Quench Zone Research Articles

Simulation study on the flow characteristic and combustion performance in a high-temperature rise combustor based on RQL under different length of quench zone

Simulation study on the flow characteristic and combustion performance in a high-temperature rise combustor based on RQL under different length of quench zone

A quench detection method for parallel co-wound HTS coils based on current redistribution

High-temperature superconducting (HTS) coated conductors (CCs) have become the preferred material for superconducting magnet applications due to their high engineering current density and high mechanical strength. However, due to the low quench zone propagation velocity of CCs, magnets wound with CCs suffer from severe quench risks. Therefore, a rapid, sensitive, and reliable quench detection method is crucial for the safe operation of such HTS magnets. In this paper, we propose a quench detection method based on current redistribution, in which two pieces of HTS CCs are soldered together at each end and insulated in the middle part, which are then parallel co-wound into a double-pancake coil. The two tightly coupled windings and low resistance joints form a very low inductance current loop, resulting in fast current redistribution between the two co-windings even at the inception of quench (with still low quench voltage). We deduced analytical solutions of the current redistribution process under different magnet operational scenarios, including constant current operation, charging and discharging, and proposed quench detection criteria. Corresponding quench tests were performed on a small scale co-wound HTS coil, and the results well verified the analytical solutions and the effectiveness of the quench detection method. Our work may be useful for lowering the risks in HTS magnet quench in various applications.

Multi-field coupled effect of thermal disturbance on quench and recovery characteristic along the hybrid energy pipe

In a novel high temperature superconducting (HTS) hybrid energy pipe, the liquefied natural gas (LNG) and electricity are transported together along the energy pipeline to attain high energy transmission efficiency. When the pipe is exposed to thermal disturbance, the protective medium, liquid nitrogen (LN2), can restrain the quench phenomenon by boiling heat transfer. In order to analyze the multi-field coupled effects of thermal disturbance on the quench and recovery process of the hybrid energy pipe, a one-dimensional quench model is originally proposed in this paper. The model can reflect the intricate interaction of fluid dynamics, boiling heat transfer and current sharing. The results indicate that the high temperature region moves towards the upstream direction in the recovery process. There are three different characteristics: thermal stable zone, quench controllable zone and quench propagation zone. The critical quench energy Qqc is 18% of the critical recovery energy Qrc and the critical quench distance lqc is 9 times as long as the critical recovery distance lrc, independent of the operation conditions. The Qqc and lqc will results in the longest recovery process of the pipe. The pulse duration hardly affects the quench and recovery characteristics. The critical equilibrium current Iec is a constant value of 1800 A, independent of the heat pulse parameters. The Iec will cause the infinite recovery time, which is harmful for the hybrid energy pipe. These rules are significant for the stable operation and design of the hybrid energy pipe. The proposed model can reflect the multi-field strong coupled effect of the thermal disturbance on the quench of system, which fulfils the fast prediction of the quench and recovery behavior.

Modeling and simulation of a multi-bed industrial reactor for renewable diesel hydroprocessing

The complexity of designing and optimizing vegetable oil hydrotreating reactors lies in describing multiple phenomena, including heat and mass transfer, hydrogen consumption, pressure drop, and a complicated network of highly exothermic reactions. This study intends to analyze the behavior of a vegetable oil hydroprocessing unit in a commercial environment via modeling and simulation techniques. In order to describe the three-phase (gas-liquid-solid) system in a detailed manner, a commercial-scale reactor model having multiple catalyst beds and inter-bed quench gas injections was constructed accounting for the heat and mass transfer between phases, the dynamic response of the system, the variation in gas phase velocity, and intraparticle effects. Based on dynamic reactor simulations, quench gas injection strategies were proposed to control the reactor temperature profile and yield of the desired products. Simulation results showed that the selection of a feed inlet temperature plays a major role in reactor overheating and quench injections must start as soon as the reactant stream reaches the inter-bed quench zone to stabilize reactor temperature more rapidly during start-up. In addition, the lengths of the catalyst beds need to be adjusted such that the heat released by chemical reactions is properly distributed along the reactor. The results overall provide useful information for the design and optimization of commercial-scale catalyst bed configurations for hydrotreating renewable feedstock. In particular, it is highlighted that by means of an appropriate gas quenching configuration, reactor temperature can be adequately controlled, allowing higher yields of green diesel.

