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1.
Entropy (Basel) ; 23(4)2021 Apr 20.
Artigo em Inglês | MEDLINE | ID: mdl-33924044

RESUMO

The natural gas hydrate plugging problems in the mixed pipeline are becoming more and more serious. The hydrate plugging has gradually become an important problem to ensure the safety of pipeline operation. The deposition and heat transfer characteristics of natural gas hydrate particles in the spiral flow pipeline have been studied. The DPM model (discrete phase model) was used to simulate the motion of solid particles, which was used to simulate the complex spiral flow characteristics of hydrate in the pipeline with a long twisted band. The deposition and heat transfer characteristics of gas hydrate particles in the spiral flow pipeline were studied. The velocity distribution, pressure drop distribution, heat transfer characteristics, and particle settling characteristics in the pipeline were investigated. The numerical results showed that compared with the straight flow without a long twisted band, two obvious eddies are formed in the flow field with a long twisted band, and the velocities are maximum at the center of the vortices. Along the direction of the pipeline, the two vortices move toward the pipe wall from near the twisted band, which can effectively carry the hydrate particles deposited on the wall. With the same Reynolds number, the twisted rate was greater, the spiral strength was weaker, the tangential velocity was smaller, and the pressure drop was smaller. Therefore, the pressure loss can be reduced as much as possible with effect of the spiral flow. In a straight light flow, the Nusselt number is in a parabolic shape with the opening downwards. At the center of the pipe, the Nusselt number gradually decreased toward the pipe wall at the maximum, and at the near wall, the attenuation gradient of the Nu number was large. For spiral flow, the curve presented by the Nusselt number was a trough at the center of the pipe and a peak at 1/2 of the pipe diameter. With the reduction of twist rate, the Nusselt number becomes larger. Therefore, the spiral flow can make the temperature distribution more even and prevent the large temperature difference, resulting in the mass formation of hydrate particles in the pipeline wall. Spiral flow has a good carrying effect. Under the same condition, the spiral flow carried hydrate particles at a distance about 3-4 times farther than that of the straight flow.

2.
Entropy (Basel) ; 23(7)2021 Jul 18.
Artigo em Inglês | MEDLINE | ID: mdl-34356454

RESUMO

The development of oil and gas resources is gradually transferring to the deep sea, and the hydrate plugging of submarine pipelines at high pressures and low temperatures is becoming an important problem to ensure the safety of pipeline operations. The swirl flow is a new method to expand the boundary of hydrate safe flow. Numerical simulation of the hydrate slurry flow characteristics in a horizontal pipeline by twisted band has been carried out, and the flow of CO2 hydrate slurry in low concentration has been simulated by the RSM and DPM models. The results show that the heat transfer efficiency is also related to Re and particle concentration. The velocity distribution has the form of symmetrical double peaks, and the peaks finally merge at the center of the pipeline. Vortexes firstly appear on both sides of the edge of the twisted band, and then move to the middle part of the twisted band. Finally, the vortex center almost coincides with the velocity center. The rotation direction of hydrate particles is the same as the twisted direction of the twisted band, twist rate (Y) is smaller, Re is larger, and the symmetric vortex lines merge farther away. The initial swirl number is mainly related to Y, but not Re. The swirl flow attenuates exponentially, and its attenuation rate is mainly related to Re, but not Y. Compared with ordinary pipelines, the swirl flow can obviously improve the transportation distance of hydrate slurry.

3.
Phys Chem Chem Phys ; 21(46): 25743-25748, 2019 Nov 27.
Artigo em Inglês | MEDLINE | ID: mdl-31720619

RESUMO

Single atom catalysts (SACs) based on 2D materials have been identified to be efficient in many catalytic reactions. In this work, the catalytic performance of Pd/Pt embedded planar carbon nitride (CN) for CO oxidation has been investigated via spin-polarized density functional theory calculations. We find that Pd/Pt can be firmly anchored in the porous CN monolayer due to the strong hybridization between Pd/Pt-d orbitals and adjacent N-2p orbitals. The resulting high adsorption energy and large diffusion barrier of Pd/Pt ensures the remarkable stability of the catalyst Pd/Pt@CN during the CO oxidation reaction. The three distinct CO reaction mechanisms, namely, Eley-Rideal (ER), Langmuir-Hinshelwood (LH), and tri-molecular Eley-Rideal (TER), are taken into consideration comparatively. Intriguingly, the oxidation reaction on Pd@CN prefers to proceed through the less common TER mechanism, where two CO molecules and one O2 molecule need to cross a small reaction barrier of 0.48 eV, and finally dissociate into two CO2 molecules. However, the LH mechanism is the most relevant one on Pt@CN with a rate-limiting reaction barrier of 0.68 eV. Moreover, the origin of the SAC's reactivity enhancement is the electronic "acceptance-donation" interaction caused by orbital hybridization between Pd/Pt and preadsorbed O2/CO. Our findings are expected to widen the catalytic application of carbon-based 2D materials.

