Hydrofluorocarbons (HFCs) have important applications in different industries; however, they are environmentally unfriendly due to their high global warming potential (GWP). Hence, reclamation of ...used hydrofluorocarbons via energy-efficient adsorption-based separation will greatly contribute to reducing their impact on the environment. In particular, the separation of azeotropic refrigerants remains challenging, such as typical mixtures of CH2F2 (HFC-23) and CHF3 (HFC-32), due to a lack of adsorptive mechanisms. Metal–organic frameworks (MOFs) can provide a promising solution for the separation of CHF3–CH2F2 mixtures. In this study, the adsorption mechanism of CHF3–CH2F2 mixtures in TIFSIX-2-Cu-i was revealed at the microscopic level by combining static pure-component adsorption experiments, molecular simulations, and density-functional theory (DFT) calculations. The adsorption separation selectivity of CH2F2/CHF3 in TIFSIX-2-Cu-i is 3.17 at 3 bar under 308 K. The existence of similar TiF62− binding sites for CH2F2 or CHF3 was revealed in TIFSIX-2-Cu-i. Interactions between the fluorine atom of the framework and the hydrogen atom of the guest molecule were found to be responsible for determining the high adsorption separation selectivity of CH2F2/CHF3. This exploration is important for the design of highly selective adsorbents for the separation of azeotropic refrigerants.
The velocity boundary layer, formed on an archery bare-shaft arrow, is computed by using two kinds of finite difference codes; an axisymmetric code and a three-dimensional code. Two types of arrow ...point, i.e., bullet point and streamlined point, are attached to a cylindrical arrow shaft. The Reynolds number, based on the shaft diameter, is varied in a range 10,000 ≤ Re ≤ 20,000, and the attack angle, α, is fixed at α = 0.0o. Critical assessment is performed on the grid dependency of velocity profiles, the difference in velocity profiles between axisymmetric and 3D computations, and the effect of interpolation method on the interpolants by comparing the spline and the tri(bi)-cubic interpolations. The results of assessment indicates that the effect of varying the number of grid points, simulation codes and the interpolation method, considered in the present study, is sufficiently small for the purpose of linear stability analysis.
Hydrogen recovery from ammonia purge gas is a desirable method to relieve the pressure of increasing demand for hydrogen. Metal-organic frameworks (MOFs) are promising adsorbents for the separation ...of the H2–N2 mixture. However, the separation of the H2–N2 mixture using MOFs remains challenging due to the lack of adsorptive mechanism. Herein, the adsorption mechanism of the H2–N2 mixture in SIFSIX-2-Cu-i has been systematically investigated with the method of a combination of excess adsorption experiments, molecular simulations, and DFT calculations. In the Grand Canonical Monte Carlo (GCMC) simulations, the polarizable force field was first applied to the adsorption of pure H2 or N2 and H2–N2 mixture in SIFSIX-2-Cu-i. Ab Initio Molecular Dynamics (AIMD) was performed to investigate the distribution of the guest molecules in the pores of SIFSIX-2-Cu-i. Finally, Density functional theory (DFT) calculations were performed to predict the transfer of charge between MOF and guest molecules. Results revealed two binding sites of H2 or N2 in SIFSIX-2-Cu-i. A relatively high thermodynamic adsorption selectivity for N2 over H2 has been observed in SIFSIX-2-Cu-i. Furthermore, SIFSIX-2-Cu-i also exhibits a greater affinity with N2 than with H2, which is probably because of the stronger induction interactions between F2 atoms and N2 molecules. These findings are of significance to guide the design of the new highly selective adsorbents for the separation of H2/N2.
•The polarizable force field was first employed to investigate the adsorption of H2 and N2 in SIFSIX-2-Cu-i.•The distribution of H2 and N2 in SIFSIX-2-Cu-i was investigated by AIMD simulations.•The redistribution of charge density in the system after adsorption was calculated by DFT studies.
Abstract The reactor is very critical to intensify the reaction rate controlled by mass transfer. Solid magnesium hydride (MgH 2 ) shows great advantages in hydrogen storage; however, poor ...liquid–solid hydrolysis kinetics limit its application. Various chemical reactors were explored and are used to improve the hydrolysis efficiency. Results show that the mixing style could affect the surface coating behavior. Specifically, the higher temperature and mixing strength could promote the MgH 2 hydrolysis. Furthermore, induced crystallization could effectively relieve coating and strengthen the hydrolysis, especially at the high mixing level. The result indicated that the mass transfer distance between crystal seed and formed MgH 2 particles played an important role in MgH 2 hydrolysis.