A visual and full-field method for detecting quench and normal zone propagation in HTS tapes

A fast and effective quench detection method is especially challenging in the development of high-field high-temperature superconducting (HTS) magnets for their safe operations and reliably releasing the stored energy during a quench. The occurrence and propagation of a quench are often accompanied by strong thermal and magneto-mechanical responses within superconducting magnets. Aiming to detect a quench in the whole process and capture the thermoelastic behavior associated with it, a new detection technique with a visual and full-field perception based on the digital image correlation (DIC) method is proposed in the present study. The experiment of a quench triggered thermally by a local spot heater is conducted for a YBCO coated conductor tape in a cryogenic chamber. The evolution and characteristics of the full-field strain in the HTS tape during the processes of a non-quench, a quench occurrence and quench propagation are intuitively presented with experimental observations. For the comparison purpose, the conventional quench detection methods by monitoring temperature and voltage signals during a quench are also utilized experimentally. The results verify the visual and full-field quench detection method, which uses a criterion of thermoelastic strain-rate for the quench occurrence and the evolution of strain contours for the normal zone propagating aspect. Additionally, a numerical quench model of coupled thermoelasticity to simulate the experiment is established and solved with the aid of Comsol multiphysics software. The quantitative results are in good agreement with the experimental measurements to prove the reliability and availability of the developed detection method. Since the DIC method is non-contact and insensitive to intense electromagnetic interferences, it is expected to provide a new technique on quench issues and some basic measurements on strain/stress behaviors in extreme environments of high-field HTS magnets in the future.

Startup and Quench Electromagnetic Simulation of a Bitter Plate TF Coil Concept For the Fusion Nuclear Science Facility (FNSF)

Current distributions during startup and quench of very large reactor relevant coil systems will vary significantly from the smaller prototype magnets. A reactor scale simulation is needed. In this study, the FNSF magnet from the 2017 study is used as an example of a full sized reactor. The intent of the study is to investigate use of HTS conductors in the FNSF and how sizing and performance might be affected. A pancake or Bitter magnet like winding pattern is investigated to allow inductive and resistive redistribution of currents. A portion of the winding pack retains some resistivity to aid in redistribution of current during a transient or quench. Resistive materials can be used to support energy absorption for stability or to provide partial current dump capability during a quench, however, the primary quench mitigation mechanism is inductive redistribution of currents around the quench zone. In this implementation, the Bitter plate is both structural - similar to radial plates in ITER and electrical, intended, to limit current concentration during ramp-up. Use of localized resistors and parallel current paths are used to encourage more uniform startup currents. The analysis is a transient electromagnetic simulation using ANSYS. It is a cyclic symmetry modeling of an individual plate and is limited by the assumption that a local quench is repeated by the cyclic symmetry. This is a concession to the model size. Results are discussed in the context of performance needed for the FNSF.

Flow field characteristics, mixing and emissions performance of a lab-scale rich-quench-lean trapped-vortex combustor utilizing a quench orifice plate combined with a bluff-body

In this study, the low emission combustion technology of Rich-Quench-Lean (RQL) has been applied in Trapped-Vortex Combustor (TVC), and the combinative RQL-TVC shows a promising low emissions performance. By utilizing a quench orifice plate combined with a bluff-body, a lab-scale RQL-TVC was designed. The flow fields of RQL-TVC were measured by 2-D PIV and predicted by 3-D numerical simulation. Flow structures, radial profiles of normalized mean axial velocity, turbulence intensity and mixing level of the quench zone were analyzed. Results reveal that the dual-vortex and the single-vortex flow patterns both exist in cavities and quench zone of RQL-TVC, and the turbulence intensity is strong in the quench zone with some reverse flows. The spiral vortex was discussed by 3-D streamlines and the detail flow structures of the quench zone were analyzed based on the numerical results. The mixing level of the quench zone was determined, and results show that the quench device enhances the mixing level compared with TVC. Combustion efficiency and emissions performance were investigated experimentally, and results demonstrate that RQL-TVC has relatively higher combustion efficiency and lower emission index of CO, UHC and NOx than the same size lab-scale TVC in present work.

Quench Measurements in a YBCO Pancake Coil at 77 K and 4.2 K in Magnetic Fields up to 10 Tesla

We measured stability and quench in a YBCO pancake coil in liquid nitrogen bath (77.3 K) and in liquid helium bath (4.2 K) with externally applied magnetic fields up to 10 T. The pancake coil was instrumented with voltage taps and thermocouples in the winding for measurements of radial and azimuthal quench propagations. A heater was placed on the inner-most part of the winding. Heat pulses of various powers and durations were generated at different coil currents to measure quench and normal zone propagation. A protection circuit with a possibility of setting different quench voltage limits was used to turn off the coil current after the voltage limit was exceeded.

