.0% and +30.3%, p < 0.01 for EC and EO, respectively). Moreover, Qy after both exercises remained at the initial level under EO conditions but significantly increased under EC conditions (+42.8%, p < 0.01 after “leg exercise” and +40.3%, p < 0.01 after “hand exercise”). Thus, the maximum exercise for the muscles of the upper limbs causes the same reduction in postural stability as analogous exercise for the muscles of the lower limbs, but the recovery period after “hand” exercise was shorter. The presence of visual information allows the baseline maintenance of postural stability and significantly reduces the strain of postural regulation while standing on a movable support after the maximum “leg exercise” and “hand exercise.”

The effect of resisted sprint training on maximum sprint kinetics and kinematics in youth

Resisted sled towing is a popular and efficient training method to improve sprint performance in adults, however, has not been utilised in youth populations. The purpose therefore was to investigate the effect of resisted sled towing training on the kinematics and kinetics of maximal sprint velocity in youth of different maturation status. Pre- and post-intervention 30 metre sprint performance of 32 children, 18 pre-peak height velocity (PHV) and 14 mid-/post-PHV, were tested on a non-motorised treadmill. The 6-week intervention consisted of ∼12 sessions for pre-PHV and 14 for mid-/post-PHV of resisted sled towing training with each sessions comprised of 8–10 sprints covering 15–30 metres with a load of 2.5, 5, 7.5 or 10% body mass. Pre-PHV participants did not improve sprint performance, while the mid-/post-PHV participants had significant (P < 0.05) reductions (percent change, effect size) in sprint time (−5.76, −0.74), relative leg stiffness (−45.0, −2.16) and relative vertical stiffness (−17.4, −0.76) and a significant increase in average velocity (5.99, 0.76), average step rate (5.65, 0.53), average power (6.36, 0.31), peak horizontal force (9.70, 0.72), average relative vertical forces (3.45, 1.70) and vertical displacement (14.6, 1.46). It seems that sled towing may be a more suitable training method in mid-/post-PHV athletes to improve 30 metre sprint performance.

Reliability of Video Motion-Analysis Systems to Measure Amplitude and Velocity of Shoulder Elevation

Dynamic shoulder motion can be captured using video capture systems, but reliability has not yet been established. To compare the reliability of 2 systems in measuring dynamic shoulder kinematics during forward-elevation movements and to determine differences in these kinematics between healthy and injured subjects. Reliability and cohort. Research laboratory. 11 healthy subjects and 10 post-superior labrum anteroposterior lesion patients (SLAP). Contrasting markers were placed at the hip, elbow, and shoulder to represent shoulder elevation and were videotaped in 2 dimensions. Subjects performed 6 repetitions of active elevation (AE) and active assisted elevation of the shoulder, and 3 trials were analyzed using Datapac (comprehensive system) and Dartfish (basic system). Amplitudes and velocities of the shoulder angle were calculated. Intraclass correlation coefficient (ICC), standard error of measurement (SEM), and levels of agreement (LOA) were used to determine intersystem and intertrial reliability. For AE, the amplitude maximum (ICC = .98-.99, SEM = 2-3°, LOA = -9° to 5°) and average velocity (ICC = .94-.97, SEM = 1°/s, LOA = -4° to 1°/s) indicated excellent intersystem reliability between systems. Intratrial reliability for minimum velocity was moderate for Datapac (ICC = .64, SEM = 4°/s, LOA = 7°/s) and poor for Dartfish (ICC = .52, SEM = 20°/s, LOA = 37°/s). Cohort results demonstrated for AE a greater amplitude for healthy v SLAP (139° ± 11° v 113° ± 13°; P = .001) and interaction for an average velocity increase of 2°/s in healthy and decrease of 2°/s in SLAP patients over the 3 trials (P = .02). Reliability ranges provide the means to assess the clinical meaningfulness of results. The cohort differences are supported when the values exceed the ranges of the SEM; hence the amplitude results are meaningful. For dynamic shoulder elevation measured using video, the assessment of velocity was found to produce moderate to good reliability. The results suggest that with these measures subtle changes in both measures may be possible with further investigations.

Force Generation by Type IV pili of Neisseria Gonorrhoeae

Type IV pili are major bacterial virulence factors supporting adhesion, surface motility, and gene transfer. During infection they mediate attachment to mammalian host cells and elicit downstream signals. The polymeric pilus fiber is a highly dynamic molecular machine that switches between elongation and retraction. We used laser tweezers to investigate the dynamics of individual pili of the human pathogen Neisseria gonorrheae. We found that the retraction velocity of bacteria adhered to an abiotic surface is bimodal and that the bimodality depends on force and on the concentration of the putative motor protein PilT [1]. When adhered to host cells the bimodality persisted at higher forces compared to an abiotic environment. This increase in average velocity is consistent with an up-regulation of PilT due to interaction with host cells. Bacteria generated considerable force during infection but the maximum force was reduced from (120±40)pN on abiotic surfaces to (70±20)pN on host cells, most likely due to elastic effects. Velocity and maximum force of pilus retraction were independent of the infection period within 1h and 24h post infection [2]. Thus the force generated by type IV pili during infection is high enough to induce cytoskeletal rearrangements in the host cell.[1] M. Clausen, M. Koomey and B. Maier, Biophys. J. 2009, 96, 1169-1177[2] D. Opitz, M. Clausen and B. Maier, ChemPhysChem 2009, 10, 1614-1618

