Gas Molecular Weight Research Articles

Onsager reciprocity as a consequence of Maxwell reciprocity for “equidiffuse” fluids

Linear irreversible thermodynamics (LIT) principles are used to show, in the hypothetical “equidiffuse” case where all of the various phenomenological diffusion coefficients appearing in the linear near-equilibrium constitutive laws governing the diffuse transport of energy, multicomponent species, entropy, and volume (although not necessarily including momentum) are taken to be equal, that the Onsager reciprocal relations pertinent to nonequilibrium thermodynamics follow automatically from Maxwell’s reciprocal relations governing equilibrium thermodynamics. As such, this constitutes a purely macroscopic proof of Onsager reciprocity, the first of its kind. Although the equality of diffusion coefficients required in the equidiffuse limiting case does not represent a realistic possibility in the case of most mixtures, its adoption as a foil in uniting reversible and irreversible thermodynamics neither violates nor conflicts with any known physical law. Indeed, in some idealized sense such equality represents a perfection of the well-known analogy between these distinct physical transport phenomena. Moreover, as shown for mixtures of chemically similar dilute gases of comparable molecular weights (e.g., consecutive members of a homologous series) the equidiffuse assumption is generally quite good. As a bonus, our analysis — by virtue of its accord with all known precepts of macroscopic physics — constitutes a satisfactory resolution of the long-standing criticism of Coleman and Truesdell [B.D. Coleman, C. Truesdell, On the reciprocal relations of Onsager, J. Chem. Phys. 33 (1960) 28–31] centered on the possibility that Onsager symmetry might be nothing more than a tautology (derisively referred to in the literature as “Onsagerism”).

Development of Multiple-Gas Analysis Method Using the Ball Surface Acoustic Wave Sensor

In the fields of energy exploitation, and for the safety and security of society, portable multiple-gas sensors are essential. Although the gas chromatograph (GC) is applicable to multiple-gas analysis, it is not portable. As a result, we have proposed the ball surface acoustic wave (SAW) GC using a ball SAW sensor, which realizes high sensitivity by the ultramultiple roundtrip propagation of a SAW and a separation column fabricated by micro-electro-mechanical-system technology. However, it takes too long for a portable GC such as the ball SAW GC to analyze mixed gases of high and low molecular weights at the same time. In this study, we developed the forward-flush (FF) method, involving two (or more) separation columns with a ball SAW sensor inserted after each column, to solve the above problem. Using the ball SAW GC with the FF method, we analyzed mixed gases of natural gas components and volatile organic compounds.

Unified correlation for overall gas hold‐up in bubble column reactors for various gas–liquid systems using hybrid genetic algorithm‐support vector regression technique

AbstractThe objective of this study is to collect the data on overall gas hold‐up (∈G) for bubble column reactors handling various gas–liquid systems and further develop a unified data‐driven model for the estimation of the same. In this work, around 3300 experimental points for ∈G have been collected from 85 open sources spanning the years 1963–2008. The data‐driven model for overall gas hold‐up has been established using hybrid Genetic Algorithm‐Support Vector Regression (GA‐SVR)‐based methodology. In the present study, GA has been used for nonlinear rescaling of the parameters. These exponentially scaled parameters are subsequently subjected for SVR training. The technique is an extension of conventional SVR technique, showing relatively enhanced results. The proposed hybrid model is based on various prominent design and operating parameters (15 in number) which includes superficial gas velocity, superficial liquid velocity, gas density, molecular weight of gas, sparger type, sparger hole diameter, number of sparger holes, liquid viscosity, liquid density, liquid surface tension, ionic strength of liquid, operating temperature, operating pressure, liquid height, and the column diameter. The estimations made by the SVR‐based unified model for ∈G shows an excellent agreement with actual values with estimation accuracy of 98.5% and % AARE of 9.32%. For ease in applicability and ready reference of the practicing engineers, the hybrid GA‐SVR‐based model in the form of software and the entire database for ∈G has been uploaded on the link http://www.esnips.com/web/UICT‐NCL.

