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91.
The extent to which technical barriers to international trade caused by non-acceptance of chemical measurement results can
be removed, largely depends on the success in building up national and international traceability structures also in metrology
in chemistry. Achieving metrological comparability of measurement results requires the definition of metrological calibration
hierarchies providing metrological traceability chains which enable the establishment of metrological traceability of measured
quantity values to a common metrological reference [1]. For pH, over the last decade, work has been carried out in a number
of countries to build up meteorological calibration hierarchies within a national framework. An overview on the metrological
traceability chain for pH is given with focus on the primary measurement procedure of pH. 相似文献
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Patrick Hergan Julia Beter Steffen Stelzer Ewald Fauster Ralf Schledjewski 《Production Engineering》2018,12(2):185-194
This paper is dealing with the influence of processing parameters for manufacturing of steel–carbon-fiber-reinforced-plastic (CFRP) hybrid plates by using the one-shot-hybrid resin-transfer-moulding (OSH-RTM) process. A design of experiments study was carried out. The quality of the manufactured parts was quantified by the bending modulus, the apparent interlaminar shear strength (ILSS), the maximum deflection and the density of the CFRP. The following changeable processing parameters were chosen: mould temperature, resin temperature, change in mass flow and maximum injection pressure. It is shown that the mould temperature and the change in mass flow show significant impact on the flexural modulus, density and maximum deflection of the plate while there is no significant impact on the apparent ILSS. Furthermore, the interaction between the mould temperature and resin temperature is having an influence on the flexural modulus and density. 相似文献
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Helge Weydahl Magnus S. Thomassen Børre T. Børresen Steffen Møller-Holst 《Journal of Applied Electrochemistry》2010,40(4):809-819
The load-following capability of a proton exchange membrane fuel cell was studied by measuring the cell voltage response to a sinusoidal current load with large amplitude and varying frequency. A mathematical model was developed, incorporating mass transport and capacitive effects as well as the membrane resistance. The model was capable of separating the faradaic and capacitive currents and predicting the observed hysteresis. At frequencies of the sinusoidal current load below 1 Hz, no appreciable hysteresis in the polarisation curve was observed. When increasing the frequency above 1 Hz, a hysteresis appeared at current densities below 0.2 A cm?2. The model related this hysteresis to capacitive effects. When using air as the cathode feed, hysteresis in the current density range 0.5 A cm?2 and higher appeared above 1 Hz compared to 100 Hz for pure oxygen. The model revealed that hysteresis observed in this current density range was caused by oxygen transport limitations. 相似文献
99.
Monodisperse, fine aerosols are needed in many applications: filter testing, experiments for testing models, and aerosol instrument calibration, among others. Usually, monodisperse fine aerosols are generated in very low concentrations, or mass flow rates, in the laboratory scale. In this work, we needed to generate aerosols with higher mass flow rate than typically available by the laboratory-scale methods, such as atomizers, nebulizers, ultrasonic generators, vibrating orifice generators, and condensation generators. Therefore, we constructed a fluidized bed aerosol generator to achieve particle mass flow rates in the range of 15-100 g/h. Monodisperse, spherical SiO2 particles of two sizes with geometrical diameters of 1.0 and 2.6 µm were used in the aerosol generator. The aerosol generator was used at both atmospheric pressure, and at high pressures up to 5 bar (abs).The particle size, mass concentration and the net average particle charge were measured after mixing the aerosol with nitrogen. The particle size distributions with both particle sizes were monodisperse, and no particle agglomerates were entrained from the fluidized bed. The behavior of the fluidized bed generator was found to be markedly different with the two particle sizes in regard to particle concentration, presumably due to different particle charging inside the generator. After determining the net average charge of the particles, an ion source Kr-85 was used to reduce the charge of the particles. This was found to be effective in neutralizing the particles. 相似文献
100.
Oliver Czuprat Steffen Werth Jürgen Caro Thomas Schiestel 《American Institute of Chemical Engineers》2010,56(9):2390-2396
A membrane reactor incorporating a hollow fiber with successive parts of oxygen permeable and passivated surface segments has been developed and was used for the oxidative dehydrogenation (DH) of propane. This membrane geometry allows a controlled oxygen feeding into the reactor over its axial length. In the oxidative DH, the thermodynamic limitation of propane DH can be overcome. By using this novel hollow fiber membrane reactor with a Pt/Sn/K DH catalyst, oxygen separation and propene formation could be established even at temperatures as low as 625°C with long‐term stability. Combining the hollow fiber membrane and the DH catalyst, the highest propene selectivity of 75% was observed at a propane conversion of 26% and 625°C whereas the best propene yield of 36% was obtained at 675°C (48% propene selectivity). The performance of this reactor is evaluated by applying various reaction conditions. © 2010 American Institute of Chemical Engineers AIChE J, 2010 相似文献