Thomas J. Overcamp

A General Gaussian Diffusion-Deposition Model for Elevated Point Sources

Abstract A modification of the Gaussian plume model is proposed for the deposition of fine and heavy particulates and gases. It combines a downward-sloping plume to account for settling and the assumption of constant deposition velocity to obtain a solution satisfying an integral mass conservation equation specifying that the decrease in the airborne flux equals the deposition. An example is given comparing this method with the conventional Gaussian model for dry deposition of gases or fine particulates.

Plume rise from two or more adjacent stacks

Abstract Three studies are presented that investigate the effect of the number of stacks and of the azimuthal angle between the direction of the wind and the line of stacks on plume rise enhancement. In the first study, observations were made of the merger and motion of thermal pairs. Thermal pairs released in one-above-the-other configurations merged more rapidly and moved faster than thermal pairs released in a side-by-side configuration. In the second study, plume rise measurements were made in a wind tunnel for plumes from two to four stacks. For a given number of plumes, the rise was higher for those cases in which the azimuthal angle was small compared to cases with a larger angle. The third study was an analysis of data from Tennessee Valley Authority field studies. Due to large scatter and the small number of observations, the results are inconclusive for cases with two, three and four plumes. The ten plume cases clearly show higher rise and the rise is larger when the azimuthal angle is small.

Effect of Reynolds Number on the Stokes Number of Cyclones

By using dimensional analysis, the Stokes number based on the cut diameter was predicted to be a function of the Reynolds number and the geometry of the cyclone. Data from various investigators were plotted versus the Reynolds number. At lower Reynolds numbers, the Stokes number decreased with increasing Reynolds number. At higher values of the Reynolds number, the data are inconclusive. For some data sets, the Stokes number approached a constant value, whereas, for other sets, the Stokes number decreased with increasing Reynolds number. The dimensionless data from this study can be used to estimate the cut diameter of geometrically similar cyclones and to make preliminary estimates for a cyclone of a different design.

Precipitation in the wake of cooling towers

Abstract A model is proposed for determining the conditions under which precipitation can occur from a natural draft cooling tower. Because the time scale for forming rain drops is large compared to the average residence time of droplets in the plume, there is no precipitation unless the wind forces the plume to mix with the aerodynamic wake of the tower and brings it to the ground. When this occurs, the small fog droplets in the plume will diffuse to the ground causing a light precipitation. A simple theory gives the heat transfer and the flux of water vapor emitted by the cooling tower. Equilibrium thermodynamics of mixing processes are used to calculate how much water vapor condenses as the plume is diluted with the surrounding air. Scaled experiments in a towing tank defined, in dimensionless variables, the conditions under which the plume will interact with the wake and strike the ground. A turbulent diffusion model combined with the thermodynamics of mixing is used to estimate the precipitation. These calculations showed that precipitation can be a tenth of a centimeter per hour when the temperature is as cold as −10°C. They also show that precipitation depends strongly on the relative humidity at warmer temperatures.

A simple approximation for estimating centerline gamma absorbed dose rates due to a continuous Gaussian plume.

A simple approximation for estimating the centerline gamma absorbed dose rates due to a continuous Gaussian plume was developed. To simplify the integration of the dose integral, this approach makes use of the Gaussian cloud concentration distribution. The solution is expressed in terms of the I1 and I2 integrals which were developed for estimating long-term dose due to a sector-averaged Gaussian plume. Estimates of tissue absorbed dose rates for the new approach and for the uniform cloud model were compared to numerical integration of the dose integral over a Gaussian plume distribution.

An Integrated Theory for Suspended-Growth Bioscrubbers

An integrated theory is developed to describe the steadystate operation of a suspended-growth bioscrubber for the control of biodegradable, volatile organic gases. The bioscrubber consists of an N-stage absorber and an oxidation reactor. A biomass slurry is circulated between the absorber and the oxidation reactor, t he pollutant is absorbed and partially oxidized in the absorber. Oxidation is completed in the oxidation reactor. Predictions of the theory show that the removal efficiency is a function of Henrys Law constant for the pollutant, the ratio of the liquid flow rate to the gas flow rate, and the number of stages. Since high efficiencies can be achieved for soluble, biodegradable, volatile organic compounds, such systems have the potential to be a low-cost control method.

Effect of a virtual origin correction on entrainment coefficients as determined from observations of plume rise

Abstract A virtual origin correction factor is introduced for bent-over jets and bent-over plumes by extrapolating the one-third law and the two-thirds law back to a point. This correction Was tested with four sets of data from model experiments and one set of pilot-scale field data. With this correction, it was found that the entrainment coefficient for jets is not a function of the speed ratio for speed ratios from three to twenty. The entrainment coefficient based on the visual centerline was found to be approximately 0.6 for both jets and plumes.

A Sorptive Slurry Bioscrubber for the Control of Acetone

ABSTRACT A sorptive slurry bioscrubber adds powdered activated carbon (PAC) to a conventional suspended-growth bioscrubber. The activated carbon increases pollutant removal from the gas phase due to adsorption on carbon. The carbon is bioregenerated in the oxidation reactor and recycled to the scrubbing column. A three-stage, conventional bioscrubber was tested with and without carbon. The experiments showed that the PAC improved the removal efficiency of the system and that bioregeneration occurred. At an inlet gas-phase acetone concentration of 50 ppmv, the steady-state removal increased from 88 to 95% when activated carbon was added to the biological slurry.

Solutions to the Gaussian cloud approximation for gamma absorbed dose

Analytical solutions of the dose rate integral for the Gaussian cloud approximation to the Gaussian plume were developed. A solution for the Ī1 integral for a ground-level source and for the Ī2 integral for an elevated source were given in terms of special functions. The Ī2 solution was also extended for the Berger buildup factor. These enable rapid computation of Ī1 and Ī2 to estimate the dose rate.

A review of the conditions leading to downwash in physical modeling experiments

Although stack downwash is not a widespread problem at modern fossil-fuel power plants and larger industrial stacks, it is a very important problem in simulating buoyant plumes in wind tunnels and towing tanks. Scaling criteria for avoiding downwash in ten subcritical model experiments have been reviewed. A comparison was made between data on the occurrence of downwash from 10 modeling studies to the theory proposed by Tatom (1986). In general, there was good agreement of Tatoms theory with the occurrence of downwash.