T-junction Configuration Research Articles

Experimental investigation on non-buoyant and buoyant flow mixing in a horizontally aligned T-junction at isothermal conditions

Periodically occurring temperature fluctuations in nuclear power piping systems have been linked to cracking and coolant leakage accidents. T-junctions where hot and cold fluids mix are particularly vulnerable. To study thermal mixing flow phenomena, an isothermal operating test bench was built using a sugar respectively a salt solution to model the cold fluid in the T-junction configuration. The experiments aimed to predict the flow phenomena of mixed fluids with different fluid densities. Different types of investigations of non-buoyant and buoyant flow mixing were conducted using qualitative and quantitative measurement techniques, such as flow visualization, planar laser-induced fluorescence method, and wire mesh sensor measurements. Jet-formation and mixing behavior (up- and downstream) were characterized by the momentum ratio and a Richardson number. Additionally, non-buoyant flow conditions as well as buoyant flow with unstable/stable stratification have been summarized and clustered in non-dimensional flow maps. Results showed that wall- and deflecting-jet formations are a risk pattern for thermal fatigue. These were identified based on mean and fluctuating mixing scalar distribution as well as spectral analysis of the mixing scalar fluctuations. The peak frequencies in the non-buoyant case were linked to the axial motion of the Kármán-like vortices, while in the buoyant mixing case, the shear layer vortices resulting from Kelvin-Helmholtz instabilities were responsible.

T-junction Configuration Performance in aTransmission Sub-system

A cement factory, namely PT Semen Imasco Asiatic, requires a large supply of power for production. However, in the area where the cement factory was established, namely Puger District, there was no electricity capable of supplying it, so PLN built the Puger substation. In the original plan, the transmission line will be built directly from GI Tanggul to GI Puger. However, because the plant must operate immediately, the electricity supply is taken from the existing Tanggul substation-Jember substation transmission line using the T-Junction configuration. In this paper, an analysis of the power flow of the Paiton-Grati subsystem will be carried out when the power supply from Tanggul Substation to Puger Substation is passed through the T-Junction configuration or when the transmission line is connected from the Tanggul Substation to the Puger Substation directly. The result of this research is that there is no significant difference between the two conditions in power losses, voltage drop, current, and power factor parameter so that the T-Junction configuration is quite feasible to use even though it is temporary.

Fabrication of zein-modified starch nanoparticle complexes via microfluidic chip and encapsulation of nisin

A microfluidic chip is a micro-reactor that precisely manipulates and controls fluids. Zein is a group of prolamines extracted from corn that can form self-assembled nanoparticles in water or a low concentration of ethanol in a microfluidic chip. However, the zein nanoparticles have stability issues, especially in a neutral pH environment due to the proximity of the isoelectric point. This study was designed 1) to evaluate the effect of octenyl succinic anhydride (OSA) modified starch on the stability of zein nanoparticles formed using a microfluidic chip and 2) to apply the zein-OSA starch for encapsulation of nisin and evaluate its anti-microbial activity in a model food matrix. A T-junction configuration of the microfluidic chip was used to fabricate the zein nanoparticles using 1% or 2% zein solution and 0–10% (w/w) of OSA starch solution. The stability of the nanoparticles in various ionic strength environments was assessed. Encapsulation efficiency and anti-microbial activity of nisin in the zein nanoparticles against Listeria monocytogenes in a fresh cheese were measured. As the concentration of OSA starch increased from 0 to 10%, effective diameter increased from 117.8 ± 14.5 to 198.7 ± 13.9 nm without affecting polydispersity indexes and zeta-potential changed toward that of the modified starch indicating the zein surface coverage by the OSA starch. The zein-OSA starch nanoparticle complexes were more stable at various sodium chloride concentrations than the zein nanoparticles without OSA starch. The encapsulation efficiency of nisin was positively correlated with the OSA starch concentration. The anti-microbial activity of nisin in the fresh cheese also increased until 3-days of storage as the concentration of the OSA starch increased, which presented both a potential and challenge toward applications.

