James A. Fay

The Spread of Oil Slicks on a Calm Sea

It is a common observation that oil, when spilled on water, tends to spread outward on the water surface in the form of a thin continuous layer. In those instances where this layer is as thin as a wave length of visible light, an iridescent color of the film, caused by light interference, is observed. This tendency to spread is the result of two physical forces: the force of gravity which causes the lighter oil to seek a constant level by spreading horizontally, just as it would on a plane horizontal solid surface, and the surface tension force of pure water, which is usually greater than that of the oil film floating on water. While the oil layer could spread while still remaining intact until it had formed a monomolecular layer, spreading usually stops when the layer is much thicker than this, most likely because of a change in the surface tension properties of the oil.

PHYSICAL PROCESSES IN THE SPREAD OF OIL ON A WATER SURFACE

ABSTRACT Formulae are recommended for calculating the extent of the spread of oil slicks on water as a function of time. They are based on empirical measurements of spreading rates and analytical and theoretical studies of the physical processes which accelerate or retard the spread of a film Both one-dimensional and two-dimensional (axisymmetric) slicks are treated. Comparisons of the recommended formulae are made with the limited number of field observations, both for the rate of spread and the maximum slick size.

A Theory of Plume Rise Compared with Field Observations

A theory for the rise of a plume in a horizontal wind is proposed in which it is assumed that, for some distance downwind of a high stack, the effects of atmospheric turbulence may be ignored in comparison with the effects of turbulence generated by the plume. The theory, an extension of the local similarity ideas used by Morton, Taylor, and Turner,1 has two empirical parameters which measure the rate that surrounding fluid is entrained into the plume. Laboratory measurements of buoyant plume motion in laminar unstratified cross flow are used to estimate the empirical parameters. Using this determination of the parameters in the theory, the trajectories of atmospheric plumes may be predicted. To make such a prediction, the observed wind velocity and temperature as functions of altitude, and flow conditions at the stack orifice, are used in numerically integrating the equations. The resulting trajectories are compared with photographs, made by Leavitt, et al.,2 of TVA, of plumes from 500 to 600 ft high sta...

Two‐Dimensional Gaseous Detonations: Velocity Deficit

The measured velocity of gaseous detonation waves is less than that predicted by the Chapman‐Jouguet plane wave theory. The velocity deficit (difference between theoretical and measured velocities) has been found earlier to vary inversely with the tube diameter and initial pressure. A quantitative explanation of this effect is advanced by determining the growth of the viscous boundary layer on the tube wall and its effect upon the flow in the reaction zone of the detonation front. It is proposed that the boundary layer displacement effect within the reaction zone produces a uniform flow divergence throughout the detonation front. The velocity deficit due to this two‐dimensional flow is determined, using measured values of reaction zone thickness. The agreement of the velocity deficit with measured values is within a factor of two for the five hydrogen‐oxygen‐inert gas mixtures and one acetylene‐oxygen mixture for which sufficient data are available.

Model of spills and fires from LNG and oil tankers

A comprehensive model for predicting the dynamics of spills from LNG and oil product tankers is constructed from fluid mechanics principles and empirical properties of oil and LNG spills on water. The analysis utilizes the significant tanker hold and discharge flow area dimensions to specify the cargo liquid outflow history and the ensuing pool characteristics, including the establishment of a pool fire. The pool fire area, duration, and heat release rate are determined as functions of the tanker cargo variables. Examples of an LNG and gasoline spill show that for likely discharge flow areas these spills may be regarded as instantaneous, simplifying the evaluation of risk consequences.

Laboratory experiments of smokestack plumes in a stable atmosphere

Abstract This research is concerned with the simulation in laboratory experiments of the motion of buoyant smokestack plumes in the atmosphere. The theoretical results of previous researchers are presented and used to determine the dimensionless parameters of the flow. The conditions for geometric similarity to field scale plumes are discussed and it is shown that Reynolds number need not be simulated provided the plumes are fully turbulent at the stack exit. The thermally-stratified wind tunnel at M.I.T. is described and its operating characteristics are discussed. The significance of maintaining supercritical flow is explained and illustrated. The results of plume rise measurements made in the tunnel are presented and shown to be accurately described by the theoretical model, with minor modifications. The geometric similarity of model plumes to field measurements of plumes is clearly demonstrated. The close agreement between laboratory experiments and field measurements lends additional credence to the contention that atmospheric turbulence does not play a significant role in plume rise phenomena.

