Low Liquid Fraction Research Articles

Simulation of melting characteristics of thermal washing of the wax layer in the pipeline based on lattice Boltzmann method

ABSTRACT The escalation of transportation costs and the obstruction of pipelines due to wax deposition significantly impact the secure and efficient production of oil fields. The thermal washing method, characterized by its simplicity and cost-effectiveness, is widely employed for dewaxing crude oil gathering pipelines. The investigation of the melting mechanism of the wax layer during thermal washing is extremely important. In this paper, the two-zone composite model of multiphase flow-porous medium in the mushy zone is introduced into the solid-liquid phase change lattice Boltzmann model based on the enthalpy method, and the problem of circumferential inhomogeneity in the melting of the wax layer and the important influence of flow and heat transfer in the mushy zone on the thermal washing are systematically investigated. The demarcation point (γ tr) between the high and low liquid fraction zones is measured to be 0.81 by microscopic experiment. The impacts of varying γ tr and Ste numbers on wax melting at different circumferential locations are analyzed in detail. The results show that the melting efficiency of wax exhibits a nonlinear enhancement from − 90° to 90°. The melting efficiency of wax decreases with increasing γ tr for wax layers between 90° and − 45°. The melting efficiency of wax increases with higher Ste numbers at all angles. The Ste number increases from 0.42 to 5.0, and the melting efficiency of the wax layer at angles ranging from 90° to − 90° increases by factors of 2.16, 2.16, 2.20, 2.61, and 3.33 respectively. The growth of the Ste number improves the warming rate and shortens the generation time of convection at the center point of the wax layer. The research findings serve as a fundamental reference for formulating a rational and efficient thermal washing scheme.

Modelling of removal of surfactants from liquid solutions in a bubble column

This paper proposes a theoretical model for the separation of a surfactant from water in a bubble column. The proposed model includes both mass balance and adsorption thermodynamics of surfactants on bubble surfaces in the liquid solution (e.i. surface equations of state and adsorption isotherms). This is very important because models, found in the literature, did not consider adsorption thermodynamics. The proposed model successfully predicted the experimental results. It was found that the separation efficacy was higher at a lower surfactant concentration in the liquid than that at a higher surfactant concentration; the reason is probably that available bubble surface areas for adsorption of the surfactant were higher at a lower surfactant concentration. A higher cross-sectional area of the column led to a better separation performance due to a larger amount of generated bubble surfaces. A low gas flow rate and low liquid fraction resulted in the best separation performance.

Ultrasound imaging of liquid fraction in foam

Flotation is an important process in liquid-solid and solid-solid separation, whereby desired solids in suspensions are recovered by their attachment to gas bubbles. Monitoring the process is essential for an increased grade and reduced water consumption. However, in situ measurements of the froth’s phases (liquid, air, particles) and / or volume flow that would be easily integrable in industrial processes are not available. The constant alternation of phases remains challenging for measurement instrumentations. In this paper, we report on pilot tests of novel instrumentation that allows for measurement of low liquid fraction based on electrodes and ultrasound transducers measurements. It offers high milliscale spatial and temporal resolution in the low liquid fraction range of foam (≤ 0.83∙10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> ). Improving the accuracy of prospective volume flow estimations, a high penetration depth of 9.2 cm was achieved. The measurement system was calibrated using homogeneous, steady foam and an integral conductivity measurement. A backscatter model was applied to reduce the effect of ultrasound shadowing and enhance quantitative liquid fraction estimates. Additionally, six cases of inhomogeneous and dynamic liquid fraction distributions were investigated qualitatively. The quantitative and qualitative validation was conducted with a reference neutron radiography measurement, showing good correspondence. This investigation distinguished between two of the three froth phases within the analyzed range. Whereby a first step towards in situ monitoring of foam parameters in industrial applications was achieved, which is especially relevant to widely used froth flotation processes.

Effect of solder joint size and composition on liquid-assisted healing

This work presents an experimental and numerical investigation of liquid-assisted healing with respect to solder joint composition and size. A damage-healing model is formulated based on entropy generation of damage and viscous material transport during healing. The model accounts for a composition-dependency of healing by introducing the liquid film thickness, the liquid viscosity and a microstructural mobility parameter. The size dependencies enter the healing model in form of the local capillary pressure of the solder joint. A viscous flow experiment illustrates the compositional dependency of local material transport and a cyclic tensile experiment shows the regain of mechanical properties, such as, stiffness and strength after healing. The flow experiment shows that material transport is retarded for solders of low liquid fraction and crack healing is limited due to partial filling of the crack. Simulation results of a solder array suggest the capillary pressure as the driving force for healing, which leads to a size-dependency of the healing evolution. The required time for complete healing increases with reduced solder dimensions due to higher capillary pressures. Microstructural mobility due to high liquid fractions also promotes healing.

