Residence Time Distribution Curves Research Articles

Analysis of stream flow and its impact on thermal performance in shell-side of heat exchangers based on flow dead zone

The performance of shell-and-tube heat exchanger (STHE) is primarily determined by different flow paths on the shell-side. The flow path and its impact on the shell-side flow in segmental baffle shell-and-tube heat exchanger with clearance (SC-STHE) is investigated qualitatively and quantitatively, by adopting stream classification and dead zone analysis method. By utilizing Residence Time Distribution (RTD) curves, the influence of different streams on fluid flow and heat transfer is discussed to reveal the intricate interconnections within the shell-side of SC-STHE. Then the cases with baffle-tube clearance (0.2–1.0 mm) and baffle-shell clearance (1.0–5.0 mm) ranges are studied. The study identifies that optimal comprehensive performance is achieved with a baffle-tube clearance of 0.6 mm, resulting in a 3.5 % improvement compared to a clearance of 0.2 mm. An increase of baffle-shell clearance results in a reduction in comprehensive performance by 8.23–19.54 %. The interactions among stream flows and potential mechanisms are discussed by analyzing the influence of each flow path on the flow dead zone volume. It is revealed that the presence of baffle-tube and baffle-shell clearances reduces the volume fraction of flow dead zones compared to structures without clearances. A-stream and E-stream are identified as pivotal, mutually influencing B-stream and C-stream while maintaining relative independence. The result indicates that an increase in baffle-tube clearance results in a 7.60 % expansion of the volume of the dead zone within the B-stream, while in the C-stream, it decreases by 2.58 %. Conversely, an increase in baffle-shell clearance reduces the volume of the dead zone in the B-stream by 5.04 % but increases it in the C-stream by 31.95 %. The flow dead zones are mainly distributed in the B-stream and C-stream regions, and the diversion effect of leakage flows improves the fluid stagnation but also leads to a decrease in turbulence intensity and flow velocity. This study reveals the complex interaction mechanisms among the stream flows, facilitating further analysis and optimization in STHE design.

Comparison of Fluid Flow and Tracer Dispersion in Four-Strand Tundish under Fewer Strand Casting and Sudden Blockage of Strand Conditions

The study focuses on the four-strand tundish as the research object, aiming at the phenomenon of fewer strand casting (stable blockage) and sudden blockage of the tundish in industrial production. Numerical simulation methods are employed to compare the velocity vectors, flow fields, residence time distribution (RTD) curves, and outflow percentage curves under stable blockage and sudden blockage of the tundishes with a double-weir structure, U-shaped weir structure, and U-shaped weir structure with holes in the front. The results indicate that, after sudden blockage of the tundish strands, the flow field transitions from an unstable four-strand flow field to a stable three-strand flow field. Both the double-weir tundish and the U-shaped weir tundish reach a stable state after 200 s, while the U-shaped weir tundish with holes in the front reaches stability after 150 s. Additionally, compared to other structures, the tundish strands of the U-shaped weir with holes in the front are less affected by blockage, showing better consistency among strands and better adaptability under non-standard casting conditions.

Preparation of inorganic salt particles by reactive crystallization in an annular swirling flow reactor

This study investigates the performance of an annular conical swirling flow reactor in liquid–liquid reactions for the preparation of inorganic salt particles. Utilizing Particle Image Velocimetry (PIV) measurements and Computational Fluid Dynamics (CFD) simulations, it was observed that the conical design effectively inhibited the attenuation of swirling flow intensity along the axial direction, with the primary mass transfer region close to the central conical wall. In comparison to a stirred reactor, calcium carbonate particles synthesized in the swirling flow reactor exhibited more uniform morphology, smoother and defect-free surface. Notably, the average particle size remained consistently within 5–6 μm (excluding the 0.3 M feedstock), whereas stirring led to particles with an average size ranging from 8-11 μm. Analysis of the residence time distribution curve revealed minimal back mixing in the swirling flow reactor, ensuring nearly equal growth time for salt particles, thus yielding particles with a uniform size distribution. As a result, the swirling flow reactor presents compelling prospects for applications in reactive crystallization.

Design, Validation, and Fabrication of a Tailored Electrochemical Reactor Using 3D Printing for Studies of Commercial Boron-Doped Diamond Electrodes.

