Depressurization Rate Research Articles

Microscopic transport and phase behaviors of CO2 injection in heterogeneous formations using microfluidics

CO2 injection into the geological formations is a promising option to enhance oil recovery while simultaneously contributing to carbon storage. Conventional core tests provide critical insights but still leave ambiguous transport mechanisms due to the limitation of real-time visualization. This study aims to directly observe the multiphase flow behaviors and phase change in CO2 injection at pore-scale using microfluidics. Our all-in-one chip design provides a universal platform to reproduce various CO2 injection strategies in the formation with permeability contrast, including flooding and huff-n-puff processes, and integrated a rapid measurement of minimum miscibility pressure (MMP). Miscible injection eliminates the capillary force in immiscible scenario, and promotes stable film-wise displacement with a higher recovery rate and an attenuated heterogeneity impact. We find that effective huff-n-puff operations require a sufficient gas concentration to generate bubbles and an adequate pressure gradient to push the dissolved gas displacement, which supports the importance of high depressurization rate from both physical phenomenon and inherent mechanism. Huff-n-puff re-energizes the reservoir after immiscible flooding through deep gas-oil interactions and induces a considerable growth in cumulative recovery. These micromodel results can significantly improve our fundamental understanding on detailed multiphase transport phenomena in CO2 injection and help to optimize implementation schemes.

Supercritical Extraction of a Natural Pyrethrin-Rich Extract from Chrysanthemum Cinerariifolium Flowers to Be Impregnated into Polypropylene Films Intended for Agriculture Applications

The extensive use of synthetic pesticides and their addition to the field presents significant environmental problems that must be minimized. The use of natural insecticides and their addition using techniques that minimize their impact in the field are widely studied by the current scientific community. In this work an extraction method based on supercritical CO2 to obtain a pyrethrin-rich natural extract from different varieties of chrysanthemum flowers is analyzed. This extract would be used in a supercritical solvent impregnation (SSI) process to produce a commercial polypropylene (PP) film with insecticidal properties to be used in greenhouses. The extract selected for the impregnation process was that obtained from the Atlantis variety at 35 °C and 10 MPa pressure. The amount of insecticide impregnated into the polymer at 55 °C and under two different pressure levels (10 MPa and 40 MPa) have been determined. A batch impregnation method (BM) with 5 h constant impregnation time and low depressurization rates were used to favor the impregnation process. The results demonstrated that this procedure was suitable to produce pyrethrin-loaded PP films that could to be used in greenhouses as a protection against pests, while allowing a more rational and moderate use of other chemical pesticides.

The effect of foaming process with supercritical CO2 on the morphology and properties of 3D porous polylactic acid scaffolds

AbstractA systematic study was carried out in order to identify the optimum processing conditions for the preparation of PLA 3D porous structures applying foaming with supercritical CO2 (sc‐CO2). Both the depressurization rate and the CO2 saturation pressure had a significant effect on the obtained sc‐CO2 PLA structures. When sc‐CO2 was instantaneously depressurized, a thin wall pore structure was formed, characterized by anisotropy with pores diameter ranging from 100 to 650 μm, whereas the scaffold porosity varied between 85% and 95%. In this case, a decrease in the porosity percentage was observed with increasing saturation pressure. A trend of increase in the pores' size was recorded from 150 to 200 bar, followed by a decrease at 300 bar. Highly organized pore structures with thicker pore walls and pores with diameters within the range of 10–350 μm and porosity and 74%–77% were fabricated when a slow depressurization rate was applied. An optimum porous structure, with average pore diameter 340 μm and porosity 88% was prepared when Psat was maintained at 200 bar, followed by instantaneous depressurization. Although this scaffold included the biggest number of closed pores in its structure, it presented the highest degree of pore interconnectivity due to CO2 bubbles' coalescence.

