7 research outputs found
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Application of X-ray micro-computed tomography on high-speed cavitating diesel fuel flows
The flow inside a purpose built enlarged single-orifice nozzle replica is quantified using time-averaged X-ray micro-computed tomography (micro-CT) and high-speed shadowgraphy. Results have been obtained at Reynolds and cavitation numbers similar to those of real-size injectors. Good agreement for the cavitation extent inside the orifice is found between the micro-CT and the corresponding temporal mean 2D cavitation image, as captured by the high-speed camera. However, the internal 3D structure of the developing cavitation cloud reveals a hollow vapour cloud ring formed at the hole entrance and extending only at the lower part of the hole due to the asymmetric flow entry. Moreover, the cavitation volume fraction exhibits a significant gradient along the orifice volume. The cavitation number and the needle valve lift seem to be the most influential operating parameters, while the Reynolds number seems to have only small effect for the range of values tested. Overall, the study demonstrates that use of micro-CT can be a reliable tool for cavitation in nozzle orifices operating under nominal steady-state conditions
Computational Fluid Dynamics of Catalytic Reactors
Today, the challenge in chemical and material synthesis is not only the development of new catalysts and supports to synthesize a desired product, but also the understanding of the interaction of the catalyst with the surrounding flow field. Computational Fluid Dynamics or CFD is the analysis of fluid flow, heat and mass transfer and chemical reactions by means of computer-based numerical simulations. CFD has matured into a powerful tool with a wide range of applications in industry and academia. From a reaction engineering perspective, main advantages are reduction of time and costs for reactor design and optimization, and the ability to study systems where experiments can hardly be performed, e.g., hazardous conditions or beyond normal operation limits. However, the simulation results will always remain a reflection of the uncertainty in the underlying models and physicochemical parameters so that in general a careful experimental validation is required.
This chapter introduces the application of CFD simulations in heterogeneous catalysis. Catalytic reactors can be classified by the geometrical design of the catalyst material (e.g. monoliths, particles, pellets, washcoats). Approaches for modeling and numerical simulation of the various catalyst types are presented. Focus is put on the principal concepts for coupling the physical and chemical processes on different levels of details, and on illustrative applications. Models for surface reaction kinetics and turbulence are described and an overview on available numerical methods and computational tools is provided
The role of kinetics and heat transfer on the performance of an industrial wallâcooled packedâbed reactor: Oxidative dehydrogenation of ethane
Catalysis engineering: From the catalytic material to the catalytic reactor
This chapter deals with the application of chemical reaction engineering and computational fluid dynamics (CFD) for the analysis and assessment of the interactions between mass and heat transport and chemical reactions. In the first part of the Chapter, we review fundamental concepts of chemical reaction engineering, by showing the potential impact of transport phenomena at the macroscale on the observed functionality of the catalytic material. This includes both the effect of the distribution of the residence times in the reactor and the impact of internal and external transport phenomena. In the second part, we illustrate modern approaches to catalytic reaction engineering based on CFD simulations. In particular, we present the algorithms to couple microkinetic models and kinetic Monte Carlo (kMC) simulations with CFD. The potentialities of the method are assessed by means of a showcase of the CFD-based analysis of a spectroscopic cell for operando experiments. This example clearly shows that transport artifacts in standard equipment may lead to an erroneous interpretation of the experiments if not properly accounted for