Increase In Bubble Diameter Research Articles

Relation between bubble behaviors in spray sheet and bubbly flow inside an air-induction fan nozzle: A visualization study

The present study aims to elucidate the relationship between bubble behaviors in the spray sheet and internal bubbly flow of the air-induction nozzle. An experimental work was performed using the visualization technique. Effects of the air inlet position and spray pressure were investigated. The results show that compared with the bubbles inside the air-induction nozzle, bubbles in the spray sheet have smaller volume but larger average diameter. Disturbance propagates in the horizontal air-inlet segment. When the air inlet position shifts toward the nozzle outlet, overall bubble volume inside the nozzle decreases by about 56%, while in the spray sheet, the bubble volume decreases by about 77%. Bubble breakup causes a decrease in overall bubble volume as bubbles travel from the inner flow passage of the nozzle to the environment. The coalescence and compression of bubbles induce the increase in average bubble diameter. When the spray pressure increases from 0.1 to 0.3 MPa, both the total bubble volume and average bubble diameter increase.

Research on factors affecting bubble and particle behavior in a three-phase flotation system based on COMSOL

ABSTRACT To investigate the impact of various parameters on bubble and particle dynamics in a flotation system, COMSOL software was utilized. The “two-phase flow – Level Set” module coupled with the “fluid particle interaction” module was used to explore the behavior of single bubbles and particle groups. The bubbles were set as a discrete phase to represent a group of floating bubbles. By combining the “Single-phase flow” module with dual “fluid-particle interaction” modules, we examined the interactions between bubble populations and particles within the system. The research results show that as the bubble diameter increases, the carrying effect of the bubbles on the particles becomes stronger. When the bubble radii are 1, 1.25, 1.5, 1.75, and 2 mm respectively, the maximum movement speed of the particles in the area increases by 3.0%, 2.3%, 5.1%, and 2.7%. The average speed of the particles increases by 7.9%, 7.3%, 9.0%, and 10.0%. Increasing the mass flow rate can increase the collision probability between particles and bubbles, thus increasing the flotation rate. However, a too high mass flow rate will make the state of bubbles unstable. When the mass flow rate is less than 1.5 kg/s, the bubbles remain stable. When the mass flow rate exceeds 1.5 kg/s, the severity of bubble splitting increases. In the study area, the irregularity of the bubble clusters results in a more chaotic flow field, leading to greater speed and displacement of the particles. Increasing the number of bubbles entering at one time and their initial speed enhances the impact of the bubble clusters on the solid particles. When the number of bubbles entering at one time is 5, 10, 15, and 20 respectively, the maximum movement speed of the particles increases by 6.9%, 8.1%, and 9.0%. When the initial speed of the bubble entering is 0, 0.1, 0.2, and 0.3 m/s respectively, the maximum movement speed of the particles increases by 6.4%, 3.0%, and 8.8%.

Origin of Basaltic Subplinian Eruption at Shishaldin Volcano (Alaska): A Vigorously Degassing Magma Reservoir Hosting Small Bubbles

AbstractThe 1999 basaltic eruption of Shishaldin volcano (Alaska) displayed a transition between Subplinian and Strombolian activity. Strombolian bubbles indicate the presence of a periodically unstable foam at the top of magma reservoir. In contrast, a long foam, whose rupture led to the eruptive column, was also able to collect in the conduit. Laboratory experiments show that long foams can be produced in a conduit by the spreading of a stable foam accumulated at the top of the reservoir. The existence of a Taylor bubble at the onset of the Subplinian phase, also reproduced by my laboratory experiments, suggests that the foam in the reservoir was just at the transition between stable and unstable. This constrains the bubble diameter prior to the Subplinian phase to be 0.034–0.038 mm when using the foam dimensionless analysis and the underlying gas flux (0.52–0.80 m3/s). The increase in bubble diameter and potentially gas flux prior to the Strombolian activity, 0.81–1.4 m3/s, is sufficient to explain the foam in transition to be unstable. The radius of the magma reservoir is small, 200–210 m, as expected. The bubble diameter is the smallest of those estimated for classical basaltic eruptions (Etna, Kı̄lauea, Erta 'Ale), while the gas flux is among the largest. A dilute suspension of small and isolated bubbles cannot explain the large gas flux at Shishaldin. This implies numerous bubbles with a gas volume fraction ≥0.63−2%, a regime for which the bubbles form bubble clusters. The diameter of these bubble clusters, 3.0–5.4 mm, is sufficient to explain large gas fluxes.

