Steady-state Gas Flow Research Articles

Effective gas flow arrangements in soil venting

Soil venting is a remediation technology specifically designed to extract contaminant vapors from vadose-zone soils through application of vacuum at one or more recovery wells installed below the surface. In the present work, screening models are developed which can contribute to the design and optimization of soil venting processes by providing means for comparative evaluation of different extraction strategies. The development of a steady-state gas flow model and a vapor-phase mass transport model permits vacuum extraction performance and venting gas flow patterns to be evaluated for desired combinations of well placement, operating pressure(s), surface capping, air injection, and soil characteristics. Additionally, the performance of the gas-flow model was assessed by comparison with laboratory and field data.

Single porous crystal membranes: mixtures in steady flow

A treatment, which uses the Langmuir adsorption isotherm as the simplest representation of the type 1 contours typical of most isotherms in porous crystals, has been developed, from the case of steady-state diffusive flow of a single gas through a porous crystal to that of flow of a mixture containing any number of components. Quantitative expressions have been obtained for the departures from sorption equilibrium for each component not only across the gas/solid interfaces but also for adsorption on the external surfaces. These departures must arise whenever the flow density, J, is finite. They are found by taking into account the mass balance equations at and across the gas/solid interfaces at entry to and departure from the crystal membrane.When Jid is the flow density which would arise for the usual but incorrect assumption of exact sorption equilibrium at and across the gas/crystal interfaces, Jid > J and the treatment leads to a simple expression for the ratio Jid/J for a single pure gas flowing alone. For the mixture of gases each component affects the flow of each of the other components and the same is true of the separation factor for any pair of gases in the mixture. In accord with this the irreversible thermodynamic formulation of mixture flow has been developed in a way that takes account of non-equilibrium at and across interfaces.

The ‘‘onion vortex’’: An adiabatic, steady-state flow of a perfect gas in the infinite domain

This Brief Communication gives a new exact solution of the nonlinear adiabatic equations of fluid flow for a perfect gas in infinite three-dimensional domain that is not the trivial constant flow. The temperature of the gas is an arbitrary function of the radius. The velocity of the gas can be described by considering concentric spheres, one for each value of the radius, which rotate about the same fixed axis through the common center of the spheres, the angular velocity of each sphere being dependent upon the temperature at the radius. The velocity of the gas at a point is then that of the sphere at that point. The nature of this flow suggests that it be named an ‘‘onion vortex.’’ It is shown that onion vortices for the same temperature distribution have an additive property, which is surprising in the context of nonlinear equations.

Steady-state thermal uniformity and gas flow patterns in a rapid thermal processing chamber

The steady-state temperature distribution and gas flow patterns in a rapid thermal processing system are calculated numerically for various process conditions. The results are verified by comparison to experimental epitaxial growth rate data. The gas flow patterns and temperature distributions depend strongly on pressure and ambient composition. Steady-state uniformity is found to be described to first order by the radiant uniformity at the wafer surface and substrate heat flow considerations alone. For high-thermal-uniformity systems, however, convective cooling does play an important role, approximately equal to that of edge losses. >

Quasi-one-dimensional method for calculating asymmetric flows through nozzles

The asymmetric steady-state inviscid adiabatic flow of a perfect gas through a subsonic/supersonic nozzle is considered. The nozzle itself is either of rectangular cross section or is axisymmetric. A first-order small asymmetry induced by an entrance flow that is oblique to the nozzle axis and has a transverse pressure gradient is allowed. The cross section of the nozzle is assumed to vary only slowly as a function of the axial distance. The case considered here is, therefore, an extension of the well-known theory of the quasi-one-dimensional flow of a perfect gas treated in standard textbooks. An integral method is used to obtain approximate results. The method is simple, yet in a test case (supersonic flow at an angle of attack through a rectangular channel) where the exact first-order result is known, a comparison shows surprisingly good agreement.

Gas velocity measurements from a close-coupled spray deposition atomizer

Gas-atomized melt spraying is used for the manufacture of metallic particulate and spray-deposited preforms. The flow behaviour of the gas in the spray is a critical component of the spraying process. Knowledge of the gas flow field generated by the atomizer is a prerequisite for characterizing the transport phenomena controlling droplet dynamics and heat transfer during droplet flight. Flow visualization, Pitot tube measurements and laser Doppler anemometry have been used in the present study to investigate the steady state gas flow field generated by a close-coupled spray deposition gas atomizer for gas flow rates of 2.0 and 2.7 l s −1 and atomizer-to-substrate distances of 180 and 360 mm. Maximum gas velocities of up to 119 m s −1 have been measured along the axis of the conical flow field generated by the atomizer. The variation in axial gas velocity perpendicular to the axis of the flow follows the form of a gaussian distribution. A mathematical model of the flow field generated by the gas atomizer has also been developed, and the predictions of the model are compared with the gas flow measurements.

