Quartz Wall Research Articles

Two-dimensional thermometry measurements in confined swirl flames using filtered Rayleigh scattering

Two-dimensional temperature measurements using filtered Rayleigh scattering (FRS) were performed in confined CH4/air swirl flames at atmospheric pressure. The investigated burner has a combustion chamber consisted of four quartz windows. The combustion chamber is 160 mm high with a square section of 50 × 50 mm2. Measurements were challenging due to the strong interference from the incident laser impinging onto quartz windows, wall reflection and Mie scattering. Comparisons between the FRS and a conventional probe-based thermocouple were conducted through several investigated cases. Five operating conditions were studied with the equivalence ratios (Φ) of the premixed CH4/air mixture covered a range of 0.67–0.83. Under each condition, five cross sections (C.S.) of the swirl flame were investigated and compared to analyze (1) the flame structures and temperature distributions of the instantaneous FRS images and (2) the uniform temperature radius as well as the joint probability density function (PDF) profiles of the averaged FRS signals. Results indicate that FRS can effectively suppress the background scattering and the average standard deviation of FRS measurements throughout the experiment is < 7.5%. The thermochemical state of the confined swirl flames is strongly influenced by Φ, leading to varieties of flame structures and temperature distributions.

Coking behavior and syngas composition of the char supported Fe catalyst of biomass pyrolysis volatiles reforming

The biomass for flammable gas production and its carbon deposition behaviour has been studied in a lab-scale fixed bed reactor, comprising pyrolysis and subsequent volatiles reforming produced in situ reaction. The distribution of pyrolysis products varies greatly with the addition of WS@5 Fe catalyst. During catalyst cycle process, both the char and heavy oil yield decreases significantly from 27.34% and 6.73% to 20.41% and 4.12%, respectively. This work also focuses on the carbon deposition of the WS@5 Fe catalyst used in the second step. The amount of coke on quartz tube wall (coke 1) decrease with increasing the temperature, and the surface carbon of the catalyst (coke 2) is found. Deactivated catalyst samples are recovered. The results present that the deactivation is attributed to the wrapping and covering of Fe by coke. There are reactions such as the coke deposition, the coke consumption, and the gasification reaction of char.

Continuous gas temperature measurement of cold plasma jets containing microdroplets, using a focussed spot IR sensor

Controlling gas temperature via continuous monitoring is essential in various plasma applications especially for biomedical treatments and nanomaterial synthesis but traditional techniques have limitations due to low accuracy, high cost or experimental complexity. We demonstrate continuous high-accuracy gas temperature measurements of low-temperature atmospheric pressure plasma jets using a small focal spot infrared sensor directed at the outer quartz wall of the plasma. The impact of heat transfer across the capillary tube was determined using calibration measurements of the inner wall temperature. Measured gas temperatures varied from 25 °C–50 °C, increasing with absorbed power and decreased gas flow. The introduction into the plasma of a stream (∼105 s−1) of microdroplets, in the size range 12 μm–15 μm, led to a reduction in gas temperature of up to 10 °C, for the same absorbed power. This is an important parameter in determining droplet evaporation and its impact on plasma chemistry.

Strategies for Scalable Gas-Phase Preparation of Free-Standing Graphene

The preparation of graphene with high quality serves as a prerequisite for its usage. Traditional methods of graphene production, represented by liquid-phase exfoliation and chemical vapor depositi...

Microstructure of Ti-Based Alloys after Rapid Solidification

Ti-6Al-4V alloy ribbons were successfully prepared by rapid solidification at different roller speeds. The morphology and microstructure of Ti-6Al-4V alloy ribbons were studied by X-ray diffractometer, scanning electron microscope and energy spectrum analysis. The effect of SiO2 on the microstructure and properties of Ti-6Al-4V alloy ribbons were discussed. It is found that the Ti-6Al-4V alloy ribbons consist of β phase with alternated distribution of α' phase and α'' phase. And quicker roller speed promotes the formation of α' phase for the higher rapid solidificationg cooling rate. According to the analysis of energy spectrum data, it is found that there is chemical reactions between the Ti-6Al-4V material and the quartz tube wall during electromagnetic induction melting at high temperature, and the Si elements are segregated at the embossment induced by quick solidification and the phase interfaces between α′ phase and β phase.

