Fouling in microstructured devices: a review Schoenitz, M; Grundemann, L; Augustin, W ...
Chemical communications (Cambridge, England),
05/2015, Letnik:
51, Številka:
39
Journal Article
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Microstructured devices are widely used for manufacturing products that benefit from process intensification, with pharmaceutical products or specialties of the chemical industry being prime ...examples. These devices are ideally used for processing pure fluids. Where particulate or non-pure flows are involved, processes are treated with utmost caution since related fouling and blocking issues present the greatest barrier to operating microstructured devices effectively. Micro process engineering is a relatively new research field and there is limited understanding of fouling in these dimensions and its underlying processes and phenomena. A comprehensive review on fouling in microstructured devices would be helpful in this regard, but is currently lacking. This paper attempts to review recent developments of fouling in micro dimensions for all fouling categories (crystallization, particulate, chemical reaction, corrosion and biological growth fouling) and the sequential events involved (initiation, transport, attachment, removal and aging). Compared to fouling in macro dimensions, an additional sixth category is suggested: clogging by gas bubbles. Most of the reviewed papers present very specific fouling investigations making it difficult to derive general rules and parameter dependencies, and comparative or critical considerations of the studies were difficult. We therefore used a statistical approach to evaluate the research in the field of fouling in microchannels.
This work reviews efforts in the greatest challenge to operate microsystems: fouling and blocking.
This contribution presents an overview over the use of ammonia as a fuel for internal combustion engines either as pure substance or in combination with ignition promotors. The concept of a ...two-component fuel mixture system consisting of ammonia and an organic solvent for storage of ammonia and as combustion enhancer is developed. Requirements toward a solvent for its use in an ammonia/solvent fuel system in internal combustion engines are summarized. Employing the quantum chemical COSMO-RS theory, a broad variety of hydrocarbons with different functional groups and carbon chain lengths as well as solvents already reported as alternative fuels in the literature are systematically screened. The resulting candidates are rated in a multicriterial approach, accounting for physical properties and phase equilibrium behavior, combustion characteristics, as well as operational properties.
Neuropsychiatric symptoms like mood changes and depression are common in patients with chronic inflammatory disorders such as infections, autoimmune diseases or cancer. The pathogenesis of these ...symptoms is still unclear. Pro-inflammatory stimuli interfere not only with the neural circuits and neurotransmitters of the serotonergic, but also with those of the adrenergic system. The pro-inflammatory cytokine interferon-gamma stimulates the biosynthesis of 5,6,7,8-tetrahydrobiopterin (BH4), which is cofactor for several aromatic amino acid monooxygenases and thus is strongly involved in the biosynthesis of the neurotransmitter serotonin and the catecholamines dopamine, epinephrine (adrenaline) and norepinephrine (noradrenaline). In macrophages, interferon-gamma also triggers the high output of reactive oxygen species, which can destroy the oxidation-labile BH4. Recent data suggest that oxidative loss of BH4 in chronic inflammatory conditions can reduce the biosynthesis of catecholamines, which may relate to disturbed adrenergic neurotransmitter pathways in patients.
The CRESST-II cryogenic dark matter search aims for the detection of WIMPs via elastic scattering off nuclei in CaWO
4
crystals. We present results from a low-threshold analysis of a single upgraded ...detector module. This module efficiently vetoes low energy backgrounds induced by
α
-decays on inner surfaces of the detector. With an exposure of 29.35 kg live days collected in 2013 we set a limit on spin-independent WIMP-nucleon scattering which probes a new region of parameter space for WIMP masses below 3 GeV/c
2
, previously not covered in direct detection searches. A possible excess over background discussed for the previous CRESST-II phase 1 (from 2009 to 2011) is not confirmed.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We present a comprehensive review of keV-scale sterile neutrino Dark Matter, collecting views and insights from all disciplines involved—cosmology, astrophysics, nuclear, and particle physics—in each ...case viewed from both theoretical and experimental/observational perspectives. After reviewing the role of active neutrinos in particle physics, astrophysics, and cosmology, we focus on sterile neutrinos in the context of the Dark Matter puzzle. Here, we first review the physics motivation for sterile neutrino Dark Matter, based on challenges and tensions in purely cold Dark Matter scenarios. We then round out the discussion by critically summarizing all known constraints on sterile neutrino Dark Matter arising from astrophysical observations, laboratory experiments, and theoretical considerations. In this context, we provide a balanced discourse on the possibly positive signal from X-ray observations. Another focus of the paper concerns the construction of particle physics models, aiming to explain how sterile neutrinos of keV-scale masses could arise in concrete settings beyond the Standard Model of elementary particle physics. The paper ends with an extensive review of current and future astrophysical and laboratory searches, highlighting new ideas and their experimental challenges, as well as future perspectives for the discovery of sterile neutrinos.