EFFERVESCENT ATOMIZATION FOR INDUSTRIAL ENERGY-TECHNOLOGY REVIEW

Effervescent atomization technology is a process employing the creation of a two-phase flow between a liquid fuel and an aerating gas. This technology is receiving renewed interest in the industrial energy field due to its applicability to alternative fuels. This paper presents a review of the principal governing parameters controlling the atomization characteristics of effervescent systems. Previous research in this field has developed a number of systematic parameters relating to the operation of effervescent atomizers but none are universally applicable, i.e., a thorough first-principles-based understanding of effervescent atomization has not yet been achieved. This paper reviews initial operating conditions (gas-to-liquid ratio, pressure drop), fluid properties (liquid viscosity, liquid surface tension, fuel type, atomizing gas molecular weight, non-Newtonian fluids), and geometric constraints (atomizer geometry, exit orifice geometry). There is considerable agreement among researchers with regard to most of these parameters. By contrast, geometric constraints have not been satisfactorily optimized. Recommendations based on experimental work do exist for most geometric constraints. These could, however, almost certainly be further optimized. Also included in this work is a thorough review of the experimental correlations required to develop effervescent atomization systems, including resultant spray characteristics, injector internal flow, and bubble energy.

Thermal-hydraulic and neutronic analyses of the submersion-subcritical, safe space (S 4) reactor

The solid-core Submersion-Subcritical Safe Space (S 4) reactor is cooled with He-28% Xe gas (molecular weight of 40 g/mole) and nominally generates 471 kWth for at least 7 years. To avoid single point failures in reactor cooling and energy conversion, the S 4 reactor core is divided into three hydraulically independent, but neutronically and thermally coupled sectors. Each sector feeds a separate Closed Brayton Cycle (CBC) power conversion loop with separate heat rejection radiator panels. Detailed thermal-hydraulic analyses of the S 4 reactor core are performed to ensure that the maximum fuel temperature during nominal operation stays below 1300 K. In addition, a neutronics analysis performed using MCNP 5 confirms that the S 4 reactor satisfies the design reactivity requirements. These are at least $ 4 of cold clean excess reactivity, at least $ 2.25 of shutdown margin, and at least $ 1 subcritical in the worst-case of submersion and flooding, following a launch abort accident. Mass estimates of the S 4 reactor design that meets both the thermal and the reactivity requirements are provided.

Fractal diffusion model used for diffusion in porous material within limited volume of stiff container

In this paper, the fractal diffusion model obtained by O’Shaugnessy and Procaccia (OP model) was used to describe the diffusion of gases in a porous material within the limited volume of a stiff container (LVSC). The theoretical solution of OP model was obtained using the method of eigenfunction expansion, and it included the theoretical solution of Fick's model. With this solution, the adsorption kinetics could be analyzed in detail. The estimating method of the pre-exponential factor of diffusivity D OP was proposed. The experimental data of adsorption kinetics of N 2 and CO 2 in γ -alumina were estimated by OP model and Fick's model for comparison, respectively. The results showed that the quantitative differences could be observed in the relative adsorption amount of adsorption process calculated by these two models. There were no qualitative differences between them, but the OP model would lead to a more realistic description of the diffusion process in a porous material since the calculated results fit more the experimental curves. The diffusivity D F of Fick's model strongly depended on concentration, while the diffusivity D OP of OP model was related to temperature, molecular weight of gases and structure of the porous material.

Molecular effects on turbulent diffusion and energy in a low speed closed flow

The coefficient of turbulent diffusion and the total turbulent energy are determined during the compression phase of a motored internal combustion engine with varying flow conditions and using intake gases with varying molecular weights. These turbulent parameters change with time and with intake gas molecular weight. However, under all flow conditions, both parameters first increase and then decrease with increasing molecular weight. In addition, a direct correlation is observed between the average values of the coefficient of turbulent diffusion and the average values of the total turbulent energy, irrespective of the molecular weight.

Studies on thermal decomposition mechanism of CL-20 by pyrolysis gas chromatography–mass spectrometry (Py-GC/MS)

The thermal decomposition study of CL-20 (hexanitrohexaazaisowurtzitane) using pyrolysis GC/MS was carried out mainly by electron impact (EI) mode. Chemical ionization (CI) mode was used for further confirmation of identified species. Mass spectrum of CL-20 decomposition products predominantly revealed fragments with m/ z 81 and 96 corresponding to C 4H 5N 2 + and C 4H 4N 2O + ions, respectively. The total ion chromatogram (TIC) of CL-20 pyrolysis shows peak within first 2 min due to the presence of low molecular weight gases. Peaks corresponding to several other products were also observed including the atmospheric gases. Cyanogen formation (C 2N 2, m/ z 52) observed to be enriched at the scan number 300–500. The low molecular mass range decomposition products formed by cleavage of C–N ring structure were found in majority. Additional structural information was sought by employing chemical ionization mode. The data generated during this study was instrumented in determining decomposition pathways of CL-20.

