Number Of Small Bubbles Research Articles

Bubbly flows in a column with submerged hollow fiber membranes

Experiments of bubbly flows in a column with submerged hollow fiber membranes are carried out to discuss the relation between bubbly flow characteristics and fouling control. Two kinds of liquids, water and xanthan gum-water solution (XG-W), are used as the liquid phases. The relaxation rates of membranes are set at 0.0 or 0.5%. The number of small bubbles with ellipsoidal shapes in water are larger than that in XG-W, while large bubbles with spherical cap shapes are remarkably observed in XG-W in spite of the presence of membranes. The rate of large bubbles is enhanced in XG-W due to bubble coalescence. The gas holdup in water is higher than that in XG-W. The gas holdup becomes higher due to the presence of membranes and membrane relaxation in both water and XG-W. For discussion on fouling control due to bubbly flows, experiments are carried out to remove pseudo sludge attached to hollow fiber membranes. The relaxation of membranes enhances the removal rate of pseudo sludge. The mean removal rate, which is the mean value of the removal rate of each membrane, increases with increasing the gas holdup. This relation is well expressed by a linear regression in the present experimental range regardless of the liquid property and membrane relaxation, that is, the gas holdup has a prospect of an indicator for estimating fouling probability.

Identification of cavitation state of centrifugal pump based on current signal

Centrifugal pump, which is widely used in water conservancy, electric power, petrochemical, ship, aerospace, and other technical fields, is the core equipment used to ensure all kinds of energy transfer. Cavitation not only affects the service life of the centrifugal pump but also seriously impacts the reliability of the process flow or device system. Due to the influence of the life, position and number of vibration sensors, the existing cavitation fault feature identification accuracy is not enough. The state analysis and characteristic recognition of the current signal under the cavitation state of the centrifugal pump are conducted in this paper based on soft sensing technology, and the signal component and judgment threshold representing the cavitation state are obtained. The following results are presented. Under different critical cavitation numbers, a small number of bubbles appeared near the suction surface of the inlet edge of the impeller, which verified the reliability of criterion for the critical cavitation number when the head coefficient decreased by 3%. The overall accuracy of binary classification cavitation recognition based on the current signal is 12.9% higher than that of three classification cavitation recognition. The recognition rate of VMD decomposition under different working conditions is higher than that of EMD, in design conditions, for example, overall accuracy improved by 7.3%, which also indicates that the obtained cavitation information of each component by VMD decomposition is richer than that obtained by EMD decomposition. Comparing different working conditions, a large flow rate easily leads to cavitation and high recognition current rate, compared with the flow of 0.75 Q and 1.25 Q, the overall accuracy is improved by 9.6%.

Electrothermally excited plasma droplet evolution on the laser-patterned surface

Droplet behavior involving electrothermal coupling fields has gradually attracted the attention of researchers, one of which includes electrosurgical scalpels that often contact biofluids. However, the evolution of bio-droplets exposed to the surface of electrosurgical scalpels is not yet well understood. Here, we experimentally studied the effect of different heating temperatures on plasma droplets on the laser-patterned surface (LPS) and the original surface (OS) under defined direct-current (DC) or alternating-current (AC) electric fields. The results show that at a lower heating temperature, the evolution of plasma droplets was dominated by electrolysis. Oxygen bubbles generated on the papillae on the LPS in the DC field inhibited the targeted adsorption of plasma proteins on this surface. In contrast, in the AC field, only a small number of bubbles was generated, which is not sufficient to inhibit protein adsorption, leading to the formation of coagulation on the papillae after heating. At higher heating temperatures, the rapid formation of coagulation resulted in the suppression of electrolysis. The plasma proteins were then transported by the Marangoni flow causing coagulation to reach a thickness of stress mutation. Stress release over the entire coagulation caused its edges to bend and then detach from the papillae. Thus, the LPS exhibited excellent anti-adhesive properties to plasma droplets under electrothermal excitations compared to the OS. This study provides valuable information for understanding the mechanisms of contact behavior between biofluids and electrosurgical scalpels and demonstrates great promise for their anti-adhesive performance.

