Deposition Coefficient Research Articles

Cell model of aerosol collection by fibrous filters in an electrostatic field

The difficulty in collecting fine particles (0.1 to 1 μm range) may require the use of fibrous filters with gas velocity of only a few centimeters per second. Kuwabara's cell model has been quite successful in the determination of the viscous flow field in aerosol filtration by fibrous filters where the Reynolds number is less than one. In this paper, Kuwabara's cell model is extended to the electrostatic filtration in a viscous flow field for both charged and dielectric spherical particles. The particles are assumed to be large enough to allow diffusion to be neglected. The utilized model takes into account the interference effects, namely the influence of neighbouring fibers on the flow field, in a more effective way than the single and three fiber models. A formula relating theoretical filter efficiency to a deposition coefficient is proposed. The filter efficiency obtained using this formula is compared to that given by the single fiber theory.

The effect of neighboring fibers on the electric field in a fibrous filter

The effect of neighboring fibres on the electric field of an electrically enhanced fibrous filter is considered. The electric field around a cylinder, to represent a fiber, surrounded by six other cylinders of equal radius is analyzed using the method of images. It was found that taking account of the neighboring fiber effects on the electrostatic field (ENFE) reduces the cell deposition coefficient and hence the efficiency of the filter. Therefore, the investigations without ENFE overestimate the efficiency of electrostatic fibrous filters. Furthermore, it would appear that the neighboring fiber effect is more important to situations where electrophoresis dominates. However, it is also shown that neighboring fiber effect is less important to the electric field than it is to the flow field.

Circulation of Na, Cl, and Br in the tropical marine atmosphere

Concentrations of Na, Cl, Br, and I in aerosols and Cl, Br, and I in inorganic gases were measured in the marine atmosphere off the west African coast (∼0°N, ∼0°W) in June 1977 and used to estimate their mean lifetimes and rates of production. Mean concentrations (in micrograms per cubic meter) during an 8‐day, stable, rain‐free period of the voyage follows: for paniculate Na 4.0, Cl 5.3, Br 0.017, and 1 0.004; for inorganic gas Cl 1.0, Br 0.012, and 1 0.013. The results of a steady state analysis suggest a ∼3‐day mean residence time for the marine aerosol during the period of our observations, a ∼667 μg m−2 d−1 loss rate of Cl (probably as HCl) from the marine aerosol, and a subsequent ‐day mean residence time in the marine atmosphere. A similar analysis for gaseous inorganic Br gave a μg m−2 d−1 mean loss rate from the marine aerosol and a ∼7‐day mean residence time. Computed dry deposition coefficients were (in centimeters per second) ∼0.4 for the marine aerosol, ∼0.77 for gaseous inorganic Cl, and ∼0.24 for gaseous inorganic Br.

Adjoint Monte Carlo electron transport in the continuous-slowing-down approximation

A model is developed for the Monte Carlo solution of the adjoint transport equation for primary electrons in one dimension. Energy loss is treated in the continuous-slowing-down approximation. The model also employs the condensed-history approximation required in forward Monte Carlo models for transport in extended media. It is tested extensively through numerous calculations of energy deposition and transmission coefficients in aluminum. Predictions are compared with results of the corresponding forward model. Agreement is generally very good. Small discrepancies are attributed to the use of uninterpolated tabular electron cross section data in both forward and adjoint models.

Evaluating Protein Quality by Estimating Energy Deposition Coefficients

Concepts of nutritional energetics were applied in this study to evaluate protein quality. Isonitrogenous purified diets containing lactalbumin, commercially prepared non-defatted corn germ or unheated isolated soybean protein were fed for 3 weeks at different levels of intake to male weanling rats. The metabolizable energy intake (MEI) that main tained total carcass energy (carcass energy maintenance coefficient) and the efficiency with which MEI was utilized to promote an increase in car cass energy (carcass energy deposition coefficient) were determined for each diet. Changes in total carcass energy were partitioned between changes in the energy of carcass fat and carcass lean (fat-free carcass). The MEI that maintained the energy of carcass fat and carcass lean (fat and lean energy maintenance coefficients) were determined. The rates of retention of MEI as fat and as lean as intake of the diet increased (fat and lean energy deposition coefficients) were estimated for each diet. Regardless of diet, there were no significant differences among energy maintenance coefficients for the total carcass, carcass fat, or carcass lean. Energy deposition coefficients for both total carcass and carcass fat were significantly higher for the lactal bumin diet than for the corn germ or soybean diets, with no significant difference between the latter two. The energy deposition coefficient for carcass lean was significantly higher for the lactalbumin diet than for the corn germ diet which in turn was significantly higher than for the soybean diet. The observed differences among the energy deposition coefficients for carcass lean were attributed to differences with which growth of lean tissue was promoted by the three dietary proteins. The advantages of using energy deposition coefficients for evaluating protein quality are discussed. J. Nutr. 108: 1555-1565, 1978.