Boron-doped diamond (BDD) electrodes are the most effective and resistant electrodic materials to perform advanced oxidation processes. Having a reactor that can provide adequate hydrodynamic conditions is mandatory to use these electrodes effectively. In this work, the diamond anode electrochemical reactor (E3L-DAER) is designed to fulfill this necessity. Several features are included to improve its efficiency, like conic inlet/outlet, flow enhancers, and a reduced interelectrode gap. The fluid dynamic validation has been performed using computer fluid dynamics (CFD) calculations, residence time distribution (RDT) curves, and mass transfer analysis. The reactor has been made using a three-dimensional (3D) printing stereolithography (SLA) technique, which allows us to build chemical-resistant reactors with nonstandard and tailored features in a cheap and fast way. The obtained results demonstrate that the designed reactor has the required fluid dynamics properties to perform reliable BDD electrode studies and applications. Finally, a BDD electrode was used to test the production of different oxidants such as persulfate, peroxophosphate, and chlorine-derived species.

Numerical modeling of fill-level and residence time in starve-fed single-screw extrusion: a dimensionality reduction study from a 3D CFD model to a 2D convection-diffusion model

This research delves into the numerical predictions of fill-level and residence time distribution (RTD) in starve-fed single-screw extrusion systems. Starve-feeding, predominantly used in ceramic extrusion, introduces challenges which this study seeks to address. Based on a physical industrial system, a comprehensive 3D computational fluid dynamics (CFD) model was developed using a porous media representation of the complex multi-hole plate die. Validations performed using real sensor data, accounting for partial wear on auger screw flights, show an ~11% discrepancy without accounting for screw wear and ~6% when considering it. A 2D convection-diffusion model was introduced as a dimensionality reduced order model (ROM) with the intention of bridging the gap between comprehensive CFD simulations and real-time applications. Central to this model’s prediction ability was both the velocity field transfer from the CFD model and calibration of the ROM diffusion coefficient such that a precise agreement of residence time distribution (RTD) curves could be obtained. Some discrepancies between the CFD and the ROM were observed, attributed to the loss of physical information of the system when transitioning from a higher fidelity CFD model to a semi-mechanistic ROM and the inherent complexities of the starved flow in the compression zone of the extruder. This research offers a comprehensive methodology and insights into reduced order modeling of starve-fed extrusion systems, presenting opportunities for real-time optimization and enhanced process understanding.

Comparative analysis and selection criteria for residence time distribution models in free water surface constructed wetlands

The assessment of wetland performance requires consideration of flow characteristics. Although various systemic models (also known as network of ideal reactors) have been proposed to simulate residence time distribution (RTD) in wetlands, these models have only been tested with very few observations. In addition, the applicability of RTD models is affected by the shape characteristics of RTD curves. However, suitable indexes and quantitative relationships are absent to represent this effect. It remains unclear how to choose a suitable model when using the RTD modeling method to analyze tracer data. This study is designed to (i) test the accuracy of typical systemic models using sufficient observations and (ii) establish model selection criteria based on the shape characteristics of RTD. Firstly, the tanks in series (TIS) model, tanks in series plus delay (TISD) model, tanks in series with exchange (TISE) model, and tanks in series with delay and exchange (TISDE) model are compared using 36 sets of observations from tracer tests in two types of free water surface constructed wetlands (vegetated ditches and vegetated ponds). The results show that the widely used TIS model is unsatisfactory for more than half of the data, the TISD model is effective for rapidly rising RTD curves, the TISE model is preferred for long-tailed RTD curves, and the TISDE model can effectively fit all RTD curves except those with multiple peaks. Then, model selection criteria are established based on ∫trtpf(t)dt (the area for the rising stage of RTD), trtp (the degree of early peak), and tdtp (the degree of long tail), where tr represents the time when tracer concentration begins to rise, tp represents the time of peak concentration, and td represents the time when concentration decreases to 1/10 of peak concentration. The optimal model for an RTD curve can be identified based on the above three indexes and the corresponding critical conditions. Finally, the relationship between wetland design parameters and RTD shape indexes is examined. The results indicate that low hydraulic loading rates, small aspect ratios, and dense vegetation favor the creation of long tails. Large water depths tend to cause multiple peaks. Long-tailed and multi-peaked RTD curves are more likely to appear in ponds than ditches. Models that account for multiple nonideal flow phenomena are required to simulate water movement in ponds.