Less is more: Unstable foams clean better than stable foams

HypothesisFoamed surfactant solutions can clean surfaces! We hypothesise that the cleaning efficiency depends on the liquid fraction and on the stability of the foam. We also hypothesise that the cleaning efficiency is the better the smaller the average bubble size is. ExperimentsThe double syringe technique was used to generate foams with varying liquid fractions but the same, very small bubble sizes with and without perfluorohexane in the gas phase. We performed cleaning tests in which the foams were applied to glass substrates contaminated with a fluorescent oil. FindingsWe found that unstable foams clean better than stable foams. Three cleaning mechanisms were identified: (1) imbibition at low liquid fractions, (2) wiping, i.e., shifting of the contact line between oil, foam and glass, at all liquid fractions, and (3) drainage at high liquid fractions. The change of the liquid fraction and of the foam stability lead to different combinations of these mechanisms and thus to different cleaning results.

Characterisation and optimisation of foams for varicose vein sclerotherapy.

Foam sclerotherapy is the process of using an aqueous foam to deliver surfactant to a varicose vein to damage vein wall endothelial cells, causing the vein to spasm, collapse and ultimately be re-absorbed into the body. Aqueous foams are complex fluids that can exhibit a significant yield stress and high effective viscosity which depend on their composition, particularly the bubble size and liquid fraction. To characterise the properties of foams used for varicose vein sclerotherapy and determine their effectiveness in the displacement of blood during sclerotherapy. Foams are modelled as yield stress fluids and their flow profiles in a model vein are predicted. Values of the yield stress are determined from experimental data for three different foams using the Sauter mean of the bubble size distribution. Along with the measured liquid fraction of the foams, this information is collected into a Bingham number which entirely characterises the process of sclerotherapy. Polydispersity in bubble size has a strong effect on the yield stress of a foam and the Sauter mean of the size distribution better captures the effects of a few large bubbles. Reducing the polydispersity increases the yield stress, and a higher yield stress results in a larger plug region moving along the vein, which is more effective in displacing blood. The width of the plug region is proportional to the Bingham number, which also has a quadratic dependence on the liquid fraction of the foam. Assuming typical values for the rate of injection of a foam, we predict that for a vein of diameter 5mm, the most effective foams have low liquid fraction, a narrow size distribution, and a Bingham number B ≈4.5. The Sauter mean radius provides the most appropriate measure of the bubble size for sclerotherapy and the Bingham number then provides a simple measure of the efficacy of foam sclerotherapy in a vein of a given size, and explains the ability of different foams to remove varicose veins. Foams containing small bubbles, with a narrow size distribution, and a low liquid fraction are beneficial for sclerotherapy.

Experimental investigation on foam formation through deformable porous media

AbstractFoam formation in porous media is a topic of growing scientific and industrial interest due to its range of applications, from daily life consumer products to oil recovery. Despite the work done so far on foams flowing through complex structures, such as rigid porous media, this subject still needs to be fully elucidated. An additional complexity to the problem arises when the porous medium is deformable, a situation which has only been faced, to our knowledge, from a modelling point of view. In this work, the investigation of foam formation in deformable porous media is carried out by using commercial sponges as a deformable porous media system, with special emphasis on the effect of confinement on foam bubble size distribution. Foam is formed by wetting the sponge with an aqueous surfactant solution and then squeezing the sponge either between two glass cover slides or between a plastic net and a cover slide. Our experimental data reveal that the latter system allows the formation of drier foams (ie, with lower liquid fraction, fL &lt; 0.3), more similar to the ones obtained in dish‐washing applications. Moreover, the effect of sponge type, in terms of material and microstructure, on final foam is presented. Our results are of potential interest for the optimization of foams in complex structures, such as in deformable porous media.

Numerical Study of a Horizontal and Vertical Shell and Tube Ice Storage Systems Considering Three Types of Tube

There is a growing interest in sustainable energy sources for energy demand growth of power industries. To align the demand and the consumption of electrical energy, thermal energy storage appears as an efficient method. In the summer days, by using a cold storage system like ice storage, peaks of the energy usage shift to low-load hours of midnights. Here, we investigate the charging process (namely solidification) numerically in an ice-on-coil thermal energy storage configuration, where ice is formed around the coil or tube to store the chilled energy. The considered ice storage system is a shell and tube configuration, with three kinds of tubes including a U-shaped tube, a coil tube with an inner return line, and a coil tube with an outer return line. Advanced 3D unsteady simulations are achieved to determine the effects of tube type and position of the ice storage (horizontal or vertical) on the solidification process. Results indicate that using a coil tube speeds up the ice formation, as compared with the simple U-shaped tube. The coil tube with an outer return line exhibits a better performance (more produced ice), as compared with the coil tube with an inner return line. After 16 h of solidification, the coil tube with the outer return line has about 1.057% and 1.32% lower liquid fraction in comparison with the coil tube with the inner return line and U-shaped tube, respectively, for both positions (vertical and horizontal).