Single steps in cleaning a fouled heat exchanger surface eventually determine the cleaning kinetic and thus the overall performance of a cleaning process. Up to date the complex mechanisms of the ...mutual supportive processes in cleaning are not yet fully understood. This contribution presents a stepwise approach to investigate the individual process steps starting with the diffusion of the cleaning agent NaOH into a WPI gel, studied at stationary and flow conditions. In the experiments, temperature affected both the diffusion step and the subsequent removal but to different extents. This was further specified and it was found that there is an induction time for the release of disengaged proteins, accounting for the speed of the temperature dependent degrading reactions.
•Distinction of the wetting behavior on the surface of a wiped film evaporator (WFE)•Quantification of single-phase preheating heights and a fully as well as partly wetted heat transfer ...surface•Assessment of evaporation capacities and overall heat transfer coefficients•Determination of minimum concentrate flows to ensure a complete wetting•Recommendations and transferability of the operating window of WFE
An analysis of different operating points during the evaporation of a subcooled feed in a wiped film evaporator (WFE) allows a conceptual segmental assessment, distinction and quantification of various wetting behaviors and heat transfer situations during the liquid film flow. In detail, single-phase heating, evaporation from a fully covered surface and evaporation from a partly covered surface may be distinguished. For each section the wetting situation is extracted. This knowledge is essential for operating wiped film evaporators within a suitable and appropriate range to prevent e.g. product damage. The experiments were conducted at a stainless steel and steam-heated wiped film evaporator with a spring-loaded, inclined comb wiper system and monoethylene glycole as evaporation fluid. Process pressure, wiper type and rotational velocity were kept constant. Variations of feed rate and driving temperature difference mark out the characteristic operating points. In case of sufficient wetting of the evaporation surface, overall heat transfer coefficients of 1800 W/(m²·K) are reached. By decreasing feed rate and assessing the achieved distillate rate minimum sump loads can be derived for a given driving temperature difference. This quantifies the position of film break-up leading to a partly covered heat transfer surface. Active heat transfer areas are extracted from the experimental data and quantified to get a more precise view on suitable process conditions of WFE and its principal operation.
Differentiation of granular bainite and polygonal ferrite in high-strength low-alloy (HSLA) steels possesses a significant challenge, where both nanoindentation and chemical analyses do not achieve ...an adequate phase classification due to the similar mechanical and chemical properties of both constituents. Here, the kernel average misorientation from electron backscatter diffraction (EBSD) was implemented into a Matlab code to differentiate and quantify the microstructural constituents. Correlative electron channeling contrast imaging (ECCI) validated the automated phase classification results and was further employed to investigate the effect of the grain tolerance angle on classification. Moreover, ECCI investigations highlighted that the grain structure of HSLA steels can be subdivided into four grain categories. Each category contained a different nanohardness or substructure size that precluded a nanoindentation-based phase classification. Consequently, the automated EBSD classification approach based on local misorientation achieved a reliable result using a grain tolerance angle of 5°.
Graphical abstract
The CRESST-II cryogenic Dark Matter search, aiming at detection of WIMPs via elastic scattering off nuclei in CaWO
4
crystals, completed 730 kg days of data taking in 2011. We present the data ...collected with eight detector modules, each with a two-channel readout; one for a phonon signal and the other for coincidently produced scintillation light. The former provides a precise measure of the energy deposited by an interaction, and the ratio of scintillation light to deposited energy can be used to discriminate different types of interacting particles and thus to distinguish possible signal events from the dominant backgrounds.
Sixty-seven events are found in the acceptance region where a WIMP signal in the form of low energy nuclear recoils would be expected. We estimate background contributions to this observation from four sources: (1) “leakage” from the
e
/
γ
-band (2) “leakage” from the
α
-particle band (3) neutrons and (4)
206
Pb recoils from
210
Po decay. Using a maximum likelihood analysis, we find, at a statistical significance of more than 4
σ
, that these sources alone are not sufficient to explain the data. The addition of a signal due to scattering of relatively light WIMPs could account for this discrepancy, and we determine the associated WIMP parameters.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
HSLA steels with different polygonal ferrite and granular bainite contents resulting from two different cooling rates were investigated. Micropillar compression tests, electron channeling contrast ...imaging (ECCI) and electron backscatter diffraction (EBSD) experiments were performed to reveal microscopic strength differences and their origin. The obtained results indicate that a higher cooling rate caused a smaller granular bainite substructure size and a higher dislocation density for both ferrite and bainite. In addition, the critical resolved shear stress (CRSS) values for both phases were found to be higher for the faster cooling process. This is ascribed to the increased dislocation density for faster cooling rather than the grain size as will be discussed in the manuscript. Interestingly, the macroscopic yield strength can be closely estimated by the CRSS obtained from micropillar compression considering the corresponding phase fractions. The achieved results can be used in future as input variables for crystal plasticity models.
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