Mass Flow Controller Research Articles

Effects of Extra-Framework Metal Centers on Zeolite-Based NH3-Sensors for Exhaust Gas Abatement

Introduction The abatement of nitrogen oxides (NOx) from lean-burn engine exhausts is nowadays mainly achieved by selective catalytic reduction using NH3 as reducing agent (NH3-SCR). In these systems, a solution of urea (AdBlue®) is injected in the exhaust, upstream the SCR unit, and converted to NH3 under operative conditions. Precisely dosing the NH3 inlet is necessary in order to achieve the highest NOx conversion and, simultaneously, to avoid NH3 slip. Since the currently employed NOx sensors are cross sensitive to NH3, precise NH3 sensors are also necessary for a correct determination of the outlet NOx concentration [1]. In this context, the emerging concept of utilizing “catalysts as sensors” can play an important role for the on-board diagnosis, specially by application of zeolite materials [2].Zeolites are proton conductors and their properties as sensing materials for NH3 detection are well documented: in situ impedance spectroscopy (IS) has proved that the adsorption of NH3 on zeolites increases the ion conductivity by forming highly mobile NH4 + species [3]. Moreover, their Cu-exchanged derivatives (e.g. Cu-SSZ-13, Cu-ZSM-5) are widely applied as NH3-SCR catalysts, due their high and stable activity in NOx conversion [1]. Nevertheless, after NH3-solvation, Cu2+ and Cu+ ions are mobile under SCR condition, potentially affecting the sensing response to NH3, as well. Our research group has recently investigated this phenomenon selectively in small-pore zeolites (i.e. Cu-SSZ-13 and Cu-SAPO-34) [5]. Here we extend our study to zeolite materials with different crystal structure and Cu-loading in order to gain deeper understanding of structural and compositional effects. Materials and Methods We synthesized a series of zeolite catalysts with different framework types, namely H-SSZ-13 (CHA), H-ZSM-5 (MFI), H-beta (BEA). On each proton-form zeolite, wet Cu ion-exchange was performed, to obtain the Cu-exchanged counterparts (i.e. Cu-SSZ-13, Cu-ZSM-5, Cu-beta) with selected levels of Cu-loading, analytically controlled via ion-coupled plasma optic emission spectroscopy (ICP-OES) in terms of Cu/Al ratio. The samples have been further characterized by powder X-ray diffraction, diffuse reflection UV/Vis spectroscopy and scanning electron microscopy. Temperature-programmed desorption using NH3 as the probe molecule (NH3-TPD) was performed over the synthesized Cu zeolites and the corresponding proton-form zeolites in order to specify the respective NH3-adsorption sites.For IS measurements, thick films of zeolite materials were deposited on gold inter-digital electrodes chips (IDE) with alumina substrate. The IDE chips are also equipped with a heating circuit on the back side to adjust the temperature. In the measuring chamber, the gas dosing was operated by means of mass flow controllers. An alternating voltage of 0.1 V was applied to the zeolite sensor in at a measuring frequency of 10 kHz. The here-presented NH3-sensing experiments were performed alternating N2 and NH3 (100 ppm in N2) flow at typical SCR operative temperature (200, 350 and 400 °C), with a total flow of 100 sccm. Prior to each sensing measurement, the investigated sample was pretreated in O2 at 450 °C for 1 h. Results and Conclusions The material characterization, before and after deposition on the IDE chips, shows that the composition and microstructure of the samples was preserved. The Cu-exchanged samples have been named after their Cu/Al ratio [e.g. Cu(x)-SSZ-13, where x = Cu/Al].Based on NH3-supported proton transport, in situ IS measurements were performed to study the NH3-zeolite interactions. The absolute impedance |Z| was employed to evaluate the sensing performances of the zeolite materials after normalization, expressing the sensing signal as IIS signal [IIS = (|Z0|-|Z|)/|Z0|, where Z0 is the impedance measured in pure N2).The results obtained at 200 °C over Cu-SSZ-13 zeolites are shown in Figure 1. As can be seen that the IIS signal of Cu-exchange SSZ-13 zeolites became significantly higher than H-SSZ-13 after exposure in NH3. Moreover, the conductivity appears to increase with increasing Cu-loading. This trend was also observed for ZSM-5 and beta samples, even though not as pronounced. This effect may be surprising, if NH4 + and H+ were considered the only mobile cationic species, as usual for proton-transport-based sensors: indeed, the IIS would be expected to decrease, since non-mobile Cu2+ substitutes H+ in the zeolite framework. Nevertheless, at the measuring frequency, short-range motion of NH3-solvated Cu complexes [i.e. Cu2+(NH3)n] are activated [4]. The contribution of these mobile cations lead to the increase of the overall ion conductivity, even compensating the loss of conventional charge carriers.These in situ IS results give important information for the implementation of Cu-zeolite as NH3-sensors in SCR systems, following the concept of “catalysts as sensors”. Further comparative measurements over BEA and MFI zeolites are ongoing, aiming at a comprehensive understanding of the interaction between NH3 and Cu-zeolite with different framework types.

