Drop Phase Research Articles

Gas Phase Pressure Drop of a Water-Sparged Aerocyclone Reactor

Air stripping of ammonia is a widely used process for the pretreatment of wastewater. Scaling and fouling on the packing surface in packed towers and a lower stripping efficiency are the two major problems in this process. New patented equipment that is suitable for the air stripping of wastewater with suspended solids has been developed. Air stripping of ammonia from water with Ca(OH)2, was performed in the newly designed gas-liquid contactor, a water-sparged aerocyclone (WSA). The pressure drop of gas phase was investigated in order to know the momentum transfer characteristic of the WSA. It was found that the gas phase pressure drop exhibited a different change tendency compared with the traditional aerocyclone, and could be divided into three characteristic stages, including low pressure drop, pressure drop jump and high pressure drop phases. The three different pressure drop areas corresponds to steady jet, spiral and fogged flow patterns of the liquid phase. The critical value for the air flow rate which caused the mass transfer coefficient to increase rapidly took place at the point where the steady jet was transformed into the spiral flow pattern.

Surfactant effects on drop formation in co-flowing fluid streams

We conduct a numerical study to investigate the effect of surfactants on the drop formation process in a co-flowing system using a hybrid volume-of-fluid (VOF) method combined with a front-tracking scheme. The drop and bulk phases are treated as incompressible Newtonian fluids, and the surfactants are modeled using a Langmuir adsorption framework. We consider the effect of soluble surfactants in the adsorption–desorption limit on the drop formation process. A drop in the co-flowing geometry typically breaks up at the primary neck, close to the primary drop, in the absence of surfactants. When surfactants are present, they accumulate in the neck region resulting in Marangoni stresses that slow down the neck thinning rate. This results in longer breakup times with larger drop volumes. At high surfactant coverages, the primary neck formation slows down enough and breakup occurs at the secondary neck, close to the remnant drop. Increasing the outer co-flowing flow weakens the retarding effect of the high surfactant coverage leading to breakup again at the primary neck. The adsorption–desorption kinetics also affects the neck breakup position, and the primary drop volume and breakup time depend non-linearly on the Biot number. For any given Biot number, a critical fractional coverage exists beyond which the drop fails to neck. The presence of a confining wall may lower the value of the critical equilibrium fractional coverage required for the drop to enter the no-necking regime.

Short-term power load forecasting using grey correlation contest modeling

Power load has the characteristic of nonlinear fluctuation and random growth. Aiming at the drawback that the forecasting accuracy of general GM(1,1) model goes down when there is a greater load mutation, this paper proposes a new grey model with grey correlation contest for short-term power load forecasting. In order to cover the impact of various certain and uncertain factors in climate and society on the model as fully as possible, original series are selected from different viewpoints to construct different forecasting strategies. By making full use of the characteristic that GM(1,1) model can give a perfect forecasting result in the smooth rise and drop phase of power load, and the feature that there are several peaks and valleys within daily power load, the predicted day is divided into several smooth segments for separate forecasting. Finally, the different forecasting strategies are implemented respectively in the different segments through grey correlation contest, so as to avoid the error amplification resulted from the improper choice of initial condition. A practical application verifies that, compared with the existing grey forecasting models, the proposed model is a stable and feasible forecasting model with a higher forecasting accuracy.

Calculation of the Drop Size Distribution and Velocities from the Integral Form of the Conservation Equations

A new formulation based on integral form of the conservation equations is developed for analyzing spray droplet and velocity statistics. Both averaged or distributions of the droplet size and velocities can be calculated using this approach, although in this work the authors focus on the droplet size statistics and only compute the averaged droplet velocities. The formulation is based on the conservation equations, and intrinsically involves few assumptions and required inputs. The key is to use the integral form so that the input and output variables are related without having to resolve the complex details of the atomization process. This new approach naturally leads to predictions of SMDs, as well as the drop size distributions and phase velocities, with SMD and drop size distributions achieving good agreement with experimental data if a liquid-phase viscous dissipation term is included. The latter point suggests that the effect of liquid-phase viscosity seems quite important, as the present method overpredicts the effect of injection pressure unless some form of the viscous dissipation is included in the energy balance equation. The use of moment-generating function for the log-normal distribution within the present formulation permits an efficient algorithm that reproduces the experimentally observed droplet size distributions. Further work remains to ascertain some aspects of the present solution approach, in particular the exact form of the viscous dissipation on the spray energy balance. The present integral formulation and the solution approach provide a fundamentally sound basis for analyzing droplet size and velocity statistics with several key parameters that may be adapted for different injector geometries, such as swirl and air-blast sprays, and injection conditions.