Experimental Study of the Rising Behavior of a Single Bubble in Shearshinning Fluids

Background: Non-Newtonian gas-liquid two-phase flows are often seen in industrial processes such as petroleum, chemical, and food engineering. The efficiency of mass and heat transfer between phases is significantly impacted by bubble rise motion in liquids. Therefore, it is crucial to deeply study the hydrodynamic characteristics of a bubble rising in non-Newtonian fluids to improve the transfer efficiency between phases and to enhance the operational efficiency of bubbling equipment. Methods: To understand the rising characteristics of a bubble in non-Newtonian fluids, a single bubble rising in shear-thinning fluids was experimentally studied using a high-speed camera. The effects of xanthan gum (XG) concentration and bubble diameter on bubble shape, trajectory, and terminal velocity were investigated. Results: Bubble terminal velocity increased with an increase in the bubble diameter and a decrease in XG concentrations. The increase rate of bubble terminal velocity varied with an increase in bubble diameter for the bubbles with different diameters and XG concentrations for the solutions with varying XG concentrations. For solutions with the same XG concentration, the Galilei and Eötvös numbers for a small bubble were relatively small but relatively large for a large bubble. Thus, the rise motion of a bubble in XG solutions becomes unsteady with an increase in bubble diameter and a decrease in XG concentrations. The unsteady characteristics of bubble motion decrease with an increase in the XG concentration of solutions. Conclusion: It was found that the influence of XG concentrations on bubble motion depends on bubble diameter since the magnitude of bubble diameter has an essential effect on the shear-thinning effect of solutions. An increase in bubble terminal velocity is mainly caused by an increase in buoyancy (i.e., bubble diameter) rather than a decrease in the apparent viscosity of solutions.

Understanding the cavitation effect of power ultrasound in cement paste

While power ultrasound (PUS) has been proven to accelerate cement hydration, it remains unclear whether cavitation occurs during this process. This study aimed to test the cavitation effect of a single bubble in cement paste through a KI oxidation experiment. An ultrasonic pressure field model was established using the linear Helmholtz equation, and the cavitation effect of a single bubble in cement paste was simulated based on the modified Keller–Miksis model. The results indicate that the conventional water-cement ratio (w/c ratio ≤1.0) does not produce transient cavitation but can produce stable cavitation. The efficiency of stable cavitation initially increases and then decreases as the bubble diameter increases. An optimum stable cavitation efficiency is achieved with a 50 μm bubble, but the bubble expansion rate remains consistently less than 40 %. Increasing the acoustic pressure to 5 atm or higher can cause the bubbles in cement paste with a water-to-cement ratio of 1.0 to expand more than tenfold. However, even when the acoustic pressure was further increased to 10 atm, no noticeable bubble expansion was observed in the cement paste with a w/c ratio of 0.30. The high viscosity of cement paste is the primary cause of the high transient cavitation threshold of bubbles.