Supercritical CO2-assisted impregnation of polylactic acid films with R-carvone: Effect of processing on loading, mass transfer kinetics, and final properties

In this work, the scCO2-assisted impregnation of polylactic acid films with R-(−)-carvone was investigated, as a route to develop an active packaging material. The effect of three process variables (CO2 density: 278 and 683 kg m−3, temperature: 40 and 60 °C, and depressurization rate: 0.6 and 6.0 MPa min−1) on loading and release kinetics of the impregnated films was investigated. ANOVA testing suggested that loading was enhanced by temperature, but decreased with CO2 density and depressurization rate, obtaining values between 6.7 and 29.8 wt%. Processing conditions also showed a significant effect on release kinetics to air, obtaining a range of diffusivity values of 10−15-10−14 m2 s−1. Final properties of the films, such as thermal, mechanical, and UV-Vis transmittance properties, were also assessed. Finally, the impregnation kinetics of carvone in scCO2-swollen films was studied at the highest loading conditions, estimating a diffusion coefficient of 1.9 × 10−11 m2 s−1.

Innovative formulations of PCL: Pluronic monoliths with copaiba oleoresin using supercritical CO2 foaming/mixing to control Aedes aegypti

Copaiba oleoresin (Co), a promising bioactive agent to control Aedes aegypti proliferation, was incorporated by supercritical carbon dioxide (scCO2) foaming/mixing method (SFM) in two types of poly(ε-caprolactone) (PCL), PCL45 and PCL50, using Pluronic F-68 (Plu) as a surfactant and porogenic agent. The SFM was performed at 35 °C, scCO2 densities of 750 and 850 kg m-3, soaking time of 2.5 h, and depressurization rate of 5 bar min-1. The physicochemical characterization of monoliths, the in vitro release, and larvicidal activity against A. aegypti larvae were evaluated. All monoliths with copaiba oleoresin presented larvicidal effects. The best results were observed for PCL45:Plu:Co (56:3:41) monoliths at 750 and 850 kg m-3. This result can be attributed to the higher hydrophobicity of PCL45 than PCL50. These findings indicate that copaiba oleoresin-loaded PCL:Plu:Co monoliths are innovative and sustainable materials capable of controlling the proliferation of A. aegypti larvae and insects to avoid mosquito-borne diseases.

Thermodynamics analysis and ice behavior during the depressurization process of methane hydrate reservoir

As potential alternative energy sources, natural gas hydrate has attracted international attentions. In order to optimize its exploitation process, the thermodynamics characteristics during hydrate dissociation were investigated in this study. Eleven reservoirs with three ratios of gas amounts in gas and hydrate phases (2.1, 2.9 and 4.6) were employed, and four exhaust rates (2.3, 4.7, 7.1 and 8.8 ln/min) were conducted to pressurize the reservoirs to 2.0 MPa. Hydrates dissociated at a constant rate during the depressurization stage, and the dissociation rate increased with higher depressurization rate, while the effect is enhancing with the increase of gas space. The temperature decreased with the dropped pressure in a similar trend, affected by both depressurization rate and hydrate saturation. During constant-pressure stage, the hydrate-bearing reservoir temperature kept at approximately −2.5 °C until ice formation, making the temperature increase to −1.5 °C. Ice formation can nearly quintuple the instantaneous rate of hydrate dissociation, while no obvious changes in hydrate dissociation before and after the end of ice melting. In addition, the induction time and existence duration of ice obey good stepwise spatial and temporal sequences. These results are great significant for pressure controlling and efficiency optimization of later period of methane hydrate exploitation.

Experimental study of the transient characteristics of a natural circulation loop under SBLOCA

Abstract In order to understand the influences of various factors on the depressurization rate under small break LOCA occurring at the upper plenum in a natural circulation loop, a basic analysis has been carried out. It is shown that the depressurization rate is influenced by system pressure, back pressure, break area, water mass in the system, heating power, operational state of the second loop, and so on. Experimental results of flow and heat transfer are also presented in this paper. The experiment was carried out at the 5 MW nuclear heating reactor test loop HRTL-5. The transient processes are described and heat transfer coefficients are estimated. The results show that flashing improves the natural circulation and the heat transfer, so the wall temperature of the heated rod can be kept at a lower level and the reactor is safe. The flow oscillation, which leads to cyclical variations of important parameters, is described and its development mechanisms are studied. It is pointed out that the interaction of pressure decreasing and bubbles producing caused by flashing is the main reason of the flow oscillation.