Optimizing the hydraulic performance of a baffled horizontal subsurface flow constructed wetland through computational fluid dynamics modelling

Baffled constructed wetlands (CWs) offer a promising solution to address low hydraulic efficiency in traditional CWs. However, there is a research gap in the field regarding the optimal length and quantity of baffles, and their comprehensive effects on hydraulic efficiency. This study is the first CFD-based assessment to comprehensively investigate the combined influence of baffle length and the number of baffles on the hydraulic efficiency of CWs. Using OpenFOAM simulations at a laboratory scale, various baffle configurations were examined with lengths ranging from 0.4 m to 0.58 m and baffle numbers varying from 0 to 11. Experimental tracer tests were conducted to validate the simulations. The high correlation coefficient (R2) between the tracer test results and simulations (ranging between 0.84 and 0.93) further underscores the reliability of the findings. Residence time distributions (RTDs) were derived from the temporal evolution of the outlet concentration of a tracer. The results indicate that augmenting the number of baffles under a fixed baffle length has a greater impact on the RTD curves, causing a backward displacement of the peak time. However, when the number of baffles is three or fewer, extending the baffle length does not significantly affect the RTD. When the baffle length is held constant at 0.58 m, there is a 58% enhancement in hydraulic efficiency as the number of baffles increases from 0 to 5. However, when maintaining a constant number of 11 baffles, increasing the baffle length from 0.4 to 0.5 m results in only a 5.5% improvement in hydraulic efficiency. Moreover, a generalized predictive equation for hydraulic efficiency was derived based on the CFD results and dimensional analysis. The study enhances the optimization of constructed wetland design by providing greater understanding of hydrodynamic behavior, leading to improved performance and applicability in practical environmental engineering.

Physical modeling and numerical investigation of fluid flow and solidification behavior in a slab caster mold using hexa‐furcated nozzle

AbstractSlag entrapment from metal–slag interface during continuous casting operations has been a major area of concern for steelmakers globally. The presence of inactive regions in the upper region of the mold poses another challenge. Proper flow behavior of the molten metal coming out of the nozzle in the mold is required to overcome these challenges. Nozzle design greatly affects the flow pattern of the molten steel inside the mold. The present investigation is an attempt to study the flow and solidification behavior in a slab caster mold with the use of a novel‐designed hexa‐furcated nozzle using numerical investigation results. The casting speed and submerged entry nozzle (SEN) depth are varied to study the effect of these parameters on minimizing the inactive zones in the mold and the steel/slag interface fluctuations. The results show that the interface fluctuation increases at higher casting speed and lower SEN depth. The residence time distribution (RTD) analysis was also performed for different cases to investigate the flow behavior. The validation of the fluid flow and RTD curve inside the computational domain is carried out with the use of physical modeling.

Flow state analysis of molten salt in shell and tube heat exchanger with perforated baffles

Addressing the issue of flow dead zones in molten salt heat exchangers in concentrating solar power generation systems, this study focuses on the conventional shell and tube heat exchanger using molten salt and heat transfer oil as the working medium. The flow dynamics of molten salt within the heat exchanger are analyzed. To quantify the volume fraction of the molten salt flow dead zones, the residence time distribution curve is employed. Four baffle salt flow configurations are comparatively assessed. Findings indicate that the four opening configurations effectively enhance the reduction of molten salt flow dead zones, with volume fraction reductions ranging from 57.8% to 68.21%. Notably, configuration 4 yields the most optimal results. Furthermore, molten salt flow states in varying regions were examined: the innermost flow dead zone exhibited the highest improvement, followed by the middle area, with the edge area showing the least enhancement. Additionally, the impact of the opening diameter on the flow dead zone was explored. The volume fraction of the molten salt flow dead zone diminishes as the opening diameter expands, with the rate of this change also decelerating. Given that molten salt at the opening manifests as a jet, enlarging the opening diameter lessens the pressure differential across the baffle, subsequently weakening the jet's intensity and its influence on the flow dead zone.

Digital Twin Design of a Turbulence Inhibitor in a Tundish Based on the Production Cluster Mining Algorithm

The lack of a direct and linear relation between inclusion removal from tundishes and the design of their turbulence inhibitors is a difficult challenge. In contrast to the traditional method of optimizing flow control devices based on the residence time distribution curve, this study used the inclusion/flow field database production clustering mining algorithm to conduct step-by-step data mining on the tundish flow field; to produce relevant facts of the flow field characteristics in the inclusion aggregation zone; and to extract the data mining results from the fact database to screen a digital twin algorithm that forecasts the inclusion aggregation area in a tundish to optimize the flow control device. The results showed that the inclusion aggregation area in the tundish impact zone is above the turbulence inhibitor and that the inclusion aggregation area outside the tundish impact zone is at the vortex center of the flow field. According to the mining results, a pseudo-code for screening the inclusion aggregation area was developed, and the turbulence inhibitor was optimized with the help of the digital convergence of the digital and physical models. Finally, in a tundish, the inclusion removal rate in molten steel was increased by 14.4%. The turbulence inhibitor designed by the digital twin method is currently being used in a Chinese steel mill.