Similarity properties in the problem of flow from a supersonic source past a spherical bluntness

The steady-state perfect gas flow from a supersonic spherical source past a spherical bluntness is considered. Based on numerical solutions to the nonviscous gas equations, boundary-layer and Navier-Stokes equations, universal relations for the heat transfer and drag parameters are constructed that apply in a wide range of Mach and Reynolds numbers for various free-stream uniformities.

Heat transfer model for the pyroelectric anemometer

A resistor-capacitor analog heat transfer model is used to calculate the thermal pyroelectric anemometer (PA) response. This is compared to the data of Frederick et al. [J. Appl. Phys. 57, 4936 (1985)] in the accompanying paper. Steady-state gas flow conditions are assumed, and the calculations apply in the regime where the transit time of the gas over the device is much less than the time period of the heat input from the ac-driven heater. Since the pyroelectric substrate is thin, the analysis is simplified to one dimension and excludes edge effects, heat losses due to the support, and thermal radiation. Further, no temperature difference is assumed at the interface between the gas and substrate, i.e., no temperature jump. The calculated dynamic response is in excellent agreement with measurements. However, the calculated level of response is 240 μV at a gas flow of 10 m/min, much lower than the 570 μV measured by Frederick et al.

Strong pressure waves in air-breathing engines

Fuel ingestion, damage from foreign objects, or a simple high-pressure compressor stall can cause strong pressure waves in air-breathing engines. These waves travel at sonic and supersonic velocities throughout all engine compartments, where they may cause structural damage. A computer program for unsteady compressible gas flow has been used to analyze and evaluate the transient flow phenomena caused by these waves. Starting with a steady-state gas flow input defining nominal pressures, velocities, and temperatures, a pressure pulse simulating an explosion is placed at some specified location. The program then computes the variations of all the flow parameters as a function of time at every point throughout the engine. The program is modularly constructed and can simulate any engine gas flow geometry by means of judicious numbering and connection of the various modules. The program has been successfully used to assess the severity of high-pressure waves in numerous cases and has correlated very well with experimental data.

Acoustic precipitation of aerosol under standing-wave condition

Acoustic agglomeration under the standing-wave condition is experimentally investigated using ammonium chloride particles. It is found that in a standing-wave agglomerator effective acoustic precipitation can be achieved at an acoustic intensity about one order of magnitude lower than that required for travelling-wave agglomerators under the same conditions in a stationary system. However, in a flow-through system, the steady-state gas flow greatly suppresses the acoustic turbulent motion which is believed to be responsible for the enhanced particle agglomeration. Thus, for a flow-through system the required acoustic intensity is higher than that for a stationary system.

The relationship between the axial permeability of wood to dry air and to a non-polar solvent

The different approaches to the use of steady-state gas flow data in the prediction of the steady-state axial permeability of wood to liquids are reviewed. Since these may be shown to have certain theoretical shortcomings, a new predictive method based on a computer analysis is presented. This and previous methods are tested experimentally; apparently, none can be relied upon to predict the liquid permeability accurately. However, it is clear that the true liquid permeability is not measured; the reasons for this are uncertain. Until this difficulty is resolved, the precision of predictive methods cannot be accurately assessed.

On a uniqueness criteria for a dusty gas model

A uniqueness criteria is developed for solutions of a model for the steady-state flow of a dusty gas when the number density of the particles is constant. The criteria depends on the physical parameters of the system and information about the velocity of the fluid and the gradient of the particle velocity field.

