1,720,980 research outputs found
An Instrument for the Determination of the Water Fraction in a Stream of Liquid Hydrocarbons also in Presence of Gas
No full textA visualisation technique for quantifying mixing in stirred tank
No full textA technique for quantifying the mixing evolution in a transparent stirred tank is proposed. It consists of capturing on video a colorisation-decolorisation process in a stirred vessel and apply the fundamentals of light absorption imaging technique in combination with image analysis. The advantages of the method developed are that 1) there is no disturbance of the fluid flow, 2) no preliminary calibration is necessary, 3) it allows to quantify the mixing evolution in the whole vessel.
This paper describes protocols for carrying this method out. In addition examples of experimental results obtained for both a standard and a non standard geometrical mixing system are given and discussed. The results indicate that the technique has significant potential to provide insight to study and compare mixing efficiency of different impellers or mixing systems
L'analizzatore elettrodinamico-termogravimetrico: applicazioni allo studio della combustione eterogenea
No full textCharacterization of high heating-rate chars from alternative fuels using an electrodynamic balance
No full textImportant advantages in the use of alternative and renewable fuels (CO2 reduction in the atmosphere, recovery of energy from wastes, limited SO,, NO, and heavy metal emissions) can be obtained only by solving technological and economical problems that make direct combustion of such fuels impractical. This is possible after a detailed investigation to determine the most important features of these materials in all steps of the thermal process. At present, few data can actually be found for the char properties of these fuels. Nevertheless, the knowledge of properties of chars (especially after severe devolatilization) is crucial for both modeling purposes (reactivity, kinetics of combustion and gasification, morphology variations, composition, and fate of pollutant precursors) and practical applications (boiler efficiency, ash deposition, and condensation causing fouling and slagging problems). This work deals with the characterization of chars from different classes of materials (biomasses, waste, and low and high volatile matter (VM) coals) obtained after a devolatilization performed in severe thermal conditions, i.e., high temperature and high heating rate. A methodological approach is developed, applied, and discussed, using an electrodynamic balance that is a versatile analyzer for the study of properties of single levitated particles. The specific heat, size, and shape distribution, and density variation between the char and the parent material are evaluated for all materials. Scanning electron microscopy (SEM) analysis is also carried Out to investigate morphological variations and support the major results obtained with the electrodynamic analyzer. (c) 2004 The Combustion Institute. Published by Elsevier Inc. All rights reserved
Macro-Instabilities in Eccentrically Agitated Vessels
No full textLaser Doppler anemometry and flow visualisation are used to shed light into the main turbulent flow features of an unbaffled vessel stirred by an eccentrically positioned Rushton turbine. Two main vortices, one above and one below the impeller, are present and the former vortex dominates the flow field, driving a strong circumferential flow around it. The vortices are not steady but oscillate slowly and periodically inducing a kind of flow instabilities, which may have a significant impact on macro-mixing. The characteristic frequencies of such flow instabilities were found to increase with reducing the impeller blade thickness, thus it is argued that their origin is related to the interaction between the impeller discharged stream and the vessel wall/bottom
Effect of shaft eccentricity and impeller blade thickness on the vortices features in an unbaffled vessel
No full textDifferent techniques, i.e. laser Doppler anemometry, flow visualisation and decolourisation, were applied in order to gain insight into the main turbulent flow features of an unbaffled vessel stirred by an eccentrically positioned Rushton turbine. Attention was paid to the effect of geometrical parameters such as eccentricity and impeller blade thickness on the flow motion. Two main vortices, one above and one below the impeller, were identified in all configurations. Decolourisation experiments showed that the two vortices behave as segregated regions. The upper vortex dominates the flow field, driving a strong circumferential flow around it. The inclination of such vortex varies with eccentricity. Importantly, the vortex is not steady but oscillates slowly and periodically inducing a kind of flow instabilities, which may have a significant impact on macro-mixing. The characteristic frequency of flow instabilities was found to increase with reducing eccentricity or impeller blade thickness. Moreover, vortex shedding phenomena from the flow-shaft interaction were observed in different configurations. © 2008 The Institution of Chemical Engineers
LDA Measurements in the Vicinity of the Baffles in a Vessel Agitated with a Rushton Turbine
No full text- …