Long term regional patterns and transfrontier exchanges of airborne sulfur pollution in Europe

This paper reports on progress to date of an ongoing effort to develop, evaluate and apply a European Regional Model of Air Pollution (EURMAP). This model is capable of calculating longterm (monthly, seasonal and/or annual) averages of the contributions from SO 2 in individual emittor countries to SO 2 and SO 4 2− concentrations, dry deposition and wet deposition in receptor countries. The model covers all of western and central Europe, a geographical area 2100 km × 2250 km in size. A trajectory-type approach is used, which involves the tracking of pollutant ‘puffs’ released from each emissions cell in an extensive 32 × 36 grid. Meteorological data in the form of wind and precipitation values from some 45 upper-air and 535 surface stations are input at 6-hourly intervals for use in the calculations of puff transport and wet deposition. A wet deposition coefficient is used that depends upon precipitation rate. The preliminary model has been used to calculate annualized as well as monthly mean maps for January, April, July and October 1973 of SO 2 and SO 4 2− concentration, dry deposition and wet deposition patterns resulting from SO 2 emissions in 13 countries in western and central Europe. The dry and wet deposition patterns are presented, along with values of calculated international exchanges of SO 2 and SO 4 2− wet and dry deposition among these various countries. The EURMAP results are compared with those from Fisher's (1975) model and the LRTAP model (Ottar, 1978; OECD, 1977). In many (but not all) respects the results from the three models are similar. The possible reasons for the differences revealed by this comparison are examined.

Methods of Shield Analysis for Protection against Electrons in Space

It is anticipated that many future manned space operations will be radiation limited and that laminated wall structures and the use of new materials will be required to reduce radiation exposure. Methods for electron shield analysis are reviewed in light of anticipated needs in the space program. The most general method is still the Monte Carlo method, which is of limited usefulness for shield analysis due to excessive computer requirements. Methods based on energy deposition coefficients or energy transmission and reflection factors are quite accurate, but are currently limited to aluminum shield material. Analytical methods based on Mar's approximation for the electron transmission factor are relatively general and computer efficient but seriously underestimate shield requirements. A correction to methods using Mar's approximate transmission factor is derived herein and results in a slightly conservative estimate of shield requirements. Techniques for laminated shield design are still lacking.

Measurements of the deposition coefficient for ice, and its application to cirrus seeding

AbstractTwo techniques have been used to measure the deposition coefficient β for water vapour molecules onto ice formed from distilled water, from 0·01M HCl and from 0·1M HCl. One involved measurement of the evaporation rates of ice spheres at laboratory pressure. the other involved measurement of the equilibrium temperature achieved by a shell of ice surrounding a resistor within which electrical power was being dissipated at a known rate; this experiment was conducted at low pressures (< 10−2torr). Measurements of β were made over the temperature range −37 to −9°C.It was found that for pure ice β increased from 10−3 at −37°C to 5 × 10−3 at −9°C. Similar temperature dependency was found for the ice specimens formed from HCl solutions, but the values of β were lower at all temperatures. This reduction was greater for the more contaminated ice.The measured values of β were employed in calculations of the distance which cirrus crystals will fall through undersaturated air below cloud base. Various humidity structures and temperature distributions were considered. For a particularly well‐documented case it was calculated that crystals of dimensions 80 and 300 μm will survive a fall of about 0·5 and 2·3 km respectively; these predictions are consistent with observation. These two values of survival depth are greater than the Maxwellian values (β = 1) by factors of about 3 and 1·2, respectively. It is concluded that in most situations the persistence of a stream of cirrus crystals is not profoundly affected by these new values of β but that in conditions conducive to the formation of middle‐level cloud the survival depths may be substantially increased.