CHF3 is a strong greenhouse gas, and its potential greenhouse effect is 14,800 times that of CO2, so recycling and reusing CHF3 positively contributes to environmental sustainability. Therefore, a ...purification and recovery process development based on the adsorption of CHF3 has become an urgent requirement. In this paper, an ultramicroporous fluorine-containing pillared metal–organic framework (MOF), SIFSIX-3-Ni, was applied to the separation of CHF3/N2. The adsorption and separation properties of SIFSIX-3-Ni for CHF3/N2 were confirmed by single-component isotherms and binary breakthrough experiments, respectively. The uptake capacity of CHF3 was 1.03 mmol g–1 at 288 K and 7.0 bar. The selectivity of CHF3/N2 reaches 23–24 at 288 K and 3.0 bar, exhibiting a high separation selectivity. The pressure swing adsorption (PSA) simulation of treating the CHF3/N2-mixed gas with the actual exhaust gas composition was investigated. The results show that the purity of CHF3 can reach 99%, it can be used as a fire extinguishing agent under the optimized operating conditions, and the recovery rate is over 83%. Experimental studies show that SIFSIX-3-Ni has a good application prospect in the separation of CHF3/N2.
Magnesium hydride (MgH2) is considered as one of the most potential hydrogen storage materials. However, limited by hydrolysis kinetics, the controllability and sustainability of MgH2 hydrolysis are ...poor. In view of this, a porous filter element is employed and optimized to improve the MgH2 hydrolysis performance. The effects of different structural parameters, operating parameters, and physical parameters on MgH2 hydrolysis performance were investigated. The controllable and continuous MgH2 hydrolysis was achieved by using the porous filter element with an appropriate overflow weir. The research in this paper can provide a reference for the continuous MgH2 hydrolysis.
Hydrofluorocarbons (HFCs) have important applications in different industries; however, they are environmentally unfriendly due to their high global warming potential (GWP). Hence, reclamation of ...used hydrofluorocarbons via energy-efficient adsorption-based separation will greatly contribute to reducing their impact on the environment. In particular, the separation of azeotropic refrigerants remains challenging, such as typical mixtures of CHsub.2Fsub.2 (HFC-23) and CHFsub.3 (HFC-32), due to a lack of adsorptive mechanisms. Metal–organic frameworks (MOFs) can provide a promising solution for the separation of CHFsub.3–CHsub.2Fsub.2 mixtures. In this study, the adsorption mechanism of CHFsub.3–CHsub.2Fsub.2 mixtures in TIFSIX-2-Cu-i was revealed at the microscopic level by combining static pure-component adsorption experiments, molecular simulations, and density-functional theory (DFT) calculations. The adsorption separation selectivity of CHsub.2Fsub.2/CHFsub.3 in TIFSIX-2-Cu-i is 3.17 at 3 bar under 308 K. The existence of similar TiFsub.6 sup.2− binding sites for CHsub.2Fsub.2 or CHFsub.3 was revealed in TIFSIX-2-Cu-i. Interactions between the fluorine atom of the framework and the hydrogen atom of the guest molecule were found to be responsible for determining the high adsorption separation selectivity of CHsub.2Fsub.2/CHFsub.3. This exploration is important for the design of highly selective adsorbents for the separation of azeotropic refrigerants.
Abstract
In this paper, an integrated design method for guidance and control laws for a short takeoff and vertical landing (STOVL) unmanned aerial vehicle (UAV) during decelerating transition and ...vertical landing phases under thrust vector control is studied. Based on the principle of time-scale separation, the outer-loop guidance law adopts an implicit dynamic inverse method to provide attainable overload vector control instructions for decelerating transition and vertical landing phases. Meanwhile, the inner-loop control law adopts an improved eigen-structure assignment method, which tracks guidance instructions and maintains a stable attitude. The attitude nozzles are joined to the attitude control with the dropping of dynamic pressure, thereby assisting aerodynamic surfaces to stabilize attitudes. Subsequently, the feasibility and effect of the control methods for a STOVL UAV during decelerating transition and vertical landing phases are verified by a 6-DOF flight simulation platform. The simulation results demonstrate that the integrated design method is beneficial for a quick evaluation of the overall scheme.
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