Selected Mathematical Models Describing Flow in Gas Pipelines

The main aim of simulation programs is to study the behavior of gas pipe networks in certain conditions. Solving a specified set of differential equations describing transient (unsteady) flow in a gas pipeline for the adopted parameters of load and supply will help us find out the value of pressure or flow rate at selected points or along selected sections of the network. Transient gas flow may be described by a set of simple or partial differential equations classified as hyperbolic or parabolic. Derivation of the mathematical model of transient gas flow involves certain simplifications, of which one-dimensional flow is most important. It is very important to determine the conditions of pipeline/transmission network operation in which the hyperbolic model and the parabolic model, respectively, should be used. Parabolic models can be solved numerically in a much simpler way and can be used to design simulation programs which allow us to calculate the network of any structure and any number of non-pipe elements. In some conditions, however, they describe the changes occurring in the network less accurately than hyperbolic models do. The need for analysis, control, and optimization of gas flows in high-pressure gas pipelines with complex structure increases significantly. Very often, the time allowed for analysis and making operational decisions is limited. Therefore, efficient models of unsteady gas flows and high-speed algorithms are essential.

Environmental measures to reduce air pollution on the territory of a specialized facility

A detailed narrowly focused survey was carried out on one of the three zones of the technological infrastructure of a specialized facility - a hangar for aircraft (LA). A general list of pollutants (SV) released into the atmosphere at the 2nd site - the hangar of a special facility was established. Generators – installations and constructs of polluting components on a specific area of stationary and mobile type, which operate at a special facility, are fixed in the selected sectors. In accordance with the nature of the released components and the nature of the emission source (stationary or mobile type), the 2nd site is divided into 4 sectors. The measurement by sectors was implemented and the concentration of emissions was calculated according to the recommended regulatory acts of the Russian Federation. Indications of the concentration of a number of substances above the regulated MPC for 2 sectors of the 2nd site for the energy and test site of the special facility have been established. In connection with the recorded results, techniques and procedures of organizational and technical regulations that contribute to minimizing the accumulation of pollutants (gases) of functioning aircraft engines are analyzed and recommended. A method of attenuation of near-Earth smoke at an interval of up to two meters from the surface where aircraft engines operate is proposed based on the analysis of environmental measures at specialized facilities. The method is based on a variation in the orientation of the outflow of gas flows from functioning aircraft engines during launch, taxiing, takeoff, landing, and passage of an aircraft (VS) along the airfield track.

The Numerical Modeling of Gas Movement in a Single Inlet New Generation Multi-Channel Cyclone Separator

The work of traditional cyclones is based on the separation of solid particles using only the centrifugal forces. Therefore, they do not demonstrate high gas-cleaning efficiency, particularly in the cases where gas flows are polluted with fine solid particles (about 20 µm in diameter). The key feature of a new-generation multi-channel cyclone separator’s structure is that its symmetrical upgraded curved elements, with openings cut with their plates bent outwards, make channels for the continuous movement of the gas flows from the inflow opening to the central axis. The smoke flue of the vertical gas outflow is located near the cover of the separating chamber. The present work is aimed at studying the applicability of two various viscosity models and their modified versions to simulate aerodynamic processes in an innovative design for a multi-channel cyclone separator with a single inflow, using the computational fluid dynamics. The research results obtained in the numerical simulation are compared to the experimental results obtained using a physical model. The main purpose of this study is to provide information on how the new design for the multi-channel cyclone affects the distribution of gas flow in the cyclone’s channels. The modified viscosity models, k-ε and k-ω, and computational meshes with various levels of detailed elaboration were analyzed. The developed numerical models of a single-inlet multi-channel cyclone separator allow the researchers to describe its advantages and possible methods of improving its new structure. The developed models can be used for simulating the fluid cleaning phenomenon in the improved fourth-channel cyclone separator and to optimize the whole research process.

Vaneless Diffuser Performance in a Super-Critical Carbon Dioxide Centrifugal Compressor With Real Gas Effects

Super-critical Carbon dioxide (s-CO2) flows are neither incompressible nor ideal gas flows. Unlike perfect gases, the enthalpy of s-CO2 near the critical point is a strong function of pressure. Incorporation of these effects is necessary for accurate modeling of flows in centrifugal compressor vaneless diffusers. This study reviews the existing vaneless diffuser modeling technique, and modifications are made to incorporate real gas effects. Like the existing procedure, the proposed formulation does not require multiple iterations for convergence. The results are obtained in a single step using a marching technique. Hence, this model can be incorporated in standard centrifugal compressor design and analysis tools, especially for super-critical carbon dioxide flows, subject to experimental validation.

Radial Motions and Radial Gas Flows in Local Spiral Galaxies

We determine radial velocities and mass flow rates in a sample of 54 local spiral galaxies by modeling high-resolution and high-sensitivity data of the atomic hydrogen emission line. We found that, although radial inflow motions seem to be slightly preferred over outflow motions, their magnitude is generally small. Most galaxies show radial flows of only a few km s−1 throughout their H i disks, either inward or outward, without any clear increase in magnitude in the outermost regions, as we would expect for continuous radial accretion. Gas mass flow rates for most galaxies are less than 1 M ⊙ yr−1. Over the entire sample, we estimated an average inflow rate of 0.3 M ⊙ yr−1 outside the optical disk and of 0.1 M ⊙ yr−1 in the outskirts of the H i disks. These inflow rates are about 5–10 times smaller than the average star formation rate of 1.4 M ⊙ yr−1. Our study suggests that there is no clear evidence for systematic radial accretion inflows that alone could feed and sustain the star formation process in the inner regions of local spiral galaxies at its current rate.