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Gas Dynamics
Published in S. Bobby Rauf, Thermodynamics Made Simple for Energy Engineers, 2021
This chapter is devoted to introduction of Gas Dynamics and topics within the realm of gas dynamics that are more common from practical application point of view. Gas dynamics constitutes the study of gases moving at high velocity. By most standards, a gas is defined as a high velocity gas when it is moving at a velocity in excess of 100 m/s or 300 ft/s. Traditional fluid dynamics tools such as the Bernoulli’s equation, and the momentum and energy conservation laws—traditionally applied in mechanical dynamics study—do not account for the role internal energy plays in gas dynamics; therefore, they cannot be applied in a comprehensive study of high velocity gases. In this chapter, we will examine the behavior of high speed gases on the basis of key thermodynamic entities, such as enthalpy, h, and internal energy, u. The gas dynamics discussion is premised largely on the fact that high velocity of a gas is achieved at the expense of internal energy; where the drop in internal energy, u—as supported by equation Eq. 9-1—results in the drop in the enthalpy, h. () h=u+p⋅v
Fundamentals of Fluid Mechanics
Published in Ethirajan Rathakrishnan, Instrumentation, Measurements, and Experiments in Fluids, 2020
In the preceding sections of this chapter, the discussions were for fluid motions where the density can be regarded as constant, i.e., incompressible. But in many engineering applications, such as designing buildings to withstand winds, the design of engines and of vehicles of all kinds – cars, yachts, trains, aeroplanes, missiles, and launch vehicles – require a study of the flow with velocities at which the gas cannot be treated as incompressible. Indeed, the flow becomes compressible. Study of such flows where the changes in both density and temperature associated with pressure change become appreciable is called gas dynamics. In other words, gas dynamics is the science of fluid flows where the density and temperature changes become important. The essence of the subject of gas dynamics is that the entire flow field is dominated by Mach waves, expansion waves, and shock waves, when the flow speed is supersonic. It is through these waves that the change of flow properties from one state to another takes place. In the theory of gas dynamics, change of state in flow properties is achieved by three means: (a) with area change, treating the fluid to be inviscid and passage to be frictionless, (b) with friction, treating the heat transfer between the surrounding system to be negligible, and (c) with heat transfer, assuming the fluid to be inviscid. These three types of flows are called isentropic flow, frictional or Fanno-type flow, and Rayleigh-type flow, respectively.
Fundamentals of Fluid Mechanics
Published in Ethirajan Rathakrishnan, Instrumentation, Measurements, and Experiments in Fluids, 2016
In the preceding sections of this chapter, the discussions were for fluid motions where the density can be regarded as constant, i.e., incompressible. But in many engineering applications, such as designing buildings to withstand winds, the design of engines and of vehicles of all kinds - cars, yachts, trains, aeroplanes, missiles, and launch vehicles - require a study of the flow with velocities at which the gas cannot be treated as incompressible. Indeed, the flow becomes compressible. Study of such flows where the changes in both density and temperature associated with pressure change become appreciable is called gas dynamics. In other words, gas dynamics is the science of fluid flows where the density and temperature changes become important. The essence of the subject of gas dynamics is that the entire flow field is dominated by Mach waves, expansion waves, and shock waves, when the flow speed is supersonic. It is through these waves that the change of flow properties from one state to another takes place. In the theory of gas dynamics, change of state in flow properties is achieved by three means: (a) with area change, treating the fluid to be inviscid and passage to be frictionless, (b) with friction, treating the heat transfer between the surrounding system to be negligible, and (c) with heat transfer, assuming the fluid to be inviscid. These three types of flows are called isentropic flow, frictional or Fanno-type flow, and Rayleigh-type flow, respectively.
Latest technologies and novel approaches in coal seam gas centrifugal compressor trains in Australia
Published in Australian Journal of Mechanical Engineering, 2019
The maximum tip speed is governed by the followings (Bloch 2006a, 2006b; Brown 2005; Forsthoffer 2011):The strength limitation: The majority of impellers are manufactured from low alloy steels and trip speeds for closed-type impellers would be limited to approximately 330 m/s. For semi-open impellers, particularly overhung ones, tip speeds up to 410 m/s have been acceptable. However, these impellers are not commonly used for CSG applications.Mach number: Maximum tip speed is restricted by gas dynamics. Mach number in flow-paths of impellers should be restricted within some constrains (Bloch 2006a, 2006b; Brown 2005; Forsthoffer 2011). The critical Mach number occurs at the eye of impeller, and as a very rough indication it should be kept below about 0.85 to avoid choking at inlet. The inlet Mach numbers of up to 0.96 (or sometime more) have been used previously. It is extremely complicated to calculate this Mach number; for this reason the impeller tip Mach number (Ma) which is easy to calculate is usually used. It is defined as ‘Ma = impeller tip speed/speed of sound at inlet conditions’.
Supersonic Gas Injector for Plasma Fueling in the National Spherical Torus Experiment
Published in Fusion Science and Technology, 2019
V. A. Soukhanovskii, W. R. Blanchard, J. K. Dong, R. Kaita, H. W. Kugel, J. E. Menard, T. J. Provost, R. Raman, A. L. Roquemore, P. Sichta
In the tokamak, supersonic gas jet operation principles are based on diverse physics fields: gas dynamics, compressible fluid mechanics, neutral gas transport, and magnetized plasma physics. An expansively cooled supersonic gas jet is obtained by expanding room temperature or cooled gas from a high-pressure reservoir through a nozzle into vacuum. In the tokamak, the gas jet interacts with low-density plasmas. It penetrates through the plasma scrape-off layer (SOL) perpendicular to the magnetic field lines, ionizes in the separatrix region, and creates a localized high-pressure plasma region. This plasmoid region expands along field lines, locally cooling and fueling the edge plasma. The radial propagation of the high-pressure gas jet through the edge plasma is determined to the first order by the fluid force balance, mainly by the relative magnitude of the plasma (magnetic and kinetic) pressure and the gas jet impact pressure. The high-pressure gas jet undergoes molecular and atomic (charge exchange, ionization) reactions as it propagates through the SOL plasma, retaining a neutral core shielded by an ionizing layer. The gas jet density plays a critical role in the penetration mechanism, as has been demonstrated by analytic and numerical modeling.10,21,22 However, a deep penetration may be inhibited by a high-density ionizing plasmoid that rapidly develops in front of the gas jet and blocks the jet from further penetration.
The Role of Methyl Radical in Soot Formation
Published in Combustion Science and Technology, 2019
Alexander Eremin, Ekaterina Mikheyeva
The purities of the substances used were as follows: C2H2: 99.9%, CH4: 99.99%, (CH3)2O: 99%, (CH3CO)2: 97%, Ar: 99.999%. Strongly diluted test mixtures with an inert gas in the shock tube reactor were required to ensure reliable one-dimensional gas dynamics in the shock tube. This process, necessitated by limitations imposed by optical diagnostic methods, allowed us to obtain more accurate kinetic data. As a result, the pressure in a shock tube did not change noticeably during the experiments. The temperature evolution behind the RSWs in the experiments was not controlled.