Rapid simultaneous evaluation of four parameters of single-component gases in nonvolatile liquids from a single data set

Proper analytical procedures presented here allow for rapid simultaneous determination of the diffusion and film-mass-transfer coefficients, the equilibrium gas pressure and solubility, and the effective equilibrium time from a model-assisted analysis of the time-limited experimental data of a gas/liquid system obtained by the method of Isothermal Pressure Decay. Being able to determine all four parameters simultaneously from the same data set, the present data interpretation method provides an additional reduction in the overall effort by a factor of four on top of the reduction in time required for data gathering. The parameter estimation method yields results with high accuracy indicating the validity of the proposed phenomenological model.     

An experimental approach for measuring carbon dioxide diffusion coefficient in water and oil under supercritical conditions

Several direct or indirect approaches have been proposed to measure diffusion coefficient of gases into liquids. The main complexity of indirect techniques such as pressure decay method is interpreting early pressure–time data which strongly affected by incubation period effect or convective instability. In the current approach, accurate apparatus and precise experimental setup including a high pressure and temperature PVT cell, a high precision Sanchez pump, heating and recording sub-system are implemented and a novel data analysis procedure is applied to modify pressure decay method. The effect of incubation period is reduced remarkably and diffusion coefficient of carbon dioxide in water in wide range of pressures and temperatures is determined and the effects of temperature, pressure and carbon dioxide phase alteration from gas to supercritical are investigated and the value of uncertainty is estimated.Furthermore, diffusion coefficient of CO_2 and methane in an oil sample from one of the Iranian southwest oil formations is determined precisely using the experimental approach while no incubation period is detected. The results showed that incubation period duration decreases with increasing diffusion coefficient. Additionally, when CO_2 state is gas, rate of increasing diffusion coefficient with pressure is decreased with temperature and when CO_2 state is supercritical, the rate of increasing diffusion coefficient with pressure is decreased significantly.     

An analytical method of estimating diffusion coefficients of gases in liquids from pressure decay tests

We present an exact solution of quasi-equilibrium model, based on pressure decay technique, to measure diffusion coefficient. The results of the quasi-equilibrium model are compared with the traditional equilibrium model and it was found that the latter is only a special case of former one. We provide new approximate solution to estimate diffusion coefficient that is more convenient to use, compared with the previously reported approaches. It also reveals that our solution is capable of taking into account greater portion of the collected pressure decay test data and is more accurate. Based on the developed solution, estimation approaches, including linear method and exponential method, are presented and applied to analyze synthetic and experimental pressure-decay data. The quasi-equilibrium model is also compared with the traditional equilibrium model. The results reveal that analysis of the test data using equilibrium model may introduce large error in estimation of diffusion coefficient. © 2018 American Institute of Chemical Engineers AIChE J, 65: 434–445, 2019     

A Simple and Rapid Evaluation of Explosive Performance – The Disc Acceleration Experiment

It is crucial in the development of a new explosive to obtain an evaluation of performance early in the process when the availability of material is limited. Evaluation requires dynamic measurements of detonation velocity, pressure, and expansion energy – typically in separate experiments that require large amounts of material, time, and expense. There is also a need for evaluation of the total available thermodynamic energy. The dynamic evaluations, in particular, have been a major hindrance to development of new explosives. The new experimental testing method to be described here requires small charges and obtains accurate measurement of all three of the detonation performance characteristics in a single test. The design, a Disc Acceleration eXperiment (DAX), provides an initial condition of steady detonation and a charge‐geometry amenable to 2D hydrodynamic simulations. The velocity history of a metal disk attached to the end of the explosive charge is measured with Photonic Doppler Velocimetry (PDV). This disc velocity data is analyzed to give both CJ pressure and expansion energy. The detonation velocity is obtained with probes along the charge length. The experiments and subsequent analyses are concentrated on LX‐16, a known PETN based explosive, for the purpose of establishing the accuracy of the method and to provide a standard for comparison with other explosives. We present details of the experimental design and also detonation velocity and PDV results from a number of experiments. The total available internal energy for the explosive was obtained from published detonation calorimetry measurements by Ornellas [1], and from thermodynamic equilibrium calculations. An equation‐of‐state (EOS) for LX‐16 was derived from hydrodynamic simulations of thin plate‐push velocity‐time data. We will show a successful comparison with a previously published Jones‐Wilkins‐Lee (JWL) EOS for PETN by Green and Lee [2–4].     

The modelling and experimental study on molecular diffusion coefficient of CO2 in N-methyl pyrolidone

In this study, batchwise absorption of CO₂ in N-methyl pyrolidone (NMP) was experimentally performed at different conditions using pressure decay method, and as a result, the equilibrium data, Henry’s law constants, and kinetic data were reported. It was shown that solubility and diffusivity are two important factors affecting the kinetic behaviour of the system. This absorption system was mathematically modelled using Fick’s second law accompanied by a time-dependent boundary condition. Thus, the diffusion coefficients of CO₂ in NMP were calculated under different operating conditions by means of the experimental kinetic data. Furthermore, the influence of temperature and pressure on the diffusion coefficient of CO₂ in NMP was analysed.     