4.
Phys Chem Chem Phys ; 20(44): 27970-27974, 2018 Nov 14.
Artigo em Inglês | MEDLINE | ID: mdl-30382262

RESUMO

Based on first-principles calculations, we study the hydrogen evolution reaction (HER) on metal-free C2N and make efforts to improve its catalytic performance. At H* coverages (θ) of 3/6 and 4/6, the free energy of hydrogen adsorption (ΔGH*) is 0.10 eV and 0.07 eV, respectively, which is competitive with the precious catalyst Pt. Moreover, ΔGH* can be modulated to zero under a tensile strain, and the strength of the strain depends on the H concentration. Experimentally, it is possible to achieve a strain of around 2% through coupling C2N with graphene, and the HER performance of the hybrids would be generally enhanced. Moreover, the catalytic activity of the hybrids is tunable via electron and hole doping of graphene. In the strong H binding cases (θ = 1/6), anchoring Mn atoms into C2N exhibits a perfect catalytic property with ΔGH* of -0.04 eV. Therefore, C2N-based catalysts are expected to be easily synthesized and highly active catalysts for the HER. These findings may shed light on replacing Pt by metal-free or/and non-precious metal counterparts.

5.
Phys Chem Chem Phys ; 20(18): 12916-12922, 2018 May 09.
Artigo em Inglês | MEDLINE | ID: mdl-29701208

RESUMO

Based on first-principles calculations, we present a systematic investigation of the electronic and magnetic properties of armchair phosphorene nanoribbons (APNRs) functionalized by 3d transition metal (TM) atoms. We found that the central hollow site is the most favorable adsorption site for Mn, Co and Ni, while Fe preferentially occupies the edge hollow site. All of the TM atoms bind to the adjacent P and their adsorption energies are in the range of -4.29 eV to -1.59 eV. Meanwhile, the large ratio of the adsorption energy to the cohesive energy of the metal bulk phase indicates that TM atoms have a preferred 2D growth mode on the edge hydrogenated armchair phosphorene nanoribbons (H-APNRs). The magnetic moments reduce by about 2-4 µB, relative to their free atom states, depending on whether the TM atom is in the high-spin or low-spin state. This reduction is mainly attributed to the electrons transferring from the high-level TM 4s shell to the low-lying 3d shell. Our results demonstrate that TM atom adsorption is a feasible approach to functionalizing the H-APNRs chemically, which results in peculiar electronic and magnetic properties for potential applications in nano-electronics and spintronics.

6.
Phys Chem Chem Phys ; 19(26): 17250-17255, 2017 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-28639681

RESUMO

Hybrid structures have attracted a great deal of attention because of their excellent properties, which can open up a way we could not foresee in materials science and device physics. Here, we investigate the electrical and optical behaviors of SiC(GeC)/MoS2 heterostructures, using first principles calculations based on density functional theory. Non-covalent bonding exists between the junctions due to the weak orbital coupling. Both junctions have optically active band gaps, smaller than that of the SiC or GeC and MoS2 layers, which result in enhanced optical adsorption under visible-light irradiation. A small number of electrons transfer from SiC/GeC to MoS2 causing its n-doping. Furthermore, the charge density states of the valence band maximum and the conduction band minimum are localized at different sides, and thus the electron-hole pairs are spatially separated. Our results provide a potential scheme for photovoltaic materials.