Multi‐modal cell structure formation of poly (lactic‐co‐glycolic acid)/superparamagnetic iron oxide nanoparticles composite scaffolds by supercritical CO2 varying‐temperature foaming

AbstractPoly (lactic‐co‐glycolic acid) (PLGA)/superparamagnetic iron oxide nanoparticles (SPIONs) composite scaffold material was prepared by supercritical carbon dioxide varying‐temperature mode method. The multi‐modal cell structure was formed, and the mechanism was explained. The nuclei formed in the heating stage grew into large pores, while the nuclei formed in the depressurization stage grew into small pores. SPIONs caused pores to rupture and coalesce into small pores or large pores. The effects of foaming parameters, including the amount of SPIONs, saturation temperature, foaming temperature, foaming pressure, and depressurization rate on the properties of the scaffolds, were systematically studied. The results showed that the addition of SPIONs could improve the porosity and mechanical properties of the scaffold, and the obvious multi‐modal cell structure could be formed. In conclusion, by changing the foaming parameters, the PLGA/SPIONs composite scaffolds with various average diameters (11.93–790.52 μm), a wide range of porosity (62.98%–93.23%) and mechanical properties (0.38–11.12 MPa) could be obtained.

Experimental investigation of CsI aerosol removal in containment spray system test facility of 700 MWe IPHWR

Post-accident management of the radionuclide in a nuclear reactor is always a focus point from the nuclear power plant safety point of view. A number of systems using different radionuclide scrubbing mechanisms are already deployed in the Indian nuclear reactors to safeguard the public during and post-accident scenario. However, it is always desirable to achieve “As Low As Reasonably Achievable” (ALARA) philosophy. In the same lines, to further strengthen the safety of Indian nuclear reactors, Containment Spray System (CSS) is introduced in 700 MWe Indian pressurized heavy water reactors to cater/mitigate the aftermath of the Design Basis Accidents (DBA) i.e., Loss Of Coolant Accident (LOCA) and Main Steam Line Break (MSLB). It provides the fast vapour suppression and radionuclide removal from containment during/post design basis accidents. In the present work the experimental investigation of the effect of water spray on the CsI aerosol scrubbing/CsI aerosol removal is studied in a scaled down facility. Experiments are also carried out for the CsI aerosol removal when spray is not operating. In order to encompass the containment pressures during DBA, 1.0 bar(g) initial vessel pressure is used to simulate the accident conditions. For simulation of aerosols after accident CsI nano particles (spherical) suspended in the air and CsI dry aerosols are used. The spray flow rate for all the experiment is kept constant approximately 11.3 lpm. However different Sauter Mean Diameter (SMD) (D32 = 590 µm, 745 µm, 1000 µm) are used to study the effect of droplet diameter on CsI aerosol removal. The temporal variation of the vessel relative pressure gas mean temperature and wall temperature is measured. Vessel depressurization rate with time is recorded. CsI aerosol removal/ CsI aerosol concentration variation with time is measured using two diverse measurements system namely scrubber method and Optical Particle Counter (OPC). Global decontamination factor and global collection efficiency is deduced based on the studies. Few tests without spray are also carried out to estimate the plate out effect on CsI aerosol removal.

Supercritical Foaming and Impregnation of Polycaprolactone and Polycaprolactone-Hydroxyapatite Composites with Carvacrol