Measurements of the deposition coefficient for ice, and its application to cirrus seeding

Measurements of the deposition coefficient for ice, and its application to cirrus seeding

Utilization of Energy for Maintenance and for Fat and Lean Gains by Mice Selected for Rapid Postweaning Growth Rate

The metabolizable energy intake (MEI) required for maintenance and the efficiency of utilization of metabolizable energy available for gain (MEA) were determined for a line of mice (rapid growth) selected for 41 generations for rapid postweaning weight gain and for a contemporarily mated line (control) that had been randomly selected. Feed intake of individually housed rapid growth and control males was restricted above maintenance or was ad libitum from 21 to 42 days of age. Regressions of change in body energy per unity metabolic body size on MEI per unit metablic body size showed that the maintenance requirement for each line of mice was 176 kcal per unit metabolic body size per day and that the rapid growth line was more efficient than the control line in utilizing MEA (50% vs. 23%) to promote an increase in body energy. Although the proportions of MEA used for fat (PF) and lean (PL) gains and the net efficiencies with which those proportions were utilized for fat (NF) and lean (NL) gains were unknown, the products of proportion and efficiency for fat gain (PF X NF or fat energy deposition coefficient) and for lean gain (PL X NL or lean energy deposition coefficient) were determined. The results demonstrate that 41 generations of selection for rapid postweaning weight gain did not change the lean energy deposition coefficient, but did alter the fat energy deposition coefficient. These data suggest that the two lines of mice use different proportions of MEA for fat gain and/or utilize MEA for fat gain at different efficiencies.

Effect of Flow Rate on Fission-Product Deposition from high-temperature Gas Streams

Abstract The deposition behavior of solid fission products has been studied. Experiments were made in an in-pile helium loop for gas flow with Reynolds number ranging from 1,300 to 13,000 at a gas temperature of about 500°C. The distributions of the fission products deposited along stainless steel tubes which had been exposed to the flow were obtained from γ-ray spectra measured with a Ge(Li) detector. The nuclides of the deposited fission products can be classified into three groups according to the distribution patterns: (a) 96Zr-Nb, 97Zr, 99Mo, 103103Ru, 132Te, (b) 91Sr, 140Ba-La, 141Ce and (c) 131 and 133I. Cesium-137 shows features of both groups (b) and (c). The deposition coefficients were obtained for the nuclides of group (a), which gave exponentially decreasing distributions. The effect of the flow rate (Reynolds number) on the deposition coefficients is discussed. For a stream with Reynolds number below 13,000, the deposition rate of metallic fission products is largely determined by the mass transfer in the boundary layer of the stream rather than by the adsorption on the surface.

Effect of Flow Rate on Fission-Product Deposition from High-Temperature Gas Streams

Abstract The deposition behavior of solid fission products has been studied. Experiments were made in an in-pile helium loop for gas flow with Reynolds number ranging from 1,300 to 13,000 at a gas temperature of about 500°C. The distributions of the fission products deposited along stainless steel tubes which had been exposed to the flow were obtained from γ-ray spectra measured with a Ge(Li) detector. The nuclides of the deposited fission products can be classified into three groups according to the distribution patterns: (a) 96Zr-Nb, 97Zr, 99Mo, 103103Ru, 132Te, (b) 91Sr, 140Ba-La, 141Ce and (c) 131 and 133I. Cesium-137 shows features of both groups (b) and (c). The deposition coefficients were obtained for the nuclides of group (a), which gave exponentially decreasing distributions. The effect of the flow rate (Reynolds number) on the deposition coefficients is discussed. For a stream with Reynolds number below 13,000, the deposition rate of metallic fission products is largely determined by the mass t...

Collection of aerosol particles by fabric filters in an electrostatic field

The deposition of uncharged aerosols on charged fibers perpendicular to the air stream in a homogeneous electrical field is analytically investigated. The simple theoretical model of a filter studied in this work consists of evenly arranged layers of equidistant parallel cylinders of infinite length normal to the flow direction. The critical trajectories of the particles are calculated by numerically solving the differential equation for the particle trajectories. The calculated values of the deposition coefficient are compared with the results of previous investigations. The influence of various dimensionless parameters on deposition is discussed.

The Transport of Radioactive Corrosion Products in High-Temperature Water—I. Recirculating loop Experiments

A stainless-steel loop containing recirculating, pressurized water at 300°C and neutral pH has been used to investigate the processes by which surfaces in nuclear reactor coolant circuits can become contaminated by radioactive corrosion products. By measuring deposition rates of activity onto metals (usually stainless steel) under different conditions and by examining exposed surfaces, it was deduced that the corrosion of the test surface controls the activation. Hence, the traditional phenomenological method of describing activation by first-order deposition and release coefficients is an oversimplification.