7.
ACS Omega ; 8(29): 26301-26316, 2023 Jul 25.
Artigo em Inglês | MEDLINE | ID: mdl-37521627

RESUMO

Aiming at the separation of mud and sand in natural gas hydrate, for the designed built-in twisted tape hydrocyclone, the numerical simulation method was used to study the effects of different types of built-in twisted tape and operating conditions on the internal flow field of the hydrocyclone, separation efficiency, and influence of hydrate particle size distribution. The research results show that the built-in twisted tape has the same swirling direction as the hydrocyclone, which is beneficial to improving the swirling intensity, and the ability to carry and separate solid particles is obviously enhanced. The built-in twisted tape hydrocyclone with a length of 300 mm has better separation efficiency and internal flow field stability. By changing the conditions of the inlet velocity and the initial concentration of hydrate particles, the comparison shows that when the inlet velocity is 8 m/s, the volume of mud and sand is 25%, the initial concentration of hydrate particles is 15%, and the built-in tape is 300 mm long. The tape hydrocyclone has the best separation efficiency. Compared with the basic hydrocyclone, the built-in twisted tape hydrocyclone with a length of 300 mm increases the separation efficiency of mud and sand by 7.49%, while the pressure drop only increases by 2.67%, showing the superiority of the built-in twisted tape structure.

8.
J Colloid Interface Sci ; 629(Pt A): 981-993, 2023 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-36152622

RESUMO

It was well recognized that the penetrated electromagnetic (EM) wave could be dissipated by means of magnetic loss, polarization loss and conduction loss. In order to improve their loss capacities and take full advantage of flower-like geometrical morphology, in this study, we proposed a simple route for the production of flower-like core@shell structure NiO/Ni@C microspheres through the carbon thermal reaction using NiO microflowers as precursor. The obtained results revealed that our proposed strategy successfully synthesized the core@shell structure magnetic carbon-based multicomponent nanocomposites without destroying the geometrical morphology of precursor. By regulating the annealing temperature, the as-prepared NiO/Ni@C microspheres with different contents of Ni and degrees of graphitization could be selectively synthesized, which effectively boosted their magnetic loss, polarization loss and conduction loss capabilities. Therefore, the elaborately designed NiO/Ni@C microspheres displayed the superior microwave absorption performances including strong absorption capability, broad absorption bandwidth and thin matching thicknesses compared to the NiO precursor. In summary, our findings not only provided a simple route to design and synthesize flower-like core@shell structure magnetic carbon-based nanocomposites as novel microwave absorbers, but also presented an effective strategy to comprehensively improve their loss capacities.

9.
Pol J Microbiol ; 72(4): 377-389, 2023 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-37817297

RESUMO

The entomopathogenic fungus Beauveria majiangensis strain MJ1015, recently isolated from white grubs on a blueberry farm in Guizhou, China, could be used as a biocontrol agent. As a first step toward determining the effect of different solid culture media, temperature, and pH on colony growth rate and sporulation, we evaluated the optimum solid medium for mycelial growth and conidia production on a commercial scale. Subsequently, we also used single-factor analysis and response surface optimization to optimize the composition of the solid culture medium. On potato dextrose agar (PDA) medium, MJ1015 grew fastest and produced the highest spore yield at 29°C and pH 5. The best solid medium for the growth and sporulation of strain MJ1015 comprised 64.70 g/l of rice, 13.00 g/l of wheat, 0.30 g/l of NaNO3, 0.36 g/l of K2HPO4 · 3H2O, and 1.00 g/l of CaCO3. Rice, NaNO3, and K2HPO4 · 3H2O were the main influencing factors. The predicted value of cultured spores using the optimal medium was 4.56 x 1010 conidia/l. The validation test results showed that the average growth rate of strain MJ1015 on the optimal medium was 85% and 96% faster than that on Sabouraud dextrose agar with yeast extracts medium (SDAY) and PDA, respectively. Sporulation was 43.90 times and 9.65 times of that produced on SDAY and PDA, respectively. Our findings provide a theoretical basis for the commercial production of B. majiangensis to control white grubs.


