Water Vapor Partial Pressure Research Articles

ПРОБЛЕМЫ И ПЕРСПЕКТИВЫ РАЗВИТИЯ ТЕХНОЛОГИЙ АЭРИРОВАНИЯ ЗЕРНА

The article analyses grain bulk, being man-made ecological system, where biotic components and their abiotic environment interact with each other. The article determines physical properties of grain bulks and air flow underlying grain aeration processes. It summarizes and classifies technological problems of grain safety which can be solved by aeration. It reveals significant problems associated with increasing preservation of freshly harvested grain. The problem is the presence of small and light impurities in grain mass, which are source of harmful microorganism concentration. The study reveals the main problems of grain aeration drying with additional heating of atmospheric air and presents their possible solutions. Aeration rate limit values are given for performing the main technological operations of grain safety. The article demonstrates importance of grain hygroscopic properties for its aeration, and moisture movement balance at different values of water vapor partial pressures in air and grain.

Characterization of Water Vapor Sorption Performance and Heat Storage of MIL-101 (Cr) Complex MgCl2, LiCl/LaCl3 System for Adsorptive Thermal Conversion.

Adsorption heat conversion systems can provide heating and cooling across time and space in a more environmentally friendly way. Porous materials are potential candidates for water-based adsorption thermal conversion, in which a metal-organic framework (MOF) has a larger specific surface area and porosity than other porous matrices. However, many MOFs with high saturated adsorption capacity have great deficiencies in performance at low water vapor partial pressure, which hinder their application in adsorption thermal conversion. To improve the water vapor adsorption performance of MIL-101 (Cr), different contents of magnesium chloride, lithium chloride, and lanthanum chloride are mixed into MIL-101 (Cr) by an impregnation method. The properties and structures of the materials are characterized by XRD, SEM, nitrogen adsorption tests, water vapor adsorption tests, TG, FTIR, and so on. The results show that the saturated water vapor adsorption capacity of the sample impregnated with salt increases by 1.5-2.3 times, up to 2.24 g/g, compared with that of the unimpregnated sample. When the partial pressure of water vapor is 0.3, the adsorption capacity increases by 5.3-7.5 times and reaches 0.68 g/g at most. The maximum heat storage density of impregnated samples can be increased by 866 J/g. Impregnated MgCl2 can greatly improve the adsorption and thermal conversion performance of MOF, and impregnated MgCl2 and the proper amount of LiCl can further improve the performance of the material system. Our experiments show that the composite impregnation of magnesium chloride and the proper amount of lithium chloride can improve the application performance of the MOF materials in the adsorption thermal conversion process.

Monitoring urban heat island intensity based on GNSS tomography technique

Monitoring urban heat island (UHI) effect is critical because it causes health problems and excessive energy consumption more energy when cooling buildings. In this study, we propose an approach for UHI monitoring by fusing data from ground-based global navigation satellite system (GNSS), space-based GNSS radio occultation (RO), and radiosonde. The idea of the approach is as follows: First, the first and second grid tops are defined based on historical RO and radiosonde observations. Next, the wet refractivities between the first and second grid tops are fitted to higher-order spherical harmonics and they are used as the inputs of GNSS tomography. Then, the temperature and water vapor partial pressure are estimated by using best search method based on the tomography-derived wet refractivity. In the end, the UHI intensity is evaluated by calculating the temperature difference between the urban regions and nearby rural regions. Feasibility of the UHI intensity monitoring approach was evaluated with GNSS RO and radiosonde data in 2010–2019, as well as ground-based GNSS data in 2020 in Hong Kong, China, by taking synoptic temperature data as reference. The result shows that the proposed approach achieved an accuracy of 1.2 K at a 95% confidence level.