대기 중 유기염소계 살충제의 가스-입자 분배

This study was performed to estimate the gas-particle partitioning of organochlorine pesticides (OCPs) in atmosphere, the samples were collected by PUF high volume air sampler for two years from June, 2000 to June, 2002. The gas phase fraction of , heptachlor epoxide, and trans-nonachlor was over 90%. But the gas phase fraction of , p,p`-DDE, endosulfan sulfate, p,p`-DDD and p,p`-DDT was range of 20% through 80%, which means the gas phase fraction of OCPs components described above is sensitive to temperature. The correlation between the gas phase fraction and molecular weight of each OCPs component was not found in this research. The slope of regression line between gas-particle partitioning coefficient() and subcooled liquid vapor(), gal-particle partitioning coefficient() and octanol-air partitioning coefficient() which show -0.54 and 0.43 was not steep. So the equilibrium state between gas and particle was not reached and in this state the particulate fraction was low.

Development of support vector regression (SVR)-based correlation for prediction of overall gas hold-up in bubble column reactors for various gas–liquid systems

The objective of this study was to develop a unified data-driven correlation for the overall gas hold-up for various gas–liquid systems using support vector regression (SVR)-based modeling technique. Over the years, researchers have amply quantified the hydrodynamics of bubble column reactors in terms of the overall gas hold-up. In this work, about 1810 experimental points were collected from 40 open sources spanning the years 1965–2007. The model for overall gas hold-up was established as a function of several parameters which include superficial gas velocity, superficial liquid velocity, gas density, molecular weight of gas, sparger type, sparger hole diameter, number of sparger holes, liquid viscosity, liquid density, liquid surface tension, operating temperature, operating pressure and column diameter of the gas–liquid system. For understanding the hold-up behavior, the data used for training the model was grouped into various gas–liquid systems viz., air–water, gas–aqueous viscous liquids, gas–organic liquids, gas–aqueous electrolyte solutions and gas–liquid systems operated over a wide range of pressure. A generalized model established using SVR was evaluated for its performance for various gas–liquid systems. Statistical analysis showed that the proposed generalized SVR-based correlation for overall gas hold-up has prediction accuracy of 97% with average absolute relative error (% AARE) of 12.11%. A comparison of this correlation with the selected system specific correlations in the literature showed that the developed SVR-based correlation significantly gives enhanced prediction of overall gas hold-up.

Partial Wetting in Trickle Bed Reactors: Measurement Techniques and Global Wetting Efficiency

Three very different techniques for measuring the catalyst wetted fractionor wetting efficiencyin trickle bed reactors have been carried out and compared. The first one based on pressure drop data performed successively in single gas then liquid phases and, then, in a gas−liquid phase is experimentally very simple but did not result in meaningful wetting efficiency estimation. The other ones, based on RTD analysis and on dye adsorption on wetted surfaces, gave similar results and were used to investigate different parameters: liquid velocity and gas molecular weight and pressure by RTD, liquid−solid interaction or affinity (contact angle) and particle shape and diameter by dye fixation. The main operating parameter is the liquid velocity while the effect of gas flow is very weak. Higher solid−liquid affinity (heptane versus water) improves wetting efficiency only at very low liquid velocity (<2 × 10-3 m/s).

