Residence time distribution from a continuous Couette flow device

This paper describes an experimental study of residence time distribution (RTD) by pulse response analysis in a continuous Couette flow device with rotating inner cylinder and stationary outer cylinder. The experiments were performed under conditions of (a) negligible and (b) significant influence of molecular diffusion and (c) Taylor vortex flow. Diethylene glycol and water were used as the test fluids with congo red dye and potassium permanganate solution as tracers respectively. A unique RTD described by an analytical expression was observed for experiments with low axial Reynolds number under the condition of negligible influence of molecular diffusion. For most experiments performed under conditions of significant influence of molecular diffusion and Taylor vortex flow regime over the ranges 0 < Ta < 118 and 0.4 < Re < 5.5, the RTD can be described by a dispersion model. The system behaves as a near-plug flow vessel at Ta ≈ 60. The critical Taylor number for this geometry as defined by the minimum dispersion number for a given flowrate is slightly higher than that without axial flow.     

Spectrum analysis of radiotracer residence time distribution for industrial and environmental applications

Radiotracer signal analysis and recognition still represents challenges in industrial and environmental applications specially in residence time distribution (RTD) measurement. This paper presents a development for the RTD signal recognition method that is based on power density spectrum (PDS). In this development, the features are extracted from the signals and/or from their higher-orders statistics (HOS) (Bispectrum and Trispectrum) instead of PDS. The HOS are estimated using direct, indirect and parametric estimations. The recognition results are analyzed and compared for different HOS estimation in order to select the best HOS estimation method for the purpose of RTD signal recognition. The artificial neural networks are used for training and testing of the proposed method. The proposed method is tested using RTD signals obtained from the measurements carried out using radiotracer technique. The simulation results show that the parametric estimation of the Trispectrum gives the higher recognition rate and is the most reliable for the RTD signal recognition.     

Investigation of hydrodynamic behaviour of a pilot-scale trickle bed reactor packed with hydrophobic and hydrophilic packings using radiotracer technique

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?C16.67?×?10^?7?m³/s and 0?C3.33?×?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.     

有机分子共振隧穿二极管

介绍了共振隧穿二极管(RTD)和有机分子共振隧穿二极管的结构、功能及工作原理，并对有机分子RTD的研究进展作了概述。     

Modelling non-homogeneous flow and residence time distribution in a single-screw extruder by means of Markov chains

Non-homogeneous velocity distribution of the flow in the channel of a single-screw extruder is taken into account by a new model developed on the basis of the Markov chains. This model allows calculating the Residence Time Distribution (RTD) as well as the influence of the operating conditions on the process at any velocity distribution in the channel. It has been used to represent experimental results on mass flow rate and RTD previously obtained by extrusion of an acrylic polymer, Eudragit E100, at different temperatures and screw rotation speeds. The diffusion coefficient is the only adjusting parameter of the model. It was shown that it does not depend on the screw rotation speed and a correlation between this diffusion coefficient and the barrel temperature was found. The model provides global understanding of the transport kinetics of the flowing material through the extruder according to its behaviour and better describes the progress of the polymer flow all along the barrel from the hopper to the die.     

Residence time distribution study for the catalytic packing MULTIPAK®

Residence time distribution (RTD) experiments were carried out using the catalytic packing MULTIPAK® in a 250 mm inner diameter column. The axial dispersion coefficients and dynamic liquid hold-up were derived from the RTD curves. Both hold-up and axial Péclet number were correlated in terms of gas and liquid Reynolds numbers. Free-draining experiments were performed to determine the dynamic and static liquid hold-ups. The measured axial dispersion coefficients were higher than those presented in other studies. The dynamic hold-up derived from RTD agreed with total hold-up from free-draining experiments. The static hold-up was found very high, even higher than the dynamic one, due to the liquid accumulated inside the catalyst bed. Possibly, the liquid considered “static” from the viewpoint of the free-draining experiments becomes “dynamic” during the normal column operation.     