Regulation of particle size and morphology of tungsten powders in bottom-blowing hydrogen reduction process

Particle size and morphology of tungsten powders determine the processing properties of tungsten products. The thermodynamic analysis indicates that the partial pressure of water vapor is an essential factor to regulate the hydrogen reduction of tungsten oxides. The investigation proposed a method of changing the particle size of tungsten powders by bottom blowing hydrogen pretreated by water bath at various temperatures. The experimental results manifested that the bottom-blowing hydrogen could eliminate discrepancies of the water vapor partial pressure in the solid powder layers, thus improving the uniformity of the tungsten powders in a crucible. The partial pressure of water vapor increased with temperatures of water bath increasing. As the water bath temperature raised from 50 °C to 80 °C, the average particle size of tungsten powders increased significantly from 3.8 μm to 12.0 μm. Chemical vapor transport was responsible for the increase in the average particle size of tungsten powders under the higher partial pressure of water vapor. In addition, the oxygen content of tungsten powders produced remained relatively stable at a lower level with the partial pressure of the water vapor increasing. This study provided theoretical foundation and technological reference for preparing the tungsten powders with superior properties (desirable homogeneity in the particle size and shape and low oxygen content).

Utilization of coal mine gas in solid oxide fuel cells: A performance evaluation

The possibility and regimes of coal mine gas utilization in solid oxide fuel cells (SOFCs) without external methane reforming were appraised using a short-stack of two membrane-electrode assemblies with the planar electrolyte-supported architecture. The stack fueled by model coal mine gas, namely 59 % CH4 - 5 % CO2 – 36 % N2 mixture humidified at 343–363 K, demonstrated a stable operation during approximately 170 h at 1123 K when the fuel humidity was higher than 38 vol%. The performance decreased with increasing steam concentration and was lower than that obtained for hydrogen fuel at the same humidity levels. The maximum power density, 157 mW/cm2 at the current density of 284 mA/cm2, was observed for 38 % humidity close to the thermodynamic limit where carbon nanotube formation may start at the SOFC anode. Decreasing water vapor partial pressure resulted in a fast degradation, accompanied with increasing ohmic and polarization losses. Subsequent microscopic analysis confirmed that these effects are indeed associated with the carbon deposition. Beyond the coking domain, the current vs. voltage dependencies of the SOFC stack can be described by a simplified model assuming that the anode kinetics is essentially governed by the electrochemical oxidation of hydrogen.

Insight into Grain and Grain‐Boundary Transport of Proton‐Conducting Ceramics: A Case Report of BaSn0.8Y0.2O3−δ

AbstractProton‐conducting ceramic electrolytes offer great potential for the development of low‐ and intermediate‐temperature solid oxide electrochemical devices, e.g., fuel cells and electrolyzers. However, the electrolyte constitutes the main bottleneck in such devices, especially at reduced temperatures, determining their overall performance and efficiency. Herein, for the first time the low‐temperature transport properties of BaSn0.8Y0.2O3−δ as a representative of proton‐conducting materials are investigated. The attention is focussed on grain and grain boundary conductivity of this ceramic material over a wide range of experimental conditions, including temperatures of 400–550 °C, oxygen partial pressures of 10−22–0.21 atm, and water vapor partial pressures of 10−5‐0.03 atm. After analyzing BaSn0.8Y0.2O3−δ with electrochemical impedance spectroscopy under these experimental conditions, the distribution of relaxation times is leveraged to evaluate the resistance, capacitance, and frequency of each electrolytic process. The data show that the BSY ceramic, prepared with CuO as a sintering additive, is characterized by three distinct processes: one is due to grain response, and two others are understood to be related to the responses of the pure and CuO‐covered grain boundaries. Therefore, this work opens a new path for the analysis of ionic, including protonic, transport along grains and grain boundaries.

