Gas Pressure Fluctuations Research Articles

Forced bed mass oscillations in gas–solid fluidized beds

A second-order mechanical vibration model is proposed to explain the oscillation phenomena and pressure fluctuations in gas–solid fluidized beds. Experiments were conducted in a 0.1-m ID gas–solid fluidized bed driven by periodic gas pulses with the frequency varying from 0.2 to 10 Hz. Experimental results indicate that the proposed mechanical vibration model, which considers the pressure fluctuation as the results of the response of the fluidized bed to the external excitation forces related to the bubble behavior in the bed, can reasonably explain the pressure fluctuations of the gas–solid fluidized bed. The behavior of pressure fluctuations is correlated with characteristics of both the bed system and excitation forces.

Flow Regime Identification in a Slurry Bubble Column from Gas Holdup and Pressure Fluctuations Analysis

AbstractAnalysis of gas holdups and pressure fluctuations are conducted in a slurry bubble column to study changes in flow regimes and comparisons are made with solid‐free bubble column. The pressure fluctuations are measured by fast response pressure transducers mounted on the column wall in the distributor and bulk regions. Air, tap water and 35 micron glass beads are used as the gas, liquid and solid phases respectively. Statistical analysis of pressure fluctuation data combined with gas holdup analysis provided information about flow regime transition and interesting insights into bubble size distributions and changes in flow structure.

Application of wavelet multi-resolution analysis to pressure fluctuations of gas–solid two-phase flow in a horizontal pipe

In order to reveal the unsteady features of gas–solid two-phase flow in both Fourier and physical spaces, the wavelet multi-resolution analysis was first employed to analyze the experimental data of the wall pressure–time signal. Then the definitions of the wavelet multi-resolution root mean square (RMS), skewness factor and probability density function (PDF) were developed and were applied to the statistical analysis of gas–solid two-phase flow in the frequency space. From the random-like pressure fluctuations, the fluctuating pressure components due to the dispersed suspension flow and the dune flow can be extracted based on the wavelet multi-resolution analysis over a time–frequency plane. It was found that the larger gas velocity results in the larger RMS pressure component at the higher frequency, while the lower gas velocity results in the larger RMS pressure component at the lower frequency. At a low velocity, the wavelet multi-resolution probability density function shifted to a unimodel from a bimodel distribution when increasing the frequency. In the acceleration region the pressure fluctuation components of the higher frequency deviated from the Gaussian-type fluctuation and resulted in the larger negative convectional skewness factor.

Pressure fluctuations in gas fluidized beds

The pressure fluctuations in a fluidized bed are a result of the actions of the bubbles. However, the bubbles may be influenced by the air supply system and by the pressure drop of the air distributor. These interactions are treated for low as well as for high velocity beds by means of a simple model of the principal frequency of the pressure fluctuations. The model includes the interaction with the air supply system and describes qualitatively two important bubbling regimes: the single bubble regime, important for systems with low pressure drop air distributors, and the exploding bubble regime for high velocity beds. .

Characterizations of flow regime transitions in a high-pressure bubble column by chaotic time series analysis of pressure fluctuation signals

In this study, experiments are carried out for a high-pressure bubble column with a perforated plate as the distributor under the operating pressure up to 15 MPa . Gas holdups and pressure fluctuation signals are measured. Analyses of standard deviation and chaotic time series on pressure fluctuation signals are conducted to determine the transition gas velocities. The results of chaotic measures, such as the largest Lyapunov exponent, metric entropy and the correlation dimension show that there are bands of transition velocities for each operating pressure. The general trend is that the transition velocities increase as the operating pressure rises. Similar trends are also found for the transition velocities obtained by the standard deviation. All the transition velocities resulting from the chaotic measures and the standard deviation show good agreements.

Cross‐Correlating the Sloan Digital Sky Survey with the Microwave Sky

While most of the microwave background (CMB) fluctuations on angular scales greater than a few arcminutes were generated at z > 800, the low-redshift universe does distort the microwave background. Since the Sloan Digital Sky Survey (SDSS) traces the structures in the low-redshift universe, we can gain additional insights into the physics of the low-redshift universe by cross-correlating microwave background maps with template maps produced from the SDSS. We present a formalism for cross-correlating data from the Microwave Anisotropy Probe (MAP) with the Sloan Survey for the thermal Sunyaev-Zeldovich (SZ) effect, the Integrated Sachs-Wolfe (ISW) effect, and weak lensing. This formalism is used to compute the signal-to-noise ratio for cross-correlating these effects with various classes of tracer objects from the SDSS. The anticipated samples of SDSS quasars and galaxies with photometrically determined redshifts are found to be good tracers for cross-correlating with the CMB. We find that the SZ-galaxy cross-correlation would give good constraints on pressure fluctuations in supercluster-scale gas. Cross-correlating weakly lensed quasars with maps of the convergence of the CMB is found to give strong constraints on Ω0 as well as the equation of state, w. We find that the ISW cross-correlation gives a poor signal-to-noise ratio using these techniques.