Direct experimental detection of hydrogen radicals in non-oxidative methane catalytic reaction

Non-oxidative conversion of methane to olefins, aromatics and hydrogen (MTOAH) has been reported recently over metal single sites such as iron and platinum. The reaction was proposed to involve catalytic activation of methane followed by gas phase C−C coupling of methyl radicals. This study using H atom Rydberg Tagging time-of-flight technique provides direct experimental evidence for the formation of hydrogen radicals during MTOAH reaction over a catalytic quartz wall reactor containing embedded iron species (denoted as Fe-reactor). Fe-reactor gives 7.3% methane conversion at 1273 K with 41.2% selectivity toward C 2 (ethane, ethylene and acetylene) and 31.8% toward BTX (benzene, toluene and xylene), respectively. The enhancing effects of hydrogen radicals on overall MTOAH performance are validated by cofeeding hydrogen donor benzene, which provides an additional route of methane activation apart from catalytic activation. H radicals (200–250 µs) during methane activation over catalytic Fe-reactor are detected successfully using the technique of H atom Rydberg tagging TOF-MS, which is capable of discriminating different H sources according to their time-of-flight velocities.

Combustion Dynamics of Annular Systems

ABSTRACT New results on the dynamics of annular combustors during ignition and combustion instabilities will be reviewed. Ignition dynamics is considered first by examining experiments carried out in a system comprising a plenum feeding premixed gaseous reactants through multiple swirling injectors and an annular combustor formed by two concentric transparent quartz walls allowing full optical access to the flame. The analysis focuses on the “light-round” process during which the flame spreads from one injector to the next eventually leading to established flames on each injector. The transparent lateral walls allow a full view of the flame propagation from a spark igniter located in the neighborhood of one injector. High speed imaging is used to examine flame displacement and deduce the ignition delay yielding a full light around of the annular combustor. Changes associated to operation with spray flames are then discussed. The second part of this article is concerned with combustion instabilities of annular systems coupled by azimuthal modes. This type of oscillation has received considerable attention in recent years because the underlying coupling is often observed in the advanced premixed combustion architectures used in modern gas turbines. Recent studies have allowed a detailed examination of the dynamics of annular devices comprising multiple swirling injectors. Experiments on annular systems and single sector configurations provide new insight on the coupling process between acoustics and unsteady combustion. Results for self-sustained combustion oscillations coupled by azimuthal modes are presented for operation with gaseous premixed reactants and with spray flames.

Anisotropic Dynamics of Binary Particles in Confined Geometries.

The diffusion dynamics of colloidal particles in a good solvent confined between two parallel quartz walls have been studied within the framework of dynamical density functional theory. The highly ordered density layers induced by interfacial effects give rise to the oscillating dynamics, resulting in position-dependent structural relaxations and diffusivities. Further investigation reveals that particle size, particle-wall interaction, and slitpore width play different roles in affecting the oscillating behaviors along different directions. As a result, the theory yields the local mean square displacements in perpendicular and parallel directions, which agree remarkably well with prior experimental measurements. The results indicate that the mean square displacements can be quantitatively predicted based on the knowledge of inhomogeneous thermodynamics and dynamics. The local and averaged free energy evolution of the binary particles has been described and presented to understand their dynamic mechanism in confined geometry.

LA-ICP-MS trace element analysis of arsenopyrite from the Samgwang gold deposit, South Korea, and its genetic implications