Polycaprolactone (PCL) and polycaprolactone-hydroxyapatite (PCL-HA) scaffolds were produced by foaming in supercritical carbon dioxide (scCO2) at 20 MPa, as well as in one-step foaming and impregnation process using carvacrol as an antibacterial agent with proven activity against Gram-positive and Gram-negative bacteria. The experimental design was developed to study the influence of temperature (40 °C and 50 °C), HA content (10 and 20 wt.%), and depressurization rate (one and two-step decompression) on the foams’ morphology, porosity, pore size distribution, and carvacrol impregnation yield. The characterization of the foams was carried out using scanning electron microscopy (SEM, SEM-FIB), Gay-Lussac density bottle measurements, and Fourier–transform infrared (FTIR) analyses. The obtained results demonstrate that processing PCL and PCL-HA scaffolds by means of scCO2 foaming enables preparing foams with porosity in the range of 65.55–74.39% and 61.98–67.13%, at 40 °C and 50 °C, respectively. The presence of carvacrol led to a lower porosity. At 40 °C and one-step decompression at a slow rate, the porosity of impregnated scaffolds was higher than at 50 °C and two- step fast decompression. However, a narrower pore size distribution was obtained at the last processing conditions. PCL scaffolds with HA resulted in higher carvacrol impregnation yields than neat PCL foams. The highest carvacrol loading (10.57%) was observed in the scaffold with 10 wt.% HA obtained at 50 °C.

Controllable fabrication of multi‐modal porous PLGA scaffolds with different sizes of SPIONs using supercritical CO2 foaming

AbstractMulti‐modal porous scaffolds can promote bone regeneration. In the present study, they were successfully fabricated from poly (lactic‐co‐glycolic acid) (PLGA)/superparamagnetic iron oxide nanoparticles (SPIONs) by supercritical CO2 foaming, where SPIONs was employed as heterogeneous nucleation agent. The effects of SPION size on pore nucleation in PLGA/SPIONs nanocomposites were investigated. It was found that the addition of smaller SPIONs size caused the reduction of pore size. Multi‐modal porous scaffolds could be available by controlling the SPIONs content, soaking temperature, pressure, and depressurization rate. The porosity of the PLGA/SPIONs scaffolds ranged from (58.68 ± 0.62)% to (94.97 ± 0.14)% could be obtained via adjusting the supercritical CO2 foaming conditions. Moreover, it was found that the compressive modulus and porosity of the scaffolds were strongly associated with the porous structure. This study provided a new green preparation method for magnetic scaffolds to realize the controllable adjustment of the multi‐mode porous scaffolds.

Deformation-induced delamination of photovoltaic modules by foaming ethylene-vinyl acetate with supercritical CO2

Photovoltaic panels are an important source of renewable energy but also represent a growing stock of complex electronic waste. Specific recycling processes are required and this article investigates the potential of supercritical CO2 foaming of the ethylene-vinyl acetate (EVA) in photovoltaic modules as a means of safely taking them apart, layer by layer. The effects of the CO2 temperature, pressure and depressurization rate on the deformation of EVA layers were characterized using in-situ measurements of area expansion and curvature during the foaming process. Peel tests were performed on treated and untreated samples to quantify the loss of adhesion at the different EVA interfaces. The data show that with the temperature set above the melting point and an initial pressure of at least 150 bar, the deformation of the EVA layers can be increased by increasing the depressurization rate. The correlation between the percentage loss of adhesion and area expansion of the EVA layers shows that the mechanical stress induced by deformation is an important factor in the delamination process. Moreover, the amount of separation achieved and the optimal combination operating parameters depend on the nature and morphology of the neighbouring layer. This process properly separates each PV module layer (glass, cell and backsheet) from EVA for their specific recycling. These results are an important first step in the development of an efficient recycling process for photovoltaic modules and other types of layered electronic devices.

Development of Porous Polyvinyl Acetate/Polypyrrole/Gallic Acid Scaffolds Using Supercritical CO2 as Tissue Regenerative Agents.

Scaffolds are advanced devices employed in tissue engineering, as they are intended to mimic the characteristics of extracellular matrices. In this respect, conjugated materials are gaining relevance in the manufacturing of the foams used for therapeutic scaffolds, since they can provide certain properties that are missing in the other polymers used to form the scaffolds. This work has, therefore, focused on the development of functional scaffolds formed by conjugated-non-conjugated polymers such as polyvinyl acetate and polypyrrole, impregnated with gallic acid as the model drug and produced by means of a supercritical CO2 foaming/impregnation process. The effects from a series of parameters such as pressure, temperature, depressurization rate, and contact time of the scaffold production process have been determined. The impregnated foams have been characterized according to their morphology, including their porosity and expansion factor, their drug loading and delivering capabilities, and their mechanical and electrical properties. The characterization of the experiments was carried out using scanning electron microscopy, liquid displacement, in vitro release, electrochemical impedance spectroscopy, and compression techniques. The results from our tests have revealed a considerable influence of all the input variables studied, as well as relevant interactions between them. Values close to 35% porosity were obtained, with a drug release of up to 10 h with a fast initial release. The best operating conditions were 353 K, 30 MPa, 0.5 MPa/min depressurization rate, and 1 h contact time. By means of the supercritical foaming/impregnation technique, scaffolds with potential in tissue engineering due to their studied properties were obtained.