Corrosion Behaviors of Ni–Cr Alloys in O2, H2O and H2O + O2 Gases at 700°C and the Effect of Temperature

Pure nickel and four binary Ni–Cr (5, 10, 20 and 30 wt%) alloys were exposed to Ar–20O2, Ar–20O2–20H2O and Ar–20H2O (vol.%) at 700°C. In dry and wet O2, three Ni–Cr alloys (5, 10 and 20 wt%) formed a three-layered structure: an external NiO layer, an inner oxide layer of NiO + Cr2O3 and an internal oxidation zone (IOZ) with Cr2O3 dispersed. The Ni–30Cr alloy formed a continuous chromia layer, with locally outer NiO islands. In pure water vapor, all alloys underwent internal oxidation, nickel metal expulsion and NiO formation. Compared with the results at 650°C, increasing the temperature to 700°C did not alter the morphology of the oxide scale, but enhanced the scale growth kinetics. A significant difference between these two temperatures was that the strong retarding effect of water vapor on NiO formation in oxygen at 650°C became insignificant at 700°C. However, in water vapor only condition, NiO formation remained much slower at both temperatures. The effects of water vapor and oxygen partial pressure on NiO formation of different alloys and the effect of temperature on scale growth kinetics and morphology were discussed.

Analysis of Interfacial Capacitance of Ni-YSZ Anode By Transient Simulation

An electrochemical impedance and equivalent circuit analysis are frequently used for electrochemical evaluation of SOFC cells. The impedance analysis enables to obtain the resistance and the capacitance components of the electrode reaction. The electrode resistance is directly related to the cell performance. The electrode capacitance can be sometimes give information about the active electrode reaction site. As to Ni-YSZ electrode, we've tried to elucidate the physical meaning of the capacitance [1]. However, it is not easy to clarify the physical origin of the electrode capacitance. Thus, the capacitance has not been used to evaluate the active reaction zone so far. In this study, the capacitance of Ni-YSZ interface will be simulated by calculating the chemical capacitance derived from YSZ. Then, the origin of the capacitance will be discussed through comparison with the previous studies [1].The structural model to simulate the Ni-YSZ model cell [1] are shown in Fig. 1., which shows simplified model according to symmetry of the cell. In order to limit the electrochemical reaction zone (triple phase boundary), a virtual reaction zone was introduced. Cell conditions for the calculation are following: temperature: 765ºC; oxygen partial pressure of the air electrode: 0.21 bar;hydrogen partial pressure: 1.00 bar, and water vapor partial pressure: 0.03 bar for fuel electrode. Transient simulation was performed to obtain the chemical capacitance by an in-house code, SIMUDEL, where mixed ionic electronic conduction and oxygen nonstoichiometry were taken into consideration [2,3] using the reported conductivity data of YSZ [4].The measured capacitance of the model cell [1] was 5×10-4 Fcm-2. On the other hand, the calculated chemical capacitance of YSZ was 2×10-3 Fcm-2. Even though the oxygen nonstoichiometry of YSZ was small, calculated chemical capacitance was much larger than the observed interfacial capacitance. These difference implies there was unknown factors to promote the response of electron in the actual Ni-YSZ interface. If a thin resistive layer was inserted between Ni and YSZ interface, the calculated chemical capacitance became smaller than that of observed. Sasaki et al. observed an incoherent interface between Ni and YSZ by TEM [5]. This kind of interface structure may be the potential cause of the complicated capacitance.This study was partially supported by NEDO, Japan.[1] M. Takeda, et. al., submitted to J. Electrochem. Soc.[2] K. Terada, et. al., ECS Trans. 35(1), 923 (2011).[3] M. Sato, et. al., Trans. Jpn. Soc. Comp. Eng. Sci. 2017, 14 (2017).[4] J.H. Park, et. al., J. Am. Ceram.Soc.,72[8],1485-87(1989).[5] T. Sasaki, et. al., Mater. Trans. 45(7), 2137 (2004).Fig. 1 Schematic diagrams of the structural model to simulate the chemical capacitance of Ni-YSZ. Figure 1

Effect of Water Vapor and Hydrogen Concentration on Power Generation Characteristics of Protonic Ceramic Fuel Cell