Mathematical Model of Proton Exchange Membrane Fuel Cell with Consideration of Water Management

One‐dimensional model on the membrane electrode assembly (MEA) of proton exchange membrane fuel cell is proposed, where the membrane hydration/dehydration and the possible water flooding of the respective cathode and anode gas diffusion layers are considered. A novel approach of phase‐equilibrium approximation is proposed to trace the water front and the detailed saturation profile once water emerges in either anode or cathode gas diffusion layer. The approach is validated by a semi‐analytical method published earlier. The novel approach is applicable to the polarization regime from open circuit voltage to the limiting current density under practical operation conditions. Oxygen diffusion is limited by water accumulation in the cathode gas diffusion layer as current increases, caused by excessive water generation at the cathode catalyst layer and the electro‐osmotic drag across the membrane. The existence of liquid water in the anode gas diffusion layer is predicted at low current densities if high degrees of humidification in both anode and cathode feeds are employed. The influences of inlet relative humidity, imposed pressure drop, and cell temperature are correlated well with the cell performance. In addition, the overpotentials attributed from individual components of the MEA are delineated against the cell current densities.     

Prediction of residual capacity in thin adsorbers

A simple reliable method to measure Residual Adsorption Capacity (RAC) of charcoal adsorbers on which a gas is physisorbed has been developed. The method consists of passing a pulse of weakly adsorbed gas(es) through the adsorption filter(s) and measuring the retention time. This retention time is then correlated to the residual adsorption capacity. In order to predict the retention time-RAC relationship for filters with various configurations and bulk densities, this pulse test was mathematically modeled. The numerical solution of the model involved estimating the transport rate parameters, using existing correlations and the moment technique. A perturbation analysis indicated that the accuracy of the model is closely associated with the estimates of adsorption equilibrium constant and the intraparticle diffusion coefficient of the test gas. The model is shown to be accurate in predicting the RAC of an adsorber under dry and humid conditions from a limited data set.     

Diffusion effects in catalytic gas oil cracking

Wojciechowski's four parameter model of catalyst decay is applied to conversion data for gas oil cracking over a diffusion limited catalyst. The parameters thus obtained are compared with those obtained previously for a diffusion free form of the same catalyst, cracking the same feed stock under identical experimental conditions. The comparison shows that the presence of diffusion affects not only the rate of catalytic cracking but also the rate of aging. It is also shown that the introduction of diffusion phenomena has no effect on the mechanism of aging. The presence of diffusion limitations however has the effect of making the feed stock appear more homogeneous in reactivity     

Flow Characteristics and Shannon Entropy Analysis of Dense‐Phase Pneumatic Conveying of Pulverized Coal with Variable Moisture Content at High Pressure

Experiments consisting of dense‐phase pneumatic conveying of pulverized coal using nitrogen were carried out in an experimental test facility, with a conveying pressure of up to 4 MPa. The influences of the conveying differential pressure, the coal moisture content, the gas volume flow rate and the superficial velocity, on the solid‐gas ratios, were investigated. The Shannon entropy analysis of the pressure fluctuation time series was developed to reveal the flow characteristics. By investigation of the distribution of the Shannon entropy at different conditions, the flow stability and the evolutional tendency of Shannon entropy, in different regimes and regime transition processes, were revealed, and the relationship between Shannon entropy and the flow regime was also established. The results indicate that the solid‐gas ratio and the Shannon entropy rise with increases in conveying differential pressure. The solid‐gas ratio and the Shannon entropy reveal preferable correlation with the superficial gas velocity. Shannon entropy is different for different flow regimes, and can be used to identify the flow regimes. Both the mass flow rate and the Shannon entropy, decrease with increases in moisture content. Shannon entropy analysis is a feasible approach to researching the characteristics of the flow regime, the flow stability and the flow regime transitions in dense‐phase pneumatic conveying systems, at high pressure.     

Experimental and theoretical investigation of molecular diffusion coefficient of propylene in NMP

In this study, the absorption of propylene in N-methyl pyrolidone (NMP) was experimentally performed at three different temperatures (276.15, 293.15, and 328.15 K) using the pressure decay method and as a result, the equilibrium data, Henry's law constants, and kinetic data were reported. It was shown that the solubility and diffusivity are two important factors affecting the kinetic behavior of the system. This absorption system was mathematically modeled using Fick's second law accompanied by a time dependent boundary condition. An analytical method followed by numerical optimization was used to estimate the diffusion coefficient of propylene in NMP at different operating temperatures. The results demonstrated that the calculated diffusion coefficient obeys an Arrhenius type model. The resulting mathematical model was applied to calculate the number of absorbed moles of the gas. It shows a deviation of about 10% in comparison with the experimental measurements. Furthermore, the time dependent concentration profile along the liquid depth was also predicted.     