Gas response to oval distortions in disk galaxies

view Abstract Citations (261) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Gas response to oval distortions in disk galaxies. Sanders, R. H. ; Huntley, J. M. Abstract Numerical hydrodynamic calculations have been carried out in order to investigate the response of a non-self-gravitating gaseous component to a rotating weak oval distortion in the axisymmetric gravitational field of a disk. The purpose of these time-dependent calculations was to determine the form of the steady-state gas density and flow distributions which would develop in the rotating frame of the oval distortion. The calculations reveal that the gas responds to the presence of the oval distortion by forming an open two-arm trailing spiral wave rotating with the angular speed of the oval distortion. The gas flow pattern is similar in form to predicted gas flow through small pitch-angle gravitational self-consistent spiral waves, although the deviations from uniform circular motion are large (approximately 75 km/s in regions of low gas density). These results may be understood from an investigation of periodic particle orbits in the rotating frame of the bar. Such an investigation implies that the presence of all three resonance regions (inner Lindblad, corotation, and outer Lindblad) within the gaseous disk is a necessary condition for such a spiral response. Publication: The Astrophysical Journal Pub Date: October 1976 DOI: 10.1086/154692 Bibcode: 1976ApJ...209...53S Keywords: Density Distribution; Flow Distribution; Galactic Structure; Gas Density; Gravitational Fields; Spiral Galaxies; Distortion; Hydrodynamic Equations; Numerical Analysis; Orbit Calculation; Steady State; Time Dependence; Astrophysics full text sources ADS |

Hypersonic flow-past of plane blunt bodies by a nonviscous radiating gas

An analytic solution is obtained in the work in a Newtonian approximation [1] for the flow-past problem for a plane blunt body by a steady-state uniform hypersonic inviscous space-radiating gas flow. The hypersonic flow-past problem for axisymmetrical blunt bodies by a nonviscous space-radiating gas has been previously considered [2–4]. In this case a satisfactory solution of the problem was obtained even in a zero-th approximation by decomposing the unknown values in terms of a parameter ɛ equal to the ratio of gas densities before and after passage of the shock wave. The solution of the problem in a zero-th approximation with respect to ɛ in the case of flow-past of plane blunt bodies does not turn out to be satisfactory, since the departure of the shock and the radiant flux to the body as gas flows into the shock layer turns out to be strongly overstated under nearly adiabatic conditions. Freeman [5] demonstrated that results may be significantly improved for flow-past of a plane blunt body by a nonradiating gas if a more precise expression is used for the tangential velocity component expressed in a new approximation with respect to the parameter ɛ. This refinement is applied in this work for solving the flow-past problem for a plane blunt body by a space-radiating gas. The distribution of the gasdynamic parameters in the shock layer, the departure of the shock wave, and the radiant heat flux to the surface of the body are found. The solution obtained is analyzed in detail for the example of flow-past regarding a circular cylinder.

Optical Doppler flowmeter for gases

A description is given of a laser flowmeter for measuring the local velocities of steady-state gas flow in large wind tunnels. The flowmeter can be used to measure velocities from 5 to 5000 m/sec and to determine the velocity profiles to within ±250 mm in the horizontal plane and to within ±15 mm in the vertical plane, relative to the selected origin of coordinates. The flowmeter comprises a single-frequency gas laser of the LG-159 type, a Farby–Perot interferometer with a dispersion range of 2000 MHz, and a photoelectric system for recording the Doppler frequency shift. The results of experimental tests of the flowmeter in the velocity range 5–100 m/sec are reported.

On the stability of galactic shocks

The stability of galactic spiral shocks is considered. A steady-state shock should be checked to see (i) if it is evolutionary; (ii) if its front is stable against bending and torsion; and (iii) if the gas flow far from the front is stable. In the present paper the evolutionary criterion is obtained, which implies that conditions in galaxies may lead to the evolutionary spiral shocks as well as to the nonevolutionary ones. In the latter case a galactic shock cannot persist — it instantly decays, emitting spontaneously spiral waves. This leads to a plausible stratification of the spiral arms, to the formation of the secondary arms, ‘spurs’ and other secondary features. The steady-state gas flow with a galactic shock (Roberts, 1969) turns out to be unstable far from the shock front, the increment being proportional to the velocity gradient. For the spiral shock calculated by Roberts (1969) the instability develops ahead of the shock front with the same growth-time of about 3×107 years for all disturbance scales. This may provide a mechanism to generate turbulence of interstellar gas and to form the patchy structure of spiral arms which are known to include the structural units (gas clouds) on all possible scales.

The permeability of dental casting investments.

Gas permeation through investment materials is important in obtaining sound castings by centrifugal or gas-pressure techniques. The equations governing permeation are presented, followed by measurements of the permeability to air of casting investments, comparing different types of material, powder : liquid ratios, and bake-out temperatures. Transient gas flow as well as steady-state gas flow are considered, and in this context, porosities have also been compared. Measurements have been made of gas flow through moulds, and the relevance of such measurements is discussed in relation to the casting process.

