Abstract
A stochastic Direct Simulation Monte Carlo (DSMC) method has been extended for handling bubble-bubble and bubble-wall collisions. Bubbly flows are generally characterized by highly correlated velocities due to presence of the surrounding liquid. The DSMC method has been improved to account for these kind of correlated collisions along with a treatment allowing the method to be used also at relatively high volume fractions. The method is first verified with the deterministic Discrete Particle/Bubble Model (DPM/DBM) using two problem cases: (a) dry granular flow of particles through two impinging nozzles and (b) 3D periodic bubble rise for mono-disperse and poly-disperse systems. The verification parameters are the total number of prevailing collisions within the system, the collision frequencies and the time-averaged liquid velocity profiles (only for the 3D-periodic bubble rise). Subsequently the method is applied to a lab-scale bubble column and validated with the experimental data of Deen et al. (2001). A computational performance comparison with the DBM is reported for the 3D periodic bubble rise case with varying overall gas fractions. The DSMC is approximately two orders of magnitude faster than the deterministic approach for the studied dense bubbly flow cases without adverse effects on the quality of the computational results.
Highlights
Flow is one of the most widely used methods for gasliquid contacting operations in the process industries
The main objective of this work is to develop a computationally inexpensive Euler-Lagrange model that can be used for large scale dense bubbly flows
This work aims to extend the Direct Simulation Monte Carlo (DSMC) approach to alleviate the volume fraction limitation observed by Pawar et al (2014) and improve the DSMC algorithm for particles/bubbles with highly correlated velocities
Summary
Flow is one of the most widely used methods for gasliquid contacting operations in the process industries. Fermentation, Fischer-Tropsch synthesis, waste water treatment and bio-reaction based processes are typically operated in bubble columns. These operations are generally mass transfer limited and to obtain reasonable yields, certain criteria have to be satisfied. These include a high gas-liquid inter-facial area and fast mixing to enhance the reactor performance. Both criteria are met in bubble columns with the additional advantage of no moving mechanical parts.
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