Fluid Dynamic Aspects Of Room Fires

Several fluid dynamic processes which play important roles in the development of accidental fires in structures are discussed. They include a review of information concerning the characteristic flow regimes of fire plumes and the properties of the flow in these regimes, and a brief review of flow through openings and in ceiling jets. Factors which lead to the development of thermal stratification in ceiling layers are also discussed

Disintegration of a liquid sheet due to gravity force

An experimental study was made of the disintegration of a liquid sheet due to gravity force. The influence of surface tension, viscosity, and density of liquids on the phenomenon of disintegration was found. Conditions of liquid sheet breaking into streams, as well as the frequency of appearance of streams and the mean diameter of droplets independent of properties of the liquid, were found experimentally

Recombination rates and non-equilibrium electrical conductivity in a seeded plasma

Experimentally determined values of electrical conductivity and electron temperature have been measured in a non-equilibrium seeded plasma. These results are in good agreement over a wide range of parameters with values calculated from a two-temperature model of the plasma. There is no doubt that the two-temperature model is valid over a wide range of gas temperatures, seed concentrations, and current densities for the argon-potassium and helium-potassium plasmas. However, the model does not give an accurate description of the plasma when the current density is below about 0.4 amp/cm^2; in this range the omission of the influence of atom-atom excitation and the influence of non-equilibrium excited state populations may explain the discrepancy between experiment and theory. In addition, the electron-elecron-ion collisional recombination rate for potassium has been measured in the argon-potassium system. The range of electron temperatures investigated was between 1900° K to 3000° K with electron densities between 3X10^(13) and 4x10^(14)/cm^3. The measured values show a scatter of 60 per cent about theoretical values calculated from present recombination-rate theory employing the Gryzinski classical collision cross sections

Experiments concerning the mechanism of flame blowoff from bluff bodies

The general problem of flame stabilization on bluff objects centers about the determination of the maximum stream velocity at which stable combustion may be achieved for various flame holder geometries, gas mixtures and conditions of the approaching combustible stream. Since the process involves both gas dynamic problems and chemical kinetic problems of great complexity, the most reasonable approach is one of similarity, that is, to determine under what conditions the behavior of one flame holder is similar to the behavior of another one. Because a very large number of physical and chemical variables is involved in a combustion problem, similarity conditions can be formulated most easily after experimental investigations have indicated which parameters or groups exert little influence on the mechanism and hence may be neglected. The experiments described in this paper were conducted with the object of clarifying the role of the more important parameters in the flame holding mechanism. The results indicate that a relatively simple formulation of the similarity conditions may be obtained in which the fluid mechanical parameters and chemical parameters are effectively separated

Combustion instability sustained by unsteady vortex combustion

The determination of an internal feedback mechanism which leads to combustion instability inside a small scale laboratory combustor is presented in this paper. During combustion instability, the experimental findings show that a large vortical structure is formed at an acoustic resonant mode of the system. The subsequent unsteady burning, within the vortex as it is convected downstream, feeds energy into the acoustic field and sustains the large resonant oscillations. These vortices are formed when the acoustic velocity fluctuation at the flameholder is a large fraction of the mean flow velocity. The propagation of these vortices is not a strong function of the mean flow speed and appears to be dependent upon the frequency of the instability. Continued existence of large vortical structures which characterize unstable operation depends upon the fuel-air ratio, system acoustics, and fuel type

Effect of flow on the acoustic reflection coefficient at a duct inlet

The effect of duct Mach number upon the acoustic reflection coefficient at the inlet of a duct with mean flow is investigated. An analysis, which models the duct inlet as a very short, one-dimensional nozzle over which the mean flow is accelerated from rest, gives good agreement with some recent experimental results. Discrepancies between the analysis and the experimental results are discussed in terms of radiation losses at the inlet and real fluid-flow effects within the duct

Behavior of Spherical Particles at Low Reynolds Numbers in a Fluctuating Translational Flow. Preliminary Experiments

The behavior of small spheres in non-steady translational flow has been studied experimentally' for values of Reynolds nunber from 0 to 3000. The aim of the work was to improve our quantitative understanding of particle transport in turbulent gaseous media, a process of extreme importance in powerplants and energy transfer mechanisms. Particles, subjected to strong sinusoidal oscillations parallel to the direction of steady translation, were found to have changes in average drag coefficient depending upon their translational Reynolds number, the frequency and amplitude of the oscillations. When the Reynolds number based on the sphere diameter was les s than 200, the synunetric translational oscillation had negligible effect on the aver age particle dr ago For Reynolds numbers exceeding 300, the effective drag coefficient was significantly increased in a particular frequency range. For example, an increase in drag coefficient of 25 per cent was observed at a Reynolds nwnber of 3000 when the amplitude of the oscillation was 2 per cent of the sphere diazneter and the disturbance frequency was approximately the Strouhal frequency. The occurrence of the maximum effect at frequencies between one and two times the Stroubal frequency strongly suggests non-linear interaction between wake vortex shedding and the oscillation in translational motions. Flow visualization studies support this suggestion