Structure of gas pressure signal at two-orifice bubbling from a common plenum

Bubble formation at two orifices with a common plenum was studied experimentally. Different modes of bubble formation were identified by means of analysis of gas pressure fluctuations measured in the plenum. Two synchronous regimes were found at low and high gas flow rates, separated by a wide range of asynchronous regimes. The effect of important operational parameters (barrier in the plenum and in the liquid, orifice spacing, water height, and column diameter) on the stability threshold of the lower synchronous regime was investigated.

Fourier analysis of nonlinear pressure fluctuations in gas–solids flow in CFB risers–Observing solids structures and gas/particle turbulence

The dynamic behaviour of gas–solids flow in a CFB riser is characterized by Fourier spectral analysis of pressure fluctuations. Time series of pressure fluctuations were recorded at different measurement positions in a lab-scale riser at gas velocities of 3.0, 4.0, and 5.0 m/s under dilute and dense flow conditions, with solids mass fluxes ranging from 0 to 232 kg/m 2s. When dense flow conditions are met at the measurement position, two regions with different power-law fall-off are observed in the power spectral density. At dilute flow conditions, no clear regions with a power-law fall-off are observed. The power in region I shows a sharp decrease from a value of ≈2–≈0.5 at the transition from dilute to dense flow at the measurement position. With increasing mass flux, the power increases to a value of approximately 2 again. The power in region II increases from a value of ≈3.5–≈5 for all measurement positions when a dense bed is formed in the bottom section of the riser. With the coherence between measurement positions, it is demonstrated that gas/particle turbulence is a negligible source for pressure fluctuations. Gas velocity fluctuations and solids clusters are the predominant sources for these fluctuations. The power-law fall-off regions are attributed to solids clusters, and explained by the typical triangular or saw-tooth shape of the pressure fluctuations.

Natural modes of multi-orifice bubbling from a common plenum

Bubble formation at multiple orifices with a common gas plenum was studied experimentally. Gas pressure fluctuations in the plenum were measured and different modes of bubble formation were identified. Main attention was paid to regular synchronous modes because of their importance in formation of uniform gas–liquid mixtures. Factors affecting the interactions among orifices on both the gas and liquid sides were identified.

Sputtering of fibrous-structured low-stress Ta films for x-ray masks

In order to achieve precise control for the internal stress of x-ray absorber films, we have controlled the sputtering-gas (Xe) pressure within ±0.002 Pa (at 0.5 Pa) using a newly developed ultrahigh-vacuum sputtering system, but we found that it was difficult to reproducibly obtain sufficiently low-stress Ta films over the long term. We therefore investigated the relationship between the internal stress and substrate temperature at a low deposition pressure (0.45 Pa). It was found that internal stress changes basically toward tensile with increasing substrate temperature because of the bimetal effect, but at substrate temperature from 205 to 220 °C, the internal stress changes toward compressive with increasing temperature. We characterized Ta films deposited at various temperatures using x-ray diffraction and secondary electron microscopy and found that a film deposited at 205 °C was columnar-structure β-Ta and that one deposited at 240 °C was fibrous-structured β-Ta. Films deposited at temperatures higher than 270 °C were rough-surfaced α-Ta. For films deposited at pressures lower than 0.8 Pa and at a substrate temperature of 240 °C, the internal stress was almost constant regardless of gas pressure fluctuation. Thus, at 240 °C and 0.45 Pa, we can deposit low-stress (<5×107 N/m2) Ta films with excellent long-term reproducibility.

乾留途中におけるコークス塊内の密度分布

A commercial-scale coke oven chamber was shock-cooled during the carbonization process, the state of carbonization inside the coke oven was studied, and analyzed the pieces sampled from the oven. Authers clarified the following facts from these studies and analyses.(1) There were two distinct features about the density distribution inside lump coke obtained from the shock-cooled oven. One was the layered density distribution in the direction parallel to the oven wall. The other was the steep decrease of the density in the part from 60 to 90mm from the oven wall.(2) We could make clear the above two facts by taking into consideration the following investigations. Gas pressure in the plastic layer changed with fluctuations of gas pressure in coal layer, and the shape of bubbles in the plastic layer were deformed with these gas pressure fluctuations.(3) Depending on the layered density distribution, permeability and tensile strength of coke have different values in the directions of oven length and width respectively.

Suppressor of gas pressure fluctuation and noise

The invention provides a pressure-fluctuation and noise suppressor having low flow resistance and high effectiveness. It is especially useful as a suppressor for an oil-injection inlet system of a positive-displacement air compressor. It has a cylinderical housing separated into ante- and main chambers by a partition. A tubular suppressing element is fixed through the partition eccentrically of the axis of the housing. The inlet of the suppressing element is in the form of a nozzle in the ante-chamber that widens away from the partition. In the main chamber, the wall of the suppressing element is perforated and the end of the suppressing element in the main chamber is closed by a conical member. An outlet tube is situated on a side wall of the housing in a plane perpendicular to the axis of the housing on an axis transecting the axes of the chambers and the suppressing element. An inlet extends into the ante-chamber diagonally from the nozzle of the suppressing element.