New Chemoresistive Gas Sensor Arrays for Outdoor Air Quality Monitoring: A Combined R&D and Outreach Activities

New Chemoresistive Gas Sensor Arrays for Outdoor Air Quality Monitoring: A Combined R&D and Outreach Activities

Selective SAW-Based Carbon Monoxide Differential Sensor Functionalized with Cobalt Corroles: Influence of Interfering Gases

Introduction During the last two decades, the potential impact of indoor air quality on human health has stimulated an interest in hazardous compounds survey such as carbon monoxide (CO) [1]. The French Institute for Health Surveillance (InVS) reports that accidental domestic poisoning by the CO affects about 1000 households in France each year [2], and is responsible for about 100 deaths. The detection of this compounds has consequently become a need. To address it, we here report results on the capability of functionalized Surface Acoustic Wave (SAW) devices for the selective detection of CO. Here we insist on the necessity to detect CO in presence of interferent such as O2 that is obviously present in the air and CO2 present in significant quantity in urban area. Material SAW delay lines based on Love waves, shown in figure 1, are used to probe mass of sensitive materials deposited as a thin layer on its surface. These devices consist in two-port delay lines built on quartz. The Love wave is generated and detected using interdigited transducers (IDTs) and the frequency operation is in the vicinity of 125 MHz. A 1.5 µm thick silica guiding layer is deposited onto the IDTs providing a propagation path which permit the guidance of the acoustic wave. For the functionalization of the sensor, we take advantage of the great capabilities of cobalt corroles to trap CO molecules at the sensor’s surface with selectivity [3]. Because of the structure of the corroles, small molecules such as N2, O2 and CO2 can be trapped within by mean of weak interactions. In the particular case of CO, stronger chemical interactions are involved reaching high selectivity for this gas. In addition to this intrinsic selectivity, a second corrole has been selected to be used as a reference. This corrole exhibits the same structure as the cobalt corrole, so that it interacts with interferents in a similar way, but has no affinity to the target gaz. Method Two SAWs delay lines (A and B) shown in figure 1 are respectively coated with cobalt- and copper-corroles by mean of a spray coating method. The quantity of corroles deposited on the device is monitored during the process to avoid the deposition of an excessive amount of corroles that would damage the sensor signal compromising its proper functioning. They are then heated at 90°C for an hour under vacuum to remove the ammonia ligands present on the cobalt to prevent the corrole’s degradation in solid state. A gas-mixing bench composed of mass-flow controllers allow for generating various gas mixtures. The so prepared mixtures are sent to a dedicated test chamber that may feature up to six delay lines. Once the sensors are in the chamber, a primary vacuum and a heating is applied to remove any contaminant. A carrier gas composed of different gas of interest (N2, O2, CO2) then flows at 500 sccm through the chamber and CO is then injected at different concentrations. The shift of the synchronous frequency of the delay lines consecutive to gas adsorption is then monitored by mean of a dedicated electronics that delivers information similar to those from a classical network analyzer. Results and Conclusions As we can see in figure 2 the differential acquisition using a copper corrole allows stabilizing the sensor’s signal. Indeed, the drift of the signal on the delay line functionalized with cobalt corrole can be compensated by subtracting the one from the delay line functionalized with copper corrole. This differential acquisition results in a stable basic level of the phase signal and also an improved repeatability of the measurements (figure 3).As expected from previous work [4], we noticed a linear correlation between CO concentration, in the 100 to 7000 ppm range, and the phase shift velocity undergone by the sensors regardless of the composition of the carrier gas (figure 4). From there, we determined the sensitivity of the sensors in presence of interfering gas. It appeared that the presence of 20 % of oxygen, known as the main interferent in this measurement, in the carrier gas tends to lower by 5.5 % the sensitivity in comparison with a pure nitrogen carrier gas (figure 4). The presence of CO2 at 20 000 ppm, which represents 50 times the mean concentration in Paris, lowers the sensitivity by 19.3 % (figure 4). From these results, the selective interaction between the cobalt corrole and CO has been verified and the possibility to use it as part of a selective CO sensor has been evidenced.