Assuntos
Beauveria , Ágar , Meios de Cultura/química , Beauveria/fisiologia , Esporos Fúngicos , Glucose
10.
ACS Omega ; 7(3): 2679-2689, 2022 Jan 25.
Artigo em Inglês | MEDLINE | ID: mdl-35097266

RESUMO

The gas-liquid contact area can be increased by the gas-liquid swirl flow, and the heat and mass transfer efficiency between gas and liquid can be enhanced by the gas-liquid swirl flow. The gas hydrate formation can be promoted by the swirl flow. The swirl flow can ensure the safety of the natural gas hydrate slurry. The flow pattern and conversion law of gas-liquid swirl with a twist tape should be investigated, and numerical simulation has been carried out by using the Reynolds stress model and the level set model. As a result, four different flow patterns are obtained, namely, swirl-stratified flow, swirl bubble flow, swirl slug flow, and swirl annular flow. The influence of gas-liquid-phase velocity on the flow pattern is investigated. The drag force generated by the two-phase slip velocity can change the gas form. At the same time, the flow pattern at different positions of the pipe will also change because of the attenuation of the swirl flow. Finally, the flow pattern map of the gas-liquid swirl flow is accomplished, and it is compared with the Mandhane flow pattern map. The flow boundary of the swirl bubble flow and the swirl annular flow is predicted.

11.
ACS Omega ; 7(36): 31961-31973, 2022 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-36120054

RESUMO

To study the gas-liquid two-phase spiral annular flow pattern and its conversion law in a horizontal tube with twist tape by spiral on-way, a numerical simulation is carried out using the RNG k-ε model, and the DPM model is adopted as the particle motion model. The research results show that three main flow patterns are obtained, which are spiraling churn flow, spiraling annular flow, and spiraling annular twine flow. The ratio of the liquid-phase to gas-phase velocity V L/V G is the main factor that affects the existence of the gas phase. When V L/V G > 1/2, the flow pattern is a spiral cluster flow; when 1/5 < V L/V G< 1/2, the flow pattern is a spiral annular flow; and when V L/V G < 1/5, the flow pattern is a spiral annular flow. Compared with the flow pattern of the local spiral flow pattern of the short twisted band, it was found that the occurrence conditions of annular flow were postponed and a new flow pattern appeared. The research results of this paper have guiding significance for the pipeline risk management of natural gas hydrates and the engineering application of the full rotation of guide strips.

12.
ACS Omega ; 7(19): 16629-16643, 2022 May 17.
Artigo em Inglês | MEDLINE | ID: mdl-35601304

RESUMO

With the development of oil and gas resources gradually extending to the deep sea, the blockage of gas hydrate is attracting more and more attention. How to inhibit hydrate blockage efficiently and economically in oil and gas gathering transportation pipelines and ensure the safe operation has become a hot and difficult point in the field of oil and gas gathering and transportation research. At present, the research on the safe flow of gas hydrate is still in the exploratory stage, and applying swirl flow to hydrate risk control technology has a great engineering application value. A systematic experimental study on the safe flow of gas hydrate in a swirl flow system is carried out herein. The experimental results show the following: (1) The laws of gas hydrate flow, transport, deposition, and pipe plugging under various experimental conditions of the swirl flow system are obtained, the safe flow region of hydrate under the swirl flow system in the pipeline is obtained, and the safe flow boundary of hydrate is expanded. (2) Beginning with the theoretical analysis of the safe flow of gas hydrate in a pipeline, the flow characteristics of gas hydrate in the flow system are described; the special flow form of swirl flow has a great influence on the safe flow law of hydrate. (3) The growth and coalescence mechanisms of spiral hydrate in two mainstream systems of separated flow and dispersed flow are explored and researched. The critical tangential velocity of flow is taken as the standard of criterion.

13.
J Colloid Interface Sci ; 608(Pt 3): 2387-2398, 2022 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-34763891

RESUMO

Nanocomposites with a three-dimensional (3D) flower-like geometrical morphology were considered as excellent microwave absorbers (MAs) because of the numerous effective sites for the multiple reflections of electromagnetic (EM) wave. Herein, for optimizing the EM matching characteristic and taking full advantage of interface polarization, a strategy of magnetic modulation was proposed to further improve the EM wave absorption performances (EMWAPs) of MoS2-based nanocomposites. We adopted a simple hydrothermal route and a combined method of hydrothermal treatment/hydrogen reduction to synthesize core@shell CoFe2O4@MoS2 and CoFe@MoO2/MoS2 flower-like nanocomposites, respectively. The obtained results indicated that the hydrogen reduction effectively improved their magnetic properties and magnetic loss capabilities, and their 3D flower-like geometrical morphologies were well maintained during the hydrogen reduction process. The obtained core@shell CoFe@MoO2/MoS2 flower-like nanocomposites presented the extraordinary comprehensive EMWAPs including the optimal reflection loss value of -54.83 dB with the matching thicknesses (dm) value of 2.05 mm and effective absorption bandwidth value of 6.40 GHz with the dm value of 2.59 mm, which were evidently superior to the properties of CoFe2O4@MoS2. Therefore, the findings provided an effective pathway to further improve EMWAPs of MoS2-based core@shell nanocomposites and the as-prepared core@shell CoFe@MoO2/MoS2 flower-like nanocomposites could be utilized as the novel high-efficient MAs.

