Mercury levels measured in urine, hair, and saliva of 245 German children ( 8 -10 years old ) are reported. Mercury concentrations in urine ranged between < 0.1 and 5.3 g / l [ geometric mean ( GM ) 0.26 g / l or 0.25 g / g creatinine; median for both, 0.22 in g / l and g / g, respectively ]. Using multiple linear regression analysis, two predictors have been found accounting for 25.3% of the variance of mercury levels in urine: the number of teeth with amalgam fillings ( 23.2% ) and the number of defective amalgam fillings ( 2.1% ). The mercury content in hair ranged from < 0.06 to 1.7 g / g ( GM 0.18 g / g; median 0.18 g / g ). The frequency of fish consumption, the smoking habits of the parents, and the age of the children accounted for 20.4% of the variance of mercury levels in hair. The correlation between the hair mercury content and urine mercury concentration was low ( r = 0.297 ). Mercury levels in saliva ranged between < 0.32 and 4.5 g / l ( median 0.16 g / l ). The mercury concentration in saliva was below the limit of quantification of 0.32 g / l in more than 70% of the samples. Mercury analysis in urine is suitable to estimate mercury exposure due to amalgam fillings, whereas hair mercury better reflects mercury intake by fish consumption. Up to now, saliva does not seem to be a suitable tool to monitor the mercury burden, at least not at low exposure levels.

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A local loss analysis based on entropy production is presented for the numerical 3D simulation of isothermal centrifugal pump flow. A finite volume method and a statistical turbulence model are employed. Wall functions for direct and turbulent entropy production in isothermal flow are derived, implemented in a node-centered finite volume scheme as a post-processing procedure and validated on an attached channel flow as well as on separated flow in an asymmetric diffuser. The integrity of the entropy wall function is demonstrated by a loss balance for a wide range of boundary layer resolution in terms of non-dimensional wall distance y+ ≈ 1 to ≈ 100. Remaining differences to the total pressure loss are traced back to the particular turbulent wall function for the flow solution within the finite volume solver and vanish towards a wall resolution of the viscous sublayer, i.e. y+ ≈ 1. Local loss analysis together with the new entropy wall function is applied to highly unsteady isothermal flow in a single-blade pump as well as to part load operation of a conventional multi-blade pump which reveals distinctive flow structures that are associated with entropy production. By these examples, it is demonstrated how efficiency characteristics of centrifugal pumps can be attributed to local loss production in particular flow regions.

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A comparative study on the highly unsteady flow field in single- and two-blade pumps is performed. Stationary pump characteristics, as well as pressure and flow rate fluctuations, are presented. Wall pressure fluctuations are measured in the suction and pressure pipe as well as at several locations within the volute casing by piezoresistive transducers. Flow rate fluctuations are evaluated by a recently presented measurement system based on an electromagnetic flow meter [1]. Measurements are accompanied by 3D flow simulations with the open-source CFD software foam-extend. A thorough grid study and validation of the simulation is performed. By a complementary analysis of measurement and simulation results, distinctive differences between both pump types are figured out, e.g.: Flow rate and pressure fluctuation magnitudes are significantly higher in the single-blade pump. In relation to the respective mean values, flow rate fluctuation magnitudes are one order lower than pressure fluctuation magnitudes for both pumps. For the two-blade pump, fluctuations attenuate towards overload irrespective of the particular pump circuit, while they rise for the single-blade pump. 3D simulation results yield detailed insight into the spatially and temporally resolved impeller-volute interaction and reveal that the single-blade impeller pushes a high-pressure flow region forward in a way as a positive displacement pump, resulting in an inherently fluctuating velocity and pressure distribution within the volute.