Structure and phase formation of nanostructural ion-plasma Ti-Cr-Al-N coatings on a hard-alloy cutting tool

A The possibility to of fabricate fabricating nanostructural Ti-Al-Cr-N coatings on a cutting hard-alloy tool with crystallites 20–60 nm in size by the method of ion-plasma arc deposition with the use of a tree-cathode system for sputtering materials and the separation of plasma flows from a drop phase is shown. The dependences of that structure and phase formation in the coating material have on the accelerating bias potential (U = −100 to −160 V) supplied to a the substrate and determining the energy of sputtered particles and condensation temperature, as well as on a the current (ICr = 90–130 A) of a the sputtering arc at a the chromium cathode and the chromium concentration that depending depends on the the current within the vapor phase and the formed coating, are determined.

Experimental investigation and numerical simulation of mass transfer during drop formation

The solvent extraction features mass transfer between drops and the surrounding immiscible liquid. Previous study indicated that drop formation plays an important role in extraction because 10–50% of total mass transfer occurs in this stage. It is necessary to have thorough understanding about the mechanism of mass transfer between the drop phase and continuous phase during drop formation. In this work, the level set approach was adopted to capture the interface, and unsteady mass transfer during drop formation was formulated and numerically simulated in an axisymmetric cylindrical coordinate system by solving the fluid motion coupled with mass transfer equations. Drop formation time and mass transfer parameters from the numerical simulation were compared with experimental data in the MIBK–acetic acid–water solvent extraction system. The numerical predictions were found in good agreement with the experimental measurements.

Inertial effects on the rheology of a dilute emulsion

The behaviour of an isolated nearly spherical drop in an ambient linear flow is examined analytically at small but finite Reynolds numbers, and thereby the first effects of inertia on the bulk stress in a dilute emulsion of neutrally buoyant drops are calculated. The Reynolds numbers, Re = a2ρ/μ and $\hat{\Rey} \,{=}\, \dot{\gamma}a^2\rho/\hat{\mu}$, are the relevant dimensionless measures of inertia in the continuous and disperse(drop) phases, respectively. Here, a is the drop radius, is the shear rate, ρ is the common density and and μ are, respectively, the viscosities of the drop and the suspending fluid. The assumption of nearly spherical drops implies the dominance of surface tension, and the analysis therefore corresponds to the limit of the capillary number(Ca) based on the viscosity of the suspending fluid being small but finite; in other words, Ca ≪ 1, where Ca = μa/T, T being the coefficient of interfacial tension. The bulk stress is determined to O(φRe) via two approaches. The first one is the familiar direct approach based on determining the force density associated with the disturbance velocity field on the surface of the drop; the latter is determined to O(Re) from a regular perturbation analysis. The second approach is based on a novel reciprocal theorem formulation and allows the calculation, to O(Re), of the drop stresslet, and hence the emulsion bulk stress, with knowledge of only the leading-order Stokes fields. The first approach is used to determine the bulk stress for linear flows without vortex stretching, while the reciprocal theorem approach allows one to generalize this result to any linear flow. For the case of simple shear flow, the inertial contributions to the bulk stress lead to normal stress differences(N1, N2) at O(φRe), where φ(≪1) is the volume fraction of the disperse phase. Inertia leads to negative and positive contributions, respectively, to N1 and N2 at O(φRe). The signs of the inertial contributions to the normal stress differences may be related to the O(ReCa) tilting of the drop towards the velocity gradient direction. These signs are, however, opposite to that of the normal stress differences in the creeping flow limit. The latter are O(φCa) and result from an O(Ca2) deformation of the drop acting to tilt it towards the flow axis. As a result, even a modest amount of inertia has a significant effect on the rheology of a dilute emulsion. In particular, both normal stress differences reverse sign at critical Reynolds numbers(Rec) of O(Ca) in the limit Ca ≪ 1. This criterion for the reversal in the signs of N1 and N2 is more conveniently expressed in terms of a critical Ohnesorge number(Oh) based on the viscosity of the suspending fluid, where Oh = μ/(ρaT)1/2. The critical Ohnesorge number for a sign reversal in N1 is found to be lower than that for N2, and the precise numerical value is a function of λ. In uniaxial extensional flow, the Trouton viscosity remains unaltered at O(φRe), the first effects of inertia now being restricted to O(φRe3/2). The analytical results for simple shear flow compare favourably with the recent numerical simulations of Li & Sarkar (J. Rheol., vol. 49, 2005, p. 1377).

