Axial dispersion and mixing of coolant gas within a separate-effect prismatic modular reactor

Multiphase Reactors Engineering and Applications Laboratory performed gas phase dispersion experiments in a separate-effect cold-flow experimental setup for coolant flow within heated channels of the prismatic modular reactor under accident scenario using gaseous tracer technique. The separate-effect experimental setup was designed on light of local velocity measurements obtained by using hot wire anemometry. The measurements consist of pulse-response of gas tracer that is flowing through the mimicked riser channel using air as a carrier. The dispersion of the gas phase within the separate-effect riser channel was described using one-dimensional axial dispersion model. The axial dispersion coefficient and Peclet number of the coolant gas phase and their residence time distribution within were measured. Effect of heating intensities in terms of heat fluxes on the coolant gas dispersion along riser channels were mimicked in the current study by a certain range of volumetric air flow rate ranging from 0.0015 to 0.0034 m3/s which corresponding to heating intensity range from 200 to 1400 W/m2. Results confirm a reduction in the response curve spreads is achieved by increasing the volumetric air velocity (representing heating intensity). Also, the results reveal a reduction in values of axial dispersion coefficient with increasing the air volumetric flow rate.

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Axial Dispersion in a Three-Phase Gas-Agitated Spray Extraction Column

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19980283 ◽

1998 ◽

Vol 63 (2) ◽

pp. 283-292 ◽

Cited By ~ 2

Author(s):

Milan Sovilj

Keyword(s):

Gas Phase ◽

Dispersion Coefficient ◽

Continuous Phase ◽

Axial Dispersion ◽

Superficial Velocity ◽

Extraction Column ◽

Dispersed Phase ◽

Dispersion Coefficients ◽

Axial Dispersion Coefficient ◽

Three Phase

The continuous-phase axial dispersion coefficients of the three-phase gas-liquid-liquid system in a gas-agitated spray extraction column 10 cm i.d. at 20 °C were examined. The system used was water as continuous phase, toluene as dispersed phase, and air as gaseous phase. The rise in the gas phase superficial velocity increased the continuous-phase axial dispersion coefficient. A non-linear dependence between the continuous-phase axial dispersion coefficient and the continuous phase superficial velocity was observed. No correlation was found between the continuous-phase axial dispersion coefficient and dispersed phase superficial velocity. The increase in the gas phase hold-up corresponded to a slight increase in the continuous-phase axial dispersion coefficient. The increase in the dispersed phase hold-up generated a growth of the continuous-phase axial dispersion coefficient. A comparison was made of the continuous-phase axial dispersion coefficients of the three-phase (air-water-toluene) and two-phase (water-toluene) systems.

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Axial dispersion in respiratory bronchioles and alveolar ducts

Journal of Applied Physiology ◽

10.1152/jappl.1988.64.6.2614 ◽

1988 ◽

Vol 64 (6) ◽

pp. 2614-2621 ◽

Cited By ~ 31

Author(s):

W. J. Federspiel ◽

J. J. Fredberg

Keyword(s):

Flow Rate ◽

Molecular Diffusion ◽

Stokes Equations ◽

Type Equation ◽

Axial Dispersion ◽

Alveolar Volume ◽

Diffusion Type ◽

Gas Dispersion ◽

Axial Dispersion Coefficient ◽

Pulmonary Acinus

The mixing of gases in the pulmonary acinus was characterized by analyzing axial gas dispersion during steady flow in models of respiratory bronchioles and alveolar ducts. An analysis (method of moments) developed for addressing dispersion in porous media was used to derive an integral expression for the axial dispersion coefficient (D*). Evaluation of D* required solving the Navier-Stokes equations for the flow field and a convection-diffusion type equation arising from the analysis. D* was strongly dependent on alveolar volume per central duct volume, the aperture size through which the alveoli communicate with the central duct, and the Peclet number (Pe). At smaller Pe (flow rate) D* was substantially smaller than the molecular diffusion coefficient, whereas at larger Pe (flow rate) D* was much greater than the Taylor-Aris result for flow-enhanced dispersion in straight tubes. Also, flow-enhanced dispersion became appreciable at smaller Pe than indicated by the Taylor-Aris result. These behaviors transcend both the lower and upper limits established previously for gas mixing in the pulmonary acinus.

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The Hydrodynamics and Mixing Performance in a Moving Baffle Oscillatory Baffled Reactor through Computational Fluid Dynamics (CFD)

Processes ◽

10.3390/pr8101236 ◽

2020 ◽

Vol 8 (10) ◽

pp. 1236

Author(s):

Hamid Mortazavi ◽

Leila Pakzad

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Dispersion Coefficient ◽

Velocity Ratio ◽

Axial Dispersion ◽

Shear Strain Rate ◽

Turbulent Length Scale ◽

Mixing Performance ◽

Axial Dispersion Coefficient ◽

Computational Fluid Dynamics Cfd

Oscillatory baffled reactors (OBRs) have attracted much attention from researchers and industries alike due to their proven advantages in mixing, scale-up, and cost-effectiveness over conventional stirred tank reactors (STRs). This study quantitatively investigated how different mixing indices describe the mixing performance of a moving baffle OBR using computational fluid dynamics (CFD). In addition, the hydrodynamic behavior of the reactor was studied, considering parameters such as the Q-criterion, shear strain rate, and velocity vector. A modification of the Q-criterion showed advantages over the original Q-criterion in determination of the vortices’ locations. The dynamic mesh tool was utilized to simulate the moving baffles through ANSYS/Fluent. The mixing indices studied were the velocity ratio, turbulent length scale, turbulent time scale, mixing time, and axial dispersion coefficient. We found that the oscillation amplitude had the most significant impact on these indices. In contrast, the oscillatory Reynolds number did not necessarily describe the mixing intensity of a system. Of the tested indices, the axial dispersion coefficient showed advantages over the other indices for quantifying the mixing performance of a moving baffle OBR.

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New regimes of dispersion in microfluidics as mediated by travelling temperature waves

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2019.0382 ◽

2019 ◽

Vol 475 (2230) ◽

pp. 20190382 ◽

Cited By ~ 1

Author(s):

Debashis Pal ◽

Suman Chakraborty

Keyword(s):

Dispersion Coefficient ◽

Dna Amplification ◽

Temperature Wave ◽

Axial Dispersion ◽

Stable Regime ◽

Axial Dispersion Coefficient ◽

Time Period ◽

Fluidic Devices ◽

Periodic Temperature ◽

Short Time

We unveil new regimes of dispersion in miniaturized fluidic devices, by considering fluid flow triggered by a travelling temperature wave. When a temperature wave travels along a channel wall, it alters the density and viscosity of the adjacent fluid periodically. Successive expansion–contraction of the fluid volume through a spatio-temporally evolving viscosity field generates a net fluidic current. Based on the temporal evolution of the axial dispersion coefficient, new regimes of dispersion—such as a short-time ‘oscillating regime’ and a large-time ‘stable regime’—have been identified, which are absent in traditionally addressed flows through miniaturized fluidic devices. Our analysis reveals that the oscillation of axial dispersion persists until the variance of species concentration becomes equal to half of the square of the wavelength of the thermal wave. The time period of oscillation in the dispersion coefficient turns out to be a unique function of the thermal wavelength and net flow velocity induced by thermoviscous pumping. The results of this study are likely to contribute towards the improvement of microscale systems that are subjected to periodic temperature variations, including microreactors and DNA amplification devices.

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