CFD Investigation on Movement Features of Hydrogen Bubble under Microgravity Environment

A designed cryogenic upper stage adopted liquid hydrogen and liquid oxygen (LH2/LO2) as an aerospace propellant. During a zero-gravity coast period in space, the wall heat leakage into the delivery tube could induce liquid propellant evaporation and two-phase flow phenomenon, so that a bubble discharge operation must be employed prior to engine restart. In this study, a CFD approach was utilized to numerically study the bubble discharge behaviors inside the LH2 delivery tube of the upper stage. The bubble motion properties under two different schemes, including positive acceleration effect and circulation flow operation, were analyzed and discussed. The results showed that the boiled hydrogen bubbles could increase to the size of the tube inner diameter and distribute randomly within the entire tube volume, and that, in order for the bubble to spill upward under the acceleration effect, a higher acceleration level than the needed value of acquiring liquid–vapor separation inside the propellant tank should be provided. When creating an acceleration level of 10−3 g0, most of the bubbles could spill upward within 700 s. Significantly, the bubbles could not be completely expelled in the created acceleration condition since a number of small bubbles always stagnate in the bulk liquid region. In the circulation flow operation, the gas volume reduction was mainly attributed to two mechanisms: the vapor condensation effect; and bubble discharge effect. For the case with a circulation flow rate of 0.2 kg/s, a complete bubble discharge purpose was reached within 820 s, while a large bubble stagnation in the spherical distributor occupied a remarkable proportion of the total time. In addition, both the liquid flow rate and liquid subcooling exert important effects on bubble performance. When applying a high circulation flow, the gas volume reduction is mainly due to the inertial effect of liquid flow, but the bubble stagnation in the spherical distributor still affects the total discharge time. The liquid subcooling influence on the gas volume reduction is more significant in smaller circulation flow cases. Generally, the present study provides valuable conclusions on bubble motions inside a LH2 delivery tube in microgravity, and the results could be beneficial to the sequence design of engine restart for the cryogenic upper stage.

Quantification of oxygen transfer coefficients in simulated hydrocarbon-based bioprocesses in a bubble column bioreactor.

This study investigates the overall volumetric oxygen transfer coefficient (KLa) in multiphase hydrocarbon-based bioprocess under a range of hydrocarbon concentrations (HC), solid loadings (deactivated yeast) (SL) and superficial gas velocities (UG) in a bubble column reactor (BCR). KLa increased with increasing UG in the air-water system; due to an increase in the number of small bubbles which enhanced gas holdup. In air-water-yeast systems, the initial addition of yeast increased KLa significantly. Further increases in SL reduced KLa, due to increases in the bubble size with increasing SL. KLa decreased when HC was added in air-water-hydrocarbon systems. However, UG, SL and HC affected KLa differently in air-water-yeast-hydrocarbon systems: an indication of the complex interactions between the yeast and hydrocarbon phases which changed the system's hydrodynamics and therefore affected KL. This work illustrates the effect of the operating conditions (SL, HC and UG) on oxygen transfer behaviour in multiphase systems.

Multiscale characterization of nanoparticles in a magnetically assisted fluidized bed

Pressure fluctuations of a fluidized bed of nanoparticles were measured during the fluidization of nanoparticles with and without a magnetic field at a frequency of 50Hz. Recurrence quantification analysis (RQA) and wavelet transform were used to determine the frequency range of various flow structures in the bed at three scales. The frequency ranges of the macro-, meso-, and micro-structures were determined to be 0–49Hz, 49–781Hz, and 781+ Hz, respectively. Comparison of the determinisms of the sub-signals with and without the external field revealed that in the presence the field, breakage of larger agglomerates occurs faster than re-agglomeration of small agglomerates into larger ones. The power spectral density function of the pressure fluctuations indicated that with an external magnetic field, the power and the frequency range of the pressure signal of macro-structures do not change noticeably. However, the power of the meso-structure signal increases and its frequency range is widened toward higher frequencies, confirming that the number of small bubbles and agglomerates increase in the bed. In addition, the energy of signal analysis indicated that the external field significantly increases the share of meso-structures in the bed, confirming the RQA results.

Experimental measurement and theoretical analysis on bubble dynamic behaviors in a gas-liquid bubble column

Bubble dynamic behaviors have significant effects on the interfacial area between gas and liquid phases, the gas-phase residence time and the efficiency of heat and mass transfer. This study mainly investigated the single bubble dynamic behaviors and the radial distribution patterns of bubbly flow in a bubble column through Particle Tracking Velocimetry (PTV) and High Speed Imaging (HSI). As the results indicate, with the bubble size increasing, bubble deformation and bubble rising velocity are intensified and bubble trajectories change accordingly. Meanwhile, theoretically calculated values of single bubble terminal velocities are in accord with experimental values. According to the study, gas-liquid interaction has a noticeable impact on multiple radial distribution patterns of bubbly flow, including bubble size, velocity, the number of small bubbles and the width of gas-liquid interaction region. Finally, a correlation is proposed in this work to predict the width of gas-liquid interaction region based on a dimensionless analysis.