Evaluation of Three New Methods For Predicting Pressure Losses In Vertical Oilwell Tubing

The reliability and relative merits have been estimated for three recently published multiphase-flow pressure-drop prediction correlations applicable to vertical tubing. Data from 726 tests, embracing broad ranges of flow rate, pipe size, API gravity, gas/liquid ratio, and water/oil ratio were used in the evaluation. It was found that no single correlation consistently performed best in every range. Introduction Six of the several correlations available for predicting pressure losses during simultaneous, predicting pressure losses during simultaneous, continuous, steady-state flow of oil, water, and gas in vertical pipes were evaluated statistically by Lawson and Brill. Three more promising correlations have recently been published - those of Beggs and Brill Aziz et al. and Chierici et al. The purpose of this paper is to extend the work of Lawson and Brill to cover the new correlations.Details of the three new methods can be found in the original sources listed in the references. The same flowing pressure surveys and related data for 726 field and experimental wells were used as were reported by Lawson and Brill. Fluid physical properties were estimated using the same correlations as employed by Lawson and Brill.Although every attempt was made by Lawson and Brill to screen data in the data bank, no doubt some questionable data have been included. In a study such as this, the quality of the data is critical. It has been found, for example, that small errors in measured gas volumes and oil formation volume factors can significantly affect the calculated results. A valid criticism of the bank is that inadequate use was made of what limited measured PVT data were available. Another possible criticism is that many of the data used were gas-water data with low gas/water ratios, a situation seldom found in practice. No claim was made that the gas-water data were meant to represent gas well production. Rather, these data are extremely valuable because of the absence of mass transfer between phases and the resulting improved accuracy of, for phases and the resulting improved accuracy of, for example, predicted in-situ phase velocities.All three of the correlations were developed from two-phase flow data, one of the phases being gas. A third phase (water) can be included if we assume that its presence does not change the physical phenomena of two-phase flow. Possible changes that could invalidate results are slippage between oil and water, formation of emulsions, and the influence of water on gas bubble coalescence and the formation of gas slugs. The degree to which such changes are present in the three-phase data is unknown.We applied the three correlations to all data, knowing full well that many of the data were beyond the range of variables used to develop the correlations. However, correlations are frequently used indiscriminately beyond their stated ranges of validity. Therefore a test of their performance over a broad range of data is of value. Validation of Programming Pressure losses calculated by a computer program of Pressure losses calculated by a computer program of each method were compared with the corresponding pressure losses reported by each author for identical pressure losses reported by each author for identical well cases. This comparision indicated the degree of agreement between the results of the two programs. JPT P. 829

Inertial and Slip Effects in Steady-State Radial Gas Flow Through Porous Media

Steady horizontal radial gas flow through porous media may be described by means of the equation(1) provided there is no slip at the gas/solid interface and provided there is no slip at the gas/solid interface and q is taken to be positive in the r direction. If one assumes that the modified gas law holds and that viscosity, compressibility, and temperature remain constant, this equation may be integrated to yield(2) which is similar in form to that proposed by Tek et al. This equation may of course be reduced to the well known form employed for Darcy flow by deleting the second term on the right-hand side. However, it has been shown that neither slip nor inertial effects should be neglected when linear laboratory gas flow tests are used to evaluate rock properties. It has been observed that the same is true for laboratory data when taken in radial tests. Although Eq. 1, modified to allow for slip, may be integrated for linear flow, radial flow yields a nonlinear ordinary differential equation with no known solution. However, an approximate solution may be developed in the following manner: To allow for slip, Eq. 1 may be modified and written as(3) where(4) If the modified gas law applies and viscosity, compressibility, and temperature are assumed to remain constant at their average values, Eq. 2 may be converted to the form(5) Substitution of Eq. 4 into Eq. 5 yields(6) If one defines(7) and(8) Eq. 6 may be written as(9) or(10) As was stated earlier there is no known solution to this nonlinear ordinary differential equation. Although this equation may be attacked with numerical techniques to estimate rock properties using flow data, the procedure is involved and difficult. However, if the ratio b/p is sufficiently small, Eq. 9 may be approximated by deleting the term (1 + b/p) in the numerator, in which case(11) or(12) This equation may be integrated between the limits ; and; to yield (13) or(14) P. 1155

The steady-state flow of a rarefied gas from a spherical source or sink

The method of characteristics is used to solve problems in the steady-state flows of a rarefied gas on the basis of approximating the kinetic equations. Numerical results are given for the solution of the problem of the flow from a spherical source or sink using the generalized Kruk equation [1] and approximating the Boltzmann equation by the method proposed by the author [2, 3], Various flow conditions are discussed: flow into a vacuum, flow into a flooded volume, flow from a sink.