Streaming potential generated by a drop moving along the centreline of a capillary

The electrical streaming potential generated by a two-phase pressure-driven Stokes flow in a cylindrical capillary is computed numerically. The potential difference ΔΦ between the two ends of the capillary, proportional to the pressure difference Δp for single-phase flow, is modified by the presence of a suspended drop on the centreline of the capillary. We determine the change in ΔΦ caused by the presence of an uncharged insulating neutrally buoyant drop at a small electric Hartmann number, i.e. when the perturbation to the flow field caused by electric stresses is negligible.The drop velocity and deformation, and the consequent changes in the pressure difference Δp and streaming potential ΔΦ, depend upon three independent parameters: the size a of the undeformed drop relative to the radius R of the capillary; the viscosity ratio λ between the drop phase and the continuous phase; and the capillary number Ca which measures the ratio of viscous to capillary forces. We investigate how the streaming potential depends on these parameters: purely hydrodynamic aspects of the problem are discussed by Lac & Sherwood (J. Fluid Mech., doi:10.1017/S0022112009991212).The potential on the capillary wall is assumed sufficiently small so that the electrical double layer is described by the linearized Poisson–Boltzmann equation. The Debye length characterizing the thickness of the charge cloud is taken to be small compared with all other length scales, including the width of the gap between the drop and the capillary wall. The electric potential satisfies Laplace's equation, which we solve by means of a boundary integral method. The presence of the drop increases |ΔΦ| when the drop is more viscous than the surrounding fluid (λ > 1), though the change in |ΔΦ| can take either sign for λ < 1. However, the difference between ΔΦ and Δp (suitably non-dimensionalized) is always positive. Asymptotic predictions for the streaming potential in the case of a vanishingly small spherical droplet, and for large drops at high capillary numbers, agree well with computations.

Motion of a drop along the centreline of a capillary in a pressure-driven flow

The deformation of a drop as it flows along the axis of a circular capillary in low Reynolds number pressure-driven flow is investigated numerically by means of boundary integral computations. If gravity effects are negligible, the drop motion is determined by three independent parameters: the size a of the undeformed drop relative to the radius R of the capillary, the viscosity ratio λ between the drop phase and the wetting phase and the capillary number Ca, which measures the relative importance of viscous and capillary forces. We investigate the drop behaviour in the parameter space (a/R, λ, Ca), at capillary numbers higher than those considered previously. If the fluid flow rate is maintained, the presence of the drop causes a change in the pressure difference between the ends of the capillary, and this too is investigated. Estimates for the drop deformation at high capillary number are based on a simple model for annular flow and, in most cases, agree well with full numerical results if λ ≥ 1/2, in which case the drop elongation increases without limit as Ca increases. If λ < 1/2, the drop elongates towards a limiting non-zero cylindrical radius. Low-viscosity drops (λ < 1) break up owing to a re-entrant jet at the rear, whereas a travelling capillary wave instability eventually develops on more viscous drops (λ > 1). A companion paper (Lac & Sherwood, J. Fluid Mech., doi:10.1017/S002211200999156X) uses these results in order to predict the change in electrical streaming potential caused by the presence of the drop when the capillary wall is charged.

CUBICALLY REGULARIZED STOKESLETS FOR FAST PARTICLE SIMULATIONS OF LOW-REYNOLDS-NUMBER DROP FLOWS

Swarms of Stokeslets have previously been shown to be effective for simulating three-dimensional, free-surface, buoyancy-driven drop flows at unit viscosity ratio, including interfacial rupture and pass-through phenomena. This article presents an efficient marker-and-cell/fast Fourier transform (MAC-FFT) algorithm that yields N log N scaling of the operations, thereby enabling accurate simulations involving millions of particles. The formerly separate steps of regularization of the Green's function (commonly used in vortex blob methods for inviscid flow) and discretization are unified by regularizing the Stokeslet over the cubical cells that form the underlying grid—as opposed to the spherical blobs used in the past. A piecewise-constant drop phase function, obtained by simple binning of the particles, thereby yields second-order quadrature of the Green's function to obtain the velocity field. An iterative cascade algorithm (adapted from Daubechies wavelets) allows the Stokes “cubelet” field to be calculated very efficiently. A similar cubelet approach is used for the cohesive forces that mimic interfacial tension. A user-friendly library of Fortran 95 subroutines ( DropLib , www.droplib.org) has been developed to carry out the simulations and visualize drop shape evolutions in three dimensions.