Metal Oxide Gas Sensors Signal Shape Processing for Selective Detection of Hydrocarbons in Realistic Air Conditions

Introduction The selective detection with high spatio-temporal resolution of hydrocarbons leakage as a result of pipelines inconsistency is a valid industrial demand [1]. Perspectives are associated with deployment of distributed networks of chemical sensors, transferring data on ambience pollution to the data processing center [2]. Miniature micromachined metal oxide semiconductor gas sensors possess a great perspective of practical use in this regard, however their long term operation in real atmosphere conditions requires improvement [3]. In this work we demonstrate improved selectivity of propane vs. methane detection in low concentrations in the ambient air of highly urbanized location by the SnO2-based semiconductor gas sensors with the modulated working temperature, using statistical analysis of “sensor response/sensor working temperature” shape representation. The obtained results of gases discrimination with artificial neural network (ANN) machine learning algorithm, used such pre-treated data as input samples, demonstrate advantages over similar classification methods without signal pre-processing, or pre-processing with previously reported methods of PCA, wavelet transformation and polynomial curve approximation. Sensor fabrication, data collection and processingThree SnO2-based materials have been used – pure SnO2, gold-modified SnO2 and bimetallic Au and Pd modified SnO2. The gas sensing materials synthesis via single step flame spray pyrolysis technique and sensors fabrication has been reported in a recent paper [4]. A fixed air flow from outside of the building of the Department of Chemistry of Moscow State University through PTFE sensor chamber was used as a background. Methane or propane were admixed to the background air flow through precise mass-flow controllers in three different concentrations from certified gas bottles. Sensors were operated in a working temperature modulation mode between 500 oC and 150 oC with period length of 60 sec. Sensitive layer resistance was measured with the 10 Hz frequency. Collected data was separated in two parts: first, collected in December 2018 was used for data processing algorithms training. Second, collected during January and February 2019, was used for the testing of elaborated data processing models. The total data set of 22440 measurement cycles,11220 of which represent an ambient air, while two data subsets of 5610 measurement cycles represent same air with admixture of methane or propane, were used for processing. The multilayer perceptron ANN-model with 2 hidden dense layers has been used for data processing model development and gases discrimination. The batch normalization and dropout techniques were implemented to avoid model overfitting.According to statistical shape analysis approach, each characteristic point of sensor response is characterized by certain gas sensor working temperature and sensitive layer resistance. All characteristic points of each single measurement cycle during analysis are converted into Kendall’s pre-shape space with removed translation and scaling factor, but with remaining rotation as well as the shape. During further processing the data samples are projected onto the unit-sphere with a pole of mean shape of sensor responses towards air without additives. Later inverse transformation of data samples leads to icon representation of response shape, eliminating possible effects of sensor baseline and response amplitude drift. Results and Conclusions Direct application of collected data to artificial neural network algorithm for methane vs. propane selective detection without any pre-processing gives a decent level of accuracy (Fig.1). However, it can be seen by the rise of discrimination error after normalization of data samples, that the main component of the sensors response, used by algorithm for gases discrimination, is of amplitude nature. It means, that the developed signal processing model may work in unstable manner when any additional gas is involved in the measurements. The use of statistical shape analysis allows to significantly improve the accuracy of discrimination of methane vs. propane in comparison with other pre-processing techniques. The remained error of gases identification is mostly related to the single day of measurements, which is associated with urban air pollution during winter heating season.

