Optimized Backflushing Process for Fibrous Media in Engine Oil Filtration and Enhancement by Ultrasound

Filter media that are made of metal fiber fleece have been qualified as a very suitable method to clean engine oils from fine particles in large diesel application. However, regeneration by backflushing of these densely packed depth filtration media is a great challenge. In experimental studies, the principles of successful hydrodynamic backflushing could be identified. Furthermore, the auxiliary effects of medium‐ and high‐power ultrasound on this process were investigated and could be qualified. Ideal process parameters for the general aim of freeing filter media from clogging particle fractions whilst using minimized amounts of flushing medium can be derived. This generates input parameters for an optimized apparatus design in real‐scale application.     

Synthesis and Bacterial Mutagenicity of Oxidized Derivatives of-Polycyclic Aromatic Hydrocarbons

A series of oxidized derivatives of nitrophenanthrene and nitrobenz[a]anthracene were synthesized and their mutagenicities in Salmonella typhimurium TA98, TA98NR, TA98/1,8-DNP₆, TA100, and TA100NR were determined. These compounds exhibited markedly different mutagenicities. Orientation of the nitro group is an important structural feature for correlation with mutagenic potency.     

Synthesis and Mutagenic Activity of Bay-Region Bridged Chrysenes

The synthesis of a series of substituted bay-region bridged chrysene derivatives is described. The method involves the oxidative photocyclization of stilbene carboxylic acids followed by dehydration with hydrofluoric acid. The photocyclization of stilbene carboxylic acids lead to secondary photolactonizations and functionalization of a bay region carbon by a novel photolytic process. The mutagenic activity of the substituted chrysenes was determined and activity levels correlated with substituent effects.     

A Device for Generating Singly Charged Particles in the 0.1–1.0-μm Diameter Range

In this paper an aerosol charger that largely avoids the production of multiply charged particles in the 0.1–1.0 μm diameter range is described. The input aerosol is first passed through an electrostatic condenser to remove all charged particles and ions. The remaining neutral aerosol then flows into a 23-cm-long, 2.1-cm inner diameter cylindrical tube; the inner surface of this tube is uniformly coated with 0.09 μCi⁶³ Ni, a 0.067 MeV β-emitter with a half-life of 92 years. At typical airflow rates of 0.2–1.0 lpm, this low-activity source of ionizing radiation produces bipolar ion concentrations ranging from 1 × 10⁴ to 9 × 10⁴ ion/cm³, which is much lower than levels required to bring the aerosol to Boltzmann charge equilibrium. At a flow rate of 1.0 lpm, particles smaller than about 1.0 μm typically interact with no more than one ion en route through the charger. Therefore, particles at the charger exit are mostly either neutral or singly charged. Charge distributions of initially-neutral mono-disperse polystyrene latex particles were measured at the exit from the charger for particle diameters ranging in size from 0.09 to 1.09 μm. It was found that, at an airflow rate of 1.0 lpm and particle size 1.09 μm, the ratios of singly, doubly, and triply charged to total positively charged concentrations were 0.75, 0.19, and 0.06 respectively; particles with more than three charges were not detected. In contrast, the analogous charge ratio at Boltzmann equilibrium is 0.28 (+ 1), 0.24 (+ 2), 0.19 (+ 3), 0.13 (+ 4), 0.08 (+ 5), 0.05 (+ 6), and 0.7 (+ 02).     

The History of Condensation Nucleus Counters

Condensation of supersaturated vapors has been used for more than a century to grow small aerosol particles to sizes that can be detected optically. This paper discusses the history of instruments that use condensation to detect particles. I divide this history into two main sections. The first of these focuses on the development of expansion-type instruments including the ''dust counters'' in which John Aitken played the decisive role and ''photoelectric nucleus counters'' primarily by L. W. Pollak and coworkers. The second section deals with the development of steady-flow condensation nucleus counters (CNCs) in which Jean Bricard and coworkers played the decisive role. The importance of calibration methodologies is also pointed out. Refinements by instrumentation manufacturers and many aerosol scientists have led to the reliable, accurate instruments that are widely used today.