Methods for calculating radiation-induced heat generation

The heat production rate at any point in a medium due to a neutron or gamma-ray field existing at that point can generally be simply related to the follwing quantities: the flux density energy spectrum at that point; the number density of various atomic constituents at that point; the energy-dependent atomic (microscopic) cross-sections for the various interactions possible between radiation types and nuclear species; and the kinetic energy of the resulting charged particle emissions, which are assumed to be locally transformed into thermal energy. The determination of each of these quantities is discussed. Precise knowledge of the radiation field flux density and its energy spectrum as a function of position in most practical cases requires a rather sophisticated use of one or more of the various methods of radiation transport calculation known. A brief review of these techniques and their capabilities are made herein. Fortunately, there are approximation formulas which are adequate for engineering purposes in many cases. Such formulas are largely based on use of the “point kernel” approach, which is strictly valid only for infinite homogeneous media; however, these are usually adequate, especially for gamma rays, which are in general of greater significance than neutrons in reactor shield heating. For gamma rays, as is well known, it is the custom to combine much of the information on atomic constituents of the medium, cross-sections for the various energy-depositing interactions, and energy of the resulting charged particles (electrons) into a coefficient which we call the “energy deposition coefficient.” This presentation also makes a particularly detailed review of this concept. It reviews the fundamental basis of energy deposition coefficients and indicates how one might best choose the correct values to use for it. Comparisons of predicted and measured heat production functions are able to be found in the literature and are briefly summarized. Discrepancies found indicate the degree of accuracy generally available with today's techniques.

Transfer of Fallout Strontium-90 to Cows’ Milk

From 1962 through 1966, the monthly 90Sr fallout rate, the accumulated deposit, and the concomitant 90Sr levels in animal forage and milk were measured in samples collected at the Colorado State University dairy farm in Fort Collins. During the growing period, 42% of the total 90Sr deposit was retained on alfalfa hay at the first cutting, 29% at the second cutting, and 23% at the third cutting. The difference between the first cutting and the two following was significant. These deposition coefficients combined with values for the area of forage utilized by the animal can be used to predict the contamination level of alfalfa hay from the measured total deposit.The total intake of 90Sr and the amount secreted in milk were measured in several groups of dairy cows. The transfer coefficients of 90Sr from diet to milk ranged from 0.05–0.09% per liter of milk per day and were in agreement with tracer and field experiments reported by other investigators. By using the appropriate deposition coefficient, forage yield, forage intake, and diet to milk transfer coefficient, the amount of 90Sr in milk was calculated from the measured total 90Sr deposit over the growing period. The calculated 90Sr in milk levels agreed reasonably well with measured values. For example, during the 1963 growing season—a period of relatively high fallout rate–the calculated amount of 90Sr in milk was 18 pCi per liter based on a measured deposit of 2.66 nCi 90Sr per m2 Milk samples collected during the same period and analyzed for 90Sr showed 20 pCi per liter.

Deposition of aerosol flowing past a cylindrical fiber in a uniform electric field

The deposition of aerosol particles from an air stream of velocity V 0 upon a circular cylindrical fiber perpendicular to the stream in a homogeneous electrical field E 0, has been investigated theoretically. The dielectric constant ϵ c of the fiber controls by means of the parameter a = (ϵ c − 1) (ϵ c + 1) the additive inhomogeneous field of the fiber, which effectuates the deposition of the particles. When computing the trajectories, both inertia and image forces for charged particles have been neglected. The computations have been made for frictionless potential flow and for viscous flow according to Lamb. For uncharged particles, the dimensionless parameter F ∼ r 8 3 E 0 2 B/ r c V 0 (where r s , B = radius and mobility of the particle; r c = radius of the fiber) determines the value of the deposition coefficient. Exact solutions for the limiting case a = 0 as well as some approximate solutions for a ≠ 0, obtained by the Runge-Kutta method, are given. For particles carrying an electrical charge q, the dimensionless parameter G = E 0 qB/ V 0 is decisive. From the exact solutions the deposition coefficient is given by ζ = G(a + 1) (G + 1) , if G > 0 , for ideal and viscous flow. With negative G, the fiber may be surrounded by a “dust-free space.”

Investigation of the transfer of radioactive substances by steam and water and of the chemical stability of deposits in the steam-water loop of the first nuclear power station

An important problem in the construction of boiling water reactors, or reactors with boiling water and superheated steam in the process channels, is the investigation of the contamination by radioactive substances of the steam generated and directed into the turbine, the physical and chemical properties of the radioactive deposits and the possibility of decontamination of the internal surfaces of the piping and the turbine. At the First Nuclear Power Station, investigations have been made into the processes of transfer of radioactive substances by the steam and water in a loop installed in the first circuit of the power station. The coefficient of deposition of substances on the internal surface of piping is determined, and the chemical stability of the deposits is examined. Problems of decontamination of some parts of the steam power equipment of the station are investigated.