Numerical and experimental study on hydrogen production via dimethyl ether steam reforming

This work presents the characteristics of catalytic dimethyl ether (DME)/steam reforming based on a Cu–Zn/γ-Al2O3 catalyst for hydrogen production. A kinetic model for a reformer that operates at low temperature (200 °C–500 °C) is simulated using COMSOL 5.2 software. Experimental verification is performed to examine the critical parameters for the reforming process. During the experiment, superior Cu–Zn/γ-Al2O3catalysts are manufactured using the sol-gel method, and ceramic honeycombs coated with this catalyst (1.77 g on each honeycomb, five honeycombs in the reactor) are utilized as catalyst bed in the reformer to enhance performance. The steam, DME mass ratio is stabilized at 3:1 using a mass flow controller (MFC) and a generator. The hydrogen production rate can be significantly affected depending on the reactant's mass flow rate and temperature. And the maximum hydrogen yield can reach 90% at 400 °C. Maximum 8% error for the hydrogen yield is achieved between modeling and experimental results. These experiments can be further explored for directly feeding hydrogen to proton exchange membrane fuel cell (PEMFC) under the load variations.

Videometric mass flow control: A new method for real-time measurement and feedback control of powder micro-feeding based on image analysis.

The present paper reports the first monitoring and control of ultra-low dose powder feeding using a camera image-based mass flow measurement system. Caffeine was fed via a single-screw microfeeder as a model active pharmaceutical ingredient (API). The mass, mass flow and sizes of the particles were successfully monitored in real-time by the developed videometric system consisting of a high-speed process camera coupled with an image analysis software. The system was also tested in feedback control mode to automatically reach the desired mass flow values by adjusting the feeder speed based on the mass flow measured by the image analysis system. Based on these features, the developed videometric system can serve as a multi-purpose PAT-tool and can provide valuable real-time information about the process which is indispensable for modern continuous pharmaceutical manufacturing.

Equipment for Testing Measuring Devices at a Low-Level Radon Activity Concentration.

The National Institute for Nuclear, Biological, and Chemical Protection, under the European project 16ENV10 MetroRADON (the European metrology program for innovation and research, EMPIR), has developed unique equipment for the testing of measuring devices at low-level radon activity concentrations. The equipment consists particularly of an airtight low-level radon chamber (LLRCH) with an inner volume of 324 liters; a Rn-222 type RF 5 flow-through source with a Ra-226 activity of 4.955 kBq developed by Czech Metrological Institute within the above-mentioned project; and a pressure vessel as a radon-free air source. The mass flow controller of the Bronkhorst EL-Flow type is a part of the apparatus and ensures the requested airflow through the radon source—partialized if necessary—through the chamber. The homogeneity of the atmosphere in the chamber is ensured by means of a continuously regulated fan (airflows in the range of 0.1–3.5 m·s−1 can be established). Another important chamber component is the measuring device of climatic conditions, since temperature, air pressure, and relative humidity must be determined. The construction of the equipment allows the time-stable radon activity concentration to be maintained at a precise level for several days. Radon concentration values can be arbitrarily and continuously set in the range from 100 Bq·m−3 to 300 Bq·m−3.

Toward CO2 Electroreduction under Controlled Mass Flow Conditions: A Combined Inverted RDE and Gas Chromatography Approach.

The use of rotating disk electrodes (RDEs) is probably the most convenient way of studying simple electrode reactions under well-defined transport conditions. Standard RDEs become, however, less expedient when the studied electrode process is a complex one, leading to the formation of various reaction products. In these cases, the accurate detection and quantification of the formed products are desirable. If the formed products are gaseous, then the usual way of quantifying them is the use of online gas chromatography (GC), a method that is not compatible with open RDE cells. In order to overcome these difficulties, we present here a sophisticated inverted RDE (iRDE) cell design. The design combines various advantages: it is amenable to the same mathematical treatment as standard (downward-facing) RDEs; it can be operated airtight and coupled to online GC; and due to its upward-facing design, the electrode surface is less prone to blockage by any formed gas bubbles. The iRDE&GC design is tested using simple model reactions and is demonstratively used for studying the electrochemical reduction of CO2, accompanied by parasitic hydrogen evolution, on a silver electrode.

