Numerical visualization of drop and opening process for parachute-payload system adopting fluid–solid coupling simulation

In order to study the fluid–solid coupling dynamic characteristics of parachute-payload system during drop process and analyze the unsteady aerodynamic characteristics under finite mass opening conditions, an adaptive moving fluid mesh method is developed on the basis of the existing arbitrary Lagrangian–Eulerian (ALE) fluid–solid coupling method. The calculation results of open force and drop velocity on the C-9 parachute demonstrate the effectiveness of this method. On this basis, the effect of canopies with three different permeability on parachute-payload system motion characteristic including opening property, steady descent property and stability is studied. Comparative analysis is conducted for structures and characteristics of vortex with different canopy materials, and interference mechanism of unsteady flow for parachute-payload system in unsteady oscillation is revealed. The results show that the adaptive moving fluid mesh method can effectively eliminate restrictions of existing simulation methods for parachute-payload system and significantly reduce calculation time. For the lightweight parachute, permeability has significant effect on kinetic characteristic of parachute-payload system. Canopy with large permeability has small opening load and structural stress in opening stage. After opening, there are mainly small vortexes distributed evenly behind the canopy with good stability. However, canopy with small permeability has obvious breath behavior and oscillation in opening stage. The main vortexes periodically shed off after opening. With the change of permeability from small to large, Parachute-payload system eventually presents three steady descent modes: conical descent, gliding descent and stable vertical descent. Graphical abstract

Removal of Heavy Metals (Fe, Mn and Cd) from Aqueous Solutions by Natural Zeolite and FeS Media

Objectives : The adsorption characteristics of Fe, Cd, and Mn in aqueous solution using zeolite and FeS media were investigated by the adsorption isotherm and kinetic model analysis.Methods : The adsorption characteristics of the heavy metals (Fe, Mn, Cd) were investigated using Langmuir or Freundlich adsorption isotherm. The analysis of pseudo-first or pseudo-second order reaction was also attempted to evaluate the rate limiting factor such as molecular diffusion or chemical adsorption on the absorbents.Results and discussion : The adsorption of the heavy metals on the zeolite and FeS media was more suitable for the Langmuir adsorption isotherm, representing that mono-layer absorption on the surface and no interaction between the absorbed solutes. The order of adsorption preference to zeolite was Fe > Cd > Mn, whereas the order of adsorption preference to FeS media was Cd > Fe > Mn. The adsorption kinetics of zeolite and FeS media were more suitable for pseudo-secondary reactions than for pseudo-primary reaction.Conclusions : The absorption capacity of FeS media for the heavy metals (Fe, Cd and Mn) in aqueous solution was higher than that of zeolite. The adsorption pattern was suitable for the Langmuir adsorption isotherm, and has kinetic characteristic by chemisorption.

Formation of Dense and High-Aspect-Ratio Iron Oxide Nanowires by Water-Vapor-Assisted Thermal Oxidation and their Cr(VI) Adsorption Properties

In this work, highly crystalline and high aspect ratio α-Fe2O3 nanowire (NWs) were successfully produced by thermal oxidation of iron in water vapor at 800°C. The process was done for 2 h and the NWs were found to be covering the foil uniformly unlike when the oxidation environment was dry whereby the NWs formed were shorted and rather dispersed. The formation of NWs was proposed to be due to a stress-driven surface diffusion during thermal oxidation process. When oxidation was done at 700 oC, we observed coral-like nanostructures. The α-Fe2O3 NWs were then used as adsorbent to remove Cr(VI) from stimulated wastewater. Removal efficiency of 97% in a 225 mg/L Cr(VI) solution was observed indicating very fast removal of Cr(VI) in the presence of the NWs. The kinetic characteristic of the adsorption was fitted to a pseudo-second-order kinetic model, and isothermal studies indicated that the α-Fe2O3 NWs exhibited an adsorption capacity of 66.26 mg/g.