Effects of partially thermally active walls on simultaneous charging and discharging of paraffin wax in a square cavity

The thermal performance of paraffin wax in a square cavity under simultaneous charging and discharging (SCD) condition is investigated. The paraffin wax is charged and discharged by partially heating and cooling walls. A computational fluid dynamics (CFD) model is developed and validated against experimental data. Numerical studies were done to explore the performance of the system with different arrangements of the hot and cold portions. Results show that heating PCM from bottom and cooling from top accelerates the melting process, and heating PCM from side and cooling from bottom increases the stored energy. In addition, the effect of positions of partially thermally active walls for each arrangement was investigated. Results show that the stronger the natural convection, the higher PCM liquid fraction. More specifically, when heating from the bottom, the best performance is achieved with the hot portion locates at the middle of bottom wall regardless of the position of cold portion; increasing the height of hot portion results in a lower liquid fraction and stored energy; increasing the height of cold portion leads to lower PCM mean temperature and then decreases the stored energy. Furthermore, it is also found the melting rate increases as the cold portion gets further away from the hot portion.

Correlation between the Liquid Fraction, Microstructure and Tensile Behaviors of 7075 Aluminum Alloy Processed by Recrystallization and Partial Remelting (RAP)

The recrystallization and partial remelting (RAP) method was applied to obtain the semisolid 7075 aluminum alloy with different liquid fractions. The effects of liquid fraction on the microstructure and tensile properties were determined in detail. The results show that during the semisolid isothermal treatment, the number of the intra-granular liquid droplets increased initially with the melting of the eutectic phases. Extension of isothermal soaking led to the coarsening and spheroidization of the intra-granular droplets. Finally, these liquid droplets merged and moved towards the grain exterior. The room temperature tensile strength of the RAP-processed AA7075 alloy, which were isothermally soaked at 600 and 610 °C, increased with the holding time from 5 to 15 min and then decreased dramatically from 15 to 25 min, whilst that soaked at 620 °C decreased monotonously. The fracture morphology exhibited intra-granular fracture mode at low liquid fractions. However, it transformed to a completely brittle and inter-granular type at high liquid fractions and the cohesive force of the liquid-solid interfaces at the grain boundaries determined the strength of the alloys. The transfer of the intra-granular liquid droplets into the inter-granular liquid phase played a significant role for the different fracture behaviors of the RAP-processed AA7075 alloy. The paper provides some reference for better controlling the microstructure and mechanical properties in semisolid processing.

Gamma densitometry measurements of gas/liquid flow with low liquid fractions in horizontal and inclined pipes

Gamma densitometry measurements of gas/liquid flow with low liquid fractions in horizontal and inclined pipes

High pressure phase equilibrium of ternary and multicomponent alkane mixtures in the temperature range from (283 to 473) K

Asymmetric multicomponent alkane mixtures can be used as model systems for reservoir fluids. We have prepared two ternary mixtures, methane/n-butane/n-decane and methane/n-butane/n-dodecane, and two multicomponent mixtures composed of methane/n-butane/n-octane/n-dodecane/n-hexadecane/n-eicosane as model reservoir fluids and measured their phase equilibrium in the temperature range from (283–473) K by using a variable volume cell with full visibility. Their phase envelopes and liquid volume fractions below the saturation pressure have been measured. Four equations of state, including Soave-Redlich-Kwong (SRK), Peng-Robinson (PR), Perturbed Chain Statistical Associating Fluid Theory (PC-SAFT), and Soave-Benedict-Webb-Rubin (Soave-BWR), have been used to predict phase equilibrium of the measured systems. PR and PC-SAFT give better results than others and Soave-BWR gives poor phase envelope predictions which are quite distinct from the predictions by other models. It is generally challenging for any of the tested models to predict all the measured phase envelopes with high accuracy. For predictive calculation of the liquid fractions, the agreement in the low pressure region is good whereas the fractions just below the saturation pressures are difficult to predict. Moreover GERG-2008 has also been tested with the measured methane/n-butane/n-decane system. It overpredicts the saturation pressures but predicts low pressure liquid fractions quite accurately.