Selection of an appropriate tracer to measure the residence time distribution (RTD) of continuous powder blending operations

Residence time distributions (RTDs) are quickly becoming an important component of the quality control strategy for continuous manufacturing (CM) of pharmaceutical products. However, methodologies for determining RTDs, including appropriate selection of tracers and proper processing of RTD data, have not been fully developed, and there is potential to improve current methods.This work aims to implement protocols for tracer selection and establish a methodology for the determination and quantitative comparison of RTD curves obtained by the pulse method. We used an extensive material property data library and multivariate analyses to select appropriate tracers for active pharmaceutical ingredient (API) of interest. Tracer performance was evaluated in two continuous blenders using pulse input experiments. The equivalence of RTDs obtained from the API and the tracer was examined for formulations with widely different blend flow properties.For the most suitable tracer candidate, material properties were determined for mixtures with different API concentrations to ensure that blend properties containing varying amounts of tracer along the RTD profile remained similar to those of the target formulation. It was observed that even small changes in the physical properties of the target formulation would result in a different tracer RTD. This observation emphasized the importance of preserving the physical properties of the blend when characterizing the dynamical behavior of a unit operation.Further, the RTD of the tracer and the API in the blender were characterized under three different base flow properties. The outcome of these experiments enabled a fair side-by-side comparison of RTDs obtained using pulses of either API or tracer for powders with a varying range of properties. In finding an appropriate tracer, RTD profiles were compared quantitively using different methods. Multivariate analysis of variance (MANOVA) was shown to be a suitable tool for RTD profile comparisons.

Hydrodynamic modelling and performance assessment of continuous-flow single-channel reactor for river water turbidity removal using electrocoagulation process

A hydrodynamic modelling of a continuous-flow single-channel (CFSC) reactor was highlighted by means of Residence Time Distribution (RTD) experimental approach using stimulus response technique and three inlet flowrates (43.66, 79.40 and 115.10 L.h−1). Axial dispersion model (ADM) was applied for approximating the RTD experimental curves in order to check the flow patterns homogeneity and identify the possible flow deviations. The CFSC reactor was then evaluated for river water treatment by electrocoagulation process. At 43.66 L.h−1, dead zones were diagnosed within the CFSC reactor and corresponding experimental RTD curve deviated from ADM. At high inlet flowrates, the hydrodynamic behaviour was highly plug-flow (Pe > 100) without flow malfunctions and a satisfactory agreement was obtained between RTD experimental curves and ADM. In contrast, at 43.66 L.h−1, the CFSC reactor exhibited higher turbidity removal (of about 91.7%) compared to high inlet flowrates, indicating that the treatment efficiency depends mainly on coagulant dose electro-dissolved per unit of time rather hydrodynamic condition. However, the associated operating cost was relatively high at 43.66 L.h−1. As for the effect of initial water quality, it was observed that, for the same coagulant dose electro-dissolved, the treatment efficiency dropped as the initial turbidity of water decreased.

The Removal of Inclusions with Different Diameters in Tundish by Channel Induction Heating: A Numerical Simulation Study.

The quality of the bloom will be impacted by the non-metallic impurities in the molten steel in the tundish, which will reduce the plasticity and fatigue life of the steel. In this research, a mathematical model of a six-flow double-channel T-shaped induction heating tundish was established, the effects of induction heating conditions on the removal of inclusions in the tundish were investigated, and the impact of various inclusion particle sizes on the removal effect of inclusions under induction heating was explored. The results show that the Residence Time Distribution (RTD) curve produced through numerical simulation and physical simulation is in good agreement. The reduction of inclusion particles in the channel is made affordable by the dual-channel induction heating technique. As the diameter of inclusion particles increases from 10 μm to 50 μm, the probability of inclusion particles being removed from the channel gradually decreases from 70.9% to 56.1%.