The Samgwang deposit, previously classified as an orogenic gold deposit, consists of several structurally controlled auriferous quartz veins hosted by metasedimentary rocks of the Precambrian Gyeonggi massif, South Korea. The gold at Samgwang occurs as electrum commonly associated with arsenopyrite. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), coupled with ore microscopy, was conducted on Au and trace elements distributed in arsenopyrite grains contained in quartz vein and wall rock samples. Resulting profiles for Au, Co, Ni, and Sb were relatively flat and showed little variability, indicating that the elements were relatively homogeneously distributed and exchanged via substitution in arsenopyrite, while variability and noisy depth profiles inferred that Pb was present as tiny inclusions or discrete particles. Furthermore, measured gold concentrations were typically higher in arsenopyrite grains from laminated quartz veins (avg. 2.07 ppm) than in grains from massive quartz veins (avg. 0.26 ppm) and wall rock samples (avg. 0.33 ppm). In the case of wall rock and massive quartz vein samples, arsenopyrite grains of euhedral shape illustrate an element distribution pattern whereby Au concentrations tend to decrease towards the rims of the analyzed grains. In contrast, the rims of arsenopyrite grains in laminated quartz vein samples recorded much higher Au concentrations of up to 20.1 ppm, with increasing Pb, Bi, and Ag, particularly within domains of fractured or recrystallized arsenopyrite grains. The newly acquired LA-ICP-MS data, along with textural evidence, may be interpreted in terms of the release and remobilization of invisible gold that was originally locked up in the arsenopyrite. This release is linked to late deformation and hydrothermal event during which the remobilized invisible gold was redeposited as electrum. In addition, there is evidence for the introduction of additional gold and other precious and base metals by the late-stage hydrothermal fluids. Based on the above and in contrast to previous genetic models, we propose a more complex metallogenic concept for Samgwang in which the economically important gold enrichment process was genetically related to intrusive activity during the waning stages of Jurassic to Early Cretaceous Daebo orogenesis.

Modeling of a xenon short arc lamp considering the behavior of tungsten vapour evaporated from electrodes

The tungsten vapour produced from the electrodes during short arc lamp operation is transported by gas convection and then deposited on the inner quartz bulb wall to form a tungsten thin film, causing the wall to blacken. We have been able to consider important phenomena for the first time by developing a unified numerical simulation model incorporating relevant sub-models. These include the absorption of the radiant energy due to blackening of the lamp and the temporal variation in the lamp parameters. The validity of the numerical simulation model is first evaluated by comparison with experimental results. The basic characteristics of the lamp obtained using the model is found to be in good agreement with the experimental results and other research results. The influence of the bulb wall blackening is then examined. The temperature of the bulb is shown strongly affected by convective heat transfer from the hot gas, and the temperature rise of the bulb after blackening is found to be primarily governed by the absorption of the radiant energy by the tungsten thin film. Through the increase in the bulb temperature, the gas temperature in the bulb is also increased. This raises the operating pressure, which increases the stress on the bulb wall. Consequently, it is demonstrated that the probability of breakage gradually increases with time due to the blackening by tungsten vapour deposition.

Characterization of Rotating Detonation Engine Injector Response Using Laser-Induced Fluorescence

Rotating detonation engine (RDE) fuel injector response was characterized in a lab-scale linear testing platform. The experimental design consists of a linear extrusion of an RDE cross section and allows rapid interchanging of modular, 3D printed inlet geometries. An array of helium jets was established within a channel, and a single combustion-driven shock pulse was presented at one end. The subsequent injector interruption and recovery were quantified using high-speed acetone planar-laser-induced fluorescence (PLIF). A quartz wall provided optical access to the channel and the injector response was visualized at up to 30 kHz. Three dynamic pressure transducers allowed the shock strength to be quantified along the length of the channel. Timescales associated with jet interruption and recovery were determined by analysis of instantaneous PLIF images and considered in conjunction with the dynamic pressure measurements. Results are presented as a function of pertinent nondimensional parameters and compared with available experimental and computational data in a full, research-scale RDE.

Wall Temperature Measurements in Gas Turbine Combustors With Thermographic Phosphors

Phosphor thermometry has been developed for wall temperature measurements in gas turbines and gas turbine model combustors. An array of phosphors has been examined in detail for spatially and temporally resolved surface temperature measurements. Two examples are provided, one at high pressure (8 bar) and high temperature and one at atmospheric pressure with high time resolution. To study the feasibility of this technique for full-scale gas turbine applications, a high momentum confined jet combustor at 8 bar was used. Successful measurements up to 1700 K on a ceramic surface are shown with good accuracy. In the same combustor, temperatures on the combustor quartz walls were measured, which can be used as boundary conditions for numerical simulations. An atmospheric swirl-stabilized flame was used to study transient temperature changes on the bluff body. For this purpose, a high-speed setup (1 kHz) was used to measure the wall temperatures at an operating condition where the flame switches between being attached (M-flame) and being lifted (V-flame) (bistable). The influence of a precessing vortex core (PVC) present during M-flame periods is identified on the bluff body tip, but not at positions further inside the nozzle.