Experimental study on bubble and droplet entrainment in vertical churn and annular flows and their relationship

Bubble and droplet entrainment plays an important role in the mass transfer between the liquid film and the gas core in churn and annular flow. In this work, bubble and droplet entrainments in vertical churn and annular flows are systematically studied in an air-water two-phase vertical flow experiment using a high-speed camera. The results show that there are three kinds of bubble entrainment and five kinds of droplet entrainment in churn and annular flows. The entrainment can be categorized as primary entrainment and secondary entrainment. The primary entrainment includes one kind of bubble entrainment, which is a large wave roll and overturn, and three kinds of droplet entrainment, which are shearing-off of waves containing bubbles, bag break-up of waves, and ligament break-up of waves. The secondary entrainment includes two kinds of bubble entrainment, which are synchronized bubble entrainment along with droplet entrainment and droplets from the gas core impacting the liquid film, and two kinds of droplet entrainment, which are droplets impacting the liquid film and the burst of bubbles. With the flow pattern transition from churn to annular flow, the dominant bubble entrainment changes from large wave roll and overturn to the synchronized bubble entrainment along with droplet entrainment accompanied by a decreasing intensity. The dominant droplet entrainment changes from shearing-off of waves containing bubbles to ligament break-up of waves with the intensity first decreasing and then increasing. There is a close relationship between bubble entrainment and droplet entrainment. The entrained bubbles reduce the strength of large-scale waves and facilitate the shearing-off of waves. A small number of droplets are entrained due to the burst of residual bubbles in the liquid film. Droplets that are generated by bag or ligament break-up of waves can directly impact the nearby liquid film, leading to synchronous bubble entrainment. A small number of bubbles can be entrapped by droplets from the gas core impacting the liquid film. The primary entrainment intensity is significantly greater than that of the secondary entrainment. With the transition from churn to annular flow, the change in the primary entrainment intensity determines the variety of the secondary entrainment intensity.

Simulation of bubble growth during the foaming process and mechanics of the solid foam

Elastomeric foams are widely used in different types of applications where different material properties are of interest in each application. All of these properties are governed by the microstructure and the properties of the material matrix. Studying the evolution of the microstructure experimentally is extremely challenging. Thus, here we use direct numerical simulations to gain an insight into the changes that happen from the creation of the gas bubbles in the liquid state, until the solidification into a cellular morphology. Furthermore, the resulting microstructure is then used directly in simulations of solid mechanical testing to determine the mechanical properties of the foam. The matrix fluid is assumed to be Newtonian and incompressible. A linear elastic isotropic material model for the solidified polymer was used to obtain the solid foam properties. The foam was described by a representative volume element (RVE), where a small number of bubbles was randomly distributed. Using this approach, the RVE can describe the bulk behavior of the foam, while remaining computationally tractable. Microstructures with volumes fraction of over 90% (2D) and 45% (3D) are accurately captured. In addition, the influence that the bubble growth rate and the initial bubble distribution of the fluid simulations have on the solid foam properties was studied.

Interaction of an acoustic wave with a multilayer medium containing a bubble liquid layer

Discrete-layered media are interesting to research since properties of each layer can significantly differ from near by ones and this can be used in technological processes. The presence of a small number of bubbles significantly increases the compressibility of the medium while the density of the bubble medium remains close to the density of the carrier liquid. From the applied point of view it is interesting that the energy of the incident wave can be completely absorbed by combining of layer properties (length, volume content of the dispersed phase, etc.). In this work, based on the equations of mechanics of dispersed media, we consider the reflection and propagation of acoustic waves passing at right angles through a three-layer medium in a pipeline containing a layer of bubble fluid. From the condition for the existence of a solution in the form of a decaying traveling wave, dispersion relations are written for each of the possible layers. Based on them, the dependences of the amplitude of the incident and transmitted waves on the propagation velocity of the pulse are analytically derived. The coefficients of reflection and transmission through the interface are obtained both in the general case and in particular cases for each layer. These ratios make it possible to calculate the possible consequences of a wave action on the considered media in the event of emergencies at work and to prevent them.