Laser spectroscopy steered 13 C-labelling of plant material in a walk-in growth chamber.

Carbon-13 (13 C)-labelled plant material forms the basis for experiments elucidating soil organic carbon dynamics and greenhouse gas emissions. Quantitative field-scale tracing is only possible if plants are labelled homogeneously in large quantities. By using a laser spectrometer to automatically steer the isotopic ratio in the chamber, it is possible to obtain large amounts of homogeneously labelled plant material. Ninety-six maize plants were labelled for 25 days until tassel formation in a 15 m3 walk-in growth chamber with a continuous air δ13 C-CO2 value of 400‰. A Los Gatos Research laser absorption spectrometer controlled the ambient δ13 C-CO2 value in the chamber through steering of the mass flow controllers with 13 C-enriched and natural abundance CO2 gas. Laser absorption spectroscopy steering kept the δ13 C value of chamber air between 368 and 426‰. The resulting 1 kg dry matter of 13 C-labelled shoots showed an average δ13 C value of 384‰ and accuracy of 8‰ (half width of the 95% confidence interval). Only the oldest leaves showed larger heterogeneity. The growth chamber eliminated variability between plants. The δ13 C value of the stabile material did not differ significantly from that of bulk material. Laser spectroscopy controlled 13 C labelling of plants in a walk-in growth chamber successfully kept the isotopic ratio of the CO2 in the chamber air constant. Therefore, large quantities of material were labelled homogeneously at the inter- and intra-plant level, thus establishing a method to provide high-quality input for quantitative isotopic tracer studies.

Forecasting continuous carbon nanotube production in the floating catalyst environment

We present validated statistical models and univariate correlations of carbon nanotube (CNT) textile properties (specific electrical conductivity, Raman G:D ratio and mass yield rate) extracted continuously from floating catalyst chemical vapour deposition (FC-CVD) reactors over a uniquely wide multivariate experimental space. This includes directly controlled reactor settings (e.g. precursor concentrations, gas flow rates, furnace temperatures and winding speeds), indirect parameters (e.g. ambient temperature and pressure), and time-dependent reactor influences such as reactor tube age. Two vertical FC-CVD reactors, with different precursor delivery architectures, were considered: 1) in which precursors were pre-mixed together as a liquid solution that was directly injected into reactor; 2) in which vaporised precursors were independently injected in the gas phase using Coriolis-based microfluidic mass flow controllers with concentrations monitored in-line using FTIR spectroscopy. Factors favouring highest electrical conductivity fibres include: lower hydrogen flows, lean fuel-to-gas mixtures, higher winding rates, higher argon flows, with many thiophene concentration interactions with other parameters; for highest Raman G:D ratios: leaner fuel-to-gas mixtures, lower thiophene concentrations, higher hydrogen flows, and greater external laboratory pressure; but for yield rate, systematic trends were harder to discern. This study demonstrates the degree of predictability in FC-CVD reactors, quantitatively ranks impact of FC-CVD parameters, and identifies regions of fibre “spinnability” which correspond well with a recent meta-analysis of experimental results in the literature.

Experimental dynamic dispatch of a 60 kW proton exchange membrane electrolyzer in power-to-gas application

A 60 kW PEM electrolyzer was modified to have dynamic dispatch capabilities through the use of an external mass flow controller and was subsequently operated and studied in detail as a part of the UC Irvine power-to-gas (P2G) demonstration project. The system operated in load following for both rooftop solar PV output and aggregated wind farm power. The electrolyzer system was able to handle 100% up and down ramps of the electrolyzer stack in sub-second intervals during variable renewable energy load following experiments. Overall system efficiency was improved by imposing a minimum load condition to avoid high parasitic losses at low power conditions, and cycling the system off/on as required and enabled by quick cold start-up capability. Performance was characterized for varying levels of part load and dynamic operation. The gas drying process was found to be a significant source of loss at low power conditions.

