Comparative analysis of drop-size measurement in highly dense sprays using shadowgraphy, PDA, and SLIPI

Atomization is a physical phenomenon that is widely encountered in many engineering and industrial applications, such as in combustion engines, spray coating, spray dryers and many more. Spray characterization involves the determination of the droplet size and velocity distributions (both probability density function and spatial). To determine these parameters experimentally, traditionally, microscopic shadowgraphy and Phase Doppler Anemometry (PDA) are used, because of their relative ease of use and high accuracy. However, the application of these techniques is limited to relatively less dense sprays. In highly dense sprays, the strong multiple scattering effects cause significant errors in the determination of relevant parameters. Therefore, the Structured Laser Illumination Planar Imaging (SLIPI) technique is adopted. In this work, comparative measurements are reported to assess the capabilities of these techniques for drop-size measurements in a highly dense spray originating from a pressure swirl nozzle

How fundamental knowledge on mass transfer in bubbly flows will help process intensification

We are in danger of losing our current standards of living due to the depletion of natural resources. It is essential to decrease the amount of waste produced. In reactor engineering, the waste production is caused by the formation of byproducts. To increase the selectivity of the reactor, the fluid dynamics should benefit the intrinsic reaction kinetics, which can only be done when each molecule has exactly the same experience. The mass transfer from a bubble is generally assessed solely by the overall mass transfer coefficient from the bubble. However, the concentration profile is far from uniform when the mass is transferred from the bubble. The obtained concentration profile seems to be confined by the hydrodynamic wake of the bubble. The obtained structures are quite stable and not easily disturbed by other bubbles. This leads to large concentration gradients in the bulk, which prevents the molecules in the liquid to have the same or a similar experience in the reactor. As this will have a large impact on the selectivity when consecutive reactors are considered. It would be essential in the future to study these local mixing profiles in bubbly flows in particular and in multi-phase flows in general

DIRECT NUMERICAL SIMULATION STUDY ON THE FREE LIQUID AREA IN LIQUID-PARTICLE AGGLOMERATES.

Multiphase flows often occur in intensified industrial processes and understanding these complex processes is instrumental in their design and optimisation. In gas-phase polymerisation reactors, the heat management is improved by injecting an inert liquid. However, the injected liquid also affects the collisional behaviour of the produced particles. The liquid can create agglomerates of particles due to cohesive forces, e.g. surface tension. The formation of these agglomerates can have a drastic effect on the efficiency of the process. To determine the lifetimes of the agglomerates, it is important to predict the evaporation rate of the liquid inside such an agglomerate. The evaporation rate of the liquid is dependent on the gas-liquid interface which can be studied using Direct Numerical Simulations (DNS), specifically a combination of a Volume of Fluid method and an Immersed Boundary method. The effect of contact angle and particle configuration on the interface area is studied in this work. This study showed that the random particle configuration has a large impact on the interface area. Due to its random nature, the six investigated configurations are not sufficient to provide a meaningful average area. To determine the interface area, more different random configurations need to be investigated in order to provide a conclusive answer

Front‐tracking simulations of bubbles rising in non‐Newtonian fluids

In the wide and complex field of multiphase flows, bubbly flows with non-Newtonian liquids are encountered in several important applications, such as in polymer solutions or fermentation broths. Despite the widespread application of non-Newtonian liquids, most of the models and closures used in industry are valid for Newtonian fluids only, if not even restricted to air-water systems. However, it is well known that the non-Newtonian rheology significantly influences the liquid and bubble behaviour. CFD represents a great tool to study such complex systems in more detail and gain useful insights on the dynamics of gas-liquid (and possibly solid) systems with the ultimate aim to help the development or the design of industrial reactors. In this study, a DNS Front Tracking (FT) method is applied to study the rise of bubbles in different power-law fluids. Detailed information is obtained regarding the flow of single or multiple bubbles, especially concerning the viscosity profile around single rising bubbles, their shapes and their rising velocity. To describe the bubble rise velocity in less detailed model, a closure for the drag force is needed. With the use of Front Tracking, an existing drag correlation, which was derived for Newtonian fluids, is adapted and improved to non-Newtonian rheologies. When the effect of the viscosity changes are limited, such as for not extreme exponents (0:5 _ n _ 1:5), the correlation can predict reasonably well the drag coefficient for power-law fluids

Progress in Applied CFD. Selected papers from 10th International Conference on Computational Fluid Dynamics in the Oil & Gas, Metallurgical and Process Industries

In the wide and complex field of multiphase flows, bubbly flows with non-Newtonian liquids are encountered in several important applications, such as in polymer solutions or fermentation broths. Despite the widespread application of non-Newtonian liquids, most of the models and closures used in industry are valid for Newtonian fluids only, if not even restricted to air-water systems. However, it is well known that the non-Newtonian rheology significantly influences the liquid and bubble behaviour. CFD represents a great tool to study such complex systems in more detail and gain useful insights on the dynamics of gas-liquid (and possibly solid) systems with the ultimate aim to help the development or the design of industrial reactors. In this study, a DNS Front Tracking (FT) method is applied to study the rise of bubbles in different power-law fluids. Detailed information is obtained regarding the flow of single or multiple bubbles, especially concerning the viscosity profile around single rising bubbles, their shapes and their rising velocity. To describe the bubble rise velocity in less detailed model, a closure for the drag force is needed. With the use of Front Tracking, an existing drag correlation, which was derived for Newtonian fluids, is adapted and improved to non-Newtonian rheologies. When the effect of the viscosity changes are limited, such as for not extreme exponents (0:5 _ n _ 1:5), the correlation can predict reasonably well the drag coefficient for power-law fluids.publishedVersio