Diffusion batteries

Batch Percolators The batch tank is not unlike a big nutsche filter it is a large circiilar or rectangiilar tank with a false bottom. The solids to be leached are dumped into the tank to a uniform depth. They are sprayed with solvent until their solute content is reduced to an economic minimum and are then excavated. Countercurrent flow of the solvent through a series of tanks is common, with fresh solvent entering the tank containing most nearly exhausted material. In a typical ore-dressing operation the tanks are 53 by 20 by 5.5 m (175 by 67 by 18 ft) and extract about 8200 Mg (9000 U.S. tons) of ore on a 13-day cycle. Some tanks operate under pressure, to contain volatile solvents or increase the percolation rate. A series of pressure tanks operating with countercurrent solvent flow is called a diffusion battery. 

The problems relating to mass transfer may be elucidated out by two clear-cut yet different methods one using the concept of equilibrium stages, and the other built on diffusional rate processes. The selection of a method depends on the type of device in which the operation is performed. Distillation (and sometimes also liquid extraction) are carried out in equipment such as mixer settler trains, diffusion batteries, or plate towers which contain a series of discrete processing units, and problems in these spheres are usually solved by equilibrium-stage calculation. Gas absorption and other operations which are performed in packed towers and similar devices are usually dealt with utilizing the concept of a diffusional process. All mass transfer calculations, however, involve a knowledge of the equilibrium relationships between phases. 

Knutson, E.O., A.C. George, L. Hinchliffe, and R. Sextro, Single Screen and Screen Diffusion Battery Method for Measuring Radon Progeny Size Distributions, 1-500 nm, presented to the 1985 Annual Meeting of the American Association for Aerosol Research,... 

Particle sizes separated by diffusion batteries. Value of h found to ... 

An aerosol size distribution can, therefore, be described in terms of the count median diameter, d, and the geometric standard deviation, a These parameters were obtained from experimental data using a diffusion battery method (Busigin et al., 1980). A diffusion battery is an assembly of a number of cylindrical or rectangular channels. The relative penetration of aerosols through different sizes of diffusion batteries at specified flow rates allows the aerosol size distribution to be calculated. 

The penetration probability of a particle passing through the diffusion battery is given by (Busigin et al., 1980)... 

F = volume flow rate through a single channel in the diffusion battery (cm3/s)... 

The penetration constants a and b for parallel plate diffusion batteries are ... 

The experimental diffusion battery penetration, g-s, is related to the theoretically calculated penetration probability, Pj C<1) by... 

The activity size distributions were determined from the calculated penetration values in the diffusion batteries using the method outlined for aerosol size measurement (equation (6) for RnWL and equations (8) and (9) for 222Pb concentration). 

The aerosol distributions are calculated in terms of a single mode, without attempting to resolve them into a major large mode and a minor very small (unattached) mode. The unattached mode is very much smaller in diameter (of molecular cluster dimensions) than the major mode of the aerosol and in underground mines its peak height is very small. To resolve such a mode would require more than the three diffusion batteries used for the measurements. 

Each serie of measurements consisted of two parallel samples with counting during and after sampling, one with the screen diffusion battery and the second as the reference sample, so that the fractional free radon daughters could be calculated. The radon daughters are collected on a membrane filter (filter diameter 25 mm, pore diameter 1.2 ym) and the decays of Po-218 and Po-214 are counted by means of alpha spectrometry with a surface barrier detector (area 300 mn ). 

Reineking, A. and J. Porstendorfer, High-volume Screen Diffusion Batteries and the Alpha Spectroscopy for Measurements of the Radon Daughter Activity Size Distributions in the Environment, J. of Aerosol Science 17 (1986) (accepted for publication). 

Approaching from another direction, Sinclair et al (1978) and Knutson et al (1984) report that diffusion battery measurements of radon daughter aerosol-size distributions often show a small peak which could be interpreted as the unattached fraction. Its position would indicate diffusion coefficients from 0.0005 to 0.05 cm /sec. 

In 1975 there was a new development in the use of wire screens Sinclair and Hoopes (1975) described a diffusion battery (for measuring the particle size of aerosols) made of very fine 635-mesh stainless steel screen. An empirical equation was developed for the collection efficiency. This diffusion battery has become one of the standard techniques in aerosol measurements. Later, Sinclair et al (1978) described a screen diffusion battery configuration suited for measuring the activity - weighted size distribution of radon daughter aerosols. 