Study of the Hot-Spot Temperature During Quench in the Nonplanar Coils of W7-X

The quench protection system of the nonplanar coils of the Wendelstein 7-X stellarator was laid out over 15 years ago. At that time, the assessment of the hot-spot temperature by a basic adiabatic model was done using design values for material and operation parameters. After the operating experience in 2016, the hot-spot temperature is reassessed with the thermal-hydraulic program THEA, using the actual values for delay and dump time. The electrical resistivity of the conduit alloy is measured over the whole range of temperatures and in magnetic fields on relevant samples of a conductor, exposed to the hardening heat treatment after winding. The results were fed into THEA. Parametric variations are studied in the calculations, e.g., testing the effect of the quench initiation zone, delay time, and dump resistor. The results suggest that the hot-spot temperature of the conduit in the case of quench is safely within the allowable values even when the dump voltage is reduced compared to the initial design value.

Effects of multi-orifice configurations of the quench plate on mixing characteristics of the quench zone in an RQL-TVC model

CO2 concentration measurements and Particle Image Velocimetry (PIV) measurements were performed to investigate the effect of multi-orifice plate geometry on mixing characteristics of a rich-burn quick-quench lean-burn trapped vortex combustor (RQL-TVC). The mixing characteristics in the quench zone were discussed in terms of the mixing degree and the mixing uniformity. And the penetration and the residence time of discrete jet flows conducted by multi-orifice plates were analyzed. The diameter (D) and the quantity (n) of orifices in the multi-orifice plate which composed two rows of orifices was varied, but the blockage ratio (BR) remains constant as approximately 81.5%. The distance of the orifice rows (h) equals D corresponding to the orifice in each plate respectively. The location of the first row is not changed, consequently the position of the second row and the orifice relative position ratio of S/D (S presents the spacing between adjacent orifice mid-points) were varied with D. Through measuring the CO2 concentration, the mixing degree and the mixing uniformity in the quench zone are determined. The penetration and residence time of discrete jet flow conducted by multi-orifice quench plates were quantified by PIV measurements. Results show that the quench plate with the smaller number and the larger diameter of orifices has the most momentum and mass corresponding to the longer penetration and residence time, so that this multi-orifice quench plate has the highest unmixedness rate. On the contrary, that with the shortest penetration is not benefit for occurring the full mixing in the quench zone. Therefore, there is an optimization of multi-orifice configuration existing for the design of multi-orifice quench plates which affect the mixing characteristics of the quench zone in RQL-TVC. The mixing progress in the quench zone depends greatly on discrete jet flows, of which the penetration depth falls into the range from 28mm to 48mm. The multi-orifice plate, designated as M6D8.0 with 6 orifices and 8.0mm-diameter, offers the intermediate length of penetration depth (approximately 35mm). The residence time of discrete jet flows derived from PIV results is between 0.6ms and 1.2ms. Most of that is less than 1ms and meets the requirement of the critical time scale of complete quick-mixing.

An Experimental Investigation of the Transient Response of HTS Non-insulation Coil

A single pancake coil without turn-to-turn insulation was tested in this paper to investigate the transient responses under different situations. We performed charging and discharging test, AC current test, and regional quench emulation test on the non-insulated (NI) coil. The experimental test results show a significant time delay for charging and discharging characteristics of NI coil and can be validated by a simple proposed equivalent electrical circuit. Under the AC operating current, the NI coil can bypass nearly all the AC current from the coil spiral path to the radial path such that it is not possible for NI coil to store or be affected by the AC magnet field. Additionally, while carrying AC current, the AC loss dissipation of NI coil is inversely proportional to the frequency of the AC operating current. When a regional quench occurs, the NI coil can bypass the current in the regional quench zone to avoid further temperature accumulated and protect the NI coil itself.

Computational Study on flow Structures of Quench Zone in a Rich-quench-lean Trapped-vortex Combustor

Abstract The quench zone is one of key issues for a rich-quench-lean(RQL)/trapped-vortex combustor(TVC). The characteristics of flow structures of quench zone were investigated computationally with the correction by the particle image velocimetry(PIV) results. RQL/TVC combines the potential advantages of the low emission staged combustion technology of RQL with TVC. TVC has been a very promising novel combustor concept offering improvements in lean blow-out, altitude relight, and operating range. Besides, compared to conventional combustors, TVC has a potential to decrease nitrogen oxides emissions. By utilizing quench devices with different sizes of holes under the same blockage ratio in mainstream position, this paper describes the characteristics of flow structures of quench zone in a RQL/TVC. The results show that, through the quench devices, the mainstream flow quickly mixes with the flow from the cavity zone under variable mixing levels which are related to the changing of different sizes of holes. The effects of turbulent intensity and unmixedness level were examined and discussed.

