Pool Diameter Research Articles

Boilover burning of oil spilled on water

In-situ burning of fuels spilled on water is of interest as a means for cleaning up these spills. It also is a potential important hazard in unwanted fires. This paper reports the results of small-scale experiments that investigate the combustion of thin layers of heating oil on water, and the events that take place in this complex combustion process, which can lead to the occurrence of explosive burning, normally referred to as boilover. The work concerns primarily the influence of the initial oil-layer thickness and pool diameter on the burning rate, time to the start of boilover, burned mass ratio, boilover intensity, and temperature history of the oil and water. The temperature measurements show that the phenomenon may be due to boiling nucleation near the oil/water interface, in sublayer water that has been superheated. The violent eruptive vaporization of the water bubbles tends to atomize the oil layer above, with subsequent projection of burning droplets. The boilover intensity appears closely related to initial oil-layer thickness and pan diameter. This is discussed in terms of surface tension effects, and growth and expansion of the water bubbles at the nucleation sites.

Estimate of the Effect of Scale on Radiative Heat Loss Fraction and Combustion Efficiency

Abstract The effect of fire size on radiative heat loss fraction (xr) and combustion efficiency (xa)Was examined by an analysis of scale for pool flames with varying diameter (D). Correlations between D and xr or xa were obtained. For 0.1m > D > lm, xr and Xa are relatively constant and independent of D. For larger pool diameters, Xi decreases with increasing D.

Assessment of the Fire Hazard Presented by a Burning Pool of Toluene Diisocyanate (TDI)

Fire tests have been conducted with TDI under conditions simulating a pool fire originating, e.g. from a leakage of stored TDI. The facilities of Cerchar * provide conditions of a free-burning, well-ventilated fire. Burning rate, heat and smoke development and toxic gas emission were determined as a function of the pool diameter up to 1 m2. Results are compared with small scale test results. Burning rate increases with increasing pool diameter reaching 2 kg/m2-min at 1 m2 area. Yields of permanent gases do not differ significantly with increasing pool area, with HCN amounting to 5 mg/g. Free TDI is found in fire gas up to 15 ppm corresponding to a yield of 7 mg/g.

Computational modeling of stationary gastungsten-arc weld pools and comparison to stainless steel 304 experimental results

A systematic study was carried out to verify the predictions of a transient multidimensional computational model by comparing the numerical results with the results of an experimental study. The welding parameters were chosen such that the predictions of the model could be correlated with the results of an earlier experimental investigation of the weld pool surface temperatures during spot gas-tungsten-arc (GTA) welding of Type 304 stainless steel (SS). This study represents the first time that such a comprehensive attempt has been made to experimentally verify the predictions of a numerical study of weld pool fluid flow and heat flow. The computational model considers buoyancy and electromagnetic and surface tension forces in the solution of convective heat transfer in the weld pool. In addition, the model treats the weld pool surface as a truly deformable surface. Theoretical predictions of the weld pool surface temperature distributions, the cross-sectional weld pool size and shape, and the weld pool surface topology were compared with corresponding experimental measurements. Comparison of the theoretically predicted and the experimentally obtained surface temperature profiles indicated agreement within ±8 pct for the best theoretical models. The predicted surface profiles were found to agree within ±20 pct on dome height and ±8 pct on weld pool diameter for the best theoretical models. The predicted weld cross-sectional profiles were overlaid on macrographs of the actual weld cross sections, and they were found to agree very well for the best theoretical models.

Fire Induced Flow Under A Sloped Ceiling

A series of fire tests was conducted under a smooth ceiling to investigate the ceiling gas flow as affected by ceiling slope, convective heat release rate of the fire and clearance between the fuel top surface and the ceiling. Besides a horizontal ceiling reference, three ceiling slopes were investigated: lo0, 20' and 30'. Pool fires were used as f i r e sources. Two pool diameters, two different fuels (heptane and methanol) and three ceiling clearances were used. In each test, measurements were made of ceiling gas temperatures, ceiling gas velocities, and fuel mass loss. Empirical correlations for the near-maximum gas velocity and excess temperature of the ceiling flow along the steepest run were established in terms of ceiling slope, radius from the point of intersection of the ceiling with the pool centerline, and characteristics of the undeflected plume at the ceiling level. The ceiling slope had a more pronounced effect on velocity variation along the steepest run than on temperature variation. In the upward direction, the rate of velocity decrease with radius was reduced significantly as the ceiling slope increased. In the downward direction, at a certain distance from the pool centerline, the flow separated from the ceiling and turned upward. The larger the ceiling slope, the sooner the turning occurred. Furthermore, the rate a t which gas temperature approached ambient i n the downward direction increased with ceiling slope, while the temperature decrease in the upward direction was not much affected by change of ceiling slope.