Controlling diffusion of 3He by buffer gases: A structural contrast agent in lung MRI

To study the influence of admixing inert buffer gases to laser-polarized (3)He in terms of resulting diffusion coefficients and the consequences for image contrast and resolution. The diffusion coefficient of (3)He was altered by admixing buffer gases of various molecular weights ((4)He, N(2), and SF(6)). The influence of the pulse sequence and the diffusion coefficient on the appearance of MRI of (laser-polarized) gases was analyzed by comparison of basic theoretical concepts with demonstrative experiments. Excellent agreement between theoretical description and observed signal in simple gradient echoes was observed. A maximum signal gain can be predicted and was experimentally validated. Images acquired under such conditions revealed improved resolution. The nature and concentration of the admixed gas defines a structural threshold for the observed apparent diffusion coefficient (ADC) as demonstrated with diffusion-weighted MRI on a pig's lung flooded with suitable gas mixtures. A novel procedure is proposed to control the diffusion coefficient of gases in MRI by admixture of inert buffer gases. Their molecular mass and concentration enter as additional parameters into the equations that describe structural contrast. This allows for setting a structural threshold up to which structures contribute to the image. For MRI of the lung this enables images of very small structural elements (alveoli) only, or in the other extreme, all airways can be displayed with minimal signal loss due to diffusion.

Exact solutions for transient mixing of two gases of different densities

This Brief Communication presents a number of exact solutions describing the transient mixing of two gases of different molecular weights. Descriptions are given for both the concentration field and the associated induced motion in one-dimensional spherical, cylindrical, and planar configurations, including mixing layers, pockets, coflow jets, and concentrated mass sources.

Aquaporin-1 Transports NO Across Cell Membranes

NO plays a role in the regulation of blood pressure through its effects on renal, cardiovascular, and central nervous system function. It is generally thought to freely diffuse through cell membranes without need for a specific transporter. The water channel aquaporin-1 transports low molecular weight gases in addition to water and is expressed in cells that produce or are the targets of NO. Consequently, we tested the hypothesis that aquaporin-1 transports NO. In cells expressing aquaporin-1, NO permeability correlated with water permeability. NO transport was reduced by 71% by HgCl2, an inhibitor of aquaporin-1. Transport of NO by aquaporin-1 saturated at 3 micromol/L NO and displayed a K(1/2) (the concentration of NO that produces half of the maximum transport rate) of 0.54 micromol/L. Reconstitution of purified aquaporin-1 into lipid vesicles increased NO influx by 316%. In endothelial cells, lowering aquaporin-1 expression with a small interfering RNA (siRNA) blunted aquaporin-1 expression by 54% and NO release by 44%. We conclude that NO transport by aquaporin-1 may allow cells to control intracellular NO levels and effects. NO transport by aquaporin-1 may play a role in central nervous system, vascular and renal function, and consequently blood pressure. Disruption of NO transport by aquaporin-1 offers an alternate cause for diseases currently explained by inadequate NO bioavailability.

Seismic characteristics of gas hydrates at Hydrate Ridge, offshore Oregon

Gas hydrate is an ice-like substance that contains low molecular weight gases (mostly methane) in a lattice of water molecules (Sloan, 1998). Gas hydrates are widely present in permafrost and deep oceanic environments around the world. Hydrate Ridge, offshore Oregon, is one of the areas where hydrates are found in relatively high concentration. In marine environments, methane hydrates are usually stable at temperatures of 0–20° C, water depths greater than 500 m, and in sediments up to 300 m below the seafloor. Small amounts of free gas are often present below the gas-hydrate stability zone (GHSZ). The hydrate-to-free-gas contact gives a strong acoustic impedance contrast, which is evident on seismic sections as a bottom-simulating reflection (BSR). Offshore gas hydrate systems have received attention from the scientific community because of their potential to be:

Formation of laser plasma channels in a stationary gas

Plasma channels with nonuniformity of about ±3.5% have been produced by a 0.3J, 100ps laser pulses in a nonflowing gas, contained in a cylindrical chamber. The laser beam passed through the chamber along its axis via pinholes in the chamber walls. Plasma channels with an electron density in the range of 1018–1019cm−3 were formed in pure He, N2, Ar, and Xe. A uniform channel forms in an optimal pressure range at a certain time delay, depending on the gas molecular weight. The interaction of the laser beam with the gas leaking out of the chamber through the pinholes was not significant. However, the formation of the ablative plasma on the walls of pinholes by the wings of radial profile of the laser beam plays an important role in the plasma channel formation and its uniformity. A low-current glow discharge initiated in the chamber improves the uniformity of the plasma channel slightly, while a high-current arc discharge leads to overdense plasma near the front pinhole and further refraction of the laser beam. These results indicate the potential for using nonflowing gas targets to create uniform plasma channels.