Effect of ECCS cold-leg injection angle on thermal hydraulic characteristics and core recovery during LBLOCA in a PWR

The Emergency Core Cooling System (ECCS) is actuated following Loss of Coolant Accidents (LOCA) to inject coolant into the primary loop through a T-junction configuration in nuclear power plants. The injection angle; i.e., the T-junction angle, in the cold leg injection system in a pressurized water reactor is an important parameter during a postulated LOCA. The amount of the break flow rate and the time at which the refill period initiates impact the thermal-hydraulic behavior of the reactor coolant system and eventually affect the integration of reactor nuclear core. In the current work, RELAP5 code is used to study the effect of the cold leg injection angle on LOCA scenario in a standard four-loop Westinghouse Pressurized Water Reactor (PWR). Injection angles investigated in the study are 45°, 90°, and 135°. The whole reactor system is simulated using RELAP5 code whilst the injection junction is numerically developed using ANSYS-FLUENT commercial code. The break flow, core recovery, and thermal-hydraulic parameters are calculated for the different injection angles. Research results are validated with published data available in the literature. The results manifest that the injection angle of 45° gives the highest and the most uniform core level during the core refilling phase, the best temperature behavior for both fuel centerline and maximum cladding temperatures, where both temperature distributions reach a stable value earlier than that of the other angles. ANSYS-FLUENT code is utilized to explain the complex mixing phenomena of fluids during the analysis.

Numerical investigation on similarity of isothermal and thermal flow mixing in a horizontal T-junction configuration

Turbulent and stratified mixing flows can cause thermal fatigue in nuclear power plant piping systems. An isothermal Mixed-Fluid-Interaction (MFI) test rig is used to investigate mixing phenomena related to High Cycle Thermal Fatigue in nuclear power plant piping systems. Here, the cold heavy branch pipe fluid of the thermal mixing Fluid Structure-Interaction (FSI) facility is modeled by a sugar or salt solution. Due to limited optical accessibility of the FSI facility a numerical similarity comparison of the flow phenomena occurring in both experimental setups (MFI/FSI) is essential. Thus, Large-Eddy Simulations are carried out which are experimentally validated by applying the Wire-Mesh-Sensor measurement technique (MFI) and temperature measurements (FSI). Numerical LES investigation on similarity between two isothermal cases, three thermal mixing cases, and one geometrically similar scaled-up thermal mixing case is performed when the momentum ratio MR and the Richardson number Ri is kept constant. A very good agreement in the spatial distribution of the time averaged mean and rms values as well as statistical fluctuations is observed between the isothermal and thermal cases. Non-dimensional power spectrum density (PSD) of the mixing scalar fluctuation showed an almost unique profile, indicating the same origin for the occurring periodical fluctuation in all cases. The non-dimensional magnitude of the dominant frequency of the mixing scalar fluctuations in terms of the Strouhal number is in the range of 0.38<Sr<0.40. In the context of similarity, it is shown that the momentum ratio and the Richardson number are mainly responsible for the jet-formation and thus for the down- and upstream flow behaviour. The influence of the inlet Reynolds numbers Rem and Reb as well as the density ratio ΓR on the normalized flow characteristics seem to be negligible in comparison.

Large-Eddy Simulation of turbulent thermal flow mixing in a vertical T-Junction configuration

Turbulent mixing of warm and cold water streams within a vertical T-junction configuration of a nuclear power plant piping system causes near-wall temperature fluctuations which may lead to High-Cycle Thermal Fatigue (HCTF) failure of the wall material. To predict frequency and amplitude of such temperature fluctuations accurately the method of Large-Eddy Simulation (LES) in the numerical simulation code OpenFOAM is used. As an experimental test case, the turbulent mixing experiment of Kamide et al. [1], where a vertical branch pipe with a cold water stream is connected from below to a horizontal main pipe with a warm water stream to form a vertical T-junction configuration. From the various observed flow patterns, the temperature and velocity data of the ‘wall jet’ are chosen as a reference because it is known to have the highest potential for thermal fatigue. Incomplete mixing and an instability associated with large turbulent structures near the junction region lead to significant temperature fluctuations close to the wall before a vertical thermal stratification further downstream stabilizes the flow. The highest near-wall fluctuation amplitudes are 26% of the temperature difference between the streams. A spectral peak occurs at a Strouhal number of 0.2. The results of the simulations demonstrate, that the mean velocity and temperature profiles of the experiments are well captured, whereas the root-mean-square (RMS) temperature fluctuations deviate from the measurements in some cases, in particular when coarse grids are used. In order to find a lower limit for the required spatial resolution three different numerical meshes with a variable number of cells up to 28 × 106 are investigated. The results demonstrate that with a sufficient mesh resolution the velocity and temperature distributions as well as the spectral peak can be simulated with good agreement to the experimental data.