Effect of microstructure on 3He migration in TiT1.9 films

Two kinds of films were prepared to study the effect of microstructure on helium migration in Ti tritides. Both films showed different release behaviors and helium bubble distributions. In the film consisting of columnar grains, a two-layered structure was observed. Inclusions with a strip feature were found at the grain boundary, and no helium bubbles were distributed in these inclusions. However, helium preferred to migrate to the boundaries of these inclusions. Bubble linkage as a ribbon-like feature developed parallel to the film surface in the film consisting of columnar grains. More cracks were developed at the grain boundaries of the film consisting of columnar grains, although the helium content in the film consisting of columnar grains was less than that in the film consisting of equiaxed grains. A surface region with a small number of bubbles, or “depleted zone”, was observed near the surface. The cracks extending to the film surface were the pathways of the critical helium released from the film. The helium migration was strongly influenced by the grain microstructure.

Research into resonance phenomena in gas-vapor bubbles

In order to calculate resonating gas bubbles, the mathematical model was supplemented by taking into account phase-transition processes on the surface of a bubble in gas-vapor media, as well as the thermal effects at gas dissolution in fluid. A series of calculations of the resonance mode for bubbles of dimensions of 0.5‒3 mm in water at temperatures from +1 to +99 °C and atmospheric pressure was performed. As a result of mathematical modeling, the possibility of resonance in gas-vapor bubbles in water in the frequency range of 0.5–5 kHz was established. It was shown that in the resonance mode the amplitude of oscillations of the wall of a bubble first increases rapidly and then is stabilized at the level of 30‒50 % of the radius. It was established that motion velocity of the walls of a bubble under resonance conditions can exceed 6 m/s. It was shown that in the compression mode internal pressure of a bubble can increase by three times or decrease by two times compared with ambient pressure. Dependence of approximation resonance frequency of air bubbles in water on their diameter was established. It was found that in the resonance mode, temperature of gas-vapor medium of a bubble periodically decreases by 6 °C and increases by 12 °C in comparison with the original one. In this case, the temperature of the surface of a bubble decreases by 1 °C and increases by 7 °C. It was shown that favorable conditions for water vapor condensation (fog formation) are created at the stage of the growth of a bubble. The schematic of the research setup and the results of field observations of gas-vapor bubbles under condition of the influence of sound waves was presented. The existence of resonance of bubbles at calculation frequencies was proved and formation of bubbles was established experimentally. The phenomena of a bubble division and its explosion were illustrated. It was found that addition of surface active substances extends the frequency range of formation of multi-bubbles by five times and contributes to an increase in the number of small bubbles inside a large one. The research results can be applied to intensification of various technological processes related to heat and mass exchange in gas-vapor systems.

Propagation characteristics of pseudo-Scholte waves at the interface between finite-thickness fluid layer and quasi-saturated porous half-space

The propagation of interface waves at the interface between a fluid-saturated porous medium and a fluid has been extensively investigated in the last three decades due to its various and wide applications in several fields including earthquake engineering and materials testing. Although the sea floor is usually covered with porous marine sediment, the previous interface wave theories are rarely used for submarine acoustic problems for the following reasons. 1) In addition to hard porous media, unconsolidated soft porous media exist widely in the seabed, which are seldom considered in previous studies. 2) The depth of seawater is limited, and in many cases it cannot be regarded as a half-space. 3) The fluid-saturated porous medium model cannot describe the effect of a small number of bubbles caused by decomposition of organic matter in the sediment. Hence, the present paper focuses on the low-frequency pseudo-Scholte waves at the interface between an overlying fluid layer of finite thickness and a quasi-saturated porous half-space. The overlying fluid is assumed to be ideal compressible water and the quasi-saturated porous media are assumed to be sandstone and unconsolidated sediment and modeled by Biot theory. A fluid equivalent model is used to analyze the effects of the bubbles in the pores. Based on the boundary conditions, the closed-form dispersion equations of far-field interface waves are derived by using classical potential function method. The velocity and attenuation of pseudo-Scholte wave are determined by Newton iteration in a reasonable rooting interval. The analytical expressions of the displacement field and fluid pressure distribution caused by pseudo-Scholte waves are also derived. Then, based on the derived theoretical formulation, the numerical examples of calculations are presented. Our calculation results show that the stiffness of porous medium significantly affects the mode, phase velocity, displacement and fluid pressure distribution of interface waves; the phase velocity of the pseudo-Scholte wave in the finite-thickness fluid/fluid-saturated porous half-space is related to the ratio of the wavelength to the thickness of the fluid layer; the phase velocity of the shear wave is insensitive to a small number of bubbles dissolved in the pores, but the existence of bubbles has a significant influence on the phase velocity of the compressional wave and the pseudo-Scholte wave. Furthermore, the existence of bubbles can significantly affect the distribution of the pore pressure.

