Please use this identifier to cite or link to this item: http://dx.doi.org/10.14279/depositonce-11418
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Main Title: In-Line Analysis of Diffusion Processes in Micro Channels by Long Distance Raman Photometric Measurement Technology—A Proof of Concept Study
Author(s): Deuerling, Julian
Keck, Shaun
Moelyadi, Inasya
Repke, Jens-Uwe
Rädle, Matthias
Type: Article
Language Code: en
Abstract: This work presents a novel method for the non-invasive, in-line monitoring of mixing processes in microchannels using the Raman photometric technique. The measuring set-up distinguishes itself from other works in this field by utilizing recent state-of-the-art customized photon multiplier (CPM) detectors, bypassing the use of a spectrometer. This addresses the limiting factor of integration times by achieving measuring rates of 10 ms. The method was validated using the ternary system of toluene–water–acetone. The optical measuring system consists of two functional units: the coaxial Raman probe optimized for excitation at a laser wavelength of 532 nm and the photometric detector centered around the CPMs. The spot size of the focused laser is a defining factor of the spatial resolution of the set-up. The depth of focus is measured at approx. 85 µm with a spot size of approx. 45 µm, while still maintaining a relatively high numerical aperture of 0.42, the latter of which is also critical for coaxial detection of inelastically scattered photons. The working distance in this set-up is 20 mm. The microchannel is a T-junction mixer with a square cross section of 500 by 500 µm, a hydraulic diameter of 500 µm and 70 mm channel length. The extraction of acetone from toluene into water is tracked at an initial concentration of 25% as a function of flow rate and accordingly residence time. The investigated flow rates ranged from 0.1 mL/min to 0.006 mL/min. The residence times from the T-junction to the measuring point varies from 1.5 to 25 s. At 0.006 mL/min a constant acetone concentration of approx. 12.6% was measured, indicating that the mixing process reached the equilibrium of the system at approx. 12.5%. For prototype benchmarking, comparative measurements were carried out with a commercially available Raman spectrometer (RXN1, Kaiser Optical Systems, Ann Arbor, MI, USA). Count rates of the spectrophotometer surpassed those of the spectrometer by at least one order of magnitude at identical target concentrations and optical power output. The experimental data demonstrate the suitability and potential of the new measuring system to detect locally and time-resolved concentration profiles in moving fluids while avoiding external influence.
URI: https://depositonce.tu-berlin.de/handle/11303/12609
http://dx.doi.org/10.14279/depositonce-11418
Issue Date: 22-Jan-2021
Date Available: 16-Feb-2021
DDC Class: 620 Ingenieurwissenschaften und zugeordnete Tätigkeiten
Subject(s): process engineering
fluid-fluid extraction
Raman effect
photometry
microchannels
droplets
local concentration measurement
optical measurement
Sponsor/Funder: BMBF, 13FH8I03IA, FH-Impuls 2016: M2edTech - Konzeption und Bau von Demonstratoren für Echtzeitsensoren und -analytik
License: https://creativecommons.org/licenses/by/4.0/
Journal Title: Micromachines
Publisher: MDPI
Publisher Place: Basel
Volume: 12
Issue: 2
Article Number: 116
Publisher DOI: 10.3390/mi12020116
EISSN: 2072-666X
Appears in Collections:FG Dynamik und Betrieb technischer Anlagen » Publications

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