Analysis of the Bubble Diameter Effect on the Gas-liquid Flow Characteristics of a Multiphase Rotodynamic Pump

Abstract In order to study the effect of bubble diameter on the gas-liquid flow in the multiphase rotodynamic pump, steady simulations with different bubble diameters were conducted using ANSYS CFX17.0. When the inlet gas content IGVF is 10%, the pump head and efficiency decrease with the increased inlet bubble diameters, and there are different downward trends at different stages of bubble diameter increase. The pump head and efficiency with small bubble diameter (d≤0.3 mm) are much higher than those of large bubble diameter(d≥0.4 mm). A small amount of gas accumulates on both the blade suction and pressure surfaces near the hub under conditions of small bubble diameters. When the bubble diameter is large, A large amount of gas accumulates on the blade suction surface, and almost no gas accumulates on the blade pressure surface. Due to the density difference between gas and liquid phases, gas accumulates near the hub. The gas content rapidly decreases when away from the hub under small bubble diameter conditions, resulting in good gas-liquid fluidity and weak gas-liquid separation.

Hydrodynamics and shape reconstruction of single rising air bubbles in water using high-speed tomographic particle tracking velocimetry and 3D geometric reconstruction

Time-resolved tomographic particle tracking velocimetry (TR-3D-PTV), also called 4D-PTV, is used here to obtain the instantaneous 3D liquid flow field information in the wake of a single rising bubble in water. Simultaneously, the bubble shape, size and velocity are determined by tomographic reconstruction of the 3D bubble shape. Both, tracer particles for PTV and bubbles, are imaged in a shadow mode with background illumination. The Lagrangian method used in this paper, especially combined with the shake the box algorithm, has big advantages compared to particle image velocimetry, in situations, where only low particle per pixel values can be obtained. In this research, single air bubbles of different sizes, with diameters of around 2.4 mm, 4.0 mm, 6.0 mm and 9.6 mm, were injected into stagnant de-ionized water. Their shape was reconstructed in 3D, and an equivalent bubble diameter was determined from this reconstruction. Compared to conventionally used 2D shadow imaging, this diameter is about 13% smaller. The 3D bubble trajectory can be analysed and decomposed into a sinusoidal function curve lateral projection and an ellipsoidal shape vertical projection. As the bubble diameter increases, the radius of the spiral trajectory is decreasing as well as the amplitude of vertical sinusoidal oscillation. The wake structure in the liquid behind the bubbles is also changing with bubble size: from simple vortex pairs for smaller bubbles to an intertwined structure of several twisted vortices for the bigger ones.Graphical abstractThree-dimensional bubble reconstruction (grey surface) and liquid stream lines coloured with velocity magnitude around an ascending air bubble in de-ionized water.

Numerical investigations on the effect of bubble injection on heat transfer of natural convection in laminar flows

AbstractIt was found that the injection of bubbles into liquid can effectively improve heat transfer efficiency, so it is important for industrial applications to investigate the effect of bubble injection on heat transfer. The effect of bubble injection on natural convective heat transfer in steady laminar flows in a vertical channel is investigated using the volume of fluid (VOF) method, and the effects of bubble diameter, Eötvös number (Eo), bubble arrangement, and bubble distance from a hot wall on the heat transfer between the hot wall and liquid are studied, respectively. The results show that bubble injection can effectively improve the heat transfer between the hot wall and liquid; an increase in bubble diameter and Eo can improve the enhancement effect of heat transfer and can expand the enhancement area of heat transfer; the closer to the hot wall a bubble is, the better the enhancement of heat transfer is; and the spacing and arrangement of bubbles also have important effects on the heat transfer between the hot wall and liquid. The comparison shows that the enhancement of heat transfer is the best for the vertical arrangement of double bubbles, which increases the local heat transfer coefficient by 3.2 times. The enhancement of heat transfer generated by bubble injection is related to the degree of disturbance of the local liquid phase caused by bubble injection. The more strongly the local liquid is disturbed, the thinner the local temperature boundary layer becomes, and the better the enhancement of heat transfer is.