Theory of stagnation-point heat transfer in a partially ionized diatomic gas

Abstract : Stagnation-point heat transfer in a partially ionized diatomic gas is considered. The concept of frozen thermal conductivity is used, and a simplified binary diffusion model of the gas is proposed. In this model the charge-exchange cross-section for atom-ion collisions is taken to be infinite so there is no relative diffusion of the atoms and the ion-electron pairs. This permits the diffusion effects to be dealt with as if there were only two components, molecules and atom-ion-electron particles, and thus greatly simplifies the calculations. However, the thermodynamic and transport properties are evaluated using all four components, molecules, atoms, ions, and electrons. With this model, calculations are made for both frozen and equilibrium boundary layers in nitrogen up to about 60,000 ft/sec, and arguments are presented for applying the results to air. The results show the equilibrium heat transfer rate to be progressively smaller than the frozen rate as the velocity increases above 30,000 ft/sec, the ratio reaching 2/3 at 50,000 ft/sec. Simple correlation formulas for the results are given.

A CORRELATION OF FIELD OBSERVATIONS OF PLUME RISE

Data from 137 sets of plume observations, comprising nearly 1 500 data points, are correlated with two simple formulae. These formulae, one for the buoyancy-dominated rise region and the other for the stratification-dominated levelled-off region of a plume, represent an approximate form of the entrainment theory of Hoult, et al. (1968)1 for the case of uniform atmospheric stratification and zero wind shear. The observations, which are those of the Tennessee Valley Authority and of Bringfelt (1968),6 were made of plumes whose source strengths ranged from 0.4 to 111 Mw and which were emitted from stacks of heights between 21 and 183 m. The two formulae are found to correlate the data equally well over all values of the stack exit and meteorological parameters, provided only that the bulk mean velocity of the stack gases exceeds the mean wind speed by at least 20%. The ratio of observed to calculated plume rise is found to be distributed log normally about the mean value. The median rise at large distances d...

An analytical diffusion model for long distance transport of air pollutants

Abstract A steady-state two-dimensional diffusion model suitable for predicting ambient air pollutant concentrations averaged over a long time period (e.g., month, season or year) and resulting from the transport of pollutants for distances greater than about 100 km from the source is described. Analytical solutions are derived for the primary pollutant emitted from a point source and for secondary pollutant formed from it. Depletion effects, whether due to wet or dry deposition or chemical conversion to another species, are accounted for in these models as first order processes. Thus, solutions for multiple point sources may be superimposed. In this model the time-averaging of the random trajectories of pollutant-contaminated air parcels is represented by horizontal diffusion in a steady, two-dimensional flow field of the time-averaged wind. The resulting concentration isopleths for a point source show significant dispersion both upwind and cross wind of the source with respect to the mean wind field. The analytical theory for the dispersion of a primary pollutant is compared with the numerical predictions of a plume trajectory model for the case of steady emission from a point source. Good overall agreement between the two models is achieved whether or not depletion by wet and dry deposition is included. The theory for the dispersion of a secondary pollutant is compared with measurements of the annual average sulfate concentration in the U.S. Calculations are carried out using SO2 emissions from electric power plants in the United States as a source inventory. Using optimum values of the dispersion parameters, the correlation coefficient of observed and calculated ambient concentrations is 0.87 for the eastern United States and 0.69 for the western region. The optimum dispersion parameters used are comparable to values quoted in the literature. The horizontal length scale characterizing the sulphate concentration distribution from a single source is about 500 km, being noticeably larger than that characterizing the primary (sulfur dioxide) distribution. Using optimum dispersion parameters, a point source of 33 kg s−1 of sulfur dioxide would give rise to a maximum annual average sulfate concentration of 1 μ m−3. A calculation of annual average SO2 concentrations in the United States is carried out using previously derived optimal values of the parameters from the sulfate calculation. The resulting isopleths are similar to measured values in the eastern U.S.

UNUSUAL FIRE HAZARD OF LNG TANKER SPILLS

Abstract The spreading and evaporation rates of liquified natural gas spilled on water are estimated theoretically. Subsequent gravitational spread and heating of the vapor evolved from the spill generates a pancake-shaped cloud in 15 minutes or less. Downwind drift of this ground-level cloud to land areas could result in its ignition and complete combustion.