Mixing Time Scale Determination in Microchannels Using Reaction Calorimetry

2019 ◽  
Vol 91 (5) ◽  
pp. 622-631 ◽  
Author(s):  
Felix Reichmann ◽  
Kai Vennemann ◽  
Timothy Aljoscha Frede ◽  
Norbert Kockmann
Keyword(s):  
Time Scale ◽  
Mixing Time ◽  
Reaction Calorimetry ◽  
Mixing Time Scale

Mixing Time Scale Measurement With Fast Exothermic Reactions Using Microchannel Reaction Calorimetry

2018 ◽  
Author(s):  
Felix Reichmann ◽  
Yannick Jirmann ◽  
Norbert Kockmann
Keyword(s):  
Heat Flux ◽  
Time Scale ◽  
Mixing Time ◽  
Main Reaction ◽  
Reaction Calorimetry ◽  
Flow Rates ◽  
Exothermic Reactions ◽  
Reaction Progress ◽  
Reaction Calorimeter ◽  
Mixing Time Scale

Continuous reaction calorimetry in microreactors is a powerful technology for the investigation of fast and exothermic reactions regarding thermokinetic data. A Seebeck element based reaction calorimeter has been designed, manufactured, and its performance has been shown in previous works using neutralization reaction in a microreactor made from PVDF-foils [1]. The Seebeck elements allow for spatial and temporal resolution of heat flux profiles across the reactor. Therefore, hot spots and regions of main reaction progress are detected. Finally, heat of reaction has been determined in good agreement with literature data [1]. However, more information can be retrieved related to chemical transformations using the continuously operated reaction calorimeter. In this work, mixing time scale is determined for instantaneous and exothermic reactions. Volumetric flow rate is varied and the region of main reaction progress is shifted within the microreactor. The reaction occurs near the reactor outlet for low flow rates. Here, mixing is dominated by diffusion. However, the reaction and hot spot are shifted towards the reactor inlet for high flow rates as convective mixing regime is reached and secondary flow profile with Dean vortices develop due to curvature of the reaction channel. Finally, mixing time scales can be derived from the location of heat flux peaks. Results display a decrease in mixing time at increased flow rates. Additionally, passive micromixers can be evaluated regarding their efficiency and comparison can be drawn. Moreover, pumps can be characterized and evaluated regarding low-pulsation dosing using the Seebeck element based reaction calorimeter.

MMC-LES of a syngas mixing layer using an anisotropic mixing time scale model

2018 ◽  
Vol 189 ◽  
pp. 311-314 ◽  
Author(s):  
Son Vo ◽  
Andreas Kronenburg ◽  
Oliver T. Stein ◽  
Matthew J. Cleary
Keyword(s):  
Time Scale ◽  
Mixing Time ◽  
Mixing Layer ◽  
Scale Model ◽  
Mixing Time Scale

A model for the mixing time scale of a turbulent reacting scalar

2003 ◽  
Vol 15 (6) ◽  
pp. 1375 ◽  
Author(s):  
Chong M. Cha ◽  
Philippe Trouillet
Keyword(s):  
Time Scale ◽  
Mixing Time ◽  
Mixing Time Scale

scholarly journals Mixing Time Scale Models for Multiple Mapping Conditioning with Two Reference Variables

2020 ◽  
Author(s):  
C. Straub ◽  
A. Kronenburg ◽  
O. T. Stein ◽  
S. Galindo-Lopez ◽  
M. J. Cleary
Keyword(s):  
Time Scale ◽  
Mixing Time ◽  
Scale Models ◽  
Mixing Time Scale

scholarly journals Effect of Vertical Vibration on the Mixing Time of a Passive Scalar in a Sparged Bubble Column Reactor

Fluids ◽  
2020 ◽  
Vol 5 (1) ◽  
pp. 6 ◽  
Author(s):  
Shahrouz Mohagheghian ◽  
Afshin J. Ghajar ◽  
Brian R. Elbing
Keyword(s):  
Void Fraction ◽  
Time Scale ◽  
Temporal Evolution ◽  
Bubble Column ◽  
Mixing Time ◽  
Passive Scalar ◽  
Bubble Column Reactor ◽  
Mean Flow ◽  
Vertical Vibrations ◽  
Mixing Time Scale