Design of Ku-band power divider using Substrate Integrated Waveguide technique

A Ku-band Substrate Integrated Waveguide power divider is proposed. In this work, the SIW power divider is designed with T-junction configuration. The SIW technique enables the power divider to have low insertion loss, low cost and features uniplanar circuit. An additional of metallic via hole is added in the center of the junction to improve the return loss performance of the Tjunction SIW power divider. The simulated input return losses at port 1 are better than 27 dB, and features equal power division of about -3.1 dB ±0.4 dB at both output ports across frequency range of 13.5-18 GHz. The SIW power divider is fabricated, and the measurement results show acceptable performances. Since there are some losses contributed by the SMA connector of the fabricated SIW power divider prototype, an additional SIW transmission line is simulated and fabricated to analyze the connector loss.

Thermal mixing in a T-junction: Novel CFD-grade measurements of the fluctuating temperature in the solid wall

This article reports new experiments performed with the purpose of generating novel data of the fluctuating temperature inside the solid in the mixing region between hot and cold water in a T-junction. This data has been measured using a novel sensor (coefh) developed at the Commissariat à l’Energie Atomique et aux Energies Alternatives (CEA) in Cadarache, France. These experiments are performed within the framework of the MOTHER project. The main objective of the MOTHER project is to validate various CFD approaches (such as LES, Hybrid i.e. RANS/LES and RANS) for transient heat transfer in a T-junction configuration including the pipe wall. Hence, the performed experiments have focused on accurately measuring and documenting the boundary conditions to be able to have a well-defined database for CFD validation. The tests are performed for two different Reynolds numbers 40000 and 60000 and for two different T-junction geometries; a sharp corner and a round corner.

Four-way waveguide power divider design for W-band applications

In this article, a four-way waveguide power divider is proposed for W-band applications. The waveguide power divider employs an improved H-plane T-junction configuration. With the introduction of a metallic tetrahedral protrusion into the waveguide junction, good impedance matching can be achieved within a wide frequency range. First, a two-way power divider is designed and analyzed, achieving almost identical amplitude and phase response at its two output ports. Then, other two same T-junctions are cascaded, respectively, at the two output ports of the two-way power divider to realize the proposed four-way power divider. The four-way power divider has been optimized, fabricated, and measured. The measurement results agree with the simulation ones reasonably, which demonstrates that the input return loss of the proposed four-way power divider maintains above 14 dB across the entire W-band with an insertion loss of less than 1.3 dB. Therefore, it could find wide applications in W-band power splitting and combining modules.

Droplet Microfluidics in Thermoplastics: Device Fabrication, Droplet Generation, and Content Manipulation using Integrated Electric and Magnetic Fields.

We have developed droplet microfluidic devices in thermoplastics and demonstrated the integration of key functional components that not only facilitate droplet generation, but also include electric field-assisted reagent injection, droplet splitting, and magnetic field-assisted bead extraction. We manufactured devices in poly(methyl methacrylate) and cyclic olefin polymer using a hot-embossing procedure employing silicon masters fabricated via photolithography and deep reactive ion etching techniques. Device characterization showed robust fabrication with uniform feature transfer and good embossing yield. Channel modification with heptadecafluoro-1,1,2,2-tetrahydrodecyltrichlorosilane increased device hydrophobicity, allowing stable generation of 330-pL aqueous droplets using T-junction configuration. Picoinjector and K-channel motifs were also both successfully integrated into the thermoplastic devices, allowing for robust control over electric field-assisted reagent injection, as well as droplet splitting with the K-channel. A magnetic field was also introduced to the K-channel geometry to allow for selective concentration of magnetic beads while decanting waste volume through droplet splitting. To show the ability to link multiple, modular features in a single thermoplastic device, we integrated droplet generation, reagent injection, and magnetic field-assisted droplet splitting on a single device, realizing a magnetic bead washing scheme to selectively exchange the fluid composition around the magnetic particles, analogous to the washing steps in many common biochemical assays. Finally, integrated devices were used to perform a proof-of-concept in-droplet β-galactosidase enzymatic assay combining enzyme-magnetic bead containing droplet generation, resorufin-β-D-galactopyranoside substrate injection, enzyme-substrate reaction, and enzyme-magnetic bead washing. By integrating multiple droplet operations and actuation forces we have demonstrated the potential of thermoplastic droplet microfluidic devices for complex (bio)chemical analysis, and we envision a path toward mass fabrication of droplet microfluidic devices for a range of (bio)chemical applications.