Controlled delivery of paracetamol and protein at different stages from core–shell biodegradable microspheres

The core–shell biodegradable microspheres loading human serum albumin (HSA) and paracetamol were fabricated with a hydrophilic alginic acid (ALG) shell and a hydrophobic poly(lactic- co-glycolic acid) (PLGA) core. The two model drugs, HSA and paracetamol, were entrapped in the shell and core, respectively. Theses microspheres were characterized in terms of morphology, mean size and size distribution, drug loading efficiency, in vitro degradation and drugs release. The optical microscopy (OM) and transmission electron microscope (TEM) photos revealed directly that the microspheres possessed core–shell structure. The degradation results showed that there were quick drop phases in weight of polymer matrix and in pH of degradation medium after 2 weeks. In vitro release profiles showed that within the initial 20 h, only HSA was almost released from the shell layers, whereas only another drug, paracetamol, was almost released from the cores in the following period.

Surface dilatational rheology measurements for oil/water systems with viscous oils

This work presents an application of the capillary pressure tensiometry (CPT) for accurate measurements of the surface dilatational elastic and loss moduli of the interface between water and transparent oil phases with viscosities up to 10,000 mPa s. Surface rheological studies involving viscous oils are not possible with other available methods due to the considerable bulk viscous forces. Theoretical estimations show that successful measurements with such systems are possible by using a suitable frequency range of the oscillating spherical drop method by CPT. Measurements with oils having viscosities between 5 and 10,000 mPa s at a frequency smaller than 1 Hz were performed using the oil as outer phase and the aqueous surfactant solution as inner (drop) phase. As predicted by the theory the measured surface elastic modulus did not depend on the viscosity (within experimental accuracy). Three different approaches to account for the contribution of the bulk shear viscosity to the measured pressure signal were analyzed and applied. The results showed that if exact numerical corrections are used the calculated loss modulus also did not depend on the viscosities of the bulk phases. The two other methods used lead to errors, sometimes significant.

Motion of deformable drops through granular media and other confined geometries

This article features recent simulation studies of the flow of emulsions containing deformable drops through pores, constrictions, and granular media. The flow is assumed to be at low Reynolds number, so that viscous forces dominate, and boundary-integral methods are used to determine interfacial velocities and, hence, track the drop motion and shapes. A single drop in a flat channel migrates to the channel centerplane due to deformation-induced drift, which increases its steady-state velocity along the channel. A drop moving towards a smaller interparticle constriction squeezes through the constriction if the capillary number (ratio of viscous deforming forces and interfacial tension forces) is large enough, but it becomes trapped when the capillary number is below a critical value. These concepts then influence the flow of an emulsion through a granular medium, for which the drop phase moves faster than the suspending liquid at large capillary numbers but slower than the suspending liquid at smaller capillary numbers. The permeabilities of the granular medium to both phases increase with increasing capillary number, due to the reduced resistance to squeezing of easily deformed drops, though drop breakup must also be considered at large capillary numbers.

Confined drop motion in viscoelastic two-phase systems

In this study, we numerically examine the buoyancy-driven, axisymmetric motion of drops through vertical cylindrical capillaries. Combinations of Newtonian and viscoelastic drop and suspending fluid phases are considered. The effects of confinement, material properties, and rheological properties of the two phases on drop mobility and deformation are examined. Four dimensionless parameters (Reynolds number, capillary number, Deborah number, and the drop-to-tube size ratio) play critical roles in determining the drop motion. In general, a Newtonian drop immersed in a viscoelastic fluid experiences an extending trailing edge, while a viscoelastic drop in a Newtonian fluid develops an indentation around the rear stagnation point. Under certain conditions, a cusped drop appears due to fluid viscoelasticity that triggers shape instability.