Effect of lifter shape and operating parameters on the flow of materials in a pilot rotary kiln: Part IV. Improvement of the hydrodynamics-related dimensionless correlations

Non-spherical particles are widely processed in industrial-scale rotary kilns. There is nonetheless a lack of simple tools that make it possible to predict their hydrodynamic behavior inside rotary kilns. This article thus focuses on the hydrodynamics of crozets flowing inside a pilot-scale rotary kiln. Thirty-eight experiments were conducted with this product. Experimental Residence Time Distribution curves were successfully obtained with a tracer pulse methodology using painted crozets. Both the experimental mean residence time and the axial dispersion coefficient were obtained by fitting the analytical expression of E(t) for the open-open boundary condition with the experimental E(t) curves. The hydrodynamic behavior observed was qualitatively in agreement with the literature. Our dimensionless models were then re-identified with all of the experimental data and simplified through statistical analysis. This study provides more robust dimensionless hydrodynamic models that can be used to reliably predict the behavior of non-spherical particle flow inside an industrial kiln.

Twin-screw granulation: Mechanistic understanding of the effect of material properties on key granule quality attributes through the analysis of mixing dynamics and granulation rate mechanisms

This study focuses on understanding the effect of material properties on granule quality attributes through the analysis of mixing dynamics and granulation rate mechanisms. Powder wettability, binder viscosity, and liquid-to-solid (L/S) ratio were the factors that were investigated in this study. The mixing occurring inside the twin-screw granulator (TSG) was quantitatively assessed by obtaining the axial dispersion coefficient from the experimentally measured residence time distribution (RTD) curves. It was observed that the quality of the nuclei fed to the kneading zone significantly affected the mixing dynamics. The quality of nuclei was governed by nucleation kinetics, which in turn was principally affected by the liquid saturation of the nuclei and the ratio of drop penetration time and encounter time, which in turn were affected by the L/S ratio and binder viscosity respectively. The hydrophobicity of the blend mainly affected the extent of nucleation. The type of nuclei entering the kneading zone and mixing dynamics in the TSG also determined whether the granulation growth mechanism was “layering-dominant” or “viscous-dominant”. It was also shown that the resultant granule quality attributes were a reflection of the growth mechanisms. Ultimately, a mechanistic link between material properties, mixing dynamics, granulation rate mechanisms, and granule quality attributes was established.

Application of residence time distribution (RTD) to enhance the performance of perforated baffled constructed wetland under unsteady flow

The perforated baffle can significantly enhance the performance of the constructed wetland. In the present study, the effects of perforation shape, number of baffles, baffle position and perforation location on the flow pattern of wetlands were investigated using NaCl impulse-response tracer test, and perforated baffles were used to improve the nitrogen removal rate of the constructed wetland. The perforated baffle optimizes the flow pattern by reducing the peak height of the RTD curve and delaying the peak occurrence time. Triangle perforation exhibits better flow pattern optimization due to its smaller area. When the inlet flow rate is 100 mL/min, the mean residence time (Tm) increases by 0.25 h. The position of the perforated baffle has a more significant effect on the flow pattern, being able to better extend hydraulic residence time (HRT) when located at the height of H/2 substrate. In addition, the perforation locations of two adjacent baffles are not on the same vertical line, which can increase the horizontal water flow velocity and improve the space utilization of the wetland. Compared to the control check constructed wetland (CKCW) without baffles, the perforated baffled constructed wetland (PBCW) exhibited a higher NH4+-N removal rate of 84.53 ± 7.48 % during stable operation. This is mainly because the perforated baffle improves the utilization of dissolved oxygen (DO) while improving the water flow distribution and extending the HRT. In conclusion, perforated baffles have considerable potential to alleviate shock loading and enhance the performance of constructed wetlands.

The study on the effect of hydrodynamic flow on the photocatalytic performance of photocatalytic reactors.

The scalability of photocatalytic reactor is the major challenge due to the inability of the light penetration when the laboratory scale reactors are ascended. It is well known that the characteristic length of photocatalytic reactor is one of the influential parameters determining the efficiency of light penetration and also affects the hydrodynamic fluid flow behaviour inside the reactor. This study visualizes hydrodynamic flow behaviour of three differently configured photocatalytic reactors through numerical simulation of the fluid mass transport inside the reactors. The three photocatalytic reactors are (1) concentric cylindrical glass tube micro-reactor (CGTR), (2) UV-LED strip photocatalytic reactor (STR) and (3) classical annular reactor (CAR) from our previous work. The simulations of flow behaviour confirmed that CGTR exhibited plug flow regime, STR exhibited arbitrary flow (in-between continuously stirred tank reactor and plug flow reactor) and CAR behaved like continuously stirred tank reactor. Also, interpretations of numerical modelling were validated through plotting experimental residence time distribution curve. Furthermore, the comparison of performance parameters revealed that the highest modified space time yield (STYmodified) 225s-1and highest modified photocatalytic space time yield (PSTYmodified) 9.375s-1/kW/m3 was obtained for plug flow reactor when compared to continuously stirred tank reactor (CAR) and arbitrary flow reactor (STR). The study confirms that decrease in characteristic length of photocatalytic reactor onsets plug flow regime, which has highest photocatalytic performance efficiency.