同向啮合双螺杆挤出机挤出过程的计算机模拟

计算机模拟研究了聚苯乙烯在TSE-35A型同向啮合双螺杆挤出机的挤出过程.计算得到不同喂料速率与不同转速下的停留时间分布,并与在线荧光法测量值对比,二者基本相符.确定了停留时间与螺杆转速及喂料速率之间的函数关系式.模拟结果还预测了喂料速率、螺杆转速等工艺参数对双螺杆内流场变量,如温度、填充率、压力及粘度等的影响.模拟计算有助于了解双螺杆挤出机内部聚合物材料流动状态及停留时间长短,从而指导实际聚合物生产.     

Nondestructive testing of glued joints

The pros and cons are considered for both traditionally applied and special low-frequency acoustic methods of the nondestructive testing of multilayered, glued constructions. The types of defects in glued constructions produced using polymer composite materials are shown; these defects may be revealed by the impedance method when adjusting the device according to the construction being tested. Methods for the nondestructive testing of the glued joints in multilayered constructions are presented and the numbers of the methodical regulation and technical documentation (RTD) developed in the FGUP VIAM are listed.     

The effects of solvent preoxidation on inhibited chemiluminescence of pyrogallol oxidation in flow injection analysis and liquid chromatography

A new extension of chemiluminescence technique using pre-oxidation of a carrier solvent before the conventional inhibited chemiluminescence detection is presented in this study. The method is based on the modification of the oxidation chemistry of pyrogallol upon contact with a flow stream consisting of an organic solvent in mixture with an aqueous solution of a soft oxidant. The final response was found to depend on the kind of solvent and the oxidant/pre-oxidant mixture employed for the oxidation of pyrogallol and the solvent, respectively. By selecting the appropriate combination two detection modalities with increased sensitivity can be achieved. The first is based on the enhancement of the analytes signal through intensification of their scavenging effect on pyrogallol oxidation and the second on the enhancement of signal above the emission induced during the pyrogallol oxidation. Various combinations of organic solvents, oxidizing and pre-oxidizing mixtures were examined for their response in inhibited chemiluminescence measurements yielding very interesting results. The analytical utility of this new technique to the improvement of previous analytical methods as well as to the development of new procedures employing flow injection analysis is demonstrated. Furthermore, the application of the proposed method in combination with liquid chromatographic analysis is also presented.     

Transport and reaction in microscale segmented gas-liquid flow

We use micro particle image velocimetry (microPIV) and fluorescence microscopy techniques to characterize microscale segmented gas-liquid flow at low superficial velocities relevant for chemical reactions with residence times of up to several minutes. Different gas-liquid microfluidic channel networks of rectangular cross section are fabricated in poly(dimethylsiloxane) (PDMS) using soft lithography techniques. The recirculation motion in the liquid segments associated with gas-liquid flows as well as the symmetry characteristics of the recirculations are quantified for straight and meandering channel networks. Even minor surface roughness effects and the compressibility of the gas phase induce loss of symmetry and enhance mixing across the centerline in straight channels. Mixing is further accelerated in meandering channels by the periodic switching of recirculation patterns across the channel center. We demonstrate a new, piezoelectrically activated flow injection technique for determining residence time distributions (RTDs) of fluid elements in multiphase microfluidic systems. The results confirm a narrowed liquid phase RTD in segmented flows in comparison to their single-phase counterparts. The enhanced mixing and narrow RTD characteristics of segmented gas-liquid flows are applied to liquid mixing and in sol-gel synthesis of colloidal nanoparticles.     

Radiotracer investigation in a rotary fluidized bioreactor

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.     

On-line monitoring of the residence time distribution along a kneading block of a twin-screw extruder

An on-line Residence Time Distribution (RTD) measuring set-up that enables the characterisation of twin screw extruders at short axial increments is presented. It uses the light emission of a fluorescent tracer (perylene) to generate concentration versus time curves, which are then used to determine the usual RTD parameters, delay time, mean residence time and variance. The system is initially mounted on a rectangular die coupled to a single screw extruder, on-line and off-line measurements being directly contrasted. Then, the optical probe is positioned at several points along the axis of a modular co-rotating twin screw extruder, on-line and off-line data being again compared. Having gained confidence in the measuring technique, an experimental unit utilizing a transparent barrel is used to characterize the evolution of RTD along a kneading block of a twin screw extruder.     