FIB-milled quartz nanopores in a sealed nanopipette

We report the use of laser-pulled quartz nanopipettes as a new platform for microfabricated nanopores. A quartz nanopipette is prepared on a laser puller and sealed closed prior to focused-ion beam (FIB) milling. A quartz nanopore can then be FIB-milled into the side walls of the sealed pipette and used to analyze single nanoparticles. This method is fast, reproducible and creates nearly cylindrical nanopores in ultrathin quartz walls with controllable diameter down to 66nm. Both pore size and wall thickness can be readily controlled in the FIB milling process by adjusting milling parameters and milling at different locations along the pipette walls. FIB-milled quartz nanopores combine the advantages of the pipette pores and silicon chip-based membrane pores into one device while avoiding many of the challenges of two popular nanopore devices. First, they can be used as a handheld probe device like a quartz pipette. Second, the use of an ultrathin quartz membrane gives them superior electric property enabling low noise recording at a higher bandwidth and a highly focused sensing zone located at a farther distance away from the highly restricted tip region. The inner and outer diameters of the resulting pore can be precisely measured using scanning electron microscopy (SEM). As an application, FIB-milled side nanopores are used to study translocation of polystyrene nanoparticles. In addition to studying the dependence of translocation time on the pore length, we demonstrate detection of nanoparticles in parallel nanopores of different lengths and use finite-element simulation to confirm the identity of the two resulting populations. Our results show that FIB-milled side nanopores are a useful platform for future analytical applications like studying nanoparticle translocation dynamics.

Counting Single Redox Molecules in a Nanoscale Electrochemical Cell.

We report the use of a Pt bipolar electrochemical nanocell and fluorescence to detect single redox molecules. A Pt nanocell is formed by depositing a Pt particle at a nanopipet orifice which separates the inside pipet volume from the bulk solution. Highly fluorescent resorufin molecules are generated on the inner Pt surface and optically detected and counted due to unique properties of the nanocell. First, the pipet is horizontally positioned on a microscope allowing one to examine a 6-μm distance from the electrode/solution interface. Second, the resazurin/resorufin molecules are confined inside a 100 nm pipet resulting in a very high signal/background ratio in fluorescence detection. Third, the small pipet size confines the motion of the redox molecules increasing the probability of transient molecular adsorption on the quartz walls. This, along with the longer diffusion distance increases the chance of fluorescence detection. The ability to count single redox molecules allows us to estimate the detection efficiency. This study shows the unique power of fluorescence-based electrochemical detection in studying single redox events. Future use of this method may enable one to study single redox events of conventional nonfluorogenic redox reactions on the outer surface of the bipolar nanoelectrode, such as oxidation of H2 catalyzed by a metal cluster electrocatalyst or a single enzyme.

Experimental determination of equilibrium CH4–CO2–CO carbon isotope fractionation factors (300–1200 °C)