ＴＩＧ アーク溶融池面の陽極挙動に関する研究（第１報） 静止ＴＩＧアークにおけるＴｉ合金板溶融池面の電流分布

The estimation of the electric current distribution on the molten pool was tride by measurement of the electric potential distribution on the back of a thin plate (3.5 mm, Ti-6Al-4V), which is one of the base metals in which it is expected that the anode distributes over the wide range on the molten pool. Electric resistivity of this plate is nearly constant with change in temperature.The measurement was carried out in a stationary TIG arc with current of 150A and arc length of 3 mm, and in the stationary state of the heat flow (molten pool diameter: 9.5 mm) which is obtained by water-cooling of the back of the plate.The result was not a Gaussian and an equi-current distribution but an equi-current density distribution (OD:8 mm) or the current distribution for equipotential surface (OD:7 mm) in which the current value at the outside was higher than at the center.

GRASSHOPPER SWIMMING AS A FUNCTION OF SEXUAL AND TAXONOMIC DIFFERENCES: EVOLUTIONARY AND ECOLOGICAL IMPLICATIONS

Swimming behavior of grasshoppers (21 species from 3 subfamilies) was assessed with respect to sexual and taxonomic differences. The parameters of swimming included capacity (the ability of individuals to reach the edge of a 100 cm diameter pool within 3 min), rate of net displacement (the time required to reach the edge of the pool, if this was greater than 3 min the subject was deemed as incapable of swimming) and orientation (the ability to reach a target of vertical stripes on the pool). Melanoplinae had a significantly greater proportion of individuals capable of swimming than Oedipodinae or Gomphocerinae. Males and females did not differ significantly in swimming capability. Considerable differences were found among species in the rate of net displacement. This rate was significantly greater for Melanoplinae than Oedipodinae, and Oedipodinae were significantly faster than Gomphocerinae. In comparing across all species, females had a significantly greater rate of net displacement than males. Several species exhibited an ability to reach the target at a rate significantly better than chance. However, at the subfamily level, only the Melanoplinae were able to orient to the target at a frequency significantly better than chance. In comparing across all species, the sexes were not found to differ in their ability to orient. Phylogenetic and ecological interpretations of the data are suggested.

AN EXPERIMENTAL INVESTIGATION OF A CYLINDRICAL VESSEL ENGULFED IN FIRE WITH A BURNING RELIEF VALVE FLARE PRESENT

Tests were performed with a 0.6 m diameter, 1.8 m long cylindrical vessel exposed to an engulfing JP4 fueled pool fire (2.5 m diameter pool) and a propane fueled simulated relief valve flare which emanated from the tank top-centre. The tank was partially filled with water and was instrumented with thermocouples and heat flux transducers. Thermocouples were also externally situated to measure fire temperatures, The tests were conducted indoors and were therefore isolated from cross winds. Tests were conducted involving only the burning relief valve flare and with both the burning flare and pool fire. Data recorded during the tests included vessel wall temperatures, heat fluxes to the vessel, lading temperatures, and fire temperatures. Results from the tests indicate that in the absence of cross wind effects, the burning relief valve flare had no significant effect on the vessel when it was already engulfed in fire. The very sooty fire acted as a shield between the flare and the vessel. However, the high momentum flare resulted in a significant change in the geometry of the burning pool fire and this in turn could affect the heat flux to remote targets Results are presented which show the response of the vessel and its lading to the different fire conditions. Comparisons are made between the results obtained here and those obtained from previously conducted tests involving full and fifth scale rail tank-cars exposed to engulfing fires

Modeling Thermal Radiation In Open Liquid Pool Fires

A non-isothermal, non-homogeneous approach has been developed for radiation analysis of moderate to large scale liquid pool fires, with a special emphasis on soot formation and the absorption and emission processes. The present field approach reveals the phenomenon of radiative energy blockage by the cold fuel and soot particles in the vicinity of the fuel bed, resulting in a variable heat flux distribution at the fuel surface. The convective contribution to the heat feedback at the fuel surface is found to decrease from 54 to 5% as the pool diameter increases from 15 to 50 cm, while the radiative contribution proportionately increases. The estimated mass evaporation rate and the total radiative output from the flame agree closely with experiment.