14.
RSC Adv ; 10(21): 12451-12459, 2020 Mar 24.
Artigo em Inglês | MEDLINE | ID: mdl-35497591

RESUMO

Hydrate generation promotion and kinetic models are key issues in the hydrate utilization technology. The formation kinetics of CO2 hydrates in a graphene oxide (GO) and sodium dodecyl sulfate (SDS) compounding accelerator system was studied experimentally, and the influences of different concentrations on the hydrate formation time and gas consumption were revealed. The results show that with the combination of GO and SDS, the formation rate of CO2 hydrates was accelerated, the induction time and generation time were shortened, and the gas consumption increased. The optimal compounding concentration was 0.005% GO and 0.2% SDS. Compared with the observations for pure water and a single 0.005% GO system, the hydrate formation time was shortened by 69.7% and 12.2%, respectively, and the gas consumption increased by 11.24% and 3.2%. A chemical affinity model of CO2 hydrate formation was established for this system. The effects of the GO and SDS compound ratio, temperature and pressure on the chemical affinity model parameters were studied from the model point of view. On using Matlab to program the model and compare it with the experimental results, very good agreement was achieved. Through research, the chemical affinity model can accurately predict the formation of hydrates in complex systems.

15.
RSC Adv ; 9(66): 38724-38729, 2019 Nov 25.
Artigo em Inglês | MEDLINE | ID: mdl-35540229

RESUMO

The electronic properties of the g-C3N4/ß-As and g-C3N4/ß-Sb heterojunctions are investigated via density functional theory. We find that both heterostructures are indirect band gap semiconductors that, when applied to a photocatalytic device, will suffer from inefficient light emission. Fortunately, the band gap of the two junctions can be adjusted by external biaxial strain. As strain increases from compression to extensive, both compounds undergo a transition from metals, indirect semiconductors to direct semiconductors. Moreover, due to the charge transfer, each junction forms a large built-in electric field, which helps to prevent the recombination of electrons and holes. Our results are expected to widen the potential applications of these heterojunctions in nanodevices.

16.
RSC Adv ; 9(56): 32644-32655, 2019 Oct 10.
Artigo em Inglês | MEDLINE | ID: mdl-35529768

RESUMO

In view of the widespread existence of swirl flow in surfactant systems in oil drilling, gas gathering, and gathering pipelines, surfactants can affect interfacial tension and thus change the flow pattern. In order to further study and master the swirl flow characteristics in surfactant systems, this experimental investigation was presented, focused on gas-liquid flow during swirl flow, and aiming to evaluate the effect of surfactant in flow patterns. The experimental medium was air and water, the swirler was a vane and the surfactant was natural coconut oil. The purity of coconut oil was 99.9%, and the concentration was 100-900 ppm. The surface tension of the surfactant solution was measured using a surface tension meter to determine the concentration of the coconut oil solution at the minimum surface tension. By analyzing the flow characteristics of the gas-liquid interface with a high-resolution camera, the flow pattern of the gas-liquid two-phase swirl flow under the surfactant system was divided into the swirl linear flow, the swirl wave stratified flow, the swirl axial flow, and the swirl dispersed flow. Compared with the gas-liquid two-phase flow swirl flow pattern without surfactant, it was found that the swirl bubble flow and the swirl slug flow were not present, which was related to the stability of the gas-liquid interface weakened by the decrease of surface tension between the gas and liquid. The effects of flow pattern, gas content, vane parameters, surfactant concentration and flow rate on pressure drop were systematically investigated. Finally, based on the experimental data, we modified the pressure drop model of the gas-liquid two-phase swirl flow under the surfactant system with the vane as the spinner. The calculated value of the pressure drop model agrees well with the experimental data. This model can provide technical support for the safe operation of oil and gas pipelines.

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