Modeling of a novel cascade-type electrocoagulation reactor using iron electrodes. Characterization of bubbling flow and coagulant dosage

This paper deals with the bubbling flow and coagulant dosage modeling in an innovative continuous cascade-type electrocoagulation (EC) reactor using iron plate electrodes. The reactor comprises seven iron plates. It is open to the atmosphere at the top to release the hydrogen bubbles produced at the cathode during the reduction of H2O. In this context, a two-phase flow model (H2OH2) was formulated. The H2OH2 flow was obtained by the solution of the Reynolds Averaged Navier-Stokes (RANS) equations for the continuous phase (H2O), which was coupled to the slip model for the dispersed phase (H2). Since H2 bubble formation co-occurs at the cathode as the aqueous solution passes through the continuous EC reactor, the two-phase flow and Laplace equations were solved simultaneously. The modeling of the ferric ion coming from the anodic dissolution was carried out by solving the diffusion-convection equation. The influence of the mean linear inflow velocity (2.63 ≤ u ≤ 2.56 cm s−1) and current density (4 ≤ j ≤ 8 mA cm−2) on the H2 dispersion and coagulant formation (Fe3+) was systematically examined. A comparison between simulated and experimental Fe3+ doses showed deviations < 4%. Excellent agreement between experimental and theoretical residence time distribution curves was obtained.

Evaluation and improvement of residence time distribution analysis methods

Although residence time distributions (RTDs) are frequently used in wetland studies, there is no consensus about the analysis method. Generally, two types of methods can be used to analyze RTD data: the method of moments and the RTD modeling method. RTD curves are obtained by tracer tests. The real RTD curves are usually imperfect due to the presence of random measurement errors, the unreasonable sampling intervals, and the premature termination of the tracer test. This study aims to find a better RTD analysis method providing robust results under these unfavorable factors, which includes: (i) evaluating the existing RTD analysis methods; (ii) improving the existing RTD analysis method using the Rational model. The influence of measurement error, sampling interval, and ending time in tracer tests on RTD analysis methods was first simulated. The results showed that effective volume ratio was a preferable indicator compared with the variance of RTD. The stability of the moment method decreased with the increase of the measurement error and sampling interval, and the accuracy of the moment method decreased with the decrease of the test time. Although the RTD modeling method showed better stability and accuracy, the implicit premise is that the RTD model adequately describes the observed data. Further, 36 observed RTD data sets were used to test the Tanks in Series (TIS) model and the empirical Rational model. The results showed that the widely used TIS model was only effective in partial cases, while the newly proposed Rational model showed broader applicability. Both the moment method and the TIS modeling method were proven to be inadequate. Finally, the moment method was improved by using Rational models to pre-process RTD data. Although the improved method is still affected by random measurement errors, it can significantly increase the accuracy of the moment method when sampling points are small or the test ends prematurely.

Understanding the Residence Time Distribution in a Transient Inline Spiking System: Modeling, Experiments, and Simulations

A transient inline spiking system is a promising tool for evaluating the performance of a virus filter in continuous operation. For better implementation of the system, we performed a systematic analysis to understand the residence time distribution (RTD) of inert tracers in the system. We aimed to understand the RTD of a salt spike, not retained onto or within the membrane pore, to focus on its mixing and spreading within the processing units. A concentrated NaCl solution was spiked into a feed stream as the spiking duration (tspike) was varied from 1 to 40 min. A static mixer was employed to mix the salt spike with the feed stream, which then passed through a single-layered nylon membrane inserted in a filter holder. The RTD curve was obtained by measuring the conductivity of the collected samples. An analytical model, the PFR-2CSTR model, was employed to predict the outlet concentration from the system. The slope and peak of the RTD curves were well-aligned with the experimental findings when τPFR = 4.3 min, τCSTR1 = 4.1 min, and τCSTR2 = 1.0 min. CFD simulations were performed to describe the flow and transport of the inert tracers through the static mixer and the membrane filter. The RTD curve spanned more than 30 min, much longer than tspike, since solutes were dispersed within processing units. The flow characteristics in each processing unit correlated with the RTD curves. Our detailed analysis of the transient inline spiking system would be helpful for implementing this protocol in continuous bioprocessing.