Dynamic modeling of Shell entrained flow gasifier in an integrated gasification combined cycle process

The Shell coal gasification system is a single-stage, up-flow, oxygen-blown gasifier which utilizes dry pulverized coal with an entrained flow mechanism. Moreover, it has a membrane wall structure and operates in the slagging mode. This work provides a detailed dynamic model of the 300MW Shell gasifier developed for use as part of an overall IGCC (integrated gasification combined cycle) process simulation. The model consists of several sub-models, such as a volatilization zone, reaction zone, quench zone, slag zone, and membrane wall zone, including heat transfers between the wall layers and steam generation. The dynamic results were illustrated and the validation of the gasifier model was confirmed by comparing the results in the steady state with the reference data. The product gases (H2 and CO) began to come out from the exit of the reaction zone within 0.5s, and nucleate boiling heat transfer was dominant in the water zone of the membrane wall due to high heat fluxes. The steady state of the process was reached at nearly t=500s, and our simulation data for the steady state, such as the temperature and composition of the syngas, the cold gas efficiency (81.82%), and carbon conversion (near 1.0) were in good agreement with the reference data.

Optimum design of flow distribution in quenching tank for heat treatment of A357 aluminum alloy large complicated thin-wall workpieces by CFD simulation and ANN approach

Based on the computational fluid dynamics (CFD) method, a quenching tank with two agitator systems and two flow-equilibrating devices was selected to simulate flow distribution using Fluent software. A numerical example was used to testify the validity of the quenching tank model. In order to take tank parameters (agitation speed, position of directional flow baffle and coordinate position in quench zone) into account, an approach that combines the artificial neural network (ANN) with CFD method was developed to study the flow distribution in the quenching tank. The flow rate of the quenching medium shows a very good agreement between the ANN predicted results and the Fluent simulated data. Methods for the optimal design of the quenching tank can be used as technical support for industrial production.

The Effects of External Pressure on the Thermal and Electrical Properties of Stacked GdBCO Coated Conductor Tapes

This study examined the effects of external pressures on the thermal and electrical stabilities of stacked GdBCO CCs through quench tests. The minimum quench energies and two-dimensional normal zone propagation velocities of stacked GdBCO CCs connected electrically in series under various external pressures were examined. The quench test results showed that the minimum quench energy increased with increasing the external pressure. Longitudinal normal zone propagation velocities were greater than transverse normal zone propagation velocities. Moreover, normal zone propagation velocities increased with increasing applied pressure implying that applied pressure resulted in increased layer-to-layer thermal contact that allowed hot spots to dissipate more easily.

Modeling of emissions from HCCI engines using a consistent 3-zone model with applications to validation of reduced chemistry

The piston crevice and the quench zone, the area of fluid close to the cylinder walls, are responsible largely for emissions in Homogeneous Charge Compression Ignition (HCCI) engines. For proper modeling of emissions from HCCI engines, the piston crevice and quench zone need to be included in the numerical model. For HCCI applications, we have developed an improved numerical model with three zones: the piston crevice zone, the quench zone close to the cylinder walls, and the cylinder zone comprising up of the rest of the cylinder. With the assumption of equal pressure for all zones, an analytical model is developed for the mass transfer between the core fluids and those in the piston crevice. The numerical model then solves for the coupled mass, energy, and species equations simultaneously leading to consistent solutions at every time step. Comparisons of the calculated results are made between this stand-alone multi-zone code, a 3-D CFD model coupled with multiple zones, and experimental data which show encouraging agreement. The present stand-alone model also provides a useful platform for development/validation of reduced chemistry for emissions.

Quench Behavior of ${\hbox {Bi}}_{2}{\hbox {Sr}}_{2}{\hbox {Ca}}_{2}{\hbox {Cu}}_{3}{\hbox {O}}_{\rm x}/{\hbox {Ag}}$ Tape With AC and DC Transport Currents and a Comparison With ${\hbox {YBa}}_{2}{\hbox {Cu}}_{3}{\hbox {O}}_{\rm x}$ Conductors

When operating in power applications, superconducting conductors often carry alternating currents (AC). Thus, understanding the quench behavior under AC conditions is essential for protecting high temperature superconductor-based devices in power applications. In this work, the quench behavior of Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Sr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Ca <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /Ag (Bi2223/Ag) tape with AC and DC transport currents is reported. The minimum quench energies and normal zone propagation velocities are measured for different DC and AC transport currents at 45 K. The frequency of the AC transport current is varied from 50 Hz to 400 Hz. AC losses are measured to analyse the background condition of AC quenches. The results are compared with those of a YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> (YBCO) coated conductor that was studied previously with identical conditions.