Experimental study on the effect of the sawtooth nozzle structure on bubble behaviors

The initial formation of bubbles has a significant impact on bubble dynamics and acoustics. Meanwhile, the bubble initial shape is affected by the nozzle boundary. In this study, the processes of bubble generated from sawtooth nozzles have been investigated by means of controlled experiments. A three-dimensional visualization imaging system is used to study bubble behaviors. The morphology and the time-frequency spectrum of the sound pressure signal are analyzed synchronously. Moreover, the effects on bubble trajectory are also studied. Results show that sawtooth nozzle is not conducive to bubble detachment, resulting in larger bubble diameters than the circular nozzle. With the gas flow rate increasing, bubble diameter increases. When the gas flow rate reaches a certain critical value, the surface tension is not sufficient to support the continued development of bubble size. Due to effect of the sawtooth structure, bubbles tend to break in the necking stage, accompanying by small bubbles. The generation of accompanying bubbles lead to the irregular generation of nearby bubbles. This study aims to reveal the effect of sawtooth nozzle structure on the initial formation of bubbles, so as to predict the flow patterns and sound signal characteristics of the bubbles.

AN INVESTIGATION OF THE EFFECT OF INITIAL BUBBLE DIAMETER ON THE BUBBLE TRAJECTORY IN THE FLOTATION COLUMN CELL USING CFD SIMULATION

The effect of initial bubble diameter on the bubble motion pattern in a flotation column has been studied by the twophase computational fluid dynamics (CFD) method. The two-phase simulations have been done using the volume of a fluid (VOF) model in ANSYS® Fluent® software. The computational field was a square cross-section column with a width of 0.1 m and a height of 1 m into which air was interred as a single bubble from the lower part of the column by an internal sparger. An experimental test has been also performed and the simulated results have been validated using the values obtained for the bubble rise velocity. A comparison of the simulation and the experimental results has confirmed that CFD can predict the bubble rise velocity profile and its value in the flotation column less than 5% relative to the experimental values. Then the simulations have been repeated with a 20% decrease and increase in the initial bubble diameter to investigate the effect of bubble diameter on the bubble flow pattern. The investigations have shown that as the bubble diameter increases, the velocity decreases and the bubble rises in a more zigzag direction as a result of two counter-rotating trailing vortices behind the bubble increasing.

Bubble behaviour investigation in a wet fluidized bed using digital image analysis

AbstractDue to the presence of liquid bridge forces, wet particles reveal totally different fluidization behaviours than dry fluidized beds. This paper studies the bubble dynamics of wet Geldart‐D particles in a wet 2D fluidized bed. A digital image analysis method is adopted to identify bubbles and extract bubble properties based on MATLAB software. During fluidization, the bubble feature analysis of optimized binary images captures the bubble size variation, bubble fraction, and bubble shape. The results show that the increasing liquid saturation promotes the gas holding capacity of the emulsion phase, leading to the decreasing bubble fraction. When the particle size grows, the stability of the emulsion phase is promoted and hence the average bubble diameter increases. As the liquid saturation increases, the enhancing liquid bridge forces limit the bubble growth and promote the bubble breakage, which contributes to the small bubbles. With respect to the wet particles, of which the diameter is 1 mm and the liquid saturation is over 15%, slugging is likely to be observed, resulting in the increasing equivalent bubble diameter. The growing liquid saturation increases the wide aspect ratio, decreases the shape factor, and disperses the dependence between the two parameters. This indicates that small and irregular bubbles are likely to be seen in wet fluidized beds.

Pool Boiling Amelioration by Aqueous Dispersion of Silica Nanoparticles.