An algorithm for predicting the hydrodynamic and mass transfer parameters in agitated reactors

A large number of experimental data points (7374) obtained in our laboratory as well as from the literature, covering wide ranges of reactor geometry (reactor diameter and type, impeller diameter and gas distribution scheme), physicochemical properties (liquid and gas density and molecular weight, liquid viscosity and surface tension, diffusivity) and operating variables (superficial gas velocity, temperature, pressure, m ixing speed, liquid height and mixtures) were used to develop empirical as well as back-propagation neural network (BPNN) correlations in order to predict the hydrodynamic and mass transfer parameters in gas–liquid agitated reactors (ARs). The empirical and BPNN correlations developed were incorporated in a calculation algorithm for predicting the gas holdup (eG), volumetric mass transfer coefficients ( kLa), Sauter mean bubble diameter (dS), gas–liquid interfacial area ( a) and liquid-side mass transfer coefficient ( kL) in ARs, operating in surface-aeration, gas-inducing and gas-sparging modes. The algorithm was used to predict the effects of liquid viscosity and hydrogen mole fraction in the feed gas (H 2 +N 2) on the hydrodynamic and mass transfer parameters for the soybean oil hydrogenation process conducted in a large-scale gas-sparging agitated reactor (7000 kg soybean oil capacity). The predictions showed that increasing the liquid-phase viscosity, mimicking the evolution of the hydrogenation of soybean oil in a batch reactor, decreased eG and increased dS, resulting in a decrease of a. The decrease of the gas holdup with increasing the liquid-phase viscosity was related to the increase of gas bubble coalescence in the reactor. Increasing liquid-phase viscosity, however, decreased kL as well as kLa values for both H2 and N2 within the range H2 mole fraction (0–1) used. This kL behavior indicated that the effect of viscosity on kL is more significant than that of dS, since kL was reported to be proportional to dS. The predictions also showed that increasing the H2 mole fraction in the feed to the reactor decreased eG and increased dS, resulting in a decrease of a and an increase of kL as well as kLa for both H2 and N2 within the range of liquid-phase viscosity used (0.0023–0.0047 Pa s). The decrease of the gas holdup with increasing the H2 mole fraction in the feed gas was attributed to the decrease of the density (momentum) of the gas mixture. The increase of kL values with increasing the H2 mole fraction in the feed gas was related to the increase of dS. The predicted kLa values indicated that the mass transfer behavior in the large-scale gas-sparging reactor proposed for soybean oil hydrogenation was controlled by the mass transfer coefficient, kL. Also, under similar conditions, kLa values for H2 in soybean oil when using the gaseous mixture (H2 +N 2) were lower than those obtained for H2 (as a single-component); and kL values for H2 were consistently greater than those of N2 within the ranges of the operating conditions used in the simulation. © 2005 Elsevier B.V. All rights reserved.

Hydrodynamic and Mass Transfer Parameters in Agitated Reactors Part II: Gas-Holdup, Sauter Mean Bubble Diameters, Volumetric Mass Transfer Coefficients, Gas-Liquid Interfacial Areas, and Liquid-Side Mass Transfer Coefficients

