Hubert Monnier

Influence of ultrasound on mixing on the molecular scale for water and viscous liquids.

Micromixing has a decisive action on the yield of fast reactions such as combustions, polymerizations, neutralizations and precipitations. The aim of this study was to test the possible effect of ultrasound on micromixing, through the phenomenon of acoustic cavitation. To evaluate the local state of micromixing, we used a system of parallel competing reactions involving the Dushman reaction between iodide and iodate, coupled with a neutralization. At first, we studied the effects of the acoustic frequency on micromixing (20-540-1000 kHz). It was found that micromixing through acoustic cavitation and acoustic streaming was more important at 20 kHz than at 540 kHz or 1 MHz. At high and low frequency, it was shown that the injection must be located near the ultrasonic emitter. The influence of the acoustic intensity proved to be predominant mostly for low intensities; for an acoustic intensity of 10 W cm(-2), a characteristic micromixing time of about 0.015 s has been obtained. Viscous media have been studied and experiments showed that micromixing is more difficult to achieve than in aqueous media, but that ultrasound may be as effective as classic stirring.

Maintenance of Low-Pressure Carburising Furnaces: A Source of PAH Exposure

Objectives Low-pressure carburising is a new technology used to harden steel; the process has been shown to be a source of considerable polycyclic aromatic hydrocarbons (PAH) pollution. Some PAH are carcinogenic, and activities such as furnace maintenance may thus represent a risk to workers. Occupational exposure during these operations should therefore be assessed. Methods In this study, the PAH-related carcinogenic risk associated with furnace maintenance was assessed by monitoring atmospheric levels of benzo[a]pyrene (BaP), a representative marker, alongside urinary levels of 3-hydroxybenzo[a]pyrene (3-OHBaP), one of its metabolites. PAH exposure levels were monitored during seven sampling campaigns in four different factories specialized in heat-treatment of mechanical workpieces for the automotive and helicopter industries. Two types of furnace were studied, and 37 individuals were monitored. Results Values up to 20-fold the French regulatory value of 150 ng/m3 for atmospheric BaP, and, for urinary 3-OHBaP values up to 40-fold the French biological limit value (BLV) of 0.35 nmol/mol of creatinine were detected. Very high concentrations of BaP, close to or even exceeding those found in coal-tar pitch (up to about 20 g/kg), were measured in residues (tars, dusts) deposited inside the furnace. Even when adequate and suitable personal protective equipment was used, urinary 3-OHBaP values often exceeded the BLV. We hypothesize that this exposure is linked to insidious and fortuitous dermal contamination through contact with factory equipment and staining.