The present study used a sparged bubble column to study the mixing of a passive scalar under bubble-induced diffusion. The effect of gas superficial velocity (up to 69 mm/s) and external vertical vibrations (amplitudes up to 10 mm, frequency <23 Hz) on the mixing time scale were investigated. The bubble-induced mixing was characterized by tracking the distribution of a passive scalar within a sparged swarm of bubbles. Void fraction and bubble size distribution were also measured at each test condition. Without vibrations (static), the bubble column operated in the homogenous regime and the mixing time scale was insensitive to void fraction, which is consistent with the literature. In addition, the temporal evolution of the static column mixing was well approximated as an error function. With vertical vibrations at lower amplitudes tested, the bubble-induced mixing was restrained due to the suppression of the liquid velocity agitations in the bubble swarm wake, which decelerates mixing. Conversely, at higher amplitudes tested, vibration enhanced the bubble-induced mixing; this is attributed to bubble clustering and aggregation that produced void fraction gradients, which, in turn, induced a mean flow and accelerated the mixing. The vibration frequency for the range studied in the present work did not produce a significant effect on the mixing time. Analysis of the temporal evolution of the concentration of the passive scalar at a fixed point within the column revealed significant fluctuations with vibration. A dimensionally reasoned correlation is presented that scales the non-dimensional mixing time with the transient buoyancy number.

Numerical and Experimental Investigations into The Effect of Gap Between Baffle and Wall on Mixing in an Oscillatory Baffled Column

2004 ◽  
Vol 2 (1) ◽  
Author(s):  
Xiong-Wei Ni ◽  
Andrew Fitch ◽  
Hongbing Jian
Keyword(s):  
Time Scale ◽  
Mixing Time ◽  
Velocity Ratio ◽  
Reynolds Numbers ◽  
Outer Edge ◽  
Experimental Investigations ◽  
Length Scale ◽  
Experimental Conditions ◽  
Eddy Simulation ◽  
Turbulence Length

We report our numerical and experimental investigation of the effect on mixing of implementing 0, 2, 4 and 6 mm gaps between the outer edge of baffles and the inner diameter of an Oscillatory Baffled Column (OBC). Large eddy simulation and digital particle image velocimetry techniques have been used to obtain the flow patterns and quantify the flow field and turbulence, such as the velocity ratio, integral length scale and mixing time scale versus the oscillatory Reynolds numbers. It is shown that the global mixing intensity and the turbulence length scale decrease, while the Kolmogorov time scale increases with increasing gap size in the range of experimental conditions tested in this work, which suggests a need for new configuration of OBC with baffle gap for certain applications involving particulates.

Preheats Effect on Distributed Reaction Fuel Reforming

2015 ◽  
Author(s):  
Richard Scenna ◽  
Ashwani K. Gupta
Keyword(s):  
Molecular Weight ◽  
Chemical Composition ◽  
Time Scale ◽  
Mixing Time ◽  
Low Molecular Weight ◽  
Fuel Reforming ◽  
Middle Distillate ◽  
Catalytic Reforming ◽  
Reaction Regime ◽  
Low Efficiency

Conventional non-catalytic fuel reforming provides low efficiency, large amounts of char and tar and limited control on chemical composition of the syngas produced. In this paper volume distributed reaction technique is used to enhance reformate quality as compared to conventional reforming that uses non-catalytic reforming. Reforming of middle distillate fuels typically utilize preheats of 300–600°C[1,2]. This work investigates the intermediate regimes between volume distributed reaction regime and conventional flame regime for the reforming of JP8 through the chemical and mixing time scale. The results showed that reformate concentrations of fixed gases and most low molecular weight hydrocarbons changed gradually with air preheats. Reaction regime did not drastically change reformate products except for acetylene. In conventional flame regime acetylene concentration rapidly increased upon on entering the reactor.

Prediction and Validation of Blowout Limits of Co-Flowing Jet Diffusion Flames—Effect of Dilution

1998 ◽  
Vol 120 (2) ◽  
pp. 167-171 ◽  
Author(s):  
M. Karbasi ◽  
I. Wierzba
Keyword(s):  
Carbon Dioxide ◽  
Time Scale ◽  
Diffusion Flames ◽  
Mixing Time ◽  
Stability Limit ◽  
Jet Fuel ◽  
Stream Velocity ◽  
Jet Diffusion Flames ◽  
Air Stream ◽  
Scale Ratio

The blowout limits of a co-flowing turbulent methane jet diffusion flame with addition of diluent in either jet fuel or surrounding air stream is studied both analytically and experimentally. Helium, nitrogen, and carbon dioxide were employed as the diluents. Experiments indicated that an addition of diluents to the jet fuel or surrounding air stream decreased the stability limit of the jet diffusion flames. The strongest effect was observed with carbon dioxide as the diluent followed by nitrogen and then by helium. A model of extinction based on recognized criterion of the mixing time scale to characteristic combustion time scale ratio using experimentally derived correlations is proposed. It is capable of predicting the large reduction of the jet blowout velocity due to a relatively small increase in the co-flow stream velocity along with an increase in the concentration of diluent in either the jet fuel or surrounding air stream. Experiments were carried out to validate the model. The predicted blowout velocities of turbulent jet diffusion flames obtained using this model are in good agreement with the corresponding experimental data.

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