Three or even four screens (at present we are temporarily limited by the number of counters) cannot determine the exact size of the large-size ("attached") component. Even though there appears to be a small peak at that size in the diffusion battery data (see fig. 4b and 5), it would be premature to speculate that about 20% activity has grown to the size of. 075y. 

Figure 5. The same data as in figure 4b plotted together with the diffusion battery data. Note, the CN counter cannot see any particle below 4.2 nm. According to rough mass balance estimate 1( - 108 small clusters per as could be present.

Cheng, Y.S. and H.C. Yeh, Theory of Screen Type Diffusion Battery,... 

Maher, E.F. and N.M. Laird, E.M. Algorithm Reconstruction of Particle Size Distribution from Diffusion Battery Data, J. Aerosol Sci. 16 557-570 (1985). 

Scheibel, H.G. and J. Porstendorfer, Penetration Measurements for Tube and Screen Type Diffusion Battery in Ultrafine Particle Size Range, J. Aerosol Sci. 15 673-679 (1984). 

Sinclair, D., A.C. George, and E.O. Knutson, Application of Diffusion Batteries to Measurement of Submicron Radioactive Aerosols, in Airborne Radioactivity (D.T. Shaw, ed.) American Nuclear Society, La Grange Park, IL, pp. 103-114 (1978). 

There is very recent evidence that there is an extremely fine mode in the particle activity size distribution. Reineking, Becker and Porstendorfer (1985) used several diffusion batteries to determine a Po-218 activity peak in the 1-3 nm diameter range. 

Particle size distributions of smaller particles have been made using electrical mobility analyzers and diffusion batteries, (9-11) instruments which are not suited to chemical characterization of the aerosol. Nonetheless, these data have made major contributions to our understanding of particle formation mechanisms (1, 1 ). At least two distinct mechanisms make major contributions to the aerosols produced by pulverized coal combustors. The vast majority of the aerosol mass consists of the ash residue which is left after the coal is burned. At the high temperatures in these furnaces, the ash melts and coalesces to form large spherical particles. Their mean diameter is typically in the range 10-20 pm. The smallest particles produced by this process are expected to be the size of the mineral inclusions in the parent coal. Thus, we expect few residual ash particles smaller than a few tenths of a micrometer in diameter (12). 

Raes, F., and A. Reineking, A New Diffusion Battery Design for the Measurement of Sub-20 nm Aerosol Particles The Diffusion Carrousel, Atmos. Environ., 19, 385-388 (1985). 

Three reviews describing applications of diffusion denuders have been published. The doctoral dissertation of Ferm (31) reflects considerable experience with single-tube denuders for the measurement of a variety of species. The review by Ali et al. (32) is extensive it provides an excellent historical and theoretical background and summarizes the literature based on the type of analyte gas determined. The focus of the most recent review, by Cheng (19), is diffusion batteries used for size discrimination of aerosols as well as diffusion denuders. Various physical designs are discussed in some detail in that review. 

If only particles larger than a certain size are of interest, this technique can be inverted by using diffusion to remove fine particles from the airstream and leaving the coarser particles to be collected on a filter. Again, techniques like this, of which the diffusion battery is the best known, also yield a standard filter and, thus, permit the use of standard analytical methods. 

The calculated size distribution of newly attached decay products is shown as curve C in Fig. 1.9. The activity median diameter is 0.16 /zm. With passage of time, the distribution would be shifted to larger particle sizes, as coagulation proceeds. George (1972) used diffusion batteries to measure the size distribution of nuclei carrying radon decay products and found activity median diameters (AMD) averaging 0.18,0.11, and 0.30 /um in a city basement, fifth floor room, and rural outside air, respectively. 

The wood or bark for tannin production is reduced to chips and shreds by passing the material through hoggers or hammer mills. Then it is extracted with warm water in diffusion batteries. The dilute solutions are evaporated to the desired concentration. Loss of solubility of the tannin can be counteracted by treatment of the concentrate with sodium sulfite. 

For the diffusion battery of Prob. 8, determine the maximum particle diameter which can be collected with 50 percent efficiency with a total flow through the unit of 1 L/min. For penetration use Eq. A-l in Fig. 10.4. 

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