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Liquid entrainment from coalescence filter media—i.e. flow induced “blow-off” of previously deposited oil—in the form of droplets is poorly understood, for one because the generated spectrum is very wide and difficult to characterize with temporal and size resolution, especially for very large drops which carry most of the mass. Such filters operate at much lower flow rates than classical demisters, often in vertical orientation, with much finer geometries, and gravity plays no direct role for entrainment. We present a novel combination of four measurement techniques used to capture the entrained oil drop spectrum from filters during operation in the size range of 0.01–2400 µm. The diameter range below 10 μm combines two established real-time methods including an electrical mobility particle spectrometer (EMPS; <1 μm) and an optical particle counter (OPC; 0.3 to 10 μm). The diameter range above 170 μm is covered by a newly developed “large drop detection system” (LDDS) based on single particle light scattering. OPC and LDDS continuously count and classify all drops originating from the entire filter coupon with a time resolution of 1 min. The EMPS was operated intermittently, following brief switches from aerosol to clear air flow. Drops in the size range between OPC and LDDS were collected and sized by an off-line method. This measuring system was applied to two representative types of glass microfiber media operated with oil mist generated from compressor oil, in order to characterize time resolved drop formation rates and spectra in the range of nanometers to millimeters. Wettable and non-wettable filter media were found to show similar entrainment characteristics, each with multi-modal drop spectra having two pronounced peaks in the ranges of 1–2 μm and 200–300 μm, respectively. During steady-state operation both modes were generated quasi-continually, the large drops at the rate of a few drops per hour and cm 2 of filter surface, the micron size drops 10 3 –10 4 times more frequently. Available indirect evidence suggests the same underlying entrainment mechanism for both types of fibrous media, namely the break-up of air bubbles formed periodically on the oil that drains on the downstream filter face. Direct detachment (blow-off) of large drops is unlikely at the prevailing operating conditions. [ABSTRACT FROM AUTHOR]

The “wet pressure drop” of oil mist filters (i.e. the increase in differential pressure of the air flow due to loading of the filter with liquid) is presented as a function of two mechanisms by which coalesced oil is transported through the filter. These mechanisms operate in separate regions of the filter and make separate (and separately measurable) contributions to the overall wet pressure drop. This new concept, which was first formulated qualitatively in a phenomenological model by Kampa et al. (2014) , leads to semi-quantitative predictions regarding the dependence of pressure drop Δ p and saturation S on filter operating conditions, filter properties and liquid properties. These predictions are first formulated and then validated for a range of wettable and non-wettable filter media in combination with 4 mineral oils of different viscosity. The key findings, summarized below, are consistent with the model and apply to both wettable and non-wettable media. Oil transport across media interfaces (i.e. transitions between regions of different porosity and/or wettability) was associated with a relatively sharp increase in pressure drop ∆ p and oil saturation S over a very thin layer of the filter (a “∆ p jump”). The magnitude of this ∆ p jump was determined by the media properties. It correlated well with the respective static break-through pressures for oil or air, but did not depend on the oil viscosity and loading rate of the filter (at constant air velocity). Oil transport through channel regions of the filter (i.e. the regions connecting interfaces) was associated with a linear increase in ∆ p with channel length and liquid throughput. The corresponding saturation level S was relatively flat throughout the channel region and lower than at an interface. (Both quantities are media dependent, of course.) An increase in oil viscosity μ (at constant oil throughput) led to different responses depending on filter wettability. [ABSTRACT FROM AUTHOR]

Highlights: [•] Two distinct transport mechanisms for coalesced liquid govern the “wet” pressure drop. [•] Transport across capillary interfaces causes Δp jumps associated with film formation. [•] Internal transport occurs via multiple parallel channels with constant Δp/length. [Copyright &y& Elsevier]

Purpose: Low radiation doses and potentially inaccurate recall of the number of past x-ray examinations have hampered designing informative studies of cancer risk associated with medical radiation exposure. We investigated whether cumulative exposure from personal diagnostic x-rays was associated with increased frequencies of chromosome translocations among radiologic technologists because they may recall past radiographic procedures better than the general public. Methods: 150 U. S. radiologic technologists who began working before 1950 were selected for blood collection and telephone interview, including past x-ray examinations. The number of and the examination types were converted to a radiation dose score with units that were an approximation of cGy. For each study subject, the frequencies of translocations were identified by whole chromosome painting. A linear Poisson regression model was used to assess the relationship between radiation dose score and translocation frequency. Results: After adjustment for age, translocation frequencies increased with increasing diagnostic RBM dose score with an estimate of 0.04 translocations per 100 CEs per unit RBM score (95% CI, 0.02 to 0.07; P=0.003). Adjustment for gender, cigarette smoking, occupational radiation dose, allowing practice x-rays while training, work with radioisotopes, and radiotherapy for benign conditions did not materially affect the slope estimate. Conclusions: Cumulative radiation exposure from routine x-ray examinations was associated with increased numbers of chromosome translocations. While the enormous benefit of radiation in disease diagnosis and patient treatment remains unquestioned, potential long-term chromosome damage and other associated health risks argue against excess use or unnecessary repeats of diagnostic x-ray examinations. [Copyright &y& Elsevier]

Purpose: To identify key daily activities in which persons working as radiologic technologists spend the majority of time outdoors. The findings will be used to design improved questionnaires to estimate retrospective UV exposure for future case-control studies of skin cancer and other malignancies to be undertaken within a large cohort of these medical radiation workers. Methods: We evaluated the self-reported activities undertaken during time spent outdoors between 9 AM and 5 PM for 125 individuals (ages 40–59 and 60+ years old) who filled out a 7–day daily activity diary in September 2004. Daily UV measurements were also recorded for each individual. We initially classified activities into 37 groupings of similar activities before determining the 7 activities that accounted for the majority of time spent outdoors. We evaluated differences by age, gender, and geographic location of the individual in addition to whether these activities were carried out on a weekday or weekend day. Results: Of a possible 13,953 daily diary entries, we ascertained that 4697 entries (totaling 1408 hours) were associated with time spent outdoors. The 7 major categories, which accounted for over 93% of the total time spent outdoors, included driving, yard work, home maintenance, walking or doing errands, recreational activities or sports, water activities, and leisure activities or relaxing outside. Differences in time spent outdoors were noted for age, gender, and weekend versus weekday. Conclusion: The results of this analysis, in conjunction with UV measurements, will be useful in developing questionnaires that more accurately estimate UV exposure in relation to cancer risks in future case-control studies. [Copyright &y& Elsevier]