Quench Analysis of the KSTAR TF Magnets and Bus Lines for the First Campaign

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In the Korea Superconducting Tokamak Advanced Research(KSTAR) device, the Toroidal Field (TF) coils were manufactured with <formula formulatype="inline"> <tex Notation="TeX">${\rm Nb}_{3}{\rm Sn}$</tex></formula>, and the bus lines with NbTi, and all the coils are cooled by supercritical helium. During the first campaign, the TF coils were operated with a steady state current of 15 kA. In case of a quench the conductor is being developed due to an unexpected effect on the superconducting strands, the current should be discharged into an external dump resistor for protection of the magnet. The development or recovery of the quench is related to the protection triggering delay time and the quench voltage. The thermo-hydraulic phenomena were simulated by the GANDALF code and the initial quench propagation condition was found from the minimum quench energy and the initial quench zone. In this paper, we determined the quench voltage level and trigger time by analysis of temperature, voltage, and pressure growth, in the magnet and bus lines, with triggering delays of <formula formulatype="inline"><tex Notation="TeX">${\rm t}=2\ {\rm s}$</tex></formula>, 3 s, 4 s, and 5 s, by analysing the effects of a temperature and voltage growth of the magnet and bus lines. </para>

Experimental Study on Laser-Induced Ignition of Swirl-Stabilized Kerosene Flames

Conventional ignition systems of aeroengines are an integral part of the combustion chamber’s structure. Due to this hardware-related constraint, the ignition spark has to be generated in the quench zone of the combustion chamber, which is far from the optimum regarding thermo- and aerodynamics. An improved ignitability of the fuel-air mixture can be found in the central zone of the combustor, where higher local equivalence ratios prevail and where mixing is favorable for a smooth ignition. It would be a major advancement in aeroengine design to position the ignition kernel in these zones. A laser system is able to ignite the fuel-air mixture at almost any location inside of the combustion chamber. Commercial laser systems are under development, which can replace conventional spark plugs in internal combustion engines and gas turbines. This study was conducted to evaluate the applicability of laser ignition in liquid-fueled aeroengines. Ignition tests were performed with premixed natural gas and kerosene to evaluate the different approaches of laser and spark plug ignition. The experiments were carried out on a generic test rig with a well-investigated swirler, allowing sufficient operational flexibility for parametric testing. The possibility of the free choice of the laser’s focal point is the main advantage of laser-induced ignition. Placing the ignition kernel at the spray cone’s shear layer or at favorable locations in the recirculation zone could significantly increase the ignitability of the system. Consequently, the laser ignition of atomized kerosene was successfully tested down to a global equivalence ratio of 0.23. Furthermore, the laser outperformed the spark plug at ignition locations below axial distances of 50 mm from the spray nozzle.

Detect-and-Activate-the-Heater Protection Technique for YBCO Coils

This paper presents the results of work, experimental and simulation, performed on an YBCO pancake coil to develop a detect-and-activate-the-heater (DAH) protection technique. In this DAH protection technique a ldquoprotection heaterrdquo (PH) is activated, upon the detection of a quench zone in a coil, to create an additional normal zone to absorb the stored magnetic energy sufficient to keep the initially quenched zone (hot spot) from overheating. It is computed that a protection heater for most coils needs to cover only a fraction of the winding to keep the quenched zone from overheating. The pancake coil used in the experiment, 100-mm i.d., 190-mm o.d., and 4.3-mm height, is dry-wound with copper plated YBCO tape, 4.3-mm wide, 96.3- mum thick, 100-m long, and is turn-to-turn insulated with 38 mum thick Nomex spacer. The pancake stores a magnetic energy of 30 J at an operating current of 80 A at 65 K. Because the smaller the magnet size, the less applicable the assumption of adiabatic conditions is and also the more beneficial NZP becomes that would otherwise be negligible in ldquolargerdquo magnets, the hot spot temperature observed in the experiment with this ldquosmallrdquo test coil was much less than that computed based on the assumptions of adiabatic conditions and no NZP. To validate the basic concept and consequences of DAH protection technique either a test coil has to be large or if the same coil is to be used, it should be tested at the temperature range close to 20-30 K so that the coil can carry a large current and thus store a large magnetic energy.