Unsteady dynamics of Taylor bubble rising in vertical oscillating tubes

The present work deals with the motion of a Taylor bubble rising through vertical oscillating pipes. The aim is to perform a more detailed and quantitative study of this unsteady flow, still seldom addressed in the literature. The investigation is restricted to high Reynolds numbers to understand inertia effects. Experimental results are provided for two different configurations: (1) pipes with two different inner diameters (9.8 mm and 20 mm) filled with water, (2) the thinner pipe ( D = 9.8 mm ) filled with four low viscous fluids. So the Bond number Bo based on the steady rise velocity varies from 13 to 57, where the effects of surface tension can be considered. The bubble trajectory is tracked by using a high-speed video camera. The average terminal and fluctuating velocity, as well as the phase shift with the oscillating plate are obtained by using image processing. The main results show that for weak acceleration, the mean velocity decreases with the relative acceleration as the fluctuating velocity increases in proportion to this acceleration. Beyond a critical relative acceleration, the average velocity increases and the fluctuating velocity increase seems to slow down. Additionally, comparisons are made with experimental results of Brannock and Kubie [Brannock, D., Kubie, J., 1996. Velocity of long bubbles in oscillating vertical pipes. Int. J. Multiphase Flow 22, 1031–1034] and numerical results of Clanet et al. [Clanet, C., Heraud, P., Searby, G., 2004. On the motion of bubbles in vertical tubes of arbitrary cross-sections: some complements to the Dumitrescu Taylor problem. J. Fluid Mech. 19, 359–376].

Using a cross-flow microfluidic chip for monodisperse UV-photopolymerized microparticles

In this paper, we report a microfluidic chip containing a cross-junction channel for the manipulation of UV-photopolymerized microparticles. Hydrodynamic-focusing is used to form a series of using 365 nm UV light to solidify the hydrogel droplets. We were able to control the size of the hydrogel droplets from 75 to 300 μm in diameter by altering the sample and by changing the flow rate ratio of the mineral oil in the center inlet channel to that of the side inlet channels. We found that the size of the emulsions increases with an increase in average velocity of the dispersed phase flow (polymer solution flow). The size of the emulsions decreases with an average velocity increase of the continuous phase flow (mineral oil flow). Experimental data show that the emulsions are very uniform. The developed microfluidic chip has the advantages of ease of fabrication, low cost, and high throughput. The emulsions generated are very uniform and have good regularity.

Drill Bit Pressure Drop During Foam Drilling Operations

Abstract Foam is one of the most frequently used drilling fluids for underbalanced drilling operations. This paper introduces a more accurate model than the existing models for estimating the pressure drop of foam flowing through the drill bit. The major difference between the proposed and existing models is that the proposed model includes the effect of foam expansion and velocity change as a function of pressure. It has been observed that pressure drop increases significantly as the upstream pressure and foam average velocity increases. For the same flow conditions, pressure drop decreases as the foam quality increases, and as the upstream pressure increases, pressure drop also increases. These events cannot be detected by existing models. In some cases, the pressure drop at the bit can be 10 times greater than the pressure drop predicted by existing models. Introduction Foam has been used as a drilling fluid in many drilling operations; especially in underbalanced drilling applications. In a number of cases, drilling with foam has shown to provide significant benefits, including increased productivity (by reducing formation damage), increased drilling rate, reduced operational difficulties associated with drilling in low pressure reservoirs (e.g. lost-circulation and differentially stuck pipe) and improved formation evaluation while drilling. Foams consist of a continuous liquid phase, forming a stable cellular structure that surrounds and entraps a gas phase. Special chemicals, called surfactants, are used to capture the gas phase; at least for a desired period of time. Foams are considered to be dry or wet, depending on the gas content. Wet foams have spherical bubbles with large amounts of liquid between the bubbles. Dry foam bubbles are polyhedral in shape, with definite contact between the bubbles. In between these two extremes, geometrical figures having both curved and flat faces can exist. Foams are thermodynamically unstable systems because they always contain more than a minimal amount of gas solution interface(1). This interface represents surface free energy, the amount of which can be estimated from knowledge of the surface tension and the interfacial area of the foam. Wherever a foam membrane breaks and the liquid coalesces, there is a decrease in surface free energy. Thus, the decomposition of foam into its constituent phase is a spontaneous process. Since the solution phase is always denser than the gaseous phase, there is a strong tendency for the liquid to separate or drain from the main body of foam unless it is circulated or agitated in some way. Foams can have extremely high viscosity. In all instances, their viscosity is greater than either the liquid or the gas that they contain(2). At the same time, their densities are much lower than the density of water. They are stable at high temperatures and pressures. So, by using foam as a drilling fluid, its high viscosity allows efficient cuttings transport and its low density allows underbalanced conditions to be established; thereby minimizing formation damage. Foams are also preferred when water influx is a problem because they can handle large amounts of water.

Channel-Unit Hydraulics on a Pool-Riffle Channel

Three riffles, two runs, and a pool were used to examine variations in water surface gradient and average velocity over a discharge range of 1.8-19.1 m3/s under conditions of stable channel geometry. Water surface gradient was measured using staff gages, and average velocity was measured using a salt tracer and conductivity probes. The discharge range during the study includes average annual low flow and peak flow. Gradient decreased over all channel units as discharge increased, but the rate of decrease was greater over runs and pools. Velocity data indicate consistent rates of increase among channel units with increasing discharge. Linear plots indicate that the rate of change in water surface and velocity for the channel units decreases at discharges greater than 8-10 m3/s, which corresponds to the transition from intermediate-scale to small-scale relative submergence. As grain roughness effectively decreases, larger patterns of flow convergence and divergence generated by form roughness increase. Declining rates of velocity increase at higher discharges suggest that flow patterns associated with form roughness are very effective at creating internal resistance and dissipating flow energy, and thus limiting the rate of increase in average velocity through each channel unit as discharge increases.