인터스키 부정지 숏턴 동작의 운동학적 분석

본 연구는 인터스키 부정지 숏턴 동작에서 우수 집단과 비우수 집단 간 운동학적 변인의 차이를 3차원 영상 분석을 통해 보다 효과적인 부정지 숏턴 동작을 모색하고자 하였다. 연구 대상은 2007년 전국스키기술선수권대회 부정지 숏턴 경기에 참가한 선수 10명을 대상으로 DLT 방법을 이용한 3차원 영상분석을 통해 운동학적 변인을 분석하였으며, 그 결과 다음과 같은 결론을 얻었다. 총 소요시간 및 국면별 소요시간은 우수 집단이 비우수 집단보다 짧게 나타났다. 신체중심은 우수 집단이 비우수 집단보다 작은 좌우이동 폭과 큰 상하이동 폭을 나타내며, 직진성을 강화하는 활주를 하였으며, 그로 인하여 좌우속도를 제어하면서 빠른 전후속도를 나타냈다. 상하속도는 드롭 인 구간에서는 느리게 하면서 범프 업 구간에서 속도를 증가시킨 것으로 나타났다. 고관절각과 슬관절각은 우수 집단이 비우수집단보다 전체 이벤트에서 모두 작게 나타났으며, 동체 전경갈 신체 기울기각은 우수 집단이 비우수 집단보다 모두 크게 나타났다. 하퇴 전경각은 우수 집단이 비우수 집단보다 모글 중앙에서 크게 나타났으며, 동체 비틀기각은 우수 집단이 비우수 집단보다 드롭 인 구간에서 오른쪽 턴 방향으로, 범프 업 구간에서 왼쪽 턴 방향으로 크게 나타났다. The purpose of this study was to analyze differences in kinematic variables for mogul short turn motion between superior and inferior group, so that it can explore more effective mogul short turn motions. To meet the goals, this study selected total 10 ski players who would participate in mogul short turn event of the National Technical Ski Championship 2007, so that it could analyze kinematic variables by way of 3D motion analysis using DLT method. As a result, this study came to the following conclusions; For total and phase-specific duration, it was found that superior group took shorter time than inferior group. Superior group's Center of Mass was stands for more high value in up-down movement skill than inferior group. However right-left movement scale was less than them. In this reason, superior group was made a straight descent at the same time made a fast front-rear velocity. In the part of up-down movement velocity show that move slowly in the drop-in phase while increased in the bump-up phase. It is show that superior group was less tinny than inferior group include joint angle and knee joint angle. However leaning angle of trunk and the body inclination angle were more high figured than inferior group. Leaning angle of lower limbs also showed high figure at the center mogul. Lastly, In the part of body torsion angle show that superior group was high figure direction of right turn in the drop-in phase while in bump-up phase, made a high figure direction of left turn.

Effect of compatibilization on the deformation and breakup of drops in step-wise increasing shear flow

Drop deformation and breakup were investigated in the presence of a block copolymer in step-wise simple shear flow using a home-made Couette cell connected to an Anton Paar MCR500 rheometer. Polyisobutylene (PIB) was used as the matrix, while five different molecular weights of polydimethylsiloxane (PDMS) were selected to provide drops with a relatively wide range of viscosity ratio. A block copolymer made of PDMS-PIB was used for interfacial modification of the drop-matrix system. The copolymer concentration was 2wt% based on the drop phase. The experiments consisted in analyzing the drop shape and measuring the variation of the length to diameter ratio, L/D, both in steady state and in transient regimes till breakup. This allowed revising of the classical Grace curve that reports the variation of the critical capillary number for breakup as a function of viscosity ratio and providing also a new one for blends compatibilized with an interfacial active agent with a given molecular weight.

Headspace single drop and hollow fiber liquid phase microextractions for HPLC determination of phenols

Two methods based on headspace single drop microextraction (HS-SDME) and headspace hollow fiber liquid phase microextraction (HS-HF-LPME) were developed and critically compared with HPLC-UV determination of phenols (including phenol (Ph), 2-chlorophenol (CP), 2,4-dichlorophenol (DCP) and 2,4,6-trichlorophenol (TCP)) in this paper. The significant parameters affecting the extraction efficiency of the target analytes in both extraction modes were studied and the optimal extraction conditions were established. Under the optimal conditions, the detection limits (S/N = 3) for Ph, CP, DCP and TCP obtained by HS-SDME-HPLC-UV and HS-HF-LPME-HPLC-UV were 2.1, 0.2, 0.8,1.1 ng/mL and 4.2, 0.4, 0.4, 0.4 ng/mL with enrichment factors of 15.8, 198.9, 159.7, 194.8 and 9.2, 149.9, 301.9, 411.1, respectively. The RSDs obtained by HS-SDME-HPLC-UV and HS-HF-LPME-HPLC-UV were 3.7, 4.0, 9.8, 6.7% and 6.3, 3.6, 3.1, 4.8% for Ph, CP, DCP and TCP, respectively. Both extraction modes have a comparable analytical performance, but HS-HF-LPME was more robust than HS-SDME, while HS-SDME was simpler than HS-HF-LPME. The two headspace microextraction modes were applied for HPLC-UV determination of target phenols in water, honey and toner samples, and the determined values obtained by both techniques were in good agreement with each other.