Understanding of the Spark Effect of Electron Collision by a Capacitive Discharge Ignition in a Constant Volume Combustion Chamber

This work is to investigate the physical effect of plasma discharge in atmospheric air using a capacitive discharge ignition (CDI) system. Also, to specifically investigate the kernel effects of CDI system, this work represents the different characteristics including the spark ignition, electric current, integral energy, spark propagation, flame growth, and kernel distribution comparing with the conventional spark ignition. In the experimental setup, the system is composed of a constant volume combustion chamber (CVCC), spark plug, transformer, capacitor device, mass flow controllers, regulators, high-speed camera, and LabVIEW software and cDAQ. The experiment carried out a wide range as the following conditions: J type spark plug, central type electrode, 1.0 mm plug gap, atmospheric air of initial pressure, 292 K of room temperature, 0.75 ms of spark duration, 420 V of CDI voltage, and 12.5 V of initial transformer voltage. As a result, the spark flame kernel of 400V CDI is increased by MEHV comparing with the conventional spark and the improved effect can be seen in 50 μs. Consequently, the plasma effect of MEHV based on CDI system has a linear characteristic regarding spark kernel growth by capacitance energy comparing with the conventional spark.

Modeling and Characterization of a Thermally Controlled Iodine Feeding System for Electric Propulsion Applications

Iodine is considered as a feasible alternative to xenon as a propellant for electric propulsion systems, thanks to its good propulsive performance, high availability, and high storage density. However, as iodine is stored in solid state at ambient temperature, current state-of-the-art propellant management systems are not suitable to be used with it. Moreover, due to its high reactivity, iodine imposes requirements on material-compatibility, hindering the use of mass flow measurement and control systems typically used with other propellants. The architecture of a controlled iodine feeding system for low power (200 W class) ion and Hall effect thrusters is presented and the resulting prototype is described. It consists of a sublimation assembly whose temperature is used to control the tank pressure, a normally-closed ON-OFF valve, and a thermal throttle to perform the fine control of the mass flow rate. A 1D thermal-fluid model concerning the vapor generation in the tank, and its evolution along the different components is detailed. The thermal throttle model has been experimentally verified using air as a working fluid. The model results agree with the measurements of the verification tests in the hypothesis of the presence of an extended region at the entrance of the pipe where the laminar flow velocity and temperature profiles are not fully developed (known as entry flow region). Finally, the system is experimentally characterized and the model of the full system is calibrated using experimental measurements. The calibration shows that the thermal throttle flow presents an entry flow region, that the viscosity is correctly modeled, and that there is a difference between the measured tank temperature and the effective sublimation temperature.

Thermal Method for Non-Destructive Control of Actual Coolant Mass Flow through a Heating Device

The studies show that expenses for heating buildings and structures account for more than 60% of total utility costs in the Russian Federation. Therefore, the issues on energy and resource conservation and improving the energy efficiency of construction projects for various purposes are relevant and priority. Infrared thermography is actively used during examination of thermomechanical equipment, building structures, external and internal engineering systems and their elements. Heat monitoring makes it possible to avoid significant costs for dismantling of controlled objects and to localize the thermal defects found during the inspection stage, thereby reducing costs of repair works. The article considers and analyzes the existing options for the quantitative analysis of thermograms. The authors propose a new method for quantitative processing of thermograms, aimed at assessing the operation of heating devices in heating systems of buildings and structures. The essence of thermal non-destructive testing technique is to determine the actual mass flow rate of coolant through the heating device.