The role of ultrasound in hydrogen removal and microstructure refinement by ultrasonic argon degassing process

In this work, the role of ultrasound in hydrogen removal and microstructure refinement by the ultrasonic argon degassing has been fully investigated by the experimental work in water and AZ91-0.4Ca magnesium melt, respectively. Ultrasound is able to break up argon gas into numbers of small bubbles and drive them diving deeply to the bottom of water, which are responsible for the efficient degassing regime of ultrasonic argon process. The argon flowrate plays a dominant role in promoting hydrogen removal effect. Meanwhile, the increasing argon flowrate can suppress the microstructure refinement, due to the subdued ultrasonic cavitation under a large argon flowrate. Mechanical properties of AZ91-0.4Ca alloy can be much promoted by the ultrasonic argon degassing process. Ultrasound is the key to achieve not only efficient degassing regime, but also microstructure refinement as well as mechanical properties promotion.

Impact of resting time between mixing and shaping on the dough porosity and final cell distribution in sandwich bread

Experiments were carried out to study the effects of resting time (also well known as first proofing) on properties of dough and bread. Three resting times were used in the experiment: 0, 10 and 20 min. The results indicated that resting time significantly (p < 0.05) affects the properties of dough and bread. Porosity of the dough increased with increase in resting time. Decrease in the number of smaller bubbles and increase in the median pore area of the bubbles present in the dough was observed as the resting time proceeded. Significant decrease (p < 0.05) in torque value was observed with increase in resting time. Elastic recovery in terms of recoil strain was highest for 0 min resting followed by 10 and 20 min resting. Degassing was found to closely related to the air content of the dough as it was found that degassing increased with resting time. Bread specific volume and the porosity fraction increased, whereas median pore area in the bread crumb decreased with resting time.

Critical heat flux triggering mechanism on micro-structured surfaces: Coalesced bubble departure frequency and liquid furnishing capability

This study presents a new critical heat flux (CHF) triggering mechanism for explaining the CHF enhancements of micro-structured surfaces. Differentiating the existing vapor recoil mechanism and hydrodynamic instability theory, this model focuses on the phenomenological observations of the boiling phenomena in which a number of small bubbles are generated, which then merge and coalesce into a large bubble. According to this model, the CHF phenomenon is governed by the frequency of the coalesced bubble departure and the liquid furnishing capability into a thin liquid–vapor layer (macrolayer). The microstructures on the surface change the evaporative mass flow rate owing to the liquid–vapor interface deformation near the triple contact line of the macrolayer, leading to a change in the coalesced bubble departure frequency. The liquid flow resistance, which increased owing to the microstructures, can affect the liquid volume flow rate available for evaporation in the macrolayer; thus, it directly alters the CHF behavior. The liquid flow resistance induced by the microstructures could contribute to the relative deterioration of the CHF value at the surface. The CHF can be directly modeled by means of the summation of the mean velocity of liquid flowing into the macrolayer due to the pressure potential induced from capillary and disjoining pressure effects, as well as the coalesced bubble departure frequency.