Simultaneous observation of organized density structures and the visible field in pool fires

Organized density structures and the visible field of pool fires were observed simultaneously with a real-time holographic interferometric method. The pool diameters d varied between 1≦ d ≦10 cm and the fuels studied were methane, LNG, n -butane, n -pentane, n -hexane, n -heptane, diesel/gasoline, liquid paraffin; methanol, ethanol, propanol, cyclohexanol, glycerin; acetaldehyde, acetone, diethyl ether; acetic acid, methyl acetate; benzene. The organized structures depend on the height x above the pool rim, the pool diameter, the fuel supply rate, the equivalence ratio and the fuel type. These structures show mono-, quasi- and nonperiodic behaviour. In the height region Δ x 1 =0 to 8 cm above the fuel surface of an n -hexane pool fire, d =4.6cm, six monoperiodic subprocesses exist with one independent frequency of 3 Hz and two harmonics of 9 and 12 Hz . The independent frequencies of the first quasiperiodic process are 12, 39 and 41 Hz in the height region Δ x 2 =8 to 16 cm. The second quasiperiodic process with the two independent frequencies of 107 and 78 Hz occurs in the height region Δ x 3 =16 to 24 cm. A third quasiperiodic process with at least the two independent frequencies of 177 Hz and 192 Hz exists in the height region Δ x 4 =24 to 32 cm. For the mean frequencies f of the monoperiodic subprocesses the correlation f ¯ ( d ) = b ¯ D B ( d ) d − 0.5 ≈ 1.83 d − 0.63 , (2.0≦ d ≦2500 cm) is derived, based on the buoyant acceleration b DB of density parcels. A density structure forming concentric ring-shaped interference fringes is defined as a density parcel. With a simplified momentum equation the axial convection velocity of fire parcels, which is up to three times faster than that of the density parcels, was calculated. Instantaneous mass densities and temperatures were calculated by the Abel-inversion, including the concentration profiles of 15 stable fire gas species. From the frequency distributions of the geometric dimensions of density parcels macro-and microscales, which agree with the scales obtained from power spectra, were determined.

General correlations of chemical species in turbulent fires

The scaling with fire size and intensity of stable molecular species in turbulent pool and buoyant jet propane fires has been investigated. The experimental apparatus consisted of porous sintered bronze burners of various diameters supplied with a gaseous fuel, a specially designed constant mass flow gas sampling probe, and H2O, O2, CO2, CO, and total hydrocarbon analyzers. Maps of time-averaged species concentrations in 190, 381, and 762 mm diameter gaseous fuel pool fires over a range of combustion heat release rates were obtained through axial and radial sampling probe traverses. Concentrations for each species throughout the flame were found to be a function only of the mixture fraction, ξ, which is the fraction of atomic species present which originated in the fuel supply. Two correlations of the assembled centerline mixture fraction data are presented. The correlating parameters are respectively 1) a virtual source term parametric in combustion heat release rate, pool diameter, and lip size; and 2) a fire “Froude” number which controls the dimensionless flame height. In the latter correlation, the data are presented in plots of ln (ξ/Q*) vs ln (z/D), where Q* is a fire “Froude” number which controls the dimensionless flame height, and z/D is the dimensionless height. These results indicate four distinct entrainment regimes: 1) counterflowing flames near the fuel surface; 2) columnar, above where the flames neck in to form a mid-axis column; 3) buoyant jet, below the flame tip; and 4) asymptotic plume, above the flame tip.

