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Abstract  

The applications of radiotracers for determination of impulse response as Residence Time Distribution (RTD) as well as technical conditions for realization of experiment in industry create special requests for data processing. The table of required corrections and methods for RTD analysis with the basic information is presented. The methods for the raise background subtraction, correction for variable flow and new algorithms for RTD analysis from response to arbitrary input function and from the response distorted by the recirculation flow in so called black or gray box system are presented.

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Microchannel-based hemodialysis has a potential to improve survival rates and quality of life for end-stage renal disease patients compared to conventional hemodialysis technology. Characterization of hydrodynamic behavior in microchannel geometries is necessary for improving flow uniformity, a critical challenge in realizing a commercial device. A test loop was developed for measuring the impulse response of a tracer dye injected into a dialyzer test article for the purpose of developing residence time distributions (RTD) to characterize lamina design. RTD variance tended to lower for designs that are more dominated, volume-wise, by the microchannel array versus the headers. RTD results also emphasize how defect issues can significantly impact a microchannel device via discrepancies between conceptual and operational devices. A multisegmented CFD model, developed for pairing with the impulse response test loop and dialyzer, showed good agreement between visual observation of the tracer in simulations and experiments, and the shape and peak of the output profiles.

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Aerobic wastewater treatment requires extensive aeration, which primary function is to provide oxygen to the biomass responsible for degradation of wastewater constituents. Besides the effective oxygen transfer efficiency aeration is responsible for fluid flow created by bubbles. In this research bubbles were released from plate diffusers and the impact on mixing were analyzed. Various aeration flow rates and initial bubble sizes were calculated. Residence time distributions in each scenario were compared applying numerical tracer study. Outcome of the calculations is that the aeration reduces the theoretical residence time significantly and therefore the traditional sizing methods needs to be revisit in wastewater treatment.

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Abstract  

In the phosphoric acid production process, the time a particle spends inside the chemical reactor (residence time) is of paramount importance to process engineers. Residence time distribution (RTD) gives information on the efficiency of the chemical reactor, on the efficiency of the process, and also the availabilities of the reactive volume for the reaction (active volume vs. dead volume). Traditionally, chemical engineers used chemical tracer to determine the RTD. However, first disadvantage is that the chemical tracer could not allow an online diagnosis: the samples containing chemical tracer have to go to a lab for analysis, second disadvantage is that the chemical tracer is less sensitive than radioactive ones because of its adsorption onto strata or its retention in rocks. Consequently, chemical tracer results are not always precise and cannot convincingly explain the multiple flow-path model. Radioactive tracers are the only tracers capable of measuring the active RTD with high degree of precision and give information on the internal recirculation rate. In this work, we will describe the application of radiotracer method for RTD measurement in the phosphoric acid production process and give results and discussion of each case encountered.

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Abstract  

A rotary fluidized bioreactor (RFBR) designed for treatment of wastewater was required to be investigated for its hydrodynamic behaviour and validation of design. A radiotracer investigation was carried out to measure residence time distribution (RTD) of wastewater in the RFBR using 82Br as a radiotracer. The radiotracer was instantaneously injected into the inlet feed line and monitored at the inlet and outlet of the reactor using collimated scintillation detectors connected to a data acquisition system. The measured RTD data was treated and simulated using a tanks-in-series model and model parameters i.e. number of tanks describing the degree of mixing was obtained. The results of the investigation showed no flow abnormalities and the reactor behaved as an ideal continuously stirred-tank reactor at all the operating conditions. Based on the results, the design of the reactor was validated.

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Abstract  

A radiotracer study was carried out in a trickle bed reactor (TBR) independently filled with two different types of packing i.e., hydrophobic and hydrophilic. The study was aimed at to estimate liquid holdup and investigate the dispersion characteristics of liquid phase with both types of packing at different operating conditions. Water and H2 gas were used as aqueous and gas phase, respectively. The liquid and gas flow rates used ranged from 0.83 × 10−7–16.67 × 10−7 m3/s and 0–3.33 × 10−4 m3 (std)/s, respectively. Residence time distribution (RTD) of liquid phase was measured using 82Br as radiotracer and about 10 MBq activity was used in each run. Mean residence time (MRT) and holdup of liquid phase were estimated from the measured RTD data. An axial dispersion with exchange model was used to simulate the measured RTD curves and model parameters (Peclet number and MRT) were obtained. At higher liquid flow rates, the TBR behaves as a plug flow reactor, whereas at lower liquid flow rates, the flow was found to be highly dispersed. The results of investigation indicated that the dispersion of liquid phase is higher in case of hydrophobic packing, whereas holdup is higher in case of hydrophilic packing.

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Abstract  

Both 9mTcO4 - and Rhodamine WT were employed as tracers to record the residence time distribution (RTD) in 5 segments located in the Almendares River in Havana City. Recovery calculations showed the conservative behavior of the 99mTcO4 - under the field conditions studied. The experimental residence time distribution curves from the second segment were convoluted for the d-Dirac injection at the beginning of the section. The spatial behavior of the conservative prompt spills throughout this river section was established for two extreme flow conditions.

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Abstract  

By means of radiotracer51Cr impregnated in the solid phase the residence time distribution of the pulp in the mixing chamber was obtained. The mathematical model constructed on the basis of the experimental distribution showed an unsatisfactory functioning of the reactor. Ways were proposed to correct this shortcoming, both in the existing chamber and in that which is being designed for a new plant.

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Abstract  

The scheme of the shaft process of simultaneous zinc and lead production is shown. The residence time distribution of zinc vapour leaving the furnace is measured using65Zn. The distribution curve is determined by deconvolution procedure of convolution integral which connects the input function, impuls response and output function. The analysis of this curve showed that in the furnace an internal zinc recirculation connected with secondary oxidation of zinc vapour takes place in the upper zone of the shaft. The localization of the secondary oxidation zone and the degree of zinc reoxidation was determined.

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Journal of Flow Chemistry
Authors: Lukas Hohmann, Safa Kutup Kurt, Sebastian Soboll, and Norbert Kockmann

For complete chemical processes, downstream operation steps are essential, but on a miniaturized scale, they are not so far developed as the microreactors. This contribution presents three different unit operations for phase and component separation. Liquid—liquid extraction is often performed in columns, which were miniaturized for higher separation efficiency and flow rates suitable for processes in flow chemistry. Two-phase mass transfer processes in capillaries benefit from rapid final phase separation, which can be performed in an in-line phase splitter based on different surface wetting behavior. Crystallization is often a final purification step, which is performed in a continuously operated helical tube setup with narrow residence time distribution. For all unit operations, design criteria are shown with typical applications. The methodology of downscaling of known equipment and employing typical microscale phenomena such as good flow control, laminar flow, or dominant surface forces leads to successful equipment design.

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