The equilibrium gas solubility (C*), gas-holdup (eG), Sauter mean bubble diameter (dS), volumetric mass transfer coefficient (kLa), gas-liquid interfacial area (a) and mass transfer coefficient (kL) of N2, O2 and air were measured in an agitated reactor operating in surface-aeration (SAR), gas-inducing (GIR) or gas-sparging (GSR) modes in pure toluene and three mixtures of organic liquids (toluene-benzoic acid-benzaldehyde) aimed at simulating the continuous liquid phase toluene oxidation (LPTO) under wide ranges of temperatures (300-453K), pressures (1-15 bar), mixing speeds (13.3-20.0 Hz), superficial gas velocities (0.000-0.004 m/s in the GSR) and liquid heights (0.171-0.268m in the SAR and GIR).C* values of the gases in the organic liquids were calculated using a modified Peng-Robinson Equation-of-State and kLa data were determined using the Transient Physical Absorption technique. The bubble size distributions as well as dS were obtained from the Photographic method, and eG values were measured through the Dispersion Height technique using the reactor’s Jerguson windows. From eG, dS and kLa experimental values, a and kL were calculated under various operating conditions. The Central Composite Statistical Design and analysis technique was used to study the effect of operating conditions on the hydrodynamic and mass transfer parameters.At constant temperature, the equilibrium solubilities (C*) of the three gases in all liquids used appeared to increase linearly with pressure and obey Henry’s Law, however, the values exhibited minima with increasing temperature. The C* values were found to increase with increasing gas molecular weight, and decrease with the addition of benzaldehyde and benzoic acid to pure toluene. A dimensionless form of Arrhenius-type equation, in which the activation energy was dependent of temperature, was developed to predict Henry’s law constant for the three gases in toluene and mixtures with a regression coefficient &gt; 99%.In the SAR, increasing N, T or decreasing H increased eG, a, kL and kLa, and decreased dS, whereas increasing P, decreased eG, a, kL and kLa. In the GIR, increasing N or decreasing H increased eG, a, kL, kLa and dS. Also, increasing T increased and then decreased eG and a; increased kL and kLa; and decreased dS. In addition, increasing P did not affect these hydrodynamic and mass transfer parameters under the operating conditions used. In the GSR, increasing N, T and UG increased eG, a, kL and kLa. Also, increasing N and T, or decreasing UG decreased dS.The addition of benzaldehyde and benzoic acid to pure toluene was found to significantly affect the hydrodynamic parameters (dS and eG), in the GSR and GIR, especially at low temperature due to formation of froth, which led to the enhancement of kLa. The hydrodynamic and mass transfer parameters obtained indicated that the behavior of the SAR was mainly dependent on kL, whereas those of the GSR and GIR were strongly affected not only by kL, but also by a. Statistical correlations were also developed to predict the hydrodynamic and mass transfer parameters obtained in this study with confidence levels &gt; 95%. These correlations could be used to model, design and scale-up the LPTO process in agitated reactors.

05/00953 Production of carbon nanotubes from coal

Time profiles of weight change of coal samples and the evolution of low molecular weight gases (H2, CH4, CO and CO2) in both steam gasification and pyrolysis of Yallourn brown coal and Taiheiyo subbituminous coal were measured using a thermobalance reactor with a micro GC and a mass spectrometer, in order to examine the reaction mechanism of steam gasification with rapid heating (100 K s−1). It was found that, in the case of slow heating, steam reacted with metaplast and promoted the evolution of tar above 623 K and that a water shift reaction took place above 873 K. Steam gasification of produced char occurred above 1023 K, increasing the evolution of CO, CO2 and H2. When the heating rate was high, steam reforming of volatile matter and steam gasification of metaplast took place parallel to metaplast formation and condensation. The char produced by pyrolysis was almost completely gasified and converted into H2 and CO2 by steam. The chemical energy of coal was mainly converted into hydrogen energy and the gasification efficiency was slightly increased by rapid heating (i.e. 100 K s−1).

Extensional bundle waveguide techniques for measuring flow of hot fluids

A bundle of acoustically slender metal rods, each thin compared to wavelength, tightly packed within a sheath, and welded closed at each end, provides a dispersion-free waveguide assembly that acts as a thermal buffer between a transducer and the hot fluid medium the flow of which is to be measured. Gas and steam flow applications have ranged up to 600 degrees C. Liquid applications have ranged from cryogenic (-160 degrees C) to 500 degrees C and include intermittent two-phase flows. The individual rods comprising the bundle usually are approximately one millimeter in diameter. The sheath, made of a pipe or tube, typically has an outside diameter of 12.7 to about 33 mm and usually is about 300 mm long. Materials for the sheath and bundle are selected to satisfy requirements of compatibility with the fluid as well as for acoustic properties. Corrosion-resistant alloys such as 316SS and titanium are commonly used. The buffers are used with transducers that are metal-encapsulated and certified for use in hazardous areas. They operate at a frequency in the range of 0.1 to 1 MHz. The radiating end of the buffer is usually flat and perpendicular to the buffer's main axis. In some cases the end of the buffer is stepped or angled. Angling the radiating faces at approximately 2 degrees to overcome beam drift at Mach 0.1 recently contributed to solving a high-temperature high-velocity flow measurement problem. The temperature in this situation was 300 degrees C, and the gas molecular weight was about 95, with pressure 0.9 to 1.1 bar.