On the measurement of local concentrations in bubbly flows for the reaction of FeII(edta) with NO using fiber optical probe

Topics of current research activities within the DFG priority program SPP 1740 “Reactive Bubbly Flows” are studies on local mass transfer and reaction processes in order to gain a deeper understanding about the coupling of hydrodynamics, mass transfer and reaction kinetics in reactive bubbly flows.
This contribution presents the results of an experimental study on reaction of FeII(EDTA) and NO. The reaction forms a very stable complex of [Fe(EDTA)NO)2-]. The aim of the experiments is the measurement of the local species concentration of the product complex in the bubble wake. For this purpose, a fiber optical probe, especially designed for this application was used. The sensor is equipped with two LED’s and optical filters of different wavelengths (λ_1 = 435 nm, λ_2 = 780 nm), respectively. The selection of the wavelengths is based on the absorption spectra of [Fe(EDTA)NO)2-], in order to provide a product specific wavelength (λ_1 = 435 nm) and reference wavelength (λ_2 = 780 nm). In that way, the concentration of the product species and information about the prevailing phase (liquid or gas) were recorded simultaneously. Experiments were carried out in a bubble column with 74mm inner diameter and single needle gas injection (see Figure 1a). Figure 1b shows an example of the time signal of the concentration of the product species, where disturbed signals due to bubble-probe interactions are removed based on the signals of the reference wavelength. In this contribution, characteristic parameters of the species concentration in the bubble wake obtained from measurements with the fiber optical probe are presented for different initial concentrations of the solution and different hydrodynamic conditions.

The authors gratefully acknowledge the financial support provided by the German Research Foundation (DFG) within Priority Program “Reactive Bubbly Flows” SPP 1740.