The proton and hole conductivities of BaZrO3-based perovskites depend on partial pressures of oxygen and water vapor. These conductivities affect the power generation characteristics of Proton Ceramic Fuel Cells (PCFCs) using the perovskite as an electrolyte. In this study, the effect of humidification conditions on the power generation characteristics of an anode-supported PCFCs was investigated.The configuration of the anode-supported PCFC was La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode/BaZr0.8Yb0.2O3-δ(BZYb) electrolyte/Ni-BZYb anode. The diameter of the effective cathode area was approx. 10 mm. The cathode gas composition was fixed at 97% concentration of air and 3% concentration of water vapor. The concentration of water vapor in the anode gas was controlled to be 3-69%. The current density-voltage characteristics and AC impedance were measured by Bio-Logic SP-150.In all water vapor concentration conditions, the cell showed the highest OCV (approximately 1 V) at 3% concentration of water vapor. However, the maximum power density was highest at 30% concentration of water vapor (346 mW/cm2). The highest maximum power density at 30% concentration of water vapor can be explained by the following reason. The OCV values decrease with increasing the concentration of water vapor because of decreasing the concentration of hydrogen. On the other hand, from the results of impedance measurements, the ohmic resistance of the cell decrease with increasing the concentration of water vapor because of increase of proton conductivity of the cell. Thus, the increase of cell voltage by increase of proton conductivity should be higher than the decrease of OCV values.【Acknowledgements】This presentation is the result of the research and development of ultra-efficient proton-conducting ceramic fuel cell devices, JPNP20003, funded by the New Energy and Industrial Technology Development Organization (NEDO), Japan. We would like to express our gratitude to all parties involved.

Benchmarking the yttrium content in the low temperature/low humidity electrical properties of yttrium-doped barium cerate

Yttrium-doped barium cerate (BCY) is one of the best proton-conducting ceramics to be used in fuel cells/electrolyzers at intermediate temperatures, due to its high hydration enthalpy and high conductivity. Nonetheless, it has commonly been discarded for these applications due to its instability in the presence of carbonaceous and humidified atmospheres. A recent work has addressed this issue, by suggesting the use of this material in very low water vapor partial pressures (pH2O ∼ 10−4 atm) [Electrochimica Acta 334 (2020) 135625] and at low temperatures (T ≤ 400 °C). Under these conditions, BCY can still offer pure protonic conductivity while also offering suitable stability. In the current work, we provide a comprehensive analysis of the effects of the acceptor dopant concentration (Y2O3) in the structural, microstructural, and electrical properties in a wide compositional series of BaCe1-xYxO3-δ (x = 0.05, 0.10, 0.20 and 0.30) at low levels of humidity in the low temperature range (100–400 °C). The results show that BaCe0.9Y0.1O3-δ (BCY10) offers the highest bulk conductivity in these conditions, while further increase in dopant concentration leads to impairment due to “proton trapping” effects. In contrast, the specific grain boundary conductivity increases with increasing dopant concentration due to a reduction of Schottky barrier height at the space-charge layer. We demonstrate that, by operating at very low temperatures (e.g., below 400 °C), the peak performing, BCY10 material can still operate at very low levels of water vapor partial pressure (pH2O ∼ 10−4 atm), where its stability can be maintained. This work paves the way for the optimization of this material, with a focus on utilizing low humidity levels and low temperatures, where it can offer a competitive advantage over that of the majority of other proton-conducting perovskites for potential applications operating under these conditions.

Experience of pumping the vacuum vessel of SST-1 during the baking cycle with indigenously developed liquid nitrogen cooled sorption pump