Close relationship between a dry-wet transition and a bubble rearrangement in two-dimensional foam.

Liquid foams are classified into a dry foam and a wet foam, empirically judging from the liquid fraction or the shape of the gas bubbles. It is known that physical properties such as elasticity and diffusion are different between the dry foam and the wet foam. Nevertheless, definitions of those states have been vague and the dry-wet transition of foams has not been clarified yet. Here we show that the dry-wet transition is closely related to rearrangement of the gas bubbles, by simultaneously analysing the shape change of the bubbles and that of the entire foam in two dimensional foam. In addition, we also find a new state in quite low liquid fraction, which is named “superdry foam”. Whereas the shape change of the bubbles strongly depends on the change of the liquid fraction in the superdry foam, the shape of the bubbles does not change with changing the liquid fraction in the dry foam. Our results elucidate the relationship between the transitions and the macroscopic mechanical properties.

Microstructure Evolution and Coarsening Mechanism of 7075 Semi-Solid Aluminum Alloy Pre-Deformed by ECAP Method

To investigate the influence of refined grains on the microstructure of 7075 aluminum alloy in semi-solid state, a new strain induced melting activation (SIMA) method was put forward containing two main stages: pre-deformation with equal channel angular pressing (ECAP) method and isothermally holding in the semi-solid temperature range. The breaking up and growth mechanisms of the grains and kinetics of equiaxed grains coarsening during the semi-solid holding were investigated. The results showed that the average grain size after ECAP extrusion decreased significantly, e.g., microstructure with average globular diameter less than 5μm was achieved after four-pass ECAP extrusion. Obvious grain coarsening had been found during isothermal holding in the semi-solid state and the roundness of the grains increased with the increasing holding time. The proper microstructure of 66.8μm in diameter and 1.22 in shape factor was obtained under proper soaking condition (at 590°C for 15 min). Two coarsening mechanisms, namely, coalescence in lower liquid fraction and Ostwald ripening in higher liquid fraction contributed to the grain growth process.

The measurement of thermodynamic performance in cryogenic two-phase turbo-expander

Liquid fraction measurement in cryogenic two-phase flow is a complex issue, especially for an industrial cryogenic system. In this paper, a simple thermal method is proposed for measuring the liquid fraction in cryogenic two-phase turbo-expander by an electric heating unit in experimental study. The liquid fraction of the cryogenic two-phase flow is determined through the heat balance built at the outlet of the turbo-expander (inlet of heating unit) and the outlet of the heating unit. Liquid fractions from 1.16% to 5.02% are obtained from five two-phase expansion cases. Under the same turbo-expander inlet pressure and rotating speed, five superheated expansion cases are tested to evaluate the wetness loss in two-phase expansion. The results show that the proposed method is successful in measuring the liquid fraction of cryogenic two-phase expansion for turbo-expander in an industrial air separation plant. The experimental isentropic efficiency ratio and the tested Baumann factor decrease with the increasing mean wetness. Based on prediction of Baumann rule, the cryogenic turbo-expander with low liquid fraction in two-phase expansion cases suffers from more severe wetness loss than that with the higher liquid fraction.

Erratum to: The Oxidation Behaviors of 7050 Aluminum Strips During Semi-solid Powder Rolling and Mechanical Properties of Strips

Semi-solid powder rolling (SSPR) is a novel strip manufacturing process, which combines powder rolling with semi-solid rolling in one step. Based on the features of SSPR, powders were heated to the semi-solid temperature range and then rolled. Therefore, oxides will form during heating and rolling. The oxidation behavior of 7050 aluminum during SSPR was analyzed and the quantity, distribution and morphology of oxides are discussed. The effects of quantity, distribution and morphology of the oxides on the microhardness of strips under different conditions were studied. The results showed that the main factor influencing the quantity of oxides is the heating temperature. The mechanism of oxidation during SSPR was found to be diffusion controlled. In the heating stage, surface oxide films hinder the diffusion. In the rolling stage, surface oxide layers were broken and so the oxidation of aluminum alloy mainly took place in the rolling stage. The formed oxides are Al2O3 with a little of MgO showing an irregular morphology with a size of 2–3 µm. High bonding quality between the oxide particles and the matrix, as well as an uniform distribution of the oxides, leads to a higher microhardness of the SSPR-ed strips. But, the bonding quality between the oxide particles and the matrix is poor under conditions of low liquid fraction and some oxides distribute non-uniformly around the grain boundaries.