Controlled fabrication of multi-core alginate microcapsules

In this work, we present a robust microfluidic platform for controlled and complete on-chip generation of alginate microcapsules with single and double liquid cores. A combined Coflow and T-junction configuration implemented in a hybrid glass-PDMS (Polydimethylsiloxane) device is used for the generation of microcapsules with oil as liquid core. Frequency matching of oil-alginate double emulsion generation with that of aqueous Calcium chloride droplet generation allows for controlled merging of the two, resulting in reliable production of microcapsules. Confocal imaging of microcapsule cross-section reveals presence of intact liquid core. In the case of double core microcapsules, the two cores are well separated by alginate layer ensuring their long term stability. The current approach is expected to have advantages over existing techniques for liquid core microcapsule generation in terms of continuity of the process, control over core stability, and non-damage to cells when used for cell encapsulation applications.

Numerical analysis of two experiments related to thermal fatigue

Abstract Jets in cross flow are of fundamental industrial importance and play an important role in validating turbulence models. Two jet configurations related to thermal fatigue phenomena are investigated: • T-junction of circular tubes where a heated jet discharges into a cold main flow and • Rectangular jet marked by a scalar discharging into a main flow in a rectangular channel. The T-junction configuration is a classical test case for thermal fatigue phenomena. The Vattenfall T-junction experiment was already subject of an OECD/NEA benchmark. A LES modelling and calculation strategy is developed and validated on this data. The rectangular-jet configuration is important for basic physical understanding and modelling and has been analyzed experimentally at CEA. The experimental work was focused on turbulent mixing between a slightly heated rectangular jet which is injected perpendicularly into the cold main flow of a rectangular channel. These experiments are analyzed for the first time with LES. The overall results show a good agreement between the experimental data and the CFD calculation. Mean values of velocity and temperature are well captured by both RANS calculation and LES. The range of critical frequencies and their amplitudes, however, are only captured by LES.

Experimental and computational study of gas bubble removal in a microfluidic system using nanofibrous membranes

This paper presents a simple and efficient method for removing gas bubbles from a microfluidic system. This bubble removal system uses a T-junction configuration to generate gas bubbles within a water-filled microchannel. The generated bubbles are then transported to a bubble removal region and vented through a hydrophobic nanofibrous membrane. Four different hydrophobic Polytetrafluorethylene membranes with different pore sizes ranging from 0.45 to 3 μm are tested to study the effect of membrane structure on the system performance. The fluidic channel width is 500 μm and channel height ranges from 100 to 300 μm. Additionally, a 3D computational fluid dynamics model is developed to simulate the bubble generation and its removal from a microfluidic system. Computational results are found to be in a good agreement with the experimental data. The effects of various geometrical and flow parameters on bubble removal capability of the system are studied. Furthermore, gas–liquid two-phase flow behaviors for both the complete and partial bubble removal cases are thoroughly investigated. The results indicate that the gas bubble removal rate increases with increasing the pore size and channel height but decreases with increasing the liquid flow rate.

Droplet formation via squeezing mechanism in a microfluidic flow-focusing device

In this work, the formation of droplets in a microfluidic flow-focusing device is studied and presented. Spurious velocities at the fluid–fluid interface were found to be very small in the lattice Boltzmann simulations. Using this technique, simulations have been performed to study the effect of geometry on formation of droplets for a microfluidic flow-focusing device. The effect of orifice width, orifice length and distance of the orifice on the mechanism of droplet formation and size of droplets is presented for different Capillary numbers. It is shown that, for Ca≪1, creation of droplets proceeds through the squeezing process that has earlier been observed in the T-junction configuration. The size of droplets increases with an increase in the (a) width, and (b) distance of orifice from the inlet. On increasing orifice length, droplet size first decreases to a minimum and increases thereafter. This study also reveals that the size of droplets becomes independent and approaches a constant beyond a critical value of the orifice length.