To achieve ultra-high vacuum in the vacuum vessel of SST-1, the baking of vacuum vessel is done to remove impurities like water vapour, carbon-dioxide and hydrocarbons etc. The maximum baking temperature of the plasma-facing components (PFCs) are around 250 °C and the vacuum vessel is around 150 °C. The gas load of water vapour increases significantly during the baking operation. Therefore, to pump the water vapour during baking, a customized liquid nitrogen cooled sorption pump was designed, fabricated and installed on the radial port of the machine. It is the first time that liquid nitrogen cooled Cryopump was used on the SST-1 machine. The pumping of water vapour, nitrogen and impurity gases was observed during the 11 days of operation. Commercial Cryopumps are operating at ∼10 K temperature and can pump hydrogen gas however, the direct mounting of these pumps during baking results in early regeneration of the pump due to high heat load. Therefore, the experience of pumping the vacuum vessel of SST-1 with the indigenous developed sorption pump in association with the Turbo-Molecular Pump (TMP) sets is discussed systematically in the present report. The partial pressure of the water vapour using TMP sets was 1.0E-6 mbar and after incorporating the sorption cryopump with the existing vacuum system, the partial pressure reached to 1.3E-7 mbar in 48 h at 230 °C PFCs temperature. The pressure attained in the vacuum vessel was ∼1.0E-7 mbar and the partial pressure of water vapour was ∼1.1E-8 mbar after ramp-down the PFCs to 50 °C temperature.

Effect of Lu-Doping on Electrical Properties of Strontium Zirconate.

SrZrO3-based perovskites are promising proton-conducting membranes for use in fuel and electrolysis cells, sensors, hydrogen separators, etc., because they combine good proton conductivity with excellent chemical stability. In the present research, the effect of Lu-doping on microstructure, phase composition, and electrical conductivity of SrZr1-xLuxO3-δ (x = 0-0.10) was investigated via X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and impedance spectroscopy. Dense ceramic samples were obtained by the solution combustion synthesis and possessed an orthorhombic perovskite-type structure. The solubility limit of Lu was revealed to lie between x = 0.03 and 0.05. The conductivity of SrZr1-xLuxO3-δ increases strongly with the addition of Lu at x < 0.05 and just slightly changes at x > 0.05. The rise of the water vapor partial pressure results in an increase in the conductivity of SrZr1-xLuxO3-δ ceramics, which confirms their hydration ability and significant contribution of protonic defects to the charge transfer. The highest conductivity was achieved at x = 0.10 (10 mS cm-1 at 700 °C, wet air, pH2O = 0.61 kPa). The conductivity behavior was discussed in terms of the defect formation model, taking into account the improvement in ceramic sintering at high lutetium concentrations.

Desiccant coated fin tube energy exchanger design optimization implementing KNN-ML tool and adsorption/desorption kinetics analysis using finite difference based transient model

In air conditioning applications, to increase energy exchange capabilities and enhance indoor air quality, the desiccant coated fin tube energy exchanger (DCFTE) appears to be a capable substitute compared to traditional energy exchangers like an adsorber bed and rotary wheel. Hence, for enhancing the air conditioning system's performance, accurate prediction of the adsorption kinetics of DCFTE is crucial. Thus, a K-Nearest Neighbor-Machine Learning (KNN-ML) tool is employed for predicting the exit and design parameters of DCFTE. The impact of the operating parameters on the performance of DCFTE has been assessed by utilizing the KNN-ML tool. To analyze the performance of DCFTE, energy exchange and dehumidification capacity are selected as the performance indices. The optimum operating conditions for a specific operational range are also found using the KNN-ML tool. Moreover, a finite difference approach-based transient model is developed to assess the inlet parameters' effect on the performance characteristics and adsorption/desorption kinetics of DCFTE. The coefficient of performance and moisture removal capacity are selected as the performance indices. Furthermore, the effect of time on the outlet air specific humidity, outlet water temperature, air temperature, and desiccant concentration during the dehumidification and regeneration process is analyzed. The effect of the water vapor partial pressure ratio on adsorption capacity is examined. Moreover, Lewis and Stanton number's influence on the DCFTE performance is analyzed by employing the transient model. Silica gel is utilized as a desiccant.

