Compressibility gas dynamic

L.L. Raja, R.J. Kee, and L.R. Petzold. Simulation of the Transient, Compressible, Gas-Dynamic, Behavior of Catalytic-Combustion Ignition in Stagnation Flows. Proc. Combust. Inst., 27 2249-2257,1998. 

Thermal similarity is achieved in the ACR by providing a temperature profile which can be held geometrically similar when scaled. The temperature profile drives the ACR chemical kinetics and is a combined result of the heat transfer attributable to cracking and the heat effects caused by the bulk fluid movement. Thus, true thermal similarity in the ACR can only be achieved in conjunction with chemical and kinematic similarity. Kinematic similarity in the ACR is made possible during scale-up by forcing geometrically similar velocity profiles. The ACR temperature, pressure, and velocity profiles are governed by compressible gas dynamics so that an additional key scale parameter is the Mach number. 

Raja LL, Kee RJ, Petzold LR Simulation of the transient, compressible, gas-dynamic behavior of catalytic combustion ignition in stagnation flows, Proc Combust Inst 27 2249—2257, 1998. 

Flows are typically considered compressible when the density varies by more than 5 to 10 percent. In practice compressible flows are normally limited to gases, supercritical fluids, and multiphase flows containing gases. Liquid flows are normally considerea incompressible, except for certain calculations involved in hydraulie transient analysis (see following) where compressibility effects are important even for nearly incompressible hquids with extremely small density variations. Textbooks on compressible gas flow include Shapiro Dynamics and Thermodynamics of Compre.ssible Fluid Flow, vol. 1 and 11, Ronald Press, New York [1953]) and Zucrow and Hofmann (G .s Dynamics, vol. 1 and 11, Wiley, New York [1976]). 

The phenomenon of critical flow is well known for the case of single-phase compressible flow through nozzles or orifices. When the differential pressure over the restriction is increased beyond a certain critical value, the mass flow rate ceases to increase. At that point it has reached its maximum possible value, called the critical flow rate, and the flow is characterized by the attainment of the critical state of the fluid at the throat of the restriction. This state is readily calculable for an isen-tropic expansion from gas dynamics. Since a two-phase gas-liquid mixture is a compressible fluid, a similar phenomenon may be expected to occur for such flows. In fact, two-phase critical flows have been observed, but they are more complicated than single-phase flows because of the liquid flashing as the pressure decreases along the flow path. The phase change may cause the flow pattern transition, and departure from phase equilibrium can be anticipated when the expansion is rapid. Interest in critical two-phase flow arises from the importance of predicting dis-... 

For the delivery of atomization gas, different types of nozzles have been employed, such as straight, converging, and converging-diverging nozzles. Two major types of atomizers, i.e., free-fall and close-coupled atomizers, have been used, in which gas flows may be subsonic, sonic, or supersonic, depending on process parameters and gas nozzle designs. In sonic or supersonic flows, the mass flow rate of atomization gas can be calculated with the following equation based on the compressible fluid dynamics ... 

Traditionally, hydrogen has heen stored, transported and used in the form of compressed gas or cryogenic liquid. Recharge-ahle metal hydrides have heen proposed as an alternative solid state storage method. A dynamic research community has assembled to explore the scientific basis and evaluate the technology of this hydrogen-metal reaction Metal hydride topics have... 

In most, but not all circumstances, the core gas temperature, T, is the natural reference temperature for the compressed gas because the highest temperature at the end of compression is responsible for the development of spontaneous ignition in the shortest time [88, 95]. Exceptionally, when the compression heats the reactants to temperatures that correspond to the region of ntc for that particular mixture, combustion may be initiated in the cooler boundary layer region. That is, gases which, at the end of compression, are colder than those in the adiabatic core control the duration of the ignition delay. This was demonstrated by Schreiber and coworkers by the simulation of alkane combustion, using various reduced kinetic schemes, in computational fluid dynamic calculations [102-104]. 

Care is needed when modeling compressible gas flows, flows of vapor-liquid mixtures, slurry flows, and flows of non-Newtonian liquids. Some simulators use different pipe models for compressible flow. The prediction of pressure drop in multiphase flow is inexact at best and can be subject to very large errors if the extent of vaporization is unknown. In most of these cases, the simulation model should be replaced by a computational fluid dynamics (CFD) model of the important parts of the plant. 

Typical characteristics of compressible flows are given next. Under certain flow conditions density changes due to momentum (flow) effects must be considered in gas dynamics [168]. In practice, such compressible flows may be divided into the following categories ... 

A most important disadvantage of this equation, though simple for the solution, was that the equation considers the incompressible nature of the medium, which results in significant deviations in the predictions of the collapse conditions from the realistic values. More recently, the gas dynamics inside collapsing bubbles has been studied considering the compressibility of liquid in Navier-Stokes equations (Moss et ah, 1999, Storey and Szeri, 1999). The equation reported by Tomita and Shima (1986) also considers the compressibility of the liquid medium. The... 

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