Self-triggering regime for synchronized formation of two droplets

This letter reports experimental results of the synchronized formation of two liquid droplets in a microfluidic device. A pair of droplets is formed periodically in a T-junction configuration with a single channel for the continuous phase and two inlets for the dispersed phase. The pair-wise droplet formation process is self-triggering, as the first droplet formed upstream triggers the breakup of the second droplet downstream. The triggered breakup happens across the different formation regimes. The effects of capillary number and flow rate ratio on the size and order of the droplets are investigated. The configuration reported here may serve as a parallel to serial sampling device for droplet-based lab-on-a-chip platforms.

Numerical Evaluation of Transport Phenomena in a T-junction Microreactor with Coils of Different Configurations

Microchannel T-junction configuration is used in chemical processing for passive mixing and reactions, because of its relatively easy control of the reaction environment. However, poor mixing and low reaction rate are some of the main drawbacks of this design. This study proposes mass-transport enhancement in a microchannel T-junction by utilizing various configurations of coiled base channel design (e.g., conical spiral, in-plane (flat) spiral, and helical spiral coils). Their mass-transport performance is investigated numerically and compared with that of the conventional straight microchannel T-junction. Laminar flow of gas flow with reactions is investigated using a three-dimensional computational fluid dynamics (CFD) model. Four different microchannel designs, three different channel Reynolds numbers, and three different helical coil diameters are investigated. The coils are made of a square cross-section tube. The results indicate that the coiled base channel displays improved mixing and conversion rate of the reactant. Finally, advantages and limitations of each design are discussed in the light of present numerical results.

The experimental observation and modelling of microdroplet formation within a plastic microcapillary array

Abstract This paper reports an experimental study of the formation of a two-phase liquid mixture in a circular capillary tube of 0.74 mm diameter. Organic liquid, the continuous phase, flowed through the capillary. Aqueous liquid, the dispersed phase, was injected through a hypodermic entering the side of the capillary and a stream of aqueous droplets was formed in the flowing organic liquid. The observed droplet diameters depended strongly on the ratio of the flow-rates between the dispersed and continuous phases: droplet diameters ranged between 480 and 64 μm. A simple model gave good predictions, matching the data and showing how the droplet diameter is dependant on the flow rates of the two phases. The flow geometry was similar to the T-junction configuration used for emulsion formation in microfluidic devices and was fabricated from an extruded plastic capillary array termed a microcapillary film (MCF).

Mass transfer enhancement in microchannel reactors by reorientation of fluid interfaces and stretching

The poor mixing in microchannel reactors, most especially in liquid-phase reactions, primarily due to the inherently diffusion-dominated laminar flow characteristic of microreactors has attracted the attention of many researchers. The aim of this research study is to investigate mass transfer enhancement in microchannel reactors, through a theoretical mixing study of the currently utilized standard, single-channel T-junction configuration as well as four proposed multi-channel, microreactor configurations. The mass transfer enhancement in the proposed configurations is achieved via ‘reorientation and stretching of fluid interfaces’ by imposing some geometric constraints on these microreactor configurations. These configurations are studied for their mixing performance by performing computational fluid dynamics (CFD) simulations of pulse tracer and flow visualization experiments, and using residence time distribution (RTD) and species mass fraction distribution (SMFD) as mixing characterization measures, respectively. Based on the criteria of low pressure drop as well as high mixing performance, the best enhanced-mixing configuration is identified and subsequently optimized. This theoretical study on laminar mixing problem in micromixers/reactors shows CFD simulations as a very useful tool for the design and optimization of micromixing/reaction configurations.

A broadband T-junction diplexer with integrated iris filters

A broad X–Ku band T-junction diplexer with high isolation between the two closely separated bands has been designed and manufactured for a satellite earth station application. The diplexer uses a conventional E-plane T-junction configuration with inductive iris filters. The excellent performance of the diplexer has been achieved by integrating the design of the T-junction with irises in the filter to enable matching and power-distribution optimization of the complete assembly. The experimental results of the diplexer show excellent agreement with the theoretical predictions. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 17: 69–72, 1998.