Gas flow model

Some early spray models were based on the combination of a discrete droplet model with a multidimensional gas flow model for the prediction of turbulent combustion of liquid fuels in steady flow combustors and in direct injection engines. In an improved spray model,[438] the full Reynolds-averaged Navier-Stokes equations were... 

ICAC Publication No. EP 7. Gas Flow Model Studies Institute of Clean Air Companies, 1993. Schwab, M.J. Johnson, R.W. Numerical design method for improving gas distribution within electrostatic precipitators. Proceedings of the American Power Conference 56th Annual Meeting, Chicago, U.S.A., April 25-27, 1994. 

In the future, the presented coupling strategy will incorporate ongoing developments within the RockFlow code concerning non-isothermal effects in multiphase (liquid/gas) flow modeling, De Jonge, Kolditz (ZAG). 

Coal is a kind of uneven double porous media made up of macro-cracks and micro-pores. Gas in coal seam remains in the macro-cracks and micropores in free state and adsorbed state. Once getting pressure relief, gas in coal seam begins to flow along the pores and fractures, while the absorbed gas is desorbed. Gas flow in Coal seam is actually a very complex process affected by many factors. In order to simplify the process, the coal seam gas flow model has the following assumptions—(Wang Xiaoliang, et. al, 2003). 

Fig. 5. For little contraction, i.e. c = o.2, the effect is moderate. The largest conversion differences are about o.o4. Therefore, application of constant gas flow models can be justified for many cases of industrial importance like separation of impurities or desired products from gas streams. If increases the deviations increase remarkably and are larger for contraction than for expansion as shown for = o.5 in Fig. 5. It is understood that constant flow models should not be applied for larger values of In the case of contraction which is more frequent in chemical reaction engineering, such values can give considerable overdesign. Only for some oxidation and hydrogenation reactions with low conversion per pass and by application of gas phase recycle may constant gas flow models still work as a useful approximation.

The Gas Flow model formulated by the Michl team (Orth et al. 1982)... 

The Gas Flow model introduced shortly thereafter by the team of Michl (Orth et al. 1982) was developed in an effort to explain the cluster ion emissions recorded fi om fi ozen matrices. This model uses many of the same assumptions used in... 

Gas flow model A model describing molecular secondary ion emission... 

Figure 3.21 Validity range of different gas flow modeling approaches. Here, pg and Uq are the mass density and the number density at standard condition of 1-atm pressure, <5 is the mean molecular spacing, and 7 is the mean molecular diameter...

The performance of fluidized-bed reactors is not approximated by either the well-stirred or plug-flow idealized models. The solid phase tends to be well-mixed, but the bubbles lead to the gas phase having a poorer performance than well mixed. Overall, the performance of a fluidized-bed reactor often lies somewhere between the well-stirred and plug-flow models. 

To appreciate the questions raised by Knudsen s results, consider first the relation between molar flow and pressure gradient for a pure gas flowing through a porous plug, rather than a capillary. The form predicted by the dusty gas model can be obtained by setting = 1, grad = 0 in equation... 

An analytical model of the process has been developed to expedite process improvements and to aid in scaling the reactor to larger capacities. The theoretical results compare favorably with the experimental data, thereby lending vahdity to the appHcation of the model to predicting directions for process improvement. The model can predict temperature and compositional changes within the reactor as functions of time, power, coal feed, gas flows, and reaction kinetics. It therefore can be used to project optimum residence time, reactor si2e, power level, gas and soHd flow rates, and the nature, composition, and position of the reactor quench stream. 

FIG. 17-14 Biihhling-hed model of Kunii and Levenspiel. dy = effective hiih-ble diameter, = concentration of A in hiihhle, = concentration of A in cloud, = concentration of A in emulsion, y = volumetric gas flow into or out of hiihhle, ky,- = mass-transfer coefficient between bubble and cloud, and k,. = mass-transfer coefficient between cloud and emulsion. (From Kunii and Leoen-spiel, Fluidization Engineering, Wiley, New York, 1.96.9, and Ktieger, Malahar, Fla., 1977.)... 

Kinetics The capacity and efficiency of biofilter operation is a function of active surface area, filter void space, target removal efficiency, gas species, gas concentration, and gas flow rate. A simphfied theoretical model described by S.P.P. Ottengraf et al. is schematically represented by in Fig. 25-18. The mass balance made around the hq-uid-phase biolayer can be described as follows ... 

This chapter is a brief diseussion of large deformation wave codes for multiple material problems and their applications. There are numerous other reviews that should be studied [7], [8]. There are reviews on transient dynamics codes for modeling gas flow over an airfoil, incompressible flow, electromagnetism, shock modeling in a single fluid, and other types of transient problems not addressed in this chapter. 

In a steady-state situation when gas flows through a porous material at a low velocity (laminar flow), the following empirical formula, Darcy s model, is valid ... 

Conveying systems normally use air as the transport medium to convey granular, crushed, or pulverized materials. Modelling the flow of pneumatic conveying and calculating its pressure loss is a problematic task. The greatest problem arises from the fact that different mass flow ratios, solid flow rate divided by the gas flow rate, imply different flow types in pneumatic conveying. Each of these flow types, which can be classified in many different ways, requires its own specific model in order to provide a concrete calculation method. 

The EXSIM code incorporates the method proposed by Hjertager (1982b, 1989) whereby the coupling between gas flow, turbulence, and combustion are modeled based on state-of-the-art methods. The characteristics of the EXSIM code are ... 

Assay of Radioactive Compounds. The radioactive samples were counted on steel planchets in a Nuclear Chicago Model D-47 low-background gas-flow counting chamber with an absolute counting efficiency (estimated by comparison with a standard) of about 20%. 

The IIEC model was also used to study the importance of various design parameters. Variations in gas flow rates and channeling in the bed are not the important variables in a set of first-order kinetics. The location of the catalytic bed from the exhaust manifold is a very important variable when the bed is moved from the exhaust manifold location to a position below the passenger compartment, the CO emission averaged over the cycle rose from 0.14% to 0.29% while the maximum temperature encountered dropped from 1350 to 808°F. The other important variables discovered are the activation energy of the reactions, the density and heat... 

To describe hypergolic heating, Anderson and Brown (A10) proposed a theoretical model based upon spontaneous exothermic heterogeneous reactions between the reactive oxidizer and a condensed phase at the gas-solid interface. In these studies, the least complex case was considered, i.e., the one in which the solid phase is instantaneously exposed to a stagnant (nonflowing) gaseous oxidizer environment. This situation can be achieved experimentally provided the sample to be tested is suddenly injected into the desired environment in a manner designed to minimize gas flow. 

Dunn et al. (D7) measured axial dispersion in the gas phase in the system referred to in Section V,A,4, using helium as tracer. The data were correlated reasonably well by the random-walk model, and reproducibility was good, characterized by a mean deviation of 10%. The degree of axial mixing increases with both gas flow rate (from 300 to 1100 lb/ft2-hr) and liquid flow rate (from 0 to 11,000 lb/ft2-hr), the following empirical correlations being proposed ... 

Kramers and Alberda (K20) have reported some data in graphical form for the residence-time distribution of water with countercurrent air flow in a column of 15-cm diameter and 66-cm height packed with 10-mm Raschig rings. It was concluded that axial mixing increased with increasing gas flow rate and decreasing liquid flow rate, and that the results were not adequately represented by the diffusion model. 

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