Dispersion and deposition of airborne Lycopodium and Ganoderma spores

SUMMARYSpores were liberated at 0.25 and 1.0m. above grass. Airborne concentrations at twenty or more points in the spore cloud were measured with specially designed and calibrated miniature suction traps, operated off a portable vacuum system. Deposition in the downwind direction was measured on artificial surfaces on the ground. Measurements were made up to 10 m. from the source.The observed increase in horizontal cross‐wind standard deviation of the Lycopodium cloud agreed well with O. G. Sutton's theory, but was incompatible with that of W. Schmidt.The coefficient of deposition, p, calculated from mean cloud concentration per c.c. and deposition to ground per cm.2, as well as the velocity of deposition, vg, varied with distance from source. Both p and vg were larger for Lycopodium than for Ganoderma, and at the greater distances tested, vg approximated to the expected terminal velocities of the particles in still air.The total number (Q0) of Lycopodium spores liberated in each experiment was known, and tentative estimates of the proportion deposited within the sampling area indicated that, under day‐time winter conditions in England, the cloud lost not less than 13 to 24% of its load within 10 m. of the source.

The dispersion of air-borne spores

Summary The deposition of air plankton, such as passively air-borne pollen grains or fungus spores, decreases with increasing distance from a source. The factors controlling the scattering of air plankton are reviewed, and observed gradients of deposition are discussed with special reference to fungi causing diseases of plants. The terminal velocities of spores are shown to depend on their dimensions and to be roughly of the order expected for smooth, spherical particles from Stokes's law, but fairly wide deviations between observed and expected values are believed due to surface roughness and asymmetry. Fungus spores have been observed to fall with velocities between 0·04 and 2·5 cm.sec., and pollen grains between 1·5 and 40 cm.sec. The mean wind velocity at 10 m. is near 300 cm.sec. Attempts to calculate the dispersal of spores as the resultant of vertical fall under gravity and horizontal wind movement are shown to apply only to non-turbulent air movement, and therefore to be inapplicable at heights more than a few millimetres above the earth's surface. Differences in rate of spore fall are probably not major factors in dispersal. It is more appropriate to consider a spore cloud in suspension in the air in process of being diluted by eddies in the course of its transport by the wind. In support of the concept of the spore cloud as a suspension it is shown that at heights in the atmosphere above the surface layers, the concentrations of pollen and spores decreases exponentially with increasing height in the manner that would be expected if particles falling under gravity were balanced by other particles diffused upwards by eddies. The values for eddy diffusivity, K , varying from 1·5 × 10 4 to 3·3 × 10 5 , deduced for spores and pollen, are of the order usually found in meteorological work. While terminal velocity may play only a small part in spore dispersal, it may be more important in causing deposition of spores brought down by eddies to the boundary layer of relatively still air a few centimetres thick at the earth's surface. The earlier theories of eddy diffusion, including that of Schmidt, are compared with recent work by Sutton who considered that the size of eddies effective in diluting a cloud, instead of remaining constant, increases with the distance travelled by the cloud. Experiments by Stepanov, in which spores were liberated from a point in the open air and trapped at various distances and in different directions, are shown to be in excellent agreement with Sutton's theory, and to lead to almost identical values for the parameters for diffusion and turbulence with those found by Sutton. Based on Sutton's theory, equations are given for the deposition of spores at various distances from a point source, and from Stepanov's data it is concluded that in travelling across i sq.cm. of surface there were deposited the equivalent of the number of spores present in a layer on the axis of the cloud about half a millimetre thick. This value is expressed as a coefficient of deposition, p , and it is regarded as a parameter of considerable biological significance. The relevance of the deposition formula is discussed. Observed gradients of air-borne plant infections originating from a point source are shown to be closely predicted by this theory. Fungi known or suspected of being splash-dispersed on the contrary show gradients incompatible with the theory. Gradients from strip sources cannot be dealt with satisfactorily at present, but an approximate formula is given, and observed gradients from strip sources are found to show reasonable agreement. The significance for plant hygiene of this interpretation of fungus spore dispersal is that, while attention should be paid to isolation, most emphasis should be placed on eliminating foci of disease within a crop.