Experimental Investigation of Pressure-volume-Temperature Mass Gauging Method Under Microgravity Condition by Parabolic Flight

Gauging the volume or mass of liquid propellant of a rocket vehicle in space is an important issue for its economic feasibility and optimized design of loading mass. Pressure-volume-temperature (PVT) gauging method is one of the most suitable measuring techniques in space due to its simplicity and reliability. This paper presents unique experimental results and analyses of PVT gauging method using liquid nitrogen under microgravity condition by parabolic flight. A vacuum-insulated and cylindrical-shaped liquid nitrogen storage tank with 9.2 L volume is manufactured by observing regulation of parabolic flight. PVT gauging experiments are conducted under low liquid fraction condition from 26% to 32%. Pressure, temperature, and the injected helium mass into the storage tank are measured to obtain the ullage volume by gas state equation. Liquid volume is finally derived by the measured ullage volume and the known total tank volume. Two sets of parabolic flights are conducted and each set is composed of approximately 10 parabolic flights. In the first set of flights, the short initial waiting time (3 ∼ 5seconds) cannot achieve sufficient thermal equilibrium condition at the beginning. It causes inaccurate gauging results due to insufficient information of the initial helium partial pressure in the tank. The helium injection after 12 second waiting time at microgravity condition with high mass flow rate in the second set of flights achieves successful initial thermal equilibrium states and accurate measurement results of initial helium partial pressure. Liquid volume measurement errors in the second set are within 11%.

Gas absorption and reaction in a wet pneumatic foam

Results for the rate of absorption of carbon dioxide gas into a pneumatic (i.e. continuously rising) foam formed from a sodium carbonate–bicarbonate buffer solution stabilised by a polyglycol frother are presented. Previous studies upon the use of gas–liquid foam for gas absorption operations have demonstrated limited potential for the technique, mainly because the liquid films rapidly become saturated with the absorbing gas due to the relatively low liquid fraction within the foam. However, by adding washwater to the free surface of the foam we created a wetter and more stable foam that (1) exhibits a high liquid fraction and therefore avoids film saturation, and (2) creates greater liquid advection past the gas-liquid surfaces, thereby enhancing the mass transfer coefficient. The interfacial area achieved within the foam was in the range 2100–3200m2m−3 (i.e. much higher than in conventional gas-liquid contactors and the liquid-side mass transfer coefficient was the same magnitude as that achieved in packed beds (i.e. 4–8×10–5ms−1). Indeed, by modelling the foam as a packed-bed of solid spheres (with no adjustable constants), the mass-transfer coefficient in a bed of closely packed solid spheres was found to be in satisfactory agreement with the mass-transfer measured in the wet gas-liquid foam. The hydrodynamic state and the slip velocity between gas and liquid phases is required for the design of wet foam absorption columns, and this can be estimated using a theory of pneumatic foam (Stevenson, 2007).

Studying foam dynamics in levitated, dry and wet foams using diffusing wave spectroscopy

We use diffusing wave spectroscopy to study the microscopic dynamics of foams. These foams are levitated diamagnetically, such that very high liquid fractions can be achieved. We find that at low liquid fraction the dynamics is dominated by local rearrangements, whereas at high liquid fraction the movement of bubbles is ballistic and large scale rearrangements are absent. This change in the microscopic dynamics coincides with a change in the scaling of coarsening on increasing the liquid fraction that we have found earlier.

&lt;i&gt;In Situ&lt;/i&gt; Microstructure Observation of Steel Grades in the Semi-Solid State for Thixoforging Process by Using Confoncal Laser Scanning Microscopy

It is necessary to well understand the microstructure evolution during high speed heating and forming for steel thixoforging, since it determines the thixotropic flow behavior of materials in the semi-solid state. A new in situ technique - high temperature Confocal Laser Scanning Microscopy (CLSM) - was developed and used for studying the microstructure evolution directly at high temperature where the microstructure in the semi-solid state could not be preserved by quenching experiments for conventional 2D characterization. Several steel grades (C38LTT, 100Cr6 and M2) were investigated during heating from the as-received state to the semi-solid state and finally cooled to the solid state).It has been found that there is a significant difference in diffusion rate of alloying elements between these grades during heating and cooling. In M2, thanks to the high content of alloying elements and their low diffusion rate, the semi-solid temperature range is greater and its microstructure in the semi-solid state could be preserved by quenching or even at a low cooling rate, which means the microstructure of M2 in the semi-solid state can be characterized in room temperature on quenched M2 samples. On the contrary, the microstructure of other steel grades 100Cr6 and C38LTT in semi-solid state can only be revealed by CLSM at high temperature because of the lower volume fraction of alloying elements and their high diffusion rate. It is very interesting to use high temperature CLSM to in situ investigate the microstructure evolution in the semi-solid state, especially at low liquid fraction.