Carbon isotope fractionation in the CO2–CO–CH4–C system was investigated at 300–1200°C at near-atmospheric pressures by thermally decomposing a variety of organic materials in sealed quartz tubes. Measured gas speciations correspond well to the expected range from thermodynamic calculations. We show that chemical and isotopic equilibrium among gas species is obtained when applying a nickel catalyst for CO2/CH4, CH4/CO, and CO2/CO at ≤600°C or without a catalyzing agent for CO2/CO at ≥800°C. The experiments define carbon isotope fractionation factors for the CO2/CH4, CO2/CO and CH4/CO pairs as(i)103ln⁡αCO2/CH4=8.9(±0.6)⋅105⋅(1T2)0.825(±0.005) (200–1200°C)(ii)103ln⁡αCO2/CO=1.07(±0.05)⋅106⋅(1T2)0.830(±0.003) (300–1200°C)(iii)103ln⁡αCH4/CO=1.1(±0.2)⋅103⋅(1T2)0.462(±0.001) (300–1200°C), which reproduce the experimental values within 0.2‰ for CO2/CH4 and CO2/CO and within 0.12‰ for CH4/CO (T in K, 1σ fit uncertainties in brackets, CO2/CH4 includes the ≤600°C experimental data of Horita, 2001). Carbon isotope fractionation factors at 1000°C are still large for CO2/CH4 and CO2/CO (6.6 and 7.5‰, respectively) but only 1.5‰ for CH4/CO.Elemental carbon precipitated through thermal decomposition of the organic starting materials yields δ13C values that depend on the X(O) = O/(O + H) of the organic starting material, i.e. the initial oxidation state of carbon in the organics. We further observe a catalytic effect of the quartz walls on chemical and isotopic exchange in the CO2/CO system, probably due to the activation of the silicate surface by H+ and OH− ions at >650°C. Our experimental results yield improved calibrations of the CO2/CH4 equilibria and the first experimental calibration of CO2/CO and CH4/CO carbon isotope fractionation. Applications are in the tracing of magmatic hydrothermal gas emissions, in carbon-precipitating COH-fluids, and in monitoring of coal-seam fires, but our results may also be applied for quality control during steel-making processes.

Investigation of wall chemical effect using PLIF measurement of OH radical generated by pulsed electric discharge

Near-wall distribution of OH radical concentration provides a measure of the wall chemical effect near a solid surface. However, it is not a straightforward process to isolate the wall chemical effect from the effect of gas-phase reactions because the OH radical distribution can be influenced by both the wall chemical effect and the effect of heat and radicals released by gas-phase reactions. In the present study, instead of the flame, OH radicals generated by a pulsed electric discharge is used in order to eliminate the interference from the gas-phase reaction. OH field with comparable concentration to a methane/air premixed flame has been achieved by tuning the input electric power of pulsed electric discharge. The wall chemical effect is investigated by comparing OH distributions near the quartz wall and the quartz wall with 100-nm-thick alumina coating, while the wall thermal boundary condition is kept identical. High-resolution near-wall measurement of OH distribution was carried out by microscopic planar laser-induced fluorescence (PLIF), and the result was analyzed with the aid of numerical simulations with a surface reaction mechanism. It is found that the initial sticking coefficients estimated on the quartz/alumina surfaces are almost the same with the results in our previous methane/air flame experiment (Saiki and Suzuki, 2013). In the present OH field with electric discharge, it is easier to investigate the radical quenching effect, as the wall chemical effect on OH is decoupled from the gas-phase reaction. The chemical action defined as the wall-normal OH concentration gradient divided by the local OH concentration, which is an index of the wall chemical effect, increases with increasing wall temperature in the OH field generated by pulsed electric discharge.

О необычном поведении расплава Al – Si в тонких капиллярах

The numerical simulation is devoted to the division of binary metal melt Al – Si filling the thin alundum or quartz capillary. The results of calculations have been gotten for cylindrical channel heated from above. Earlier the behaviour of the similar eutectic melts Pb – Sn, Pb – Bi, Zn – Al, Cd – Bi, Bi – Sb, Cu – Sn, Cu – Pb was considered experimentally and theoretically. The adequate theory of the observed physical phenomena was constructed for these pairs of metals. In experiments the binary melt was prepared to be homogeneous at the initial moment of time. The relatively quick and significant division of a mixture on components was observed for each binary melt. The specific feature of the process was found, namely, the heavy component moved to the lower part of the capillary. The character concentrations difference on the edges of the channel reached to the sufficiently big value 20 %. The explanation of the similar phenomenon has been done by the authors of this article and is based on the assumption of the key role of the interfacial tension on the boundary between melt and alundum wall. It is supposed that the condition of non-wetting is fulfilled on the alundum or quartz walls of the capillary for the metal pairs listed above. Thus, the surface active component appears on the interphase over the phenomenon of adsorption. In experiments under discussion the small temperature gradient oriented vertically upward takes place always in the working space of the smelting furnace. So the thermocapillary force arises on the interphase and generates the large-scale movement in the volume. The equations and laws of interfacial hydrodynamics are valid in this case and can be applied to describe the heat and mass transfer in the liquid binary metals. The transfer of heavy surface-active agent takes place along the direction where the surface tension increases i.e. to the down edge of the capillary. Heavy component continues to accumulate in lower part of the channel so long as all fluxes, caused by external forces, will be equilibrated in the volume and on the surface by the concentration-capillary force and diffusion. On the other hand it has been discovered experimentally that the alloy Al – Si behaves as anomalous melt in relation to all tested pairs of metals. On the contrary to the previous data the heavy component (silicon) accumulates in the top part of the capillary. The explanation of such anomaly is given in this article. It is necessary only to take into account in theoretical model the fact that the light aluminum is surface-active agent in our pair of metals. This component is pressed out of the volume on the surface and under the action of thermocapillary force is transferred downwards along boundary of a channel. Then it returns inside the volume near the bottom by means of the desorption. This process generates the unstable stratification since the light component is located in lower part and at the same time the heavy one is lifted to the top of the capillary. In spite of convective instability there is no large-scale transfer of the light admixture upwards because of heating from above and big hydrodynamic resistance of a thin capillary. The estimations and direct numerical modeling show that the thermocapillary mechanism dominates above the resulting Archimedean force for given geometry, therefore inflow of a light component to the bottom part of a capillary prevails of a loss that causes accumulation of the aluminum in the bottom of channel.