Probabilistic evaluation of streamline topologies for the detection of preferential flow configurations in PIV applications

While PIV allows the extraction of instantaneous streamlines, the availability of typically thousands of patterns hampers a statistical understanding of the underlying flow topology. A particular application is oscillating gas jets, encountered in scientific and industrial studies dealing with mass transfer and flow control. Multiple methods, such as statistical moments (including mean, variance, skewness, and kurtosis), proper orthogonal decomposition (POD), and Hartigan’s dip test are common post-processing methodologies. However, as demonstrated in this paper, they do not provide sufficient in-depth information from a statistical perspective to attribute probabilities to potential flow topologies. In this work, a novel approach to describe probability distributions based on extracted streamline patterns is proposed. Based on the available streamline patterns, the convolution with adaptive Gaussian kernels reveals the probability density function of the flow topology. The proposed methodology, as well as more traditional post-processing approaches, are assessed on the basis of synthetic flow fields and experimental PIV data of oscillating impinging gas jets, demonstrating the added value of the streamline probability map in characterising the scrutinised flow.

EFFECT OF VARYING VOLTAGE ON ELECTRON DENSITY IN OXYGEN HOMOGENEOUS DIELECTRIC BARRIER DISCHARGE UNDER ATMOSPHERIC PRESSURE

The formation of uniform dielectric barrier discharges (DBDs) under atmospheric pressure is a remarkable achievement with the addition of electronegative gasses in closed reactors. This work is the part of dielectric barrier discharge achieved under atmospheric pressure. A uniform glow discharge is produced in capacitive discharge reactor. An alternating voltage source (0-2.5) kV having frequency of 50Hz is applied across the two parallel disc electrodes. A couple of dielectrics (glass) used as a discharge barriers one on each electrode. The oxygen gas injected into the reactor controlled by mass flow controller with flow rate 30ml/min. The current-voltage waveforms for oxygen discharge achieved, fulfilling the basic conditions of discharge homogeneity. The diagnostic techniques rely on electrical discharge method and power balance method to differentiate discharges and estimate the electron density for different values of applied voltages. A significant relation is found indicating the variation of electron density with applied voltage.

Development of upper air simulator for the calibration of solar radiation effects on radiosonde temperature sensors

AbstractFor the accurate measurement of temperature in the upper air by using radiosondes, one prerequisite is the compensation of solar radiation effects that cause sensor heating. The development at the Korea Research Institute of Standards and Science (KRISS) of an upper air simulator (UAS) that can simulate radiation effects is reported. The UAS can independently control four environmental parameters: irradiance, temperature, pressure and air speed. An entire radiosonde can be installed in the test chamber and the measurement data transmitted remotely via an antenna. Solar irradiance is mimicked by using a solar simulator that irradiates the radiosonde sensor. The temperature of the test chamber is controlled from −70 to 20°C by placing it inside a climatic chamber. The pressure and ventilation speed in the test chamber are modulated using combinations of sonic nozzles, a mass flow controller and a vacuum pump. A ventilation speed of 5 m·s−1, which mimics the speed of ascent of the radiosondes when lifted using a balloon, is achieved at pressures as low as 7 hPa. The capability of controlling the environmental parameters independently and the stability of each parameter are presented. As a proof of concept, the radiation‐induced bias on the temperature sensor of a commercial radiosonde Vaisala RS41 is measured. The effect of each parameter is investigated by varying it while keeping the other parameters fixed. Radiosonde calibration using the UAS at the KRISS will help improve the traceability of upper air measurements to the International System of Units.

Developing flow pattern maps for accelerated two-phase capillary flows

The prediction of flow pattern transitions is extremely important to understand the coupling of thermal and fluid dynamic phenomena in two phase systems and it contributes to the optimum design of heat exchangers. Two phase flow regimes have been extensively studied under controlled mass flow rate and velocity. On the other hand, less effort has been spent in the literature on the cases where the flow motion is purely thermally induced and consequently the mass flow rate or the velocity of the phases are not known a priori. In the present work, flow pattern transitions and bubble break-up and coalescence events have been investigated in a passive two phase wickless capillary loop, where the mass flow rate is intrinsically not controllable. Modified Froude, Weber and Bond numbers have been introduced, considering the actual acceleration of the fluid and the length of the bubble as merit parameters for the transitions. The proposed nondimensional investigation was developed by analysing experimental data obtained with ethanol and FC-72, as working fluids, different heat input levels (from 9 to 24 W) as well as three different gravity levels (through a parabolic flight campaign). A new empirical diabatic flow pattern map for accelerated two-phase capillary flows is presented, together with quantitative criteria for the calculation of the flow regime transitions, defining the physic limits for the bubble coalescence and break-up. This kind of new regime maps will be useful to the further development of comprehensive designing tools for passive two-phase wickless heat transfer devices.