An Attempt to Optimize Supercritical CO2 Polyaniline-Polycaprolactone Foaming Processes to Produce Tissue Engineering Scaffolds.

Conjugated polymers are biomaterials with high conductivity characteristics because of their molecular composition. However, they are too rigid and brittle for medical applications and therefore need to be combined with non-conductive polymers to overcome or lessen these drawbacks. This work has, consequently, focused on the development of three-dimensional scaffolds where conductive and non-conductive polymers have been produced by combining polycaprolactone (PCL) and polyaniline (PANI) by means of supercritical CO2 foaming techniques. To evaluate their therapeutic potential as implants, a series of experiments have been designed to determine the most influential variables in the production of the three-dimensional scaffolds, including temperature, pressure, polymer ratio and depressurization rate. Internal morphology, porosity, expansion factor, PANI loads, biodegradability, mechanical and electrical properties have been taken as the response variables. The results revealed a strong influence from all the input variables studied, as well as from their interactions. The best operating conditions tested were 70 °C, 100 bar, a ratio of 5:1 (PCL:PANI), a depressurization rate of 20 bar/min and a contact time of 1 h.

Preparation of Glass Fiber/Poly(Ether Ether Ketone) Composite Foam with Improved Compressive Strength and Heat Resistance

Glass fiber/poly(ether ether ketone) (GF/PEEK) composite foams with improved compressive strength and heat resistance can be successfully prepared using a simple and environmentally friendly supercritical carbon dioxide (sc‐CO2) foaming technology. The cell morphologies of the foams can be controlled by adjusting the GF content and foaming parameters, including the saturation temperature, saturation time, saturation pressure, and depressurization rate. With a foam density of 0.55 g cm−3, the PEEK‐based composite foam having 30% GF content has a 10% compressive strength of 11.07 MPa, and its density varies negligibly up to 330.0 °C. The GF/PEEK composite foams having high GF contents show significantly better properties than those having low GF contents as a result of the supporting and strengthening effect of the GF in the PEEK cell walls. The GF/PEEK composite foams also show good corrosion resistance. As a result of these properties, the GF/PEEK composite foams are promising high‐performance materials for use in extreme environments.

Steam Explosion Pretreatment of Lignocellulosic Biomass: A Mini-Review of Theorical and Experimental Approaches.

Steam Explosion (SE) is one of the most efficient and environmentally friendly processes for the pretreatment of lignocellulosic biomass. It is an important tool for the development of the biorefinery concept to mitigate the recalcitrance of biomass. However, the two distinct steps of SE, steam cracking and explosive decompression, leading to the breakdown of the lignocellulosic matrix have generally been studied in empiric ways and clarification are needed. This mini-review provides new insights and recommendations regarding the properties of subcritical water, process modeling and the importance of the depressurization rate.

Speckle-Based Sensing of Microscopic Dynamics in Expanding Polymer Foams: Application of the Stacked Speckle History Technique.

Microscopic structural rearrangements in expanding polylactide foams were probed using multiple dynamic scattering of laser radiation in the foam volume. Formation and subsequent expansion of polylactide foams was provided by a rapid or slow depressurization of the “plasticized polylactide–supercritical carbon dioxide” system. Dynamic speckles induced by a multiple scattering of laser radiation in the expanding foam were analyzed using the stacked speckle history technique, which is based on a joint mapping of spatial–temporal dynamics of evolving speckle patterns. A significant decrease in the depressurization rate in the case of transition from a rapid to slow foaming (from 0.03 MPa/s to 0.006 MPa/s) causes dramatic changes in the texture of the synthesized stacked speckle history maps. These changes are associated with transition from the boiling dynamics of time-varying speckles to their pronounced translational motions and are manifested as significant slopes of individual speckle traces on the recovered stacked speckle history maps. This feature is interpreted in terms of the actual absence of a new cell nucleation effect in the expanding foam upon slow depressurization on the dynamic scattering of laser radiation.