Wall temperature measurements at elevated pressures and high temperatures in sooting flames in a gas turbine model combustor

Wall temperatures were measured with thermographic phosphors on the quartz walls of a model combustor in ethylene/air swirl flames at 3 bar. Three operating conditions were investigated with different stoichiometries and with or without additional injection of oxidation air downstream of the primary combustion zone. YAG:Eu and YAG:Dy were used to cover a total temperature range of 1000–1800 K. Measurements were challenging due to the high thermal background from soot and window degradation at high temperatures. The heat flux through the windows was estimated from the temperature gradient between the in- and outside of the windows. Differences in temperature and heat flux density profiles for the investigated cases can be explained very well with the previously measured differences in flame temperatures and flame shapes. The heat loss relative to thermal load is quite similar for all investigated flames (15–16%). The results complement previous measurements in these flames to investigate soot formation and oxidation. It is expected, that the data set is a valuable input for numerical simulations of these flames.

Transformation of waste crystalline silicon into submicro β-SiC by multimode microwave sintering with low carbon emissions

This paper presents a novel method for the transformation of waste crystalline silicon, including waste polysilicon (photovoltaic industry), single crystal silicon (waste chip), and activated carbon (AC) into submicro β-SiC in timescales of minutes using a multimode microwave rotary tube reactor under open-air conditions. This research addressed the difficult problem of microwave sintering temperature measurement by using light conducted by a quartz tube wall. The synthesis underwent a liquid-solid reaction at 1450±50°C for 6–8min, which is a noticeable improvement when compared to industrial processes, where a heating time of 30h and temperatures of 2200–2400°C are commonly needed. Theoretical calculations show that the new synthesis method for β-SiC consumes 4.1–4.8 times less energy than modern production methods using quartz sand (SiO2) as the raw material, and CO2 emission using this method is reduced by 76–79%.

Experimental demonstration of a novel approach to increase power conversion potential of a hydrocarbon fuelled, portable, thermophotovoltaic system

A novel, compact mesoscale thermophotovoltaic (TPV) power generating system using a combination of porous media combustion and a simple band-pass filtering method has been proposed and experimentally studied. The novelty in this work is the idea of harvesting the heat produced in the microcombustor via the silicon carbide (SiC) porous media which becomes an effective radiator owing to its high emissivity. This is then combined with wafers that have a high optical transmissivity in the part of the spectrum that is useful for power conversion using the TPV system. In this work, we utilised two combustor wafers (silicon and quartz) with suitable thermal and optical properties. Quartz having a high transmissivity of 0.9 compared to silicon (<0.6) proved to be superior in performance when combined with the porous media combustion for TPV power generation. To further illustrate the combination of effects, we also performed experiments in which porous media was not inserted in the combustor and the radiation was effectively from the hot combustor walls. In this case, silicon which has a higher emissivity than the quartz performs better. Overall the TPV power generation was SiC+quartz>SiC+Si>pure Si walls>pure quartz walls.