Региональные особенности изменения норм основных климатических параметров на территории России

The regional features of changes in the normals of the main climatic parameters (air temperature, precipitation, water vapor tension, sea level pressure) on the territory of Russia are studied for three 30-year periods: 1961–1990, 1981–2010, and 1991–2020. Climate normals are calculated in accordance with the WMO requirements. In addition to the difference in the normals for stations, the values averaged over the territory of quasihomogeneous climatic regions are calculated. Seasonal changes in the regime of the main climatic parameters in certain regions of Russia over the past decades are revealed. In the last thirty years, a slowdown in warming in all seasons has been revealed on the territory of Russia. Summer precipitation normals for 1991–2020 decreased in most of the country, however, a significant increase in precipitation was found in the southern regions of Yakutia, the Amur region, and Primorye. For the regime of sea level pressure, the greatest changes are revealed in winter. The differences in climatic normals obtained in the present study can be considered as one of the indicators of climate change that are differently manifested in different regions of Russia. The information can be useful for developing preventive adaptation measures under changing climate. Keywords: climate, climate normal, air temperature, precipitation, air pressure, partial water vapor pressure, regional features

Scale transition: Pore network study of how pore structure affects the macroscopic parameters of the continuum model for drying

The scale transition from discrete pore network model (PNM) simulations to one-equation continuum model (CM) of drying has been investigated in previous studies for uniformly structured porous media. This investigation is extended in the present work to porous media with widely different pore size distributions, as well as to those with spatially correlated networks of small and large pores. The key questions examined here are how and to what extent pore-structural features can be reflected in the local macroscopic parameters of the one-equation CM derived by traditional homogenization. For this purpose, three-dimensional model capillary structures with monomodal and bimodal pore size distributions are generated and drying simulations are conducted at the limit of viscous-capillary dominated regime. By leveraging volume-averaged data obtained from PNM simulations the one-equation CM is parameterized and thus its local parameters are expressed in dependence on the pore structure. The simulation results show that for the monomodal and bimodal pore structures the profiles of the moisture transport coefficients are complex and non-unique over the entire drying process. Moreover, the deviation of the water vapor partial pressure from the saturation vapor pressure in the presence of liquid water – which is referred to as non-local equilibrium effect – is less pronounced for the bimodal pore structure compared to the monomodal pore structures. Finally, comparisons are performed between the volume-averaged data obtained at different stages of drying by the discrete simulations with monomodal and bimodal pore structures and results of the continuum model of drying.

Wet to Dry Controls Lanthanide Scandate Synthesis

The choice of temperature and gas conditions used in a water pressure-controlled reactor is guided by density functional theory (DFT) to synthesize nearly phase-pure lanthanide scandate nanoparticles (LnScO3, Ln = La, Nd, Sm, Gd). In this synthetic method, low water-vapor partial pressures, well below water's gas liquidus, inhibit particle growth, while an excess of water vapor results in undesired rare-earth hydroxide and oxyhydroxide secondary phases. The optimal humidity for high-purity LnScO3 particle synthesis is shown to vary with the lanthanide; DFT is used to calculate the thermodynamics of secondary phase formation for each lanthanide tested such that the role of water vapor may be quantified and used to maintain phase purity (greater than 96 mol %) across the series. The combination of thermodynamic calculation and experimental confirmation with this pressure-controlled reactor provides an opportunity to explore analogous syntheses of other inorganic perovskite nanoparticles.

Effect of scandium on the phase composition, microstructure and electrical conductivity of strontium hafnate

Effect of Sc-doping on crystal structure, morphology and conductivity of SrHfO3 was studied for the first time. SrHf1-xScxO3-δ (x = 0–0.15) was synthesized by solid state reaction and examined using Rietveld refinement of X-ray diffraction patterns, scanning electron microscopy and four-probe DC technique. It was shown that scandium incorporates into the crystal lattice of SrHfO3 and SrHf1-xScxO3-δ crystallizes in the orthorhombic Pbnm space group. Sc-doping enhances the grain growth and sinterability, which results in increased density of ceramics. The conductivity of SrHf1-xScxO3-δ increases with increasing Sc-content, which is consistent with the common model of oxygen vacancies formation. Increase in conductivity with increasing water vapor partial pressure indicates a significant contribution of protons to charge transport. High ionic conductivity is combined with high ion transference numbers, which makes SrHf1-xScxO3-δ promising electrolytes for use in electrolysis cells producing clean hydrogen from steam and fuel cells converting chemical energy into electricity.