Static and dynamic radiance structures in pool fires

Digital image analysis of pool fire photograms and flame radiance measurements, time-averaged and instantaneous, was applied in observing static and dynamic radiance structures in the visible and infrared spectral ranges. Small-view-angle pyroelectric radiometer measurements as well as measurements of instantaneous radiances with Si- and Ge-photodiodes and of flame temperatures, concentrations of stable species and gas flow velocities were carried out. Time-averaged fields of radiances L ¯ λ ( y , x ) are defined as static equidensitometric structures consisting of symmetric W- or M-shaped core structures and elliptical plume structures. The fuel type and the pool diameter change only the geometric part of the core and plume structures. The structures L ¯ λ ( y , x ) in the visible spectrum represent in good approximation the spatial distribution of the radiances L ¯ r a d ( y , x ) in the infrared spectrum. Volumetric emission coefficient Ψ ¯ λ ( r , x ) are determined by Abel-inversion from L ¯ λ ( y , x ) . A simplified model, based on the assumptions of the optical thin limit and inhomogeneities in temperatures and species concentrations is presented to calculate Ψ ¯ λ ( r , x ) . The dynamic radiance structures are totally unsymmetric and show monoperiodic and nonperiodic properties. Formation frequencies for fire parcels, fire mushrooms, soot parcels and hot spots as well as oscillation frequencies for visible fire shapes are determined. Spatial power spectra are calculated from instantaneous radiance profiles by Fourier analysis. The macroscales determined depend strongly but the microscales only weakly on the height x above the fuel surface. It seems that the microscales reach a lower limit of 5 mm.

The structure and radiation of an ethanol pool fire

The structure of the flame above a burning 0.5 m diameter pool of ethanol has been examined. The average concentration of CO 2, CO, H 2O, and hydrocarbons, the mean and standard deviation of temperature, and the mean velocity are reported from the surface up to 1.5 diameters downstream. The local soot absorption coefficient has been found to be less than 0.7 m −1 everywhere in the fire using a fiber optic laser attenuation probe. Instantaneous temperatures measured simultaneously at 11 positions along the diameter show no correlation between fluctuations on the centerline and at the edge of the fire, and moderate correlation between thermocouple pairs located at similar radial positions across the fire. In all cases the cross-correlation is maximum where the time delay is zero for any given height. The temperature probability distribution and a measured dominant flickering frequency of 1.96 Hz are consistent with observations made in other moderate sized pool fires of various fuels. The radiative loss in the first 0.75 m is 19% of the 72.8 kW thermal input. Measurements of radiant intensity distributions from the fire are compared to values predicted from nonisothermal radiation models. When account is taken of the low frequency, large scale fluctuations in temperature, concentration, and soot absorption coefficient, predictions of intensity are in closer agreement with experiment than predictions from models based only upon time mean temperature and composition. The data reported here provide a comprehensive basis for evaluation of other fire and radiation models as well.

Air entrainment into buoyant jet flames and pool fires

A simple model for the fire dynamics of turbulent fires is proposed and then used to derive correlations for air entrainment into turbulent jet fires and pool fires. Five parameters are identified to control the fire dynamics: the pool diameter D, the total buoyancy flow B ∞, a buoyancy force per unit mass at the adiabatic stoichiometric temperature ( ΔT ad T ∞ )g , the ambient density ϱ ∞, and the stoichiometric mass air to fuel ratio S. These parameters lead by dimensional arguments to correlations for air entrainment rates, which are further refined by using a simplified physical model. Three distinct regimes for air entrainment are identified in turbulent pool fires: (a) close to pool surface where entrainment rates vary as Z 1 2 (where Z is the vertical distance from the source), (b) near the neck-in area where entrainment rates vary as Z 3 2 , and (c) farther downstream but below the flame tip where entrainment rates vary as Z 5 2 . The proposed correlations are used to plot experimental data from which proportionality coefficients are determined. It is shown, also, that there is a relationship between entrainment rates up to the flame tip and visible flame feights; such a relationship would allow one to estimate entrainment rates by measuring visible flame heights.

Chemical effects on molecular species concentrations in turbulent fires

The measurement and modeling of molecular species concentrations in turbulent pool and buoyant jet flames is described. The experimental parameters included burner diameter (2.8 mm jet nozzle, 190, 381, and 762 mm pools), theoretical combustion heat release rate (10–283 kW), lip size (0–25 mm), and fuel (CH 4, C 3H 8). Time-averaged species concentrations were obtained through axial and radial sampling probe traverses. A novel sampling probe was developed which provides a constant mass flow of flame gases that is not biased toward either hot or cold gas eddies. Local concentrations of major gas species (fuel, O 2, CO, CO 2, H 2O, N 2) in the fire are correlated by the mixture fraction, which is the fraction of atomic species present which originated in the supplied fuel. The correlation appears to be independent of pool diameter, lip size, and heat release rate. These turbulent correlations differ from the corresponding curves for laminar flames primarily due to composition broadening resulting from time average measurements of widely fluctuating components. We obtained higher than expected concentrations of CO and CO 2 in centerline measurements near the fuel source. An attempt is made ot explain these findings based on non-equal species diffusivity and local radiative extinction. The correlations obtained in this work form the basis for two closely related models: (1) for predicting mean species concentrations in turbulent flames by weighting laminar data with an assumed pdf of the mixture fraction, and (2) the chemical scaling of turbulent pool fires using Froude modeling principles. These applications are briefly discussed.

