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

ASME 2017 15th International Conference on Nanochannels, Microchannels, and Minichannels ◽

10.1115/icnmm2017-5539 ◽

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.

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

ASME 2018 16th International Conference on Nanochannels, Microchannels, and Minichannels ◽

10.1115/icnmm2018-7627 ◽

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.

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