Choked liquid flow in nozzles: Crossover from heterogeneous to homogeneous cavitation and insensitivity to depressurization rate

The critical mass flow rate is the maximum flow rate that can pass through a constrained geometry such as a nozzle. For liquid CO2, it has been shown that homogeneous relaxation models systematically underpredict the critical mass flow rate. In this work, we demonstrate that a delay of the phase transition is necessary to reproduce experiments. To analyze this in further detail, two methodologies are presented: (1) the delayed homogeneous relaxation model (Delayed HRM), and (2) the metastable isentrope model (MIM). Delayed HRM is a relaxation model that can readily be incorporated into a spatially distributed description of the fluid flow, e.g. in ejectors. MIM assumes isentropic flow and instantaneous equilibrium up to the limit of metastability, and yields a geometry-independent critical mass flux as the solution of a set of algebraic equations. We compare the two methodologies to available experimental data on the critical mass flow rates of CO2 and H2O through nozzles, finding that they give nearly identical predictions. This suggests that the critical mass flow rate is mostly determined by the achievable degree of metastability before onset of phase change, and is rather insensitive to dynamic variables such as the depressurization rate or the rate of relaxation towards equilibrium. Using the limit of metastability predicted by homogeneous nucleation theory works well at high temperatures, rendering the methodologies completely predictive. They deviate on average 11% from experimental data on CO2, and thus outperform homogeneous relaxation models by a large margin, even when the latter employs several fitted parameters. Especially good agreement was found with experiments that employ a lubrication oil, which is hypothesized to suppress heterogeneous nucleation. The limit of superheat at lower temperatures must be described by heterogeneous nucleation theory. For water and CO2 we find a crossover between homogeneous and heterogeneous nucleation at T≈590 K and T≈285 K respectively. Moreover, the predicted limit of superheat falls on a single curve in the temperature–pressure space of water, and we present an empirical correlation of this curve. By combining this expression with the above methodologies, we obtained an average deviation of 3% with available experimental data on H2O mass flow rates.

Supercritical solvent impregnation of alginate wound dressings with mango leaves extract

Supercritical CO2 and a mango leaves extract were used to impregnate calcium-sodium alginate wound dressings. Two methods of impregnation were developed: batch and semi-continuous supercritical impregnation. The influence of parameters such as pressure, temperature and depressurization rate on the impregnation process was studied in terms of the antioxidant capacity of the samples and the impregnation load of polyphenols present in the mango leaves extract. The higher load of mango polyphenols and strong antioxidant capacity were obtained in batch mode at 30 MPa, 35°C and at fast depressurization rate. Semi-continuous mode behaved in a similar way but with lower results according to obtained impregnation percentages in the assayed conditions. The antioxidant capacity of the processed samples was verified by DPPH method, and to confirm the presence of the antioxidant particles and their distribution on the matrix, the processed alginate wound dressings were studied by UPLC-MS and Scanning Electron Microscopy (SEM).

Numerical Simulation of Turbulent Flow for non-Newtonian Fluid in two kinds Complex Annulus Channel

During the polymer flooding multi-layered injection process, it is difficult to achieve large pressure drop and small viscosity loss at the same time in the injection allocators. To address this issue, two kinds of flow channel structures are designed. They are ring groove structure and spindle groove structure. CFD software FLUENT is used to simulate the flow characteristics of non-Newton fluid flowing in the above structures, which are complex annular channels. By comparing the pressure drop, velocity contours and turbulent kinetic energy, the spindle groove structure is preferred. It has large throttle depressurization and big solution viscosity retention rate within a limited length. The influence from different flow channels structure on pressure drop is limited, but the impact on viscosity loss is great.