Interaction of a vortex ring with a single bubble: bubble and vorticity dynamics

The interaction of a single bubble with a single vortex ring in water has been studied experimentally. Measurements of both the bubble dynamics and vorticity dynamics have been done to help understand the two-way coupled problem. The circulation strength of the vortex ring (${\it\Gamma}$) has been systematically varied, while keeping the bubble diameter ($D_{b}$) constant, with the bubble volume to vortex core volume ratio ($V_{R}$) also kept fixed at about 0.1. The other important parameter in the problem is a Weber number based on the vortex ring strength $(\mathit{We}=0.87{\it\rho}({\it\Gamma}/2{\rm\pi}a)^{2}/({\it\sigma}/D_{b});a=\text{vortex core radius},{\it\sigma}=\text{surface tension})$, which is varied over a large range, $\mathit{We}=3{-}406$. The interaction between the bubble and ring for each of the $\mathit{We}$ cases broadly falls into four stages. Stage I is before capture of the bubble by the ring where the bubble is drawn into the low-pressure vortex core, while in stage II the bubble is stretched in the azimuthal direction within the ring and gradually broken up into a number of smaller bubbles. Following this, in stage III the bubble break-up is complete and the resulting smaller bubbles slowly move around the core, and finally in stage IV the bubbles escape. Apart from the effect of the ring on the bubble, the bubble is also shown to significantly affect the vortex ring, especially at low $\mathit{We}$ ($\mathit{We}\sim 3$). In these low-$\mathit{We}$ cases, the convection speed drops significantly compared to the base case without a bubble, while the core appears to fragment with a resultant large decrease in enstrophy by about 50 %. In the higher-$\mathit{We}$ cases ($\mathit{We}&gt;100$), there are some differences in convection speed and enstrophy, but the effects are relatively small. The most dramatic effects of the bubble on the ring are found for thicker core rings at low $\mathit{We}$ ($\mathit{We}\sim 3$) with the vortex ring almost stopping after interacting with the bubble, and the core fragmenting into two parts. The present idealized experiments exhibit many phenomena also seen in bubbly turbulent flows such as reduction in enstrophy, suppression of structures, enhancement of energy at small scales and reduction in energy at large scales. These similarities suggest that results from the present experiments can be helpful in better understanding interactions of bubbles with eddies in turbulent flows.

Turbulence Modulation by Small Bubbles in the Vertical Upward Channel Flow

The liquid turbulence modulation by small bubbles was investigated detailedly in a vertical upward channel flow with a finite number of small bubbles with the developed Eulerian-Lagrangian method. Small bubbles are treated as pointwise spheres subject to gravity, drag, added mass, pressure gradient, lift, and wall lift forces. The momentum transfer between phases was realized through interphase forces. The present investigation shows that the liquid turbulence is intensified near the wall and is slightly weakened in the channel central region due to the bubble addition. The turbulence modulation mechanisms by bubbles were also analyzed in the paper.

In vivo microvascular mosaics show air embolism reduction after perfluorocarbon emulsion treatment

Massive arteriolar gas embolism (AGE) has never been evaluated in vivo using intravital microscopy and previous perfluorocarbon (PFC) emulsions were only effective in AGE when administered before AGE. We implemented a new system for quantitative studies of massive AGE using brightfield microscopy and tested a treatment with a third-generation PFC emulsion after massive AGE. We studied bubble dynamics in cremaster muscles from anesthetized rats after AGE was induced by direct air injection into the femoral artery ipsilateral to the studied muscle. Using a motorized microscope stage and a color camera, in vivo microvascular mosaics were produced on-line from over 2000 digital images to evaluate multiple networks in order to investigate the distribution, lodging, breaking, reduction and moving of 105 air bubbles in microvessels. Thirty minutes after PFC treatment, there was a reduction of 80% in bubble volume while untreated and saline-treated rats showed significantly smaller decreases of 33% and 40%, respectively (p<0.05). Air bubbles also dissolved into a larger number of smaller bubbles after PFC treatment. The proposed methodology may prove useful for rapid in vivo data acquisition from large networks. Since large air bubbles broke-up, decreased in length and volume, and moved toward smaller microvessels, the study provides quantitative data to support a mechanism by which PFC may improve tissue blood flow following massive AGE. The findings suggest that this new generation of PFC emulsions administered after severe AGE may reach compromised microvascular networks and provide help to alleviate microvascular obstruction by increasing air bubble reabsorption.

A-B Phase Conversion and Coexistence of Superfluid 3He in Aerogel

We have studied phase transition of superfluid 3He at 2.4 MPa in cylindrical aerogel by NMR method. When the liquid is cooled down from the normal state, the A-like phase appears below superfluid transition temperature T which is suppressed in comparison with the transition temperature of the bulk liquid. With further cooling below the certain temperature T , , the A-like phase is converted into the B-like phase gradually. Both phases stably coexist within about 90 μK. When you keep the temperature constant in which both phases coexist, the A-B phase conversion stops. With furthermore cooling, the whole liquid becomes the B-like phase. The cwNMR spectra at the coexistence state suggest that the B-like phase is not uniformly distributed in the A-like phase like a large number of small bubbles in a liquid, but separated as a whole from the A-like phase. By applying a field gradient which changes as a function of square of radius, we found that the A-like phase is in the edge part with a cylindrical shape and the B-like phase is in the central part with a columnar shape.