Mixing Characteristics of External Loop Airlift Bioreactor using Electrical Resistance Tomography

In the present work, a novel packed bed external loop pneumatically agitated airlift bioreactor with an internal gas distributor (perforated plate) between two rolls of packing in the riser was designed and built. This novel approach combines advantages of packed bed and external loop airlift bioreactors. The main objective of this research work was to characterize the hydrodynamic performance of this novel reactor through a non-intrusive flow visualization technique called electrical resistance tomography (ERT). The tomography images, which were generated using a linear back projection algorithm, were employed to explore the effects of different design parameters and operating conditions. These include the effect of the two packing in the riser and the internal gas distributor (perforated plate) installed between the two packing. Other parameters investigated include the effect of sparger configuration, gas flow rate, and liquid height in the bioreactor on the different hydrodynamic parameters such as gas holdup, mixing time, and liquid circulation velocity. Results showed that the gas holdup and mixing time increased in the presence of the gas distributor, while the riser superficial liquid velocity was decreased. Furthermore, gas holdup and mixing time increased, superficial liquid velocity decreased when decreasing liquid height in the reactor, and when using packing or gas distributor between two packings in the riser. These results can be used to improve mixing characteristics in external loop airlift bioreactors for wider range of applications.

Mixing Characteristics of External Loop Airlift Bioreactor using Electrical Resistance Tomography

In the present work, a novel packed bed external loop pneumatically agitated airlift bioreactor with an internal gas distributor (perforated plate) between two rolls of packing in the riser was designed and built. This novel approach combines advantages of packed bed and external loop airlift bioreactors. The main objective of this research work was to characterize the hydrodynamic performance of this novel reactor through a non-intrusive flow visualization technique called electrical resistance tomography (ERT). The tomography images, which were generated using a linear back projection algorithm, were employed to explore the effects of different design parameters and operating conditions. These include the effect of the two packing in the riser and the internal gas distributor (perforated plate) installed between the two packing. Other parameters investigated include the effect of sparger configuration, gas flow rate, and liquid height in the bioreactor on the different hydrodynamic parameters such as gas holdup, mixing time, and liquid circulation velocity. Results showed that the gas holdup and mixing time increased in the presence of the gas distributor, while the riser superficial liquid velocity was decreased. Furthermore, gas holdup and mixing time increased, superficial liquid velocity decreased when decreasing liquid height in the reactor, and when using packing or gas distributor between two packings in the riser. These results can be used to improve mixing characteristics in external loop airlift bioreactors for wider range of applications.

CFD Modelling of a Hydrogen/Air PEM Fuel Cell with a Serpentine Gas Distributor

Hydrogen-fueled fuel cells are considered one of the key strategies to tackle the achievement of fully-sustainable mobility. The transportation sector is paying significant attention to the development and industrialization of proton exchange membrane fuel cells (PEMFC) to be introduced alongside batteries, reaching the goal of complete de-carbonization. In this paper a multi-phase, multi-component, and non-isothermal 3D-CFD model is presented to simulate the fluid, heat, and charge transport processes developing inside a hydrogen/air PEMFC with a serpentine-type gas distributor. Model results are compared against experimental data in terms of polarization and power density curves, including an improved formulation of exchange current density at the cathode catalyst layer, improving the simulation results’ accuracy in the activation-dominated region. Then, 3D-CFD fields of reactants’ delivery to the active electrochemical surface, reaction rates, temperature distributions, and liquid water formation are analyzed, and critical aspects of the current design are commented, i.e., the inhomogeneous use of the active surface for reactions, limiting the produced current and inducing gradients in thermal and reaction rate distribution. The study shows how a complete multi-dimensional framework for physical and chemical processes of PEMFC can be used to understand limiting processes and to guide future development.

CFD-PBM simulation of hydrodynamics of microbubble column with shear-thinning fluid

A numerical simulation was performed to study the hydrodynamics of micro-bubble swarm in bubble column with polyacrylamide (PAM) aqueous solution by using computational fluid dynamics coupled with population balance models (CFD-PBM). By considering rheological characteristics of fluid, this approach was able to accurately predict the features of bubble swarm, and validated by comparing with the experimental results. The gas holdup, turbulent kinetic energy and liquid velocity of bubble column have been elucidated by considering the influences of superficial gas velocity and gas distributor size respectively. The results show that with the rise of the superficial gas velocity, the gas holdup and its peak width increase significantly. Especially, the curve peak corresponding to high gas velocity tends to drift obviously toward the right side. Except for the occurrence of a smooth holdup peak at the column center under the condition of the moderate distributor size, the gas holdups for the small and large distributor sizes become flat in the radial direction respectively. The distribution of turbulent kinetic energy presents an increasingly asymmetrical feature in the radial direction and also its variation amplitude enhances obviously with the rise of gas velocity. The increase in gas distributor size can enhance markedly turbulent kinetic energy as well as its overall influenced width. At the low and moderate superficial gas velocity, the curves of the liquid velocity in radial direction present the Gaussian distributions, whereas the perfect distribution always is broken in the symmetry for high gas velocity. Both liquid velocities around the bubble column center and the ones near both column walls go up consistently with the gas distributor size, especially near the walls at the large distributor size condition.

Non-Plasma Dry Etcher Design for 200 mm-Diameter Silicon Carbide Wafer

For improving the productivity of the semiconductor silicon carbide power devices, a very large diameter wafer process was studied, particularly for the non-plasma wafer etching using the chlorine trifluoride gas. Taking into account the motion of heavy gas, such as the chlorine trifluoride gas having the large molecular weight, the transport phenomena in the etching reactor were evaluated and designed using the computational fluid dynamics. The simple gas distributor design for a 200-mm-diameter wafer was evaluated in detail in order to uniformly spread the etchant gas over the wide wafer surface.