Collection efficiency measurements

Collection Efficiency. Single-Tube Denuders. For the appropriate design of a diffusion-based collection device for an intended application, the ability to estimate the collection efficiency a priori is of considerable help. Although the theoretical soundness of the Gormley-Kennedy equation (equation 1) is not questioned, it is based on the assumption that the uptake probability of the analyte gas at the wall is unity that is, the wall is truly a perfect sink , and every collision results in uptake. This assumption is unrealistic. In recent years, this issue has been reexamined. McMurry and Stolzenburg (42) showed for a liquid-coated denuder how the uptake probability (discussed by the authors in terms of the mass accommodation coefficient ) can be evaluated from collection efficiency measurements. Murphy and Fahey (43) utilized the mathematical solution originally developed for hemodialyzers by Cooney et al. (44) this treatment assumes a constant uptake probability that may be less than unity. To use the Murphy-Fahey approach, however, this probability must be precisely known. 

The determination of kinetic parameters from collection efficiency measurements alone is most suitable when values of the latter lie between 0.1 and 0.8 (5), which corresponds to k values in the range of —0.5-10. Assuming d = 200 nm as the closest distance that is achievable reliably with disk-shaped UMEs of the type used for SECM kinetic measurements, this translates to an upper range for ki values of 1.25 X 104 to 2.5 X 105 s, for a typical D value of 10 5 cm2 s-1. Lower values of k, are, of course, accessible by employing larger d values. 

Therefore, the collection efficiency measures what the percentage of the R produced at the disk electrode can be detected... 

On the average the collection efficiencies, measured using standard EPA method, were approximatly 98.5% for the 300 mm as well as for the 400 mm plate spacings and 97.5% for the 500 mm plate spacing. 

P.R. Unwin. The ECE-DISPl problem—General resolution via double channel electrode collection efficiency measurements. J Electroanal Chem. 297 103 (1991). 

Several manual and continuous analytical techniques are used to measure SO2 in the atmosphere. The manual techniques involve two-stage sample collection and measurement. Samples are collected by bubbling a known volume of gas through a liquid collection medium. Collection efficiency is dependent on the gas-liquid contact time, bubble size, SO2 concentration, and SO2 solubility in the collection medium. The liquid medium contains chemicals which stabilize SO2 in solution by either complexation or oxidation to a more stable form. Field samples must be handled carefully to prevent losses from exposure to high temperatures. Samples are analyzed at a central laboratory by an appropriate method. 

If the gas to be measured contains sulfur dioxide, it has to be scrubbed from the gas before oxidation of the reduced compounds can occur. The gas is scrubbed using an SO2 scrubber. This may contain citrate buffer solution (potassium citrate or sodium citrate). The collection efficiency of the sulfur diox ide may be as high as 99%. 

Decontamination factor A logarithmic scale used to measure the collection efficiency of a particulate collection device. 

As mentioned earlier some measures will be chosen because improvements in these areas were part of the project justification. It is most likely that these will be efficiency measures. Calculation of these measures generally requires analysis of data or specific data collection exercises. There is a relatively high cost associated with preparing these measures so they should be used prudently. In choosing efficiency measures, you should use only those where you have comparative data about the current management systems. For example, if there is no information on the number of hours dedicated to PSM and ESH, don t use this to try to demonstrate the improvement in efficiency. 

For many of the efficiency measures, the relevant data is collected during audits or by analysis of records. It is likely that your company has an internal reporting cycle with which you should coordinate your meas-... 

The primary measure of baghouse-system performance is its ability to consistently remove dust and other particulate matter from the dirty-air stream. Pressure drop and collection efficiency determine the effectiveness of these systems. 

Obviously, experiments designed to measure cross-sections as a function of energy are needed. At present, tandem experiments are not capable of high precision at low energies because one must assume details of collision mechanics and because it is difficult to estimate collection efficiencies in forward scattering geometry (15). The extension of all known techniques to lower energy (64, 65) and the further development of pulse methods (58) offer the possibility for advances in this area. 

Those fixed-angle measurements reported to date have all used either a heated effusive inlet, or heated gas cell for sample admission [55, 56, 61, 62, 65]. Probably the higher sample number densities these sources generate, compared to a supersonic beam source, provides some compensation for the reduced collection efficiency in the fixed-angle measurement. 

Collection efficiency is a measure of the amount of material collected by the sampler relative to the amount of material to which the sampler was exposed. Collection efficiencies for many types of samples can be obtained from literature references. If not available in the literature, collection efficiencies can be obtained by comparing the amount collected by the sampler with the amount collected by samplers with known collection efficiency (e.g., nominal 100% for isokinetic samplers). Alternatively, the collection efficiency can be determined by measuring the amount of material collected in a low-speed wind mnnel or spray chamber relative to the release of a known amount of material. Some samplers have collection efficiencies below 100% (e.g., wide collectors sampling small droplets), while others may exceed 100% if they sweep the air of more material than passes a given location based on sampling area alone (e.g., high-volume air samplers). 

In the past three years, MC-ICPMS has emerged as an alternative to TIMS for precise measurement of the U-series isotopes with comparable or better precision. U-Th isotopes can now be routinely measured at the sub-permil level. Previously, this had only been demonstrated using charge-collection TIMS applied to thorium isotope measurement. Data collection efficiency, sample size requirements, and detection limits can also be greatly improved over TIMS. For the U- U- Th system applied to carbonate samples, this has extended the dating range beyond 600,000 years, and °Th-age uncertainties of 2000 years are now attainable on 300,000 year-old samples (e g., Stirling et al. 2001). 

Our analytical interest now is to know iR as a direct measure of discgenerated red collected at the ring. Again the solution123 of the differential convection-diffusion equation needs a complex mathematical treatment, resulting in an involved equation for the so-called collection efficiency... 

---