Drift deposition model

Development and Verification of a Wet Cooling Tower Drift Deposition Model... 

This paper discusses preliminary results of a model which is designed to predict drift deposition drop size distributions and number flux. The influence of evaporation and the drop breakaway process are studied by using both a bulk breakaway criteria and a distributed partial breakaway criteria for each drop size. Comparisons are made at several downwind receptor sites for drop size distribution and number flux. 13 refs, cited. 

The FSCBG aerial spray computer program is the result of more than a decade of refinement and verification of spray dispersion models used by the USDA Forest Service and the U. S. Army for predicting the drift, deposition and canopy penetration of particles and drops downwind from aircraft releases. This paper describes the mathematical framework of the models and selected applications of the models to military and Forest Service projects. 

The FSCBG aerial spray models and computer program are a result of more than a decades effort in the development, refinement and application of models for use by the U. S. Army and USDA Forest Service in predicting drift, deposition and canopy penetration from aerial releases. During the 1960 s, the U. S. 

Several new developments that enhance efforts to minimize drift are described. Models that predict near field effects of aircraft and mesoscale winds are available. The need for additional efforts to describe flow within canopy and description of conditions for inertial deposition on target elements is outlined. 

The principal outputs are deposition and drift, but the models can be programmed to give intermediate information on drop velocity, evaporation, flow fields, and other factors. 

In summary, we now have models that account for all important forces influencing the dispersion and deposit of aerial sprays. We have estimates of inputs to make the models useful to forest managers. Further improvement in model results, particularly drift estimation, depends on better meteorological input. 

Evaporation Module. Evaporation can significantly alter the aerosol size distribution as the spray cloud descends from the aircraft release height to deposit on the ground. The net effect of evaporation, because of reductions in the drop size and thus a decrease in gravitational settling velocity, is to decrease deposition near the source and increase the downwind drift of spray drops or vapor. The FSCBG model has two options that can be used to account for the evaporation of material. 

Experimental proof of control of the mask temperature with the chiller in a Gen 2 OVPD module under process conditions (showerhead heated to 325 °C) was achieved by in situ temperature measurement, as shown in Fig. 9.4. The experiments were performed at atmospheric pressure and at a deposition pressure of 0.9 mbar typical for OVPD, and for chiller temperatures between 5 and 30 °C. The mask temperature can be linearly controlled by the chiller temperature. The observed AT of 6.5 degrees is in good agreement with modeling prediction of 3 degrees in Fig. 9.3. In addition, measurements during a typical OVPD deposition time of 2 to 6 min confirmed there is no temperature drift under process conditions over time. The data prove that heat conductance and radiation is perfectly compensated by the chiller capacity. 

The presence of other plants, such as tree or vine rows, or shelter belts, has a considerable influence on the distance that small spray droplets travel, or in the interception of spray in general. Modelling distribution of spray deposits in such environments is much more complex aud is not yet at a stage that it can be applied to operational situations. The usability to do so will lead to improvements in the deposition of spray within a spray area, as well as within the canopy, and it will be used to define spray drift interception. This could become an important part of spray mitigation management plans, especially relevant to the use in horticulture of relatively hazardous insecticides. 

On the one hand, the cross sections that are derived from swarm data cannot be expected to possess the accuracy and detailed structure of good beam measurements or ab initio calculations, but, on the other hand, they naturally produce (if the procedure is carried out well) cross-section sets that accurately reproduce the macroscopic observables that are relevant to real plasmas. Such quantities are drift velocities or mobilities, which are directly connected with the power deposition in a discharge plasma, diffusion coefficients, and attachment and ionization coefficients, which are intimately related to the ionization balance of a plasma. These are the quantities that are used directly in most plasma models and that are measured in laboratory plasmas. 

The repository geometry is based on the Japanese H12 project (JNC, 2000). Because of repetitive symmetry, the simulations were conducted on a one-quarter symmetric model containing one deposition hole (Figure 2). The upper and lower boundaries are placed at vertical distances of 50 m from the drift floor according to the BMTl definition (Nguyen et al., 2003). 

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