Design of a micro glass cell apparatus for pure gas‐nonvolatile liquid phase behaviour study

A micro syringe is used as a constant volume cell for gas–liquid equilibrium (GLE) study. The cell is made of glass and has a volume of <100 µL. It can operate at pressures up to 13 MPa and temperatures up to 115°C. Two different experimental procedures are presented for systems with nonvolatile low and high viscosity liquids. A micro magnetic stir bar is used to mix the gas–liquid mixtures inside the cell. Since the internal volume of the cell is small, a short mixing time is sufficient for the gas–liquid mixtures to reach equilibrium. The solubility values are measured by using the pressure decay method. The experimental procedures are validated by measuring the carbon dioxide (CO₂) solubility in water and highly viscous bitumen. The experimental results are in good agreement with the available literature data which shows that the technique works well. © 2011 Canadian Society for Chemical Engineering     

Comparison of Concentration Profiles for Boundary Layers in Absorption with Chemical Reaction Processes

An analysis of five different systems of absorption‐with‐chemical‐reaction in gas‐liquid reactors, commonly encountered in various industrial processes, is presented. To analyze the interphase mass transfer from gas to liquid, the rate limiting parameters and the concentrations at the gas‐liquid interface were determined on the basis of pertinent theories. The calculations presented, are based on the Whitman theory for gas and liquid phase mass transfer coefficients and Henry equilibrium constants. The necessary diffusion coefficients were calculated from existing correlations, and the corresponding chemical reaction rate constants were obtained from the literature, assuming pseudo first order chemical reaction. The process parameters required (pressure, temperature, and the gas‐liquid contact time) were within the values that occur in industrial processes. The results presented, are the concentration profiles in the boundary layers for the systems studied, calculated and graphically presented, together with the gas and liquid film thicknesses and Hatta numbers, obtained from calculations for the liquid phase mass transfer. The results may contribute to a better understanding of the absorption‐with‐chemical‐reaction processes in industrial plants, thus lowering the operational costs of these processes and alleviating the ecological problems of existing technologies.     

Transient analysis of gas flow in a straight pipe

In the present work, numerical simulation has been done to analyze transients in gas flow and pressure in a horizontal straight pipe. For a single gas pipeline, eight representative cases corresponding to different causes of transient behaviour are simulated to predict unsteady state flow and the evolution of pressure profiles. The numerical results show that depending upon the pipe dimensions and operating variables such as pressure and gas flow rate, transient effects in the pipeline may last for a long time and/or over significant length of pipe. The simulations predict an initial surge in gas flow rate greater than the final steady‐state value if the pressure drop across the pipe is increased. Similarly, initial flow rate may decrease below the final steady‐state value if the pressure drop is decreased. In case of complete closure of a valve, oscillations in both pressure and mass flow rate are observed, which gradually decay and the steady state conditions of no flow are ultimately achieved. The present results are compared with a published work from the literature. A reasonably good agreement is found between these two predictions. The present study is of practical significance in safe design and operation of a gas delivery system.     

Hydrodynamic Characteristics in the Counter‐Flow Total Spray Tray

The capacity of a column is limited by the distribution of gas and liquid, especially in case of large‐diameter cross‐flow trays. In order to solve the bottleneck, a new counter‐flow tray named total spray tray (TST) was put forward. Taking air/water as medium, the hydrodynamic behavior, including the pressure drop, weeping, entrainment, and clear liquid height, was investigated, in comparison with the CTST, which had a higher capacity. Based on experimental data, the correlations of the TST pressure drop were established by regression analysis method. The experimental results show that the TST has a lower wet pressure drop and less weeping. More interestingly, its clear liquid height can be self‐adjusting with the variation of the gas kinetic energy factor, which is beneficial to improving the capacity.     

Water sorption kinetics in light‐cured poly‐HEMA and poly(HEMA‐co‐TEGDMA); determination of the self‐diffusion coefficient by new iterative methods