Stratospheric chlorine processing after the 2020 Australian wildfires derived from satellite data

The 2019 to 2020 Australian summer wildfires injected an amount of organic gases and particles into the stratosphere unprecedented in the satellite record since 2002, causing large unexpected changes in HCl and ClONO2. These fires provided a novel opportunity to evaluate heterogeneous reactions on organic aerosols in the context of stratospheric chlorine and ozone depletion chemistry. It has long been known that heterogeneous chlorine (Cl) activation occurs on the polar stratospheric clouds (PSCs; liquid and solid particles containing water, sulfuric acid, and in some cases nitric acid) that are found in the stratosphere, but these are only effective for ozone depletion chemistry at temperatures below about 195 K (i.e., largely in the polar regions during winter). Here, we develop an approach to quantitatively assess atmospheric evidence for these reactions using satellite data for both the polar (65 to 90°S) and the midlatitude (40 to 55°S) regions. We show that heterogeneous reactions apparently even happened at temperatures at 220 K during austral autumn on the organic aerosols present in 2020 in both regions, in contrast to earlier years. Further, increased variability in HCl was also found after the wildfires, suggesting diverse chemical properties among the 2020 aerosols. We also confirm the expectation based upon laboratory studies that heterogeneous Cl activation has a strong dependence upon water vapor partial pressure and hence atmospheric altitude, becoming much faster close to the tropopause. Our analysis improves the understanding of heterogeneous reactions that are important for stratospheric ozone chemistry under both background and wildfire conditions.

Electrical and sensing properties of indium-doped barium cerate

Systematic analysis of electrical characteristics of BaCe0.75In0.25O3-δ (BCI25) sintered sample was performed in a dry and a wet argon atmosphere in the 250 °C–700 °C temperature range. The water vapor sensing properties of BCI25 porous film and its response and recovery times were investigated under different conditions of temperature and water vapor concentration. The 30 μm thick film obtained from the powder calcined at 1050 °C exhibited sensitivity comparable to that of the sintered sample with a significantly shorter response and recovery times. While the sensitivity of the film gradually decreased with a decrease in partial pressure of water vapor (p(H2O)), a noticeable sensitivity was still observed at p(H2O) of 200 Pa. Decrease in conductivity depended logarithmically on the partial pressure of water with the slope of 0.52 that is close to the theoretical value. After several cycles, the reusability test proved an almost unchanged ratio between the impedance value in the dry and the wet Ar atmosphere (p(H2O) = 2.34 kPa), which implied that BCI25, having good stability and sensitivity, is a promising high-temperature humidity sensor.

Nonisothermal Evaporation of Sessile Drops of Aqueous Solutions with Surfactant

In recent decades, electronic devices have tended towards miniaturization, which necessitates the development of new cooling systems. Droplet cooling on a heated wall is effectively used in power devices with high heat flux densities. The use of a surfactant leads to an increase in the diameter of the wetted spot and the rate of droplet evaporation. Despite the wide interest and numerous works in this area, there are still unexplored questions regarding the influence of surfactant and wall temperature on convection, of nonisothermality, and of the decrease in the partial pressure of vapor with increasing surfactant concentration. This work experimentally studies the effect on the rate of droplet evaporation of wall temperature in the range 20–90 °C and of the concentration of surfactant in an aqueous solution of sodium lauryl sulfate (SLS) from 0 to 10,000 ppm. It is shown for the first time that an inversion of the evaporation rate related to the droplet diameter occurs with increasing wall temperature. The influence of key factors on the evaporation of a water droplet with SLS changes with temperature. Thus, at a slightly heated wall, the growth of the droplet diameter becomes predominant. At high heat flux, the role of nonisothermality is predominant. To determine the individual influence of the surfactant on the partial pressure of water vapor, experiments on the evaporation of a liquid layer were carried out. The obtained results and simplified estimates may be used to develop existing calculation models, as well as to optimize technologies for cooling highly heated surfaces.