Kohärente Kurzzeit‐Strukturen und momentane Brechzahl‐, Dichte‐ und Temperaturprofile in einer n‐Hexan‐Tankflamme

Ber Bunsenges Phys Chem

Banhardt

et al. 1983

Flammen / Holografische Synchroninterferometrie / Koharente Strukturen 1 Stromungs-Instabilitaten / Transporterscheinungen Coherent structures of pool flames are visualized by the synchronous holographic interferometry. -There are large coherent structures which have periodical properties and small coherent structures both with periodical and statistical properties. The periodical phenomena can be classified into three types of instabilities. The first type is a low-frequency instability with frequencies of the order of 12 Hz (for a n-hexan pool flame, d = 4.6 cm) and depends considerably on the pool diameter. The second and third types have frequencies in the order of 300 Hz and 500 Hz, which depend mainly on the fuel type. -The statistical properties of the small coherent structures indicate that the turbulent exchange coefficients for heat and matter have values six times larger than the exchange coefficients for the momentum. The turbulent Prandtl numbers, Schmidt numbers and Lewis numbers are functions of the distance from the fuel surface. These functions vary between the following limits: 0.16 5 Pr, 5 0.35, 0.19 5 Sc, 0.35 and 0.74 Let 5 1.29.

Periodische und statistische Eigenschaften kohärenter Kurzzeit‐Strukturen in Tankflammen

Ber Bunsenges Phys Chem

Banhardt

et al. 1983

Visualization of Organized Structures in Buoyant Diffusion Flames

Ber Bunsenges Phys Chem

Balluff

et al. 1985

In pool fires of liquid hydrocarbons static equidensitometric structures (2 types) and dynamic radiance structures (18 types) are obtained from flame photograms evaluated with an image analysis computer system. A third kind of structures, the dynamic synchronous structures (9 types) are visualized with a holographic real‐time interferometry method. ‐ The control parameters of the observed structures are the pool diameter, the height above the fuel surface, the density of the fuel vapor and the volumetric fuel flow rate. ‐ The dynamic radiance structures have 4 monoperiodic subprocesses with a frequency of 12 Hz (n‐hexane pool fire, d = 4.6 cm) which depend strongly on the pool diameter and show 18 statistical characteristics. The dynamic synchronous structures of the same pool fire show a quasiperiodic region I with 7 sub‐processes at 11, 13 and 3 Hz. In a quasiperiodic region II, 8 sub‐processes exist at the frequencies 11, 12, 13, 39 and 41 Hz. In addition there are 17 statistical characteristics. ‐ The effects of the observed dynamic structures on turbulent exchange processes in pool fires are calculated and lead to turbulent Prandtl‐, Schmidt‐ and Lewis‐numbers between 0.3 and 1.

Erforschung von Schadenfeuern flüssiger Kohlenwasserstoffe als Beitrag zur Sicherheit von Chemieanlagen

Chemie Ingenieur Technik

Balluff

et al. 1985

Das Gefahrenpotential von Schadenfeuern in Chemieanlagen wird am Beispiel von Tank-und Pool-Flammen aufgezeigt. Die Bedeutung und Funktion fluiddynamischer, organisierter Strukturen fur die Verbrennungsvorgange in Schadenfeuern wird dargelegt. Kurz erlautert werden die angewandten experimentellen Methoden zur Sichtbarmachung organisierter Strukturen. Ausfiihrlich behandelt werden die Einfliisse dieser Strukturen auf die sicherheitstechnisch relevanten GroBen Abbrandgeschwindigkeit und Warmezone, maximaler Basisdurchmesser eines Schadenfeuers, Flammenlange und -Neigung sowie Strahlungswarmestrom in die Umgebung. Zur Berechnung der entfernungsabhangigen Bestrahlungsstarke eines Schadenfeuers wird neben dem Punktquellenmodell und dem Zylinder-Flammenstrahlungsmodell ein neues Modell, das Ballen-Strahlungsmodell, vorgestellt. Es beriicksichtigt die iiberlagerte Warmestrahlung von Flammenballen (hot spots) und RulSballen sowie den Blockierungseffekt kalter Brennstoffballen. Die Anwendung dieses Modells fiihrt auf zeitlich gemittelte, maximale Bestrahlungsstarken von E -4 W/cm2, die fur Schadenfeuer mit einem Pool-Durchmesser >14 m bei den meisten Brennstoffen gemessen werden. Diese Werte liegen etwa urn den Faktor 3 niedriger als die mit dem Zylinder-Flammenstrahlungsmodell berechneten Bestrahlungsstarken. Die sich daraus ergebenden Konsequenzen, z. B. fur die Sicherheitsabstande benachbarter Tanks, werden diskutiert. Investigation of hazardous fires of liquid hydrocarbons ascontribution to the safety of chemical plants. This article illustrates the danger potential of hazardous fires, such as pooland tank fires in chemical plants. The importance and the role of fluid dynamic organized structures for the combustion processes are presented. Experimental methods used for the visualization of these organized structures are also explained. The influence of such structures on the safety data, burning rate, maximum pool fire diameter, flame height and flame tilt, and the total radiative power is dealt with in detail. The point source model and the solid flame radiation model are discussed for calculation of the distance-dependent irradiance of a pool fire. A new model, the parcel-radiation model, considers the radiation of hot spots, soot parcels, and the effect of radiation blockage by cooler, unburnt fuel parcels. Application of the parcel-radiation model leads to a calculated maximum irradiance of E -4 W/cm2, which is verified experimentally for most pool fires with diameters > 14 m. These irradiances are three times smaller than the values calculated by the solid flame radiation model. The consequences for safe separation distance between two adjacent pools are discussed.