The present investigation is concerned with the determination of self‐diffusion coefficient (D) of water in methacrylate‐based biomaterials following Fickian sorption by two new methods: the Iterative and the Graphical methods. The D value is traditionally determined by means of the initial slope of the corresponding sorption curve and the so‐called Stefan's approximation. The proposed methods using equations without approximations and data resulting from the whole sorption range reach to accurate values of D, even when the sorption curve does not present an initial linear portion. In addition to D, the Graphical method allows the extrapolation of the mass of the sorbed water at equilibrium (M_∞), even when the equilibrium specimen's mass fluctuates around its limited value (m_∞). The test of the proposed procedures by means of ideal and Monte Carlo simulated data revealed that these methods are fairly applicable. The obtained D values compared with those determined by means of the Stephan's method revealed that the proposed methods provide more accurate results. Finally, the proposed methods were successfully applied to the experimental determination of the diffusion coefficient of water (50°C) in the homopolymer of 2‐hydroxyethyl methacrylate (HEMA) and in the copolymer of HEMA with triethylene glycol dimethacrylate (98/2 mol/mol). These polymers were prepared by light curing (λ = 470 nm) at room temperature in presence of camphorquinone and N,N‐dimethylaminoethyl methacrylate as initiator. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Experimental Study of Oxygen Mass Transfer Coefficient in Bubble Column with High Temperature and High Pressure

The volumetric gas‐liquid mass transfer coefficient, k_Lα, for oxygen was studied by using the dynamic method in slurry bubble column reactors with high temperature and high pressure. The effects of temperature, pressure, superficial gas velocity and solids concentration on the mass transfer coefficient are systemically discussed. Experimental results show that the gas‐liquid mass transfer coefficient increases with the increase in pressure, temperature, and superficial gas velocity, and decreases with the increase in solids concentration. Moreover, k_Lα values in a large bubble column are slightly higher than those in a small one at certain operating conditions. According to the analysis of experimental data, an empirical correlation is obtained to calculate the values of the oxygen volumetric mass transfer coefficient for a water‐quartz sand system in two bubble columns with different diameter at high temperature and high pressure.     

Solid Propellant Burning Rate From Strand Burner Pressure Measurement

Strand burner pressure–time data are analyzed to determine if the propellant burning rate can be extracted. This approach is based on strand burner pressure–time history that is related to the temperature change due to exothermic reaction heating of chamber gases and gas addition to the chamber by propellant combustion products. In support of this method, chemical equilibrium calculations were made to project product composition, internal energy, and other needed properties. A mathematical model was formulated and solved numerically and the calculated burning rates were compared with the experimental wire‐break time results provided simultaneously and with the propellant manufacturer's results, when available. The comparisons reveal that the approach has merit and that more accurate pressure determination coupled with additional thermochemical information and strand burner gas temperature measurements has the potential to make this approach a viable technique and one that can be applied in conjunction with other burning rate measurements. The proposed method is similar to a well‐developed technique which is commonly applied to ballistic powders but with adjustments for the differences in geometry, pressure, and time of event.     

炭分子筛上氧、氮吸附特性的实验测定

针对BF型炭分子筛孔结构的特点,利用双分散孔结构吸附模型,采用色谱扰动-应答方法,对微孔扩散控制传质机理进行了实验认定,测定了O2的吸附平衡常数K、扩散时间常数Dc/rc2以及O2、N2两组分常温下的吸附等温线.     

Optimization of Ring‐Closing Metathesis: Inert Gas Sparging and Microwave Irradiation

A systematic study of a ring‐closing metathesis towards a tetrasubstituted double bond as part of a seven‐membered ring in a 5.7.5‐tricyclic guaianolide system is described. By combining two techniques, namely sparging an inert gas through the solution together with dielectric heating via microwave irradiation a high‐yielding ring‐closing metathesis reaction in this particularly challenging case was achieved. The results obtained compare favorably with conventional heating conditions or with microwave irradiation in a closed system. The key aspects seem to be that rapid microwave irradiation diminishes catalyst decay by allowing the required high reaction temperature to be reached quickly and homogeneously and thereby providing enough energy for a successful metathesis reaction, while inert gas sparging is purging off evolving ethylene to shift the equilibrium to the product.     

CO2 removal by single and mixed amines in a hollow‐fiber membrane module—investigation of contactor performance

This work investigates CO₂ removal by single and blended amines in a hollow‐fiber membrane contactor (HFMC) under gas‐filled and partially liquid‐filled membrane pores conditions via a two‐scale, nonisothermal, steady‐state model accounting for CO₂ diffusion in gas‐filled pores, CO₂ and amines diffusion/reaction within liquid‐filled pores and CO₂ and amines diffusion/reaction in liquid boundary layer. Model predictions were compared with CO₂ absorption data under various experimental conditions. The model was used to analyze the effects of liquid and gas velocity, CO₂ partial pressure, single (primary, secondary, tertiary, and sterically hindered alkanolamines) and mixed amines solution type, membrane wetting, and cocurrent/countercurrent flow orientation on the HFMC performance. An insignificant difference between the absorption in cocurrent and countercurrent flow was observed in this study. The membrane wetting decreases significantly the performance of hollow‐fiber membrane module. The nonisothermal simulations reveal that the hollow‐fiber membrane module operation can be considered as nearly isothermal. © 2014 American Institute of Chemical Engineers AIChE J, 61: 955–971, 2015