Mechanisms of the breakup of liquid jets

A general theory of the onset of breakup of liquid jets in an ambient gas is given. The theory is based on the linear stability analysis of a viscous liquid jet with respect to spatially growing disturbances. The three independent parameters in the theory are the Reynolds number /?, the Weber number We, and the gas-to-liquid density ratio Q. The numerical results obtained from a single characteristic equation over a wide range of the parameter space reveal that there are two fundamentally different mechanisms of the jet breakup. The first is the capillary pinching that breaks up the jet into segments. The second is the capiUary wave resonance with the gas pressure fluctuation that generates droplets much smaUer than the jet diameter. An argument based on the boundary-layer instability theory is used to demonstrate that the shear waves at the liquid-gas interface plays a secondary role in the jet breakup.

Effect of changes in systemic oxygen tension on middle ear gas exchange.

The effect of alterations in the systemic oxygen tension on middle ear (ME) gas exchange was studied in three juvenile rhesus monkeys (Macaca mulatta) using five different inspired oxygen concentrations ranging from 15% to 100%. The anesthetized animals were ventilated for 4 hours, breathing the set of predetermined, constant oxygen-nitrogen gas mixtures. During this period, arterial and venous oxygen and carbon dioxide partial pressures were measured at 30-minute intervals; total ME gas pressure was determined indirectly using tympanometry at 10-minute intervals. Systemic oxygen blood gas tension showed predictable changes which were dependent on the fraction of inspired oxygen. However, fluctuations in the total ME gas pressure were insignificant. Findings suggested that increased systemic oxygen partial pressure does not influence ME gas exchange.

On the influence of internal hydrogen of fatigue thresholds of HSLA steel

The transition of the existing natural gas grid infrastructures towards transport and storage of hydrogen gas plays a prominent role in the global decarbonization of the energy landscape. Hydrogen absorption into pipeline steels may lead to a ductility decrease, particularly in the presence of stress concentrations. Hydrogen lowers the fracture resistance of steels, which may render them to become susceptible to crack extension under static loading. Furthermore, due to fluctuations in gas pressure and applied loads on the pipeline structure, hydrogen assisted fatigue crack growth could take place (even at relatively low hydrogen gas partial pressures). Therefore, the use of existing pipeline systems (initially not designed) for pressurized gaseous hydrogen transport requires prior confirmation of their fitness-for-service. Mechanical (load level and cycle frequency), material (microstructure, chemical composition and the presence of welds), and environmental variables (gas pressure, gas composition and temperature) influence the severity of hydrogen embrittlement by gaseous hydrogen. Investigations have indicated that the take-up of hydrogen by pipeline steel may be mitigated by the addition of gas impurities, i.e. inhibitors, to the gas mixture. The current work presents a literature overview of the relevant aspects in this consideration, indicating ample scope for further research in all abovementioned aspects.

A chromatographic method for the determination of low surface areas

This study describes and discusses the application of a gas chromatographic method developed to measure the specific area of solids. It is especially useful for those solids that exhibit particularly low specific areas. It is shown that for the latter particular attention must be paid to the design of the gas mixing chamber used because fluctuations in gas pressure during adsorption and desorption of the adsorbate may alter the composition of the gas vector. The precision of the method is discussed and several examples of its applications are given.

The relative diffusion of strong magnetic fields and tenuous gases

General equations are given for treating the diffusion of a magnetic field in a fluid with electrical conductivity and a resistive diffusion coefficient. Consequences of nonnegligible gas motion are investigated by considering the one-dimensional problem where a tenuous isothermal gas with pressure expressed as a function of x-coordinate and time is enmeshed in a magnetic field in the y-direction. Approximate equations are obtained for the case of weak fluctuations in gas or field pressure, and the properties of a nonlinear diffusion equation are illustrated with the example of an initial thin slab of gas confined by a uniform field on either side. The advance of a gas front into a nonvanishing gas density is illustrated by using the progressive wave solution. Application of the results to the evolution of streamers and filaments observed in the solar corona is briefly discussed

Statistical Error in Molecular Cross Section Measurements

The probability that a set of counts of particles transmitted over a measured path through a gas at a sequence of pressures can correspond to a particular value of the total cross section is calculated. From this, recipes are given for determining the best value of the cross section and of its mean square deviation, for evaluating the random and systematic errors in the cross section caused by random fluctuations in gas pressure and errors in the reading of gas pressure, and for prescribing the parameters of an experiment to achieve maximum precision in a given time of measurement.

Density and pressure fluctuations in gas fluidized beds

AbstractA Bench‐scale size fluidization system was constructed for the purpose of conducting experiments to determine density and pressure fluctuations in gas fluidized beds. Density fluctuations and bubble sizes were measured with a photocell device and β‐ray absorption. Pressure fluctuations were determined with a conductivity cell. The frequency distributions of the density and pressure fluctuations and bubble sizes were determined as functions of several variables. They could be described by dimensionless coefficients and X2‐distributions with different degrees of freedom. Such variables as distance from the gas distribution plate, bed height, particle size, gas flow rate, and internal screens were considered.