Mixing Time Scale Determination in Microchannels Using Reaction Calorimetry

Abstract

Mixing time scales are derived from heat flux profiles for an instantaneous and exothermic reaction in a commercially available microreactor. A continuous reaction calorimeter, based on numerous heat flux sensors, is used to record spatially resolved heat flux profiles in steady state. Total volumetric flow rate is varied at constant flow rate ratio and the region of main reaction progress is shifted within the microreactor according to the advancement of the mixing process. Secondary flow patterns, induced by Dean mixing elements within the microchannel at higher flow rates, enhance the mixing. Results display a decrease in mixing time at increased flow rates and energy dissipation rate. Additionally, the passive micromixer is evaluated regarding its efficiency.

Characterization of reaction enthalpy and kinetics in a microscale flow platform

“…In calorimetry, early implementations include channels with integrated thin film thermopiles [10][11][12] and microstructured devices coupled with commercially available calorimeters. 13,14 Since then various techniques have been utilized to measure heat released in microchannels: heat flux measurement utilizing thermoelectric effect, [10][11][12][15][16][17][18][19][20][21][22] energy balance based on temperature measurements with thermocouples 23 or infrared cameras, [24][25][26] or a combination of several techniques. 27 Depending on the applied method, reaction conversion is measured either directly in the microreactor by colorimetry, 20,21,24 estimated from the heat released at varied flow rates, 15,[17][18][19][20]26 or by analysing samples off-line.…”

“…18 Similar approach was used by Reichmann et al to evaluate the extent of mixing. 20,21 Zhang et al realized spatially resolved calorimetric measurements using an infrared camera and stainless steel tubing as a microreactor. 25,26 By adjusting flow rates to obtain full or partial conversion, both reaction enthalpy as well as kinetics were measured within the same device at the fraction of time normally needed in conventional equipment.…”

Software-guided microscale flow calorimeter for efficient acquisition of thermokinetic data

“…The calorimeter's setup and its peripheral equipment have been described in previous works of Reichmann et al [14,15]. A central programmable logic controller (PLC) (LabManager ® , HiTec Zang GmbH, Germany) has been added to the experimental setup to automate the execution of calibration and experiments.…”

“…1. Compared to the setup in [15], only four Peltier elements are used here, whose projection area is about 4.5 times larger than the previously used ones. The microreactor is made of glass and features a Y-mixer to contact the incoming fluids and 19 chicane mixers to improve mixing.…”

Equipment and Separation Units for Flow Chemistry Applications and Process Development

“…The planar structure of the Seebeck elements allows for using different plate reactors with microstructured channels made of various materials. The use of this calorimeter concept also enables an experimental estimation of mixing times . Based on the position of the maximum of heat production, the mixing time can be inferred from the flow velocity of reagents with very fast reaction kinetics.…”