Identification of Non-Volatile Compounds Generated during Storage That Impact Flavor Stability of Ready-to-Drink Coffee

Coffee brew flavor is known to degrade during storage. Untargeted and targeted LC/MS flavoromics analysis was applied to identify chemical compounds generated during storage that impacted the flavor stability of ready-to-drink (RTD) coffee. MS chemical profiles for sixteen RTD coffee samples stored for 0, 1, 2, and 4 months at 30 °C were modeled against the sensory degree of difference (DOD) scores by orthogonal partial least squares (OPLS) with good fit and predictive ability. Five highly predictive untargeted chemical features positively correlated to DOD were subsequently identified as 3-caffeoylquinic acid, 4-caffeoylquinic acid, 5-caffeoylquinic acid, 3-O-feruloylquinic acid, and 5-O-feruloylquinic acid. The increase in the six acidic compounds during storage was confirmed by sensory recombination tests to significantly impact the flavor stability of RTD coffee during storage. A decrease in pH, rather than an increase in total acidity, was supported to impact the coffee flavor profile.     

Determination of residence time distribution in polymer processing apparatus using tracer techniques

Tracer techniques, based on neutron activation analysis and ashing procedures, are discussed with reference to measurement of material residence time distribution (RTD) through polymer processing apparatus. Particular emphasis is given to details of experimental techniques employed, their reproducibility, and ultimately to their application for characterisation of polymer RTD in twin-screw extrusion and injection moulding machinery.     

Automated exploration and exploitation of flow-injection response surfaces

Three-dimensional plots of instrumental responses vs. chemical concentrations or flow parameters have been 1 obtained in an automated manner on a computer-controlled flow-injection methods development system. Consideration of several alternative responses for flow-injection systems is shown to help characterize a chemistry more thoroughly and reveal the best experimental conditions. One may see the effects of individual experimental variables (reagent concentrations, pH, flow-rates, etc.), the interactions of these variables, instrumental factors and limitations of the surface exploration procedure employed. Chemical systems studied were the photometric determination of phosphate, palladium(II), iron(II) and persulfate. The propriety of automated response surface mapping is demonstrated and the efficacies of simplex and grid search approaches to response surface exploration are contrasted. Responses obtained include absorbance at peak maximum, relative standard deviation of maximum absorbance, time from injection to peak maximum and wavelength of maximum absorbance. Higher dimensional response surface representations of peak shape and absorbance spectra are also presented. The results show that the response chosen governs the general shape of the surface and the height at any point. This approach to automated characterization of chemical reactions in flow analysis is critically assessed.     

System of programs for activation analysis calculations: (SPAAC)

Steady state conditions are assumed in impulse response analysis and well explained in literature for the tracer test to realise the results, but this is not always the case when dealing with the wastewater treatment plants, where flow processes are always in unsteady state conditions. Beside stimulus response, the flow rate has to be measured at the same during experiment. Several figures were prepared to demonstrate the influence of variable flow rate, these figures are important in order to understand the changes of impulse response by variable flow rate. The unexpected change in the flow rate should be strictly observed to avoid misinterpretation the impulse response results. The base information in data treatment for variable flow analysis of impulse are presented, to assist in data treatment and to obtain more practical performance of the WSP.     

Mean residence time of Markov processes for particle transport in fludized bed reactors

A new approach for studying the particle dynamics and RTD (residence time distribution) in processes is to formulate stochastic models. A common question to all models for RTD is whether Danckwerts’ law for mean residence time holds. In this paper we revisit a Markov process that has been proposed by Dehling et al. (1999) as a stochastic model for particle transport in fluidized bed reactors. Under the volumetric flow balance conditions, we deduce different boundary conditions at the entrance and the exit of the reactor, and in both discrete model and continuous model we show that processes satisfy Danckwerts’ law, stating that the mean residence time of particle transport in fluidized bed reactors equals V/v, where V denotes the volume of the reactor occupied by the fluid and v the volumetric inflow rate.     

Radiotracer investigation of phosphoric acid and phosphatic fertilizers production process

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.