Algorithm for direct numerical simulation of emulsion flow through a granular material

A multipole-accelerated 3D boundary-integral algorithm capable of modelling an emulsion flow through a granular material by direct multiparticle-multidrop simulations in a periodic box is developed and tested. The particles form a random arrangement at high volume fraction rigidly held in space (including the case of an equilibrium packing in mechanical contact). Deformable drops (with non-deformed diameter comparable with the particle size) squeeze between the particles under a specified average pressure gradient. The algorithm includes recent boundary-integral desingularization tools especially important for drop–solid and drop–drop interactions, the Hebeker representation for solid particle contributions, and unstructured surface triangulations with fixed topology. Multipole acceleration, with two levels of mesh node decomposition (entire drop/solid surfaces and “patches”), is a significant improvement over schemes used in previous, purely multidrop simulations; it remains efficient at very high resolutions ( 10 4 – 10 5 triangular elements per surface) and has no lower limitation on the number of particles or drops. Such resolutions are necessary in the problem to alleviate lubrication difficulties, especially for near-critical squeezing conditions, as well as using ∼ 10 4 time steps and an iterative solution at each step, both for contrast and matching viscosities. Examples are shown for squeezing of 25–40 drops through an array of 9–14 solids, with the total volume fraction of 70% for particles and drops. The flow rates for the drop and continuous phases are calculated. Extensive convergence testing with respect to program parameters (triangulation, multipole truncation, etc.) is made.

Effects of matrix viscoelasticity on viscous and viscoelastic drop deformation in a shear flow

The deformation of a Newtonian/viscoelastic drop suspended in a viscoelastic fluid is investigated using a three-dimensional front-tracking finite-difference method. The viscoelasticity is modelled using the Oldroyd-B constitutive equation. Matrix viscoelasticity affects the drop deformation and the inclination angle with the flow direction. Numerical predictions of these quantities are compared with previous experimental measurements using Boger fluids. The elastic and viscous stresses at the interface, polymer orientation, and the elastic and viscous forces in the domain are carefully investigated as they affect the drop response. Significant change in the drop inclination with increasing viscoelasticity is observed; this is explained in terms of the first normal stress difference. A non-monotonic change – a decrease followed by an increase – in the steady-state drop deformation is observed with increasing Deborah number (De) and explained in terms of the competition between increased localized polymer stretching at the drop tips and the decreased viscous stretching due to change in drop orientation angle. The transient drop orientation angle is found to evolve on the polymer relaxation time scale for highDe. The breakup of a viscous drop in a viscoelastic matrix is inhibited for smallDe, and promoted at higherDe. Polymeric to total viscosity ratio β was seen to affect the result through the combined parameter βDeindicating a dominant role of the first normal stress difference. A viscoelastic drop in a viscoelastic matrix with matched relaxation time experiences less deformation compared to the case when one of the phases is viscous; but the inclination angle assumes an intermediate value between two extreme cases. Increased drop phase viscoelasticity compared to matrix phase leads to decreased deformation.

Ultramultiple-level storage in TiN∕SbTeN double-layer cell for high-density nonvolatile memory

We report a phase-change nonvolatile memory (NVM) concept based on a TiN∕SbTeN (N-doped Sb2Te3) double-layer structure, which can be used for ultramultiple-level storage (UMLS). SbTeN shows a gradual resistivity drop and good phase stability with increasing annealing temperature, a characteristic which makes it suitable for UMLS applications. We demonstrate that the number of distinguishable resistance levels can readily reach 16 and even higher. These levels in this study result from the initial threshold switching and the subsequent current-controlled crystallization induced by Joule heating. The latter allows the creation of many distinct levels, thus, enabling the low-cost ultrahigh-density NVM.