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.

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

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

Seebeck Calorimeter for the Characterization of Highly Exothermic Reactions in a Microreactor Made From PVDF-Foils

2017 ◽  
Author(s):  
Felix Reichmann ◽  
Stefan Millhoff ◽  
Yannick Jirmann ◽  
Norbert Kockmann
Keyword(s):  
Heat Flux ◽  
Reaction Calorimetry ◽  
Acid Base ◽  
Chemical Reactors ◽  
Exothermic Reactions ◽  
Thermoelectric Voltage ◽  
Calibration Methods ◽  
Transfer Measurement ◽  
Color Indicator

Reaction calorimetry is one of the most important steps in designing chemical reactors. This contribution describes a continuously operated micro calorimeter using Seebeck elements for microreactors made of PVDF-foils. Seebeck elements allow for local and temporal resolution of heat flux profiles. Various calibration methods for the Seebeck effect based heat flux sensors are presented. Here, the direct correlation between measured thermoelectric voltage and heat flux is found to be the most promising one. Commissioning of the calorimeter and validation of its performance are done by means of heat transfer measurement of warm water and an acid base reaction. Obtained reaction enthalpy values of the neutralization reaction of acetic acid and sodium hydroxide agree very well with literature data. The progression of the reaction can be followed optically using phenolphthalein as color indicator and can be compared to measured data. Heat profiles over the course of the microreactor were shown and checked for consistency. Consequently, this approach helps to characterize reactors and aids reactor development.

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.

Reaction Calorimetry in Microreactor Environments—Measuring Heat of Reaction by Isothermal Heat Flux Calorimetry

2017 ◽  
Vol 21 (5) ◽  
pp. 763-770 ◽  
Author(s):  
Gabriel Glotz ◽  
Donald J. Knoechel ◽  
Philip Podmore ◽  
Heidrun Gruber-Woelfler ◽  
C. Oliver Kappe
Keyword(s):  
Heat Flux ◽  
Reaction Calorimetry ◽  
Heat Of Reaction

Effects of Taper Configurations on Heat Transfer and Pressure Drop in Single-Phase Flows in Microgaps

2020 ◽  
Author(s):  
Debora C. Moreira ◽  
Gherhardt Ribatski ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Single Phase ◽  
Bubble Nucleation ◽  
Low Flow ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Inlet Section ◽  
Flow Rates

Abstract This paper presents a comparison of heat transfer and pressure drop during single-phase flows inside diverging, converging, and uniform microgaps using distilled water as the working fluid. The microgaps were created on a plain heated copper surface with a polysulfone cover that was either uniform or tapered with an angle of 3.4°. The average gap height was 400 microns and the length and width dimensions were 10 mm × 10 mm, resulting in an average hydraulic diameter of approximately 800 microns for all configurations. Experiments were conducted at atmospheric pressure and the inlet temperature was set to 30 °C. Heat transfer and pressure drop data were acquired for flow rates varying from 57 to 485 ml/min and the surface temperature was monitored not to exceed 90 °C to avoid bubble nucleation, so the heat flux varied from 35 to 153 W/cm2 depending on the flow rate. The uniform configuration resulted in the lowest pressure drop, and the diverging one showed slightly higher pressure drop values than the converging configuration, possibly because the flow is most constrained at the inlet section, where the fluid is colder and presents higher viscosity. In addition, a minor dependence of pressure drop with heat flux was observed due to temperature dependent properties. The best heat transfer performance was obtained with the converging configuration, which was especially significant at low flow rates. This behavior could be explained by an increase in the heat transfer coefficient due to flow acceleration in converging gaps, which compensates the decrease in temperature difference between the fluid and the surface due to fluid heating along the gap. Overall, the comparison between the three configurations shows that converging microgaps have better performance than uniform or diverging ones for single-phase flows, and such effect is more pronounced at lower flow rates, when the fluid experiences higher temperature changes.

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