Mathematical Modeling of the Process Hydrotreatment of Diesel Fuel Based on the Kinetic Characteristics of Its Fractions

The principles of mathematical modeling of the diesel fuel hydrotreatment process as a multicomponent reaction system are considered. Feedstock containing a large number of organosulphuric components from the standpoint of increasing the level of model adequacy and calculation accuracy can be characterized by the total sulfur content in the raw material as a whole (1), the total sulfur content in pseudocomponents in the feedstock or its narrow fractions (2), the concentration of individual organosulphuric substances (3). It is shown that in cases 1 and 2, the concept of the reaction rate constant as a constant that characterizes the physico-chemical process is degenerate, and in calculations it should be considered as a kinetic characteristic that takes into account the inhomogeneity of the chemical process over time. As the hydrogenated feedstock comes into contact with the hydrogen-containing gas, the most active organosulfuric components with a high reaction rate constant are first hydrogenated on the catalyst, and at the final stage of the process, the less active components with a low reaction rate constant are hydrogenated. Examples of calculating the dependence of the kinetic characteristic and the total sulfur content in the hydrogenate in two broad fractions of diesel fuel on the time of contact of the reaction medium with the catalyst and the subsequent compounding of the fractions into diesel fuel.

Assessment and Performance Evaluation of Water Hammer in Hydroelectric Plants With Hydropneumatic Tank and Pressure Regulating Valve

The simulation approach of pipeline systems, pressure regulating valve (PRV), and hydropneumatic tank (HPT) in hydropower plants (HPP) is performed. The article used suitable protection devices such as hydropneumatic tank and pressure regulating valves to protect the hydro-electric system against water hammer negative effects. The method of characteristics solves hydraulic transient in the HPP system. This article simulates transient phenomena in a hydro-electric power system using FORTRAN language. The aim was to find out and diminish the water hammer at the entrance of the spiral case as well as the pipeline system. The paper has four major philosophies: simulation with no protection, simulation with hydropneumatic tank, simulation with pressure regulating valve, and the combination of hydropneumatic tank with the pressure regulating valve. The results show that a combination of the pressure regulating valve and the hydropneumatic tank is adequate appliances to lessen the effect of water hammer/transient flow in a hydropower plant system. However, in the transient process of the water diversion system, the gas' kinetic characteristic in the hydropneumatic tank has certain complexity when there is high fluctuation in the surge chamber. The study proved that the wicket gate's stepwise could cut down the impact of the water hammer automatically than applying the linear closure law on the network. The automated pressure regulating valve with a high opening stepwise can decrease the negative impact of water hammer significantly. The results from this research paper show that pipeline diameter has crucial factors that influence hydraulic transient in hydropower plant systems.

Neutron and Neutron-Breeding Medium Interaction Process Description Within the Physical Birth-and-Death Model

Analytic methods for nuclear reactor physics problems are still of current interest. They allow the physical interpretation to be obtained for studied processes within simple mathematical apparatus. This work proposes a new approach of neutron and neutronbreeding medium interaction process description based on birth-and-death model. This approach was named the physical birth-and-death model. The equations for the main kinetic characteristic are presented and reactivity values are estimated for two subcritical nuclear assemblies: MASURCA and KUCA.

Cu(II) and As(V) Adsorption Kinetic Characteristic of the Multifunctional Amino Groups in Chitosan

Amino groups in the chitosan polymer play as a functional group for the removal of cations and anions depending on the degree of protonation, which is determined by the solution pH. A hydrogel beadlike porous adsorbent was used to investigate the functions and adsorption mechanism of the amino groups by removal of Cu(II) as a cation and As(V) as an anion for a single and mixed solution. The uptakes of Cu(II) and As(V) were 5.2 and 5.6 μmol/g for the single solution and 5.9 and 3.6 μmol/g for the mixed solution, respectively. The increased total capacity in the presence of both the cation and anion indicated that the amino group (NH2 or NH3+) species was directly associated for adsorption. The application of a pseudo second-order (PSO) kinetic model was more suitable and resulted in an accurate correlation coefficient (R2) compared with the pseudo first-order (PFO) kinetic model for all experimental conditions. Due to poor linearization of the PFO reaction model, we attempted to divide it into two sections to improve the accuracy. Regardless of the model equation, the order of the rate constant was in the order of As(V)-single > Cu(II)-single > As(V)-mixed > Cu(II)-mixed. Also, the corresponding single solution and As(V) showed a higher adsorption rate. According to intraparticle and film diffusion applications displaying two linear lines and none passing through zero, the rate controlling step in the chitosan hydrogel bead was determined by both intraparticle and film diffusion.