Non-metallic oxide nanofluids have recently attracted interest in pool boiling heat transfer (PBHT) studies. Research work on carbon and silica-based nanofluids is now being reported frequently by scholars. The majority of these research studies showed improvement in PBHT performance. The present study reports an investigation on the PBHT characteristics and performance of water-based silica nanofluids in the nucleate boiling region. Sonication-aided stable silica nanofluids with 0.0001, 0.001, 0.01, and 0.1 particle concentrations were prepared. The stability of nanofluids was detected and confirmed via visible light absorbance and zeta potential analyses. The PBHT performance of nanofluids was examined in a customized boiling pool with a flat heating surface. The boiling characteristics, pool boiling heat transfer coefficient (PBHTC), and critical heat flux (CHF) were analyzed. The effects of surface wettability, contact angle, and surface roughness on heat transfer performance were investigated. Bubble diameter and bubble departure frequency were estimated using experimental results. PBHTC and CHF of water have shown an increase due to the nanoparticle inclusion, where they have reached a maximum improvement of ≈1.33 times over that of the base fluid. The surface wettability of nanofluids was also enhanced due to a decrease in boiling surface contact angle from 74.1° to 48.5°. The roughness of the boiling surface was reduced up to 1.5 times compared to the base fluid, which was due to the nanoparticle deposition on the boiling surface. Such deposition reduces the active nucleation sites and increases the thermal resistance between the boiling surface and bulk fluid layer. The presence of the dispersed nanoparticles caused a lower bubble departure frequency by 2.17% and an increase in bubble diameter by 4.48%, which vigorously affects the pool boiling performance.

Numerical Investigation on the Dynamic Flow Pattern in a New Wastewater Treatment System

Currently, industries seek to optimize the development of technology from energy-saving, economic, and environmental perspectives. Dissolved air flotation (DAF) is one of the most effective wastewater treatment systems. However, it requires considerable energy and causes significant operating costs. A recently emerged application of using fluidic oscillators (FOs) to generate microbubbles has attracted extensive attention, as it consumes much less energy and has proven to be a more energy-efficient technique. In this article, a microbubble generator based on FOs is introduced into the flotation tank, and an energy-saving water treatment system, namely fluidic air flotation (FAF), is presented. Using the computational fluid dynamics (CFD) method, the flow pattern of the FAF is investigated. It is observed that FAF generates a dynamic flow pattern, which is beneficial for bubble removal. At the upper part of the separation zone, the flow pattern exhibits a wavy shape. The flow pattern at the lower part switches between clockwise and counterclockwise. The air distribution of the separation zone is also studied. It is found that the height of the “white water” zone almost linearly decreases with the increase in bubble diameter and diffuser size. FAF consumes almost no energy and occupies a small area, and it is expected to provide a promising solution to develop a new generation of the wastewater treatment system.

Experimental investigation of trajectories, velocities and size distributions of bubbles in a continuous-casting mold

A ¼-scale water-model experiment is conducted to investigate the trajectories, velocities and size distribution of bubbles in a continuous-casting mold. A high-speed camera and a laser are used to record the transient bubble distribution. The region of interest is delimited to include the motion range of floating bubbles in the upper mold, and divided into 70 subregions of seven rows and 10 columns. Information on the trajectories, velocities and size distributions of bubbles is obtained from image sequences, using the ImageJ software. The effects of water/gas flow rates on the transport and size distribution of bubbles are studied. The results show that the motion range of larger bubbles decreases toward the submerged entry nozzle (SEN) and the floating direction of larger bubbles moves closer to vertical. The increase in water flow rate increases the level transportation distance of bubbles along the jet flow and the intensity of upper circulation flow, which has a complex effect on bubble transportation near the SEN. An increase in the gas flow rate contributes to the ascending flow near the SEN and significantly increases the bubble number in the region of interest for the entire bubble-diameter range, without causing an increase in mean bubble diameter.