Evaluation of the accuracy and precision of a new generation indirect calorimeter in canopy dilution mode.

Indirect calorimetry (IC) is the only way to measure in real time energy expenditure (EE) and to optimize nutrition support in acutely and chronically ill patients. Unfortunately, most of the commercially available indirect calorimeters are rather complex to use, expensive and poorly accurate and precise. Therefore, an innovative device (Q-NRG®, COSMED, Rome, Italy) that matches clinicians' needs has been developed as part of the multicenter ICALIC study supported by the two academic societies ESPEN and ESICM. The aim of this study was to evaluate the accuracy and intra- and inter-unit precision of this new device in canopy dilution mode invitro and in spontaneously breathing adults. Accuracy and precision of oxygen consumption (VO2) and carbon dioxide production (VCO2) measurements were evaluated invitro and in 15 spontaneously breathing healthy adults by interchanging three Q-NRG® units in a random order. Invitro validation was performed by gas exchange simulation using high-precision gas mixture and mass flow controller. Accuracy was calculated as error of measured values against expected ones based on volume of gas infused. Respiratory coefficient (RQ) accuracy was furthermore assessed using the ethanol-burning test. To evaluate the intra- and inter-unit precisions, the coefficient of variation (CV%=SD/Mean*100) was calculated, respectively, from the mean±SD or the mean±SD of the three mean values of VO2, VCO2, RQ and EE measured by each Q-NRG® units. Invivo accuracy measurement of the Q-NRG® was assessed by simultaneous comparison with mass spectrometry (MS) gas analysis, using Bland-Altman plot, Pearson correlation and paired t-test (significance level of p=0.05). Invitro evaluation of the Q-NRG® accuracy showed measurement errors <1% for VO2, VCO2 and EE and <1.5% for RQ. Evaluation of the intra- and inter-unit precision showed CV% ≤1% for VO2 and EE and CV% ≤1.5% for VCO2 and RQ measurements, except for one Q-NRG® unit where CV% was 2.3% for VO2 and 3% for RQ. Very good inter-unit precision was confirmed invivo with CV% equal to 2.4%, 3%, 2.8% and 2.3% for VO2, VCCO2, RQ and EE, respectively. Comparison with MS showed correlation of 0.997, 0.987, 0.913 and 0.997 for VO2, VCO2, RQ and EE respectively (p≤0.05). Mean deviation of paired differences was 1.6±1.4% for VO2, -1.5±2.5% for VCO2, -3.1±2.6% for RQ and 0.9±1.4% for EE. Both invitro and invivo measurements of VO2, VCO2, RQ and EE on three Q-NRG® units showed minimal differences compared to expected values and MS and very low intra- and inter-unit variability. These results confirm the very good accuracy and precision of the Q-NRG® indirect calorimeter in canopy dilution mode in spontaneously breathing adults.

Airflow energy harvesting through diamagnetically levitated magnet rotor

An airflow energy harvester by using diamagnetic levitation technology to generate electricity is presented in this paper. The energy harvester consists of a lifting magnet, an upper pyrolytic graphite plate, a magnet rotor, two centrosymmetric nozzles, induction coils, and a lower pyrolytic graphite plate. The lifting magnet is used to exert an upward force on the magnet rotor, so the levitated magnet rotor can stably levitate. In order to study the output characteristics of the energy harvester, two streams of airflow are applied to the magnet rotor to form a force couple. The relationship between the induced voltage and the airflow rate was analyzed and tested by simulation and experiment. In this paper, the flow rate was controlled by the mass flow controller, and the output voltage under different airflow rates was recorded. It was found that the peak induced voltage of the coil could reach 2.8 V when the flowrate was 3000 sccm.