Visualization of Organized Structures in Buoyant Diffusion Flames

AbstractIn 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.

Periodische und statistische Eigenschaften kohärenter Kurzzeit‐Strukturen in Tankflammen

AbstractCoherent 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:

Buoyant plumes of large-scale pool fires

A series of large-scale pool fire tests were conducted to investigate the variation of plume gas temperature and velocity. Three pool diameters: 1.219 m, 1.737 m and 2.438 m, were selected; four fuels with drastically different heat release rates were employed. In each test, measurements were made of plume gas temperatures and velocities and weight loss of the fuel pool. The measured plume temperature profiles at several elevations were fitted with Gaussian distributions in order to determine plume centerline position and centerline values of gas temperatures and velocities. The plume convective heat flux was then determined from the fitted profiles of plume temperatures and velocities. The plume centerline temperature followed the 2/3 power of the convective heat flux, Q c , and the −5/3 power of the pulme height with respect to the virtual source location, z-z o , down to the level where intermittent flames were found; the centerline gas velocity varied as the 1/3 power of Q c and −1/3 power of z-z o . The virtual source locations were found to be related to the flame heights. For large values of the ratio of flame height versus pool diameter, the distance from the flame tip to the virtual source is proportional to the 2/5 power of the convective heat flux and the virtual source location correlates well with a parameter 10 sed for flame correlation. For small flame-height to pool-diameter ratios, in several tests, the virtual source locations were below the pool surface; however, the virtual source moved upward as the pool diameter increased or the convective heat flux per unit pool surface increased.

Simplified radiation modeling of pool fires

A convenient, widely accessible radiation model has been developed to simplify calculations of radiant heat transfer from pool fires. The non-homogeneous, non-isothermal fires are described by an equivalent homogeneous, isothermal, spectrally gray volume of flame gases defined by a composite flame shape. Input parameters for this model are obtained with conventional camers and radiometers. Those parameters are 1) the axisymmetric flame shape for particular fuel scale, and configuration derived from photographs; 2) an averaged absorption-emission coefficient, k¯f, from flame transmittance measurements and 3) an averaged flame temperature, T¯f, from measurements with a radiometer viewing the flames through a horizontal slit. The averaging of radiative properties accounts for most flame inhomogeneities. Simple analytic expressions are provided for calculations of radiative feedback to the fuel surface and radiant transfer to targets away from the fire. Results of those analytic calculations are in good agreement with exact numerical computations and with experiments. The simplified model is verified with measurements on 381-mm and 730-mm diameter PMMA pool fires. A two-fold variation in average pyrolysis rates is induced at the 381-mm scale by systematic variation of the distance between the fuel surface and the container lip. Composite photographic flame shapes were obtained for seven 381-mm diameter pool fires with lip sizes between 0 and 76 mm, and for the 730 mm pool with a 13-mm lip. Identifical averaged radiation property parameters k¯f, T¯f were used with those respective flame shapes. Calculated radiant feedback and radiation transfer to target locations are in good agreement with measurement for the range of pool fires investigated.

Influence of oxygen depletion on the radiative properties of PMMA flames

This work presents data on the flame properties of polymethyl methacrylate (PMMA) pool fires burning in nitrogen-diluted atmospheres. The measurements were performed on a 30-cm diameter pool fire equipped with a fuel level control device, with which it was possible to maintain constant mass loss rate for the duration of the test. The tests were performed in a water-cooled enclosure. The measured quantities were: Schmidt temperature, emittance, radiative power per unit height along the flame, mass loss rate and flame shape. Values for these properties were measured at four different ambient oxygen concentrations. The results were very repeatable. It was found that mass loss rate, flame emittance, and total radiation all decreased significantly with decreasing ambient oxygen concentration, while the Schmidt flame temperature was much less sensitive. The results may be interpreted as indicating that a drop in the ambient oxygen concentration influences the fire primarily through a decrease in soot concentration. The total heat release per unit flame volume was found to be weakly dependent on oxygen concentration.