Influence of Aeration Microporous Aperture on Oxygen Mass Transfer Efficiency in Terms of Bubble Motion Flow Field

Microporous aeration has been widely used to restore eutrophic water bodies. The gas–liquid mass transfer in the aeration process has a significant influence on the improvement of water quality. Therefore, the influence mechanism of oxygen mass transfer is worth studying. However, the influence of bubble movement characteristics on oxygen mass transfer has not been systematically studied. Thus, the present study explored the influence mechanism of microporous apertures on oxygen mass transfer in terms of bubble motion characteristics by investigating the oxygen mass transfer process and the feature of bubble movement under different aeration microporous aperture sizes. The results showed that the mass transfer efficiency was reduced as the micropore aperture increased from 200 to 400 μm. and the reduction rate was 7.17% when the aperture increased from 200 to 300 μm, which was lower than that from 300 to 400 μm (19.17%). Furthermore, the micropore aperture showed a positive correlation with the time-averaged velocity field. With the increase in aperture, the bubble velocity gradient (from the center to both sides of the edge) increased from about 0.2 to 0.4 m/s, which increased the oxygen mass transfer effect. The increase of micropore aperture caused the increase of average Sauter bubble diameter and the decrease of specific surface area of bubbles. In addition, the negative effects of the reduction of specific surface area and the shortening of bubble residence time on oxygen mass transfer efficiency were greater than the positive effects of the increase of turbulent kinetic energy. When the aperture changes from 300 to 400 μm, the shortening of bubble residence time should have played a major role. This study provides some theoretical parameters for investigating the mechanism of oxygen mass transfer in microporous aeration.

Experimental investigation on the effect of surface characterization of electrodes on the gas bubble dynamics in electrolyte flow and performance of FLA batteries by using PIV

Generation of oxygen and hydrogen bubbles at vicinity of the electrodes FLA battery at SOC 60%. In the flooded lead_acid batteries (FLAB), gas bubbles are initially formed on the surface of the electrodes, which are produced by electrochemical reactions, and then released into the electrolyte. In the present investigation, the effect of surface characterization of electrodes of FLAB on the gas bubble dynamic parameters in the electrolyte flow at different charging/discharging rates (C-rates) are studied utilizing particle image velocimetry (PIV) method. The results show that the capacity of FLAB have a linear behavior due to changes in each of the two parameters of the surface characterization of electrodes and the C-rate. At all State of charges (SOCs) of FLAB cells in different tests, increasing average roughness ( Ra ) and average wavelength of the roughness ( λa ) in the electrode surfaces, results in an increase in average bubble diameter and bubble rising velocity. Nevertheless, a sharp decrease in the void fraction of bubbles within the electrolyte was observed due to the increment in λa and Ra . Also, the effect of the rising movement of gas bubbles within the electrolyte on the average electrolyte velocity pattern in the gap between the electrodes by changing the surface characterization of electrodes are investigated in detail.

Analysis of phase interaction and gas holdup in a multistage multiphase rotodynamic pump based on a modified Euler two-fluid model

Due to the effect of unit stages, the gas-liquid flow and the interphase forces in the multistage multiphase pump are more disordered, which will affect the energy conversion efficiency. However, the characteristics of phase interaction and gas holdup in such a pump are not clear. In this study, based on a modified Euler two-fluid model, simulations of a multiphase rotodynamic pump with two stages were carried out with medium combinations of air-water and air-crude. The characteristics of phase interaction and gas holdup were analyzed at different inlet gas void fractions (IGVFs), and inlet bubble diameters. The results show that the overall changing trend of interphase forces is the same between the first and second stages at different IGVFs, but the magnitudes of interphase forces in the second stage are slightly smaller, especially for the medium combination of air-water. Moreover, the drag is more sensitive to the IGVF, while the lift and added mass force are more sensitive to the medium viscosity. As the increase of the inlet bubble diameter, the difference of the gas holdup effect in the pump increases gradually at IGVF = 9.0%, and the maximum almost occurs in the first stage guide vane (S1). When the bubble diameter increases to 0.7 mm, the degree of gas accumulation and gas-liquid velocity difference increase significantly, resulting in a significant increase of the disordered degree of lift and added mass force.

Direct numerical simulation of bubble dynamics and heat transfer during nucleate boiling on the micro-pin-finned surfaces

The pool boiling on the micro-pin-finned surfaces was numerically investigated using the curvilinear coupled Volume of Fluid and level set method (VOSET) with phase change. The information interaction problem on the boundary of a complex domain was solved by the partition identification function and unstructured storage. The experiment and simulation of single bubble growth on the micro-pin-finned surface were conducted, whose results agree with each other and validate the accuracy of the numerical method. The bubble characteristics such as bubble shape, temperature distribution, pressure field and micro flow were analyzed and compared with that on the smooth surface, which demonstrates that the vortex near the three-phase contact line plays a significant role in the bubble growth and boiling heat transfer. The effects of wall superheat, gravity level, contact angle and the height of micro-pin-fins were investigated. With the increase of superheat, the average heat flux and bubble diameter increase while the departure time decreases. Under microgravity, the bubble diameter and departure time are larger compared with terrestrial gravity, which deteriorates the heat transfer performance. The fin height basically has no effect on the initial bubble growth. However, there exists a critical fin height leading to the smallest departure diameter and time. Besides, the double bubble coalescence on the micro-pin-finned surface was also investigated. The bubble growth rate reduces after the coalescence. During the coalescence, the surface energy converts into kinetic energy causing the violent deformation of the bubble shape, which promotes the liquid supply and increases the wall heat flux.

Investigation of the Gas-Liquid Two-Phase Flow and Separation Behaviors at Inclined T-Junction Pipelines.

The T-junction is a novel type of separator used in the petroleum and gas industry. It is used to achieve the gas–liquid or liquid–liquid two-phase separation. To obtain an applicative T-junction separator, in the present study, the gas–liquid two-phase separation characteristics in multiple inclined T-junctions were investigated through a series of numerical simulations and field experiments. Two representative multiphase modes, namely, the Euler model and the mixture model, were chosen for this study. Comparisons of the field experiments were made to obtain a highly accurate simulation model. The mixture model was chosen to be better suited for this study. It is used to investigate the gas–liquid two-phase flow and the separation behaviors, which include the effect of inlet flow velocity, inlet bubble diameter, and the split ratio of two outlets. The results indicate that the best flow split ratio exists when the two-phase separation reaches the best consequence, and the best flow split ratio changes when the separation demands of gas or liquid are different. Furthermore, the separation efficiency keeps decreasing as the inlet velocity is increased. Hence, the inlet mixture velocity should be reduced to improve the gas–liquid two-phase separation. More specifically, to obtain a better separation for the same throughput, the size of the T-junction should be increased. Moreover, the separation efficiency increases as the inlet bubble diameter increases. Consequently, the results can be used to design the T-junction as an industrial separator, which can then be directly used in petroleum and gas production.

Visualization-based nucleate pool boiling heat transfer enhancement on different sizes of square micropillar array surfaces

Visualization-based nucleate pool boiling experiments are carried out on different sizes of square micropillar array surfaces (SMAS) and plain surface using deionized water as working fluid at atmospheric pressure. The quantitative measurements of the bubble dynamics, including the nucleation site density, the bubble departure diameter and the frequency, are obtained using a high-speed camera with microscope. The obtained results show that the SMAS, with square micropillar in the range of 0.2–0.8 mm height and width (the pitch between the micropillar is equal to the micropillar width), has a considerably lower wall superheat, which enhanced the heat transfer coefficient (HTC) by 32–203% compared to the plain surface. Generally, the boiling heat transfer intensifies with the increase in the square micropillar height keeping the width constant. But the tendency reverses at high heat flux levels. The high-speed visualization reveals that the higher square micropillar has faster bubble departure frequency at low heat flux, because higher micropillar is conducive to induce capillary flow and aids in separating the paths of departing bubble and replenishment liquid. However, the increase of bubble diameter at high heat flux restrains bubble departure with higher square micropillar. In addition, the increase of square micropillar width is conducive to enhancing the boiling heat transfer and the tendency is reversed at high heat flux levels when the square micropillar height is